Singularity Container Ation User Guide

User Manual:

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Singularity Container Documentation
Release 2.5.2
User Docs
Jul 16, 2018

CONTENTS

1

2

3

Quick Start
1.1 Installation . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Overview of the Singularity Interface . . . . . . . . . .
1.3 Download pre-built images . . . . . . . . . . . . . . . .
1.4 Interact with images . . . . . . . . . . . . . . . . . . .
1.4.1
Shell . . . . . . . . . . . . . . . . . . . . . . .
1.4.2
Executing Commands . . . . . . . . . . . . . .
1.4.3
Running a container . . . . . . . . . . . . . . .
1.4.4
Working with Files . . . . . . . . . . . . . . .
1.5 Build images from scratch . . . . . . . . . . . . . . . .
1.5.1
Sandbox Directory . . . . . . . . . . . . . . .
1.5.2
Writable Image . . . . . . . . . . . . . . . . .
1.5.3
Converting images from one format to another .
1.5.4
Singularity Recipes . . . . . . . . . . . . . . .

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7

Introduction
2.1 Welcome to Singularity! . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.1
Mobility of Compute . . . . . . . . . . . . . . . . . . . . . . . .
2.1.2
Reproducibility . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.3
User Freedom . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.4
Support on Existing Traditional HPC . . . . . . . . . . . . . . . .
2.2 A High Level View of Singularity . . . . . . . . . . . . . . . . . . . . . .
2.2.1
Security and privilege escalation . . . . . . . . . . . . . . . . . .
2.2.2
The Singularity container image . . . . . . . . . . . . . . . . . .
2.2.2.1 Copying, sharing, branching, and distributing your image
2.2.2.2 Supported container formats . . . . . . . . . . . . . . .
2.2.2.3 Supported URIs . . . . . . . . . . . . . . . . . . . . . .
2.2.3
Name-spaces and isolation . . . . . . . . . . . . . . . . . . . . .
2.2.4
Compatibility with standard work-flows, pipes and IO . . . . . . .
2.2.5
The Singularity Process Flow . . . . . . . . . . . . . . . . . . . .
2.3 The Singularity Usage Workflow . . . . . . . . . . . . . . . . . . . . . .
2.3.1
Singularity Commands . . . . . . . . . . . . . . . . . . . . . . .
2.4 Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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15

Installation
3.1 Before you begin . . . . . . .
3.2 Install the master branch . . .
3.3 Install a specific release . . .
3.4 Install the development branch
3.5 Remove an old version . . . .

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i

4

5

6

7

8

ii

Build a Container
4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Downloading a existing container from Singularity Hub . . .
4.3 Downloading a existing container from Docker Hub . . . . .
4.4 Creating --writable images and --sandbox directories
4.4.1 --writable . . . . . . . . . . . . . . . . . . . .
4.4.2 --sandbox . . . . . . . . . . . . . . . . . . . . .
4.5 Converting containers from one format to another . . . . . . .
4.6 Building containers from Singularity recipe files . . . . . . .
4.6.1 --force . . . . . . . . . . . . . . . . . . . . . . .
4.6.2 --section . . . . . . . . . . . . . . . . . . . . .
4.6.3 --notest . . . . . . . . . . . . . . . . . . . . . .
4.6.4 --checks . . . . . . . . . . . . . . . . . . . . . .
4.7 More Build topics . . . . . . . . . . . . . . . . . . . . . . .

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21
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26

Build Environment
5.1 Cache Folders . . . . . . . . . .
5.2 Temporary Folders . . . . . . . .
5.3 Pull Folder . . . . . . . . . . . .
5.4 Environment Variables . . . . . .
5.5 Cache . . . . . . . . . . . . . . .
5.5.1
Defaults . . . . . . . . .
5.5.1.1 Docker . . . . .
5.5.1.2 Singularity Hub
5.5.2
General . . . . . . . . .

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Container Recipes
6.1 Overview . . . . . . . . . . . .
6.1.1
Header . . . . . . . . .
6.1.2
Sections . . . . . . . .
6.1.2.1 %help . . . .
6.1.2.2 %setup . . . .
6.1.2.3 %files . . . .
6.1.2.4 %labels . . .
6.1.2.5 %environment
6.1.2.6 %post . . . .
6.1.2.7 %runscript . .
6.1.2.8 %test . . . . .
6.2 Apps . . . . . . . . . . . . . .
6.3 Examples . . . . . . . . . . . .
6.4 Best Practices for Build Recipes

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31
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43
43

Singularity Flow
7.1 Building Images . . . . . . . . . . . . . . . . . .
7.1.1
The Singularity Flow . . . . . . . . . . .
7.1.2
1. Development Commands . . . . . . .
7.1.2.1 Sandbox Folder . . . . . . . . .
7.1.2.2 Writable Image . . . . . . . . .
7.1.3
2. Production Commands . . . . . . . . .
7.1.3.1 Recommended Production Build
7.1.3.2 Production Build from Sandbox .

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49
50

Bind Paths and Mounts
8.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.1
System-defined bind points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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8.1.2

9

User-defined bind points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.2.1 Specifying Bind Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.1.2.2 Binding with Overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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52

Persistent Overlays
9.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2 Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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10 Running Services
10.1 Why container instances? . . . . .
10.2 Container Instances in Singularity .
10.3 Nginx “Hello-world” in Singularity
10.4 Putting all together . . . . . . . . .
10.4.1 Building the image . . . .
10.4.2 Running the Server . . . .
10.4.3 Making it Pretty . . . . . .
10.5 Important Notes . . . . . . . . . .

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11 Container Checks
11.1 Tags and Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.2 What checks are available? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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66

12 Environment and Metadata
12.1 Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.2 Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12.3 Container Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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13 Reproducible SCI-F Apps
13.1 Why do we need SCI-F? . . . .
13.1.1 Mixed up Modules . .
13.1.2 Container Transparency
13.1.3 Container Modularity .
13.1.4 Sections . . . . . . . .
13.1.5 Interaction . . . . . . .
13.2 Cowsay Container . . . . . . .

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14 Singularity and Docker
14.1 TLDR (Too Long Didn’t Read) . . . . . . . . . . .
14.2 Import a Docker image into a Singularity Image . .
14.3 Quick Start: The Docker Registry . . . . . . . . . .
14.4 The Build Specification file, Singularity . . . . . . .
14.5 How does the runscript work? . . . . . . . . . . . .
14.6 How do I specify my Docker image? . . . . . . . .
14.7 Custom Authentication . . . . . . . . . . . . . . . .
14.7.1 Authentication in the Singularity Build File
14.7.2 Authentication in the Environment . . . . .
14.7.3 Testing Authentication . . . . . . . . . . .
14.8 Best Practices . . . . . . . . . . . . . . . . . . . . .
14.8.1 1. Installation to Root . . . . . . . . . . . .
14.8.2 2. Library Configurations . . . . . . . . . .
14.8.3 3. Don’t install to $HOME or $TMP . . . .
14.9 Troubleshooting . . . . . . . . . . . . . . . . . . .

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15 Troubleshooting
15.1 No space left on device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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iii

15.2
15.3
15.4
15.5
15.6
15.7

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16 Appendix
16.1 build-docker-module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.1.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.1.3 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.2 build-shub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.2.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.2.3 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.3 build-localimage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.3.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.3.3 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4 build-yum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4.3 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.5 build-debootstrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.5.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.5.3 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6 build-arch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6.3 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.7 build-busybox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.7.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.7.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.7.3 Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.8 build-zypper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.8.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.8.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.9 Singularity Action Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.9.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10 Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.1 Command Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.1.1 The Singularity command . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.1.1.1 Options and argument processing . . . . . . . . . . . . . . . . . . . .
16.10.1.1.2 Singularity Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.1.2 Commands Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.1.3 Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.2 build . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.2.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.2.2.1 Download an existing container from Singularity Hub or Docker Hub
16.10.2.2.2 Create –writable images and –sandbox directories . . . . . . . . . . .
16.10.2.2.3 Convert containers from one format to another . . . . . . . . . . . . .

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iv

Segfault on Bootstrap of Centos Image . . . . . . . . . .
How to use Singularity with GRSecurity enabled kernels .
The container isn’t working on a different host! . . . . . .
Invalid Argument or Unknown Option . . . . . . . . . . .
Error running Singularity with sudo . . . . . . . . . . . .
How to resolve “Too many levels of symbolic links” error

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16.10.2.2.4 Build a container from a Singularity recipe . . . . . . . . . . . . .
16.10.3 exec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.3.1 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.3.1.1 Printing the OS release inside the container . . . . . . . . . . . .
16.10.3.1.2 Printing the OS release for a running instance . . . . . . . . . . .
16.10.3.1.3 Runtime Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.3.1.4 Special Characters . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.3.1.5 A Python example . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.3.1.6 A GPU example . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4 inspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4.1 JSON Api Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4.2 Inspect Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4.2.1 Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4.2.2 Runscript . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4.2.3 Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4.2.4 Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4.2.5 Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.4.2.6 Deffile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5 pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.1 Singularity Hub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.1.1 How do tags work? . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.1.2 Image Names . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.1.3 Custom Name . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.1.4 Name by commit . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.1.5 Name by hash . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.1.6 Pull to different folder . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.1.7 Pull by commit . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.5.2 Docker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.6 run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.6.2 Runtime Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.6.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.6.3.1 Defining the Runscript . . . . . . . . . . . . . . . . . . . . . . .
16.10.7 shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.7.1 Change your shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.7.1.1 Bash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10.7.2 Shell Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11 Image Command Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.1 image.export . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.2 image.expand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.2.1 Increasing the size of an existing image . . . . . . . . . . . . . . . . . . . .
16.11.3 image.import . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.4 image.create . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.4.1 Creating a new blank Singularity container image . . . . . . . . . . . . . .
16.11.4.1.1 Overwriting an image with a new one . . . . . . . . . . . . . . .
16.12 Instance Command Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.1 instance.start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.1.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.1.2.1 Start an instance called cow1 from a container on Singularity Hub
16.12.1.2.2 Start an interactive shell within the instance that you just started .
16.12.1.2.3 Execute the runscript within the instance . . . . . . . . . . . . . .
16.12.1.2.4 Run a command within a running instance . . . . . . . . . . . . .
16.12.2 instance.list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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16.12.2.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.2.2.1 Start a few named instances from containers on Singularity Hub
16.12.2.2.2 List running instances . . . . . . . . . . . . . . . . . . . . . . .
16.12.3 instance.stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.3.2 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.3.2.1 Start a few named instances from containers on Singularity Hub
16.12.3.2.2 Stop a single instance . . . . . . . . . . . . . . . . . . . . . . .
16.12.3.2.3 Stop all running instances . . . . . . . . . . . . . . . . . . . . .
16.13 Deprecated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.13.1 bootstrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.13.1.1 Quick Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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CHAPTER

ONE

QUICK START

This guide is intended for running Singularity on a computer where you have root (administrative) privileges. If you
are learning about Singularity on a system where you lack root privileges, you can still complete the steps that do not
require the sudo command. If you need to request an installation on your shared resource, check out our requesting an
installation help page for information to send to your system administrator.

1.1 Installation
There are many ways to install Singularity but this quick start guide will only cover one.
git clone https://github.com/singularityware/singularity.git
cd singularity
./autogen.sh
./configure --prefix=/usr/local
make
sudo make install

Singularity must be installed as root to function properly.

1.2 Overview of the Singularity Interface
Singularity’s command line interface allows you to build and interact with containers transparently. You can run
programs inside a container as if they were running on your host system. You can easily redirect IO, use pipes, pass
arguments, and access files, sockets, and ports on the host system from within a container. The --help option gives
an overview of Singularity options and subcommands as follows:
$ singularity --help
USAGE: singularity [global options...]  [command options...] ...

GLOBAL OPTIONS:
-d|--debug

Print debugging information
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(continued from previous page)

-h|--help

Display usage summary

-s|--silent

Only print errors

-q|--quiet

Suppress all normal output

--version
-v|--verbose

Show application version
Increase verbosity +1

-x|--sh-debug Print shell wrapper debugging information

GENERAL COMMANDS:
help

Show additional help for a command or container

selftest

Run some self tests for singularity install

CONTAINER USAGE COMMANDS:
exec

Execute a command within container

run

Launch a runscript within container

shell

Run a Bourne shell within container

test

Launch a testscript within container

CONTAINER MANAGEMENT COMMANDS:
apps

List available apps within a container

bootstrap

*Deprecated* use build instead

build

Build a new Singularity container

check

Perform container lint checks

inspect

Display a container's metadata

mount

Mount a Singularity container image

pull

Pull a Singularity/Docker container to $PWD

COMMAND GROUPS:
image

Container image command group

instance

Persistent instance command group

CONTAINER USAGE OPTIONS:
(continues on next page)

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(continued from previous page)

see singularity help 
For any additional help or support visit the Singularity
website: https://github.com/singularityware/singularity

For any additional help or support visit the Singularity website: https://www.sylabs.io/contact/ Singularity uses positional syntax. Global options follow the singularity invocation and affect the way that Singularity runs any
command. Then commands are passed followed by their options. For example, to pass the --debug option to the
main singularity command and run Singularity with debugging messages on:
$ singularity --debug run shub://GodloveD/lolcow

And to pass the --containall option to the run command and run a Singularity image in an isolated manner:
$ singularity run --containall shub://GodloveD/lolcow

To learn more about a specific Singularity command, type one of the following:
$ singularity help 
$ singularity --help 
$ singularity -h 
$ singularity  --help
$ singularity  -h

Users can also write help docs specific to a container or for an internal module called an app. If those help docs exist
for a particular container, you can view them like so.
$ singularity help container.simg

# See the container's help, if provided

$ singularity help --app foo container.simg

# See the help for foo, if provided

1.3 Download pre-built images
You can use the pull and build commands to download pre-built images from an external resource like Singularity Hub
or Docker Hub. When called on a native Singularity images like those provided on Singularity Hub, pull simply
downloads the image file to your system.
$ singularity pull shub://vsoch/hello-world
˓→world-master.simg

# pull with default name, vsoch-hello-

$ singularity pull --name hello.simg shub://vsoch/hello-world
˓→name

# pull with custom

Singularity images can also be pulled and named by an associated GitHub commit or content hash. You can also use
pull with the docker:// uri to reference Docker images served from a registry. In this case pull does not just
download an image file. Docker images are stored in layers, so pull must also combine those layers into a usable
Singularity file.

1.3. Download pre-built images

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$ singularity pull docker://godlovedc/lolcow

# with default name

$ singularity pull --name funny.simg docker://godlovedc/lolcow # with custom name

Pulling Docker images reduces reproducibility. If you were to pull a Docker image today and then wait six months
and pull again, you are not guaranteed to get the same image. If any of the source layers has changed the image will
be altered. If reproducibility is a priority for you, try building your images from Singularity Hub. You can also use
the build command to download pre-built images from an external resource. When using build you must specify
a name for your container like so:
$ singularity build hello-world.simg shub://vsoch/hello-world
$ singularity build lolcow.simg docker://godlovedc/lolcow

Unlike pull, build will convert your image to the latest Singularity image format after downloading it.
build is like a “Swiss Army knife” for container creation. In addition to downloading images, you can use build
to create images from other images or from scratch using a recipe file . You can also use build
to convert an image between the 3 major container formats supported by Singularity. We discuss those image formats
below in the Build images from scratch section.

1.4 Interact with images
Once you have an image, you can interact with it in several ways. For these examples we will use a hello-world.
simg image that can be downloaded from Singularity Hub like so.
$ singularity pull --name hello-world.simg shub://vsoch/hello-world

1.4.1 Shell
The shell command allows you to spawn a new shell within your container and interact with it as though it were a
small virtual machine.
$ singularity shell hello-world.simg
Singularity: Invoking an interactive shell within container...

# I am the same user inside as outside!
Singularity hello-world.simg:~/Desktop> whoami
vanessa

Singularity hello-world.simg:~/Desktop> id
uid=1000(vanessa) gid=1000(vanessa) groups=1000(vanessa),4(adm),24,27,30(tape),46,113,
˓→128,999(input)

shell also works with the shub:// and docker:// URIs. This creates an ephemeral container that disappears
when the shell is exited.

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$ singularity shell shub://vsoch/hello-world

1.4.2 Executing Commands
The exec command allows you to execute a custom command within a container by specifying the image file. For
instance, to list the root (/) of our hello-world.simg image, we could do the following:
$ singularity exec hello-world.simg ls /
anaconda-post.log

etc

lib64

mnt

root

singularity

bin

home

lost+found

opt

run

srv

usr

dev

lib

media

proc

sbin

sys

var

tmp

exec also works with the shub:// and docker:// URIs. This creates an ephemeral container that executes a
command and disappears.
$ singularity exec shub://singularityhub/ubuntu cat /etc/os-release

1.4.3 Running a container
Singularity containers contain runscripts. These are user defined scripts that define the actions a container should
perform when someone runs it. The runscript can be triggered with the run command, or simply by calling the
container as though it were an executable.
$ singularity run hello-world.simg
$ ./hello-world.simg

run also works with shub:// and docker:// URIs. This creates an ephemeral container that runs and then
disappears.
$ singularity run shub://GodloveD/lolcow

1.4.4 Working with Files
Files on the host are reachable from within the container.
$ echo "Hello World" > $HOME/hello-kitty.txt
$ singularity exec vsoch-hello-world-master.simg cat $HOME/hello-kitty.txt
Hello World

This example works because hello-kitty.txt exists in the user’s home directory. By default singularity bind
mounts /home/$USER, /tmp, and $PWD into your container at runtime. You can specify additional directories to
bind mount into your container with the - -bind option. In this example, the data directory on the host system is bind
mounted to the /mnt directory inside the container.

1.4. Interact with images

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$ echo "I am your father" >/data/vader.sez
$ ~/sing-dev/bin/singularity exec --bind /data:/mnt hello-world.simg cat /mnt/vader.
˓→sez
I am your father

1.5 Build images from scratch
As of Singularity v2.4 by default build produces immutable images in the squashfs file format. This ensures reproducible and verifiable images. However, during testing and debugging you may want an image format that is writable.
This way you can shell into the image and install software and dependencies until you are satisfied that your container will fulfill your needs. For these scenarios, Singularity supports two other image formats: a sandbox format
(which is really just a chroot directory), and a writable format (the ext3 file system that was used in Singularity
versions less than 2.4).
For more details about the different build options and best practices, read about the singularity flow.

1.5.1 Sandbox Directory
To build into a sandbox (container in a directory) use the build --sandbox command and option:
$ sudo singularity build --sandbox ubuntu/ docker://ubuntu

This command creates a directory called ubuntu/ with an entire Ubuntu Operating System and some Singularity
metadata in your current working directory. You can use commands like shell, exec , and run with this directory
just as you would with a Singularity image. You can also write files to this directory from within a Singularity session
(provided you have the permissions to do so). These files will be ephemeral and will disappear when the container is
finished executing. However if you use the --writable option the changes will be saved into your directory so that
you can use them the next time you use your container.

1.5.2 Writable Image
If you prefer to have a writable image file, you can build a container with the --writable option.
$ sudo singularity build --writable ubuntu.img docker://ubuntu

This produces an image that is writable with an ext3 file system. Unlike the sandbox, it is a single image file. Also
by convention this file name has an “.img” extension instead of “.simg” . When you want to alter your image, you
can use commands like shell, exec, run, with the --writable option. Because of permission issues it may be
necessary to execute the container as root to modify it.
$ sudo singularity shell --writable ubuntu.img

1.5.3 Converting images from one format to another
The build command allows you to build a container from an existing container. This means that you can use it to
convert a container from one format to another. For instance, if you have already created a sandbox (directory) and
want to convert it to the default immutable image format (squashfs) you can do so:

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$ singularity build new-squashfs sandbox

Doing so may break reproducibility if you have altered your sandbox outside of the context of a recipe file, so you are
advised to exercise care. You can use build to convert containers to and from writable, sandbox, and default
(squashfs) file formats via any of the six possible combinations.

1.5.4 Singularity Recipes
For a reproducible, production-quality container, we recommend that you build a container with the default (squashfs)
file format using a Singularity recipe file. This also makes it easy to add files, environment variables, and install
custom software, and still start from your base of choice (e.g., Singularity Hub). A recipe file has a header and a body.
The header determines what kind of base container to begin with, and the body is further divided into sections (called
scriptlets) that do things like install software, setup the environment, and copy files into the container from the host
system. Here is an example of a recipe file:
Bootstrap: shub
From: singularityhub/ubuntu

%runscript
exec echo "The runscript is the containers default runtime command!"

%files
/home/vanessa/Desktop/hello-kitty.txt

# copied to root of container

/home/vanessa/Desktop/party_dinosaur.gif

/opt/the-party-dino.gif #

%environment
VARIABLE=MEATBALLVALUE
export VARIABLE

%labels
AUTHOR vsochat@stanford.edu

%post
apt-get update && apt-get -y install python3 git wget
mkdir /data
echo "The post section is where you can install, and configure your container."

To build a container from this definition file (assuming it is a file named Singularity), you would call build like so:
$ sudo singularity build ubuntu.simg Singularity

1.5. Build images from scratch

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In this example, the header tells singularity to use a base Ubuntu image from Singularity Hub. The %runscript
section defines actions for the container to take when it is executed (in this case a simple message). The %files
section copies some files into the container from the host system at build time. The %environment section defines
some environment variables that will be available to the container at runtime. The %labels section allows for custom
metadata to be added to the container. And finally the %post section executes within the container at build time after
the base OS has been installed. The %post section is therefore the place to perform installations of custom apps.
This is a very small example of the things that you can do with a recipe file . In addition to building a container from
Singularity Hub, you can start with base images from Docker Hub, use images directly from official repositories such
as Ubuntu, Debian, Centos, Arch, and BusyBox, use an existing container on your host system as a base, or even take
a snapshot of the host system itself and use that as a base image. If you want to build Singularity images without
having singularity installed in a build environment, you can build images using Singularity Hub instead. If you want a
more detailed rundown and examples for different build options, see our singularity flow page.

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CHAPTER

TWO

INTRODUCTION

This document will introduce you to Singularity, and the links in the bar to the left will give you more detail on using
the software. If you want to get a quick rundown, see our quickstart. If you want to understand which commands
are best fit for your usecase, see our build flow page. There is also a separate Singularity Administration Guide that
targets system administrators, so if you are a service provider, or an interested user, it is encouraged that you read that
document as well.

2.1 Welcome to Singularity!
Singularity is a container solution created by necessity for scientific and application driven workloads. Over the
past decade and a half, virtualization has gone from an engineering toy to a global infrastructure necessity and the
evolution of enabling technologies has flourished. Most recently, we have seen the introduction of the latest spin on
virtualization. . . “containers”. People tend to view containers in light of their virtual machine ancestry and these
preconceptions influence feature sets and expected use cases. This is both a good and a bad thing. . . For industry
and enterprise-centric container technologies this is a good thing. Web enabled cloud requirements are very much
in alignment with the feature set of virtual machines, and thus the preceding container technologies. But the idea of
containers as miniature virtual machines is a bad thing for the scientific world and specifically the high performance
computation (HPC) community. While there are many overlapping requirements in these two fields, they differ in
ways that make a shared implementation generally incompatible. Some groups have leveraged custom-built resources
that can operate on a lower performance scale, but proper integration is difficult and perhaps impossible with today’s
technology. Many scientists could benefit greatly by using container technology, but they need a feature set that differs
somewhat from that available with current container technology. This necessity drives the creation of Singularity and
articulated its four primary functions:

2.1.1 Mobility of Compute
Mobility of compute is defined as the ability to define, create and maintain a workflow and be confident that the
workflow can be executed on different hosts, operating systems (as long as it is Linux) and service providers. Being
able to contain the entire software stack, from data files to library stack, and portably move it from system to system
is true mobility. Singularity achieves this by utilizing a distributable image format that contains the entire container
and stack into a single file. This file can be copied, shared, archived, and standard UNIX file permissions also apply.
Additionally containers are portable (even across different C library versions and implementations) which makes
sharing and copying an image as easy as cp or scp or ftp.

2.1.2 Reproducibility
As mentioned above, Singularity containers utilize a single file which is the complete representation of all the files
within the container. The same features which facilitate mobility also facilitate reproducibility. Once a contained

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workflow has been defined, the container image can be snapshotted, archived, and locked down such that it can be
used later and you can be confident that the code within the container has not changed.

2.1.3 User Freedom
System integrators, administrators, and engineers spend a lot of effort maintaining their systems, and tend to take a
cautious approach. As a result, it is common to see hosts installed with production, mission critical operating systems
that are “old” and have few installed packages. Users may find software or libraries that are too old or incompatible
with the software they must run, or the environment may just lack the software stack they need due to complexities
with building, specific software knowledge, incompatibilities or conflicts with other installed programs.
Singularity can give the user the freedom they need to install the applications, versions, and dependencies for their
workflows without impacting the system in any way. Users can define their own working environment and literally
copy that environment image (single file) to a shared resource, and run their workflow inside that image.

2.1.4 Support on Existing Traditional HPC
Replicating a virtual machine cloud like environment within an existing HPC resource is not a reasonable goal for
many administrators. There are a lots of container systems available which are designed for enterprise, as a replacement for virtual machines, are cloud focused, or require unstable or unavailable kernel features. Singularity supports
existing and traditional HPC resources as easily as installing a single package onto the host operating system. Custom
configurations may be achieved via a single configuration file, and the defaults are tuned to be generally applicable
for shared environments. Singularity can run on host Linux distributions from RHEL6 (RHEL5 for versions lower
than 2.2) and similar vintages, and the contained images have been tested as far back as Linux 2.2 (approximately 14
years old). Singularity natively supports InfiniBand, Lustre, and works seamlessly with all resource managers (e.g.
SLURM, Torque, SGE, etc.) because it works like running any other command on the system. It also has built-in
support for MPI and for containers that need to leverage GPU resources.

2.2 A High Level View of Singularity
2.2.1 Security and privilege escalation
A user inside a Singularity container is the same user as outside the container This is one of Singularities defining
characteristics. It allows a user (that may already have shell access to a particular host) to simply run a command
inside of a container image as themselves. Here is a scenario to help articulate this:
%SERVER and %CLUSTER are large expensive systems with resources far exceeding those of my personal workstation. But because the are shared systems, no users have root access. The environments are tightly controlled and
managed by a staff of system administrators. To keep these systems secure, only the system administrators are granted
root access and they control the state of the operating systems and installed applications. If a user is able to escalate
to root (even within a container) on %SERVER or %CLUSTER, they can do bad things to the network, cause denial
of service to the host (as well as other hosts on the same network), and may have unrestricted access to file systems
reachable by the container.
To mitigate security concerns like this, Singularity limits one’s ability to escalate permission inside a container. For
example, if I do not have root access on the target system, I should not be able to escalate my privileges within the
container to root either. This is semi-antagonistic to Singularity’s 3rd tenant; allowing the users to have freedom of
their own environments. Because if a user has the freedom to create and manipulate their own container environment,
surely they know how to escalate their privileges to root within that container. Possible means could be setting the
root user’s password, or enabling themselves to have sudo access. For these reasons, Singularity prevents user context
escalation within the container, and thus makes it possible to run user supplied containers on shared infrastructures.
This mitigation dictates the Singularity workflow. If a user needs to be root in order to make changes to their containers,
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then they need to have an endpoint (a local workstation, laptop, or server) where they have root access. Considering
almost everybody at least has a laptop, this is not an unreasonable or unmanageable mitigation, but it must be defined
and articulated.

2.2.2 The Singularity container image
Singularity makes use of a container image file, which physically contains the container. This file is a physical
representation of the container environment itself. If you obtain an interactive shell within a Singularity container,
you are literally running within that file. This simplifies management of files to the element of least surprise, basic
file permission. If you either own a container image, or have read access to that container image, you can start a shell
inside that image. If you wish to disable or limit access to a shared image, you simply change the permission ACLs to
that file. There are numerous benefits for using a single file image for the entire container:
• Copying or branching an entire container is as simple as cp
• Permission/access to the container is managed via standard file system permissions
• Large scale performance (especially over parallel file systems) is very efficient
• No caching of the image contents to run (especially nice on clusters)
• Containers are compressed and consume very little disk space
• Images can serve as stand-alone programs, and can be executed like any other program on the host
2.2.2.1 Copying, sharing, branching, and distributing your image
A primary goal of Singularity is mobility. The single file image format makes mobility easy. Because Singularity
images are single files, they are easily copied and managed. You can copy the image to create a branch, share the
image and distribute the image as easily as copying any other file you control!
If you want an automated solution for building and hosting your image, you can use our container registry Singularity
Hub. Singularity Hub can automatically build Singularity recipe files from a GitHub repository each time that you
push. It provides a simple cloud solution for storing and sharing your image. If you want to host your own Registry,
then you should check out Singularity Registry. If you have ideas or suggestions for how Singularity can better support
reproducible science, please reach out!.
2.2.2.2 Supported container formats
• squashfs: the default container format is a compressed read-only file system that is widely used for things like
live CDs/USBs and cell phone OS’s
• ext3: (also called writable) a writable image file containing an ext3 file system that was the default container
format prior to Singularity version 2.4
• directory: (also called sandbox) standard Unix directory containing a root container image
• tar.gz: zlib compressed tar archive
• tar.bz2: bzip2 compressed tar archive
• tar: uncompressed tar archive
2.2.2.3 Supported URIs
Singularity also supports several different mechanisms for obtaining the images using a standard URI format.

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• shub:// Singularity Hub is our own registry for Singularity containers. If you want to publish a container, or give
easy access to others from their command line, or enable automatic builds, you should build it on Singularity
Hub.
• docker:// Singularity can pull Docker images from a Docker registry, and will run them non-persistently (e.g.
changes are not persisted as they can not be saved upstream). Note that pulling a Docker image implies assembling layers at runtime, and two subsequent pulls are not guaranteed to produce an identical image.
• instance:// A Singularity container running as service, called an instance, can be referenced with this URI.

2.2.3 Name-spaces and isolation
When asked, “What namespaces does Singularity virtualize?”, the most appropriate response from a Singularity use
case is “As few as possible!”. This is because the goals of Singularity are mobility, reproducibility and freedom, not
full isolation (as you would expect from industry driven container technologies). Singularity only separates the needed
namespaces in order to satisfy our primary goals.
Coupling incomplete isolation with the fact that a user inside a container is the same user outside the container, allows
Singularity to blur the lines between a container and the underlying host system. Using Singularity feels like running in
a parallel universe, where there are two timelines. In one timeline, the system administrators installed their operating
system of choice. But on an alternate timeline, we bribed the system administrators and they installed our favorite
operating system and apps, and gave us full control but configured the rest of the system identically. And Singularity
gives us the power to pick between these two timelines. In other words, Singularity allows you to virtually swap
out the underlying operating system for one that you’ve defined without affecting anything else on the system and
still having all of the host resources available to us. It’s like ssh’ing into another identical host running a different
operating system. One moment you are on Centos-6 and the next minute you are on the latest version of Ubuntu that
has Tensorflow installed, or Debian with the latest OpenFoam, or a custom workflow that you installed. But you are
still the same user with the same files running the same PIDs. Additionally, the selection of name-space virtualization
can be dynamic or conditional. For example, the PID namespace is not separated from the host by default, but if you
want to separate it, you can with a command line (or environment variable) setting. You can also decide you want to
contain a process so it can not reach out to the host file system if you don’t know if you trust the image. But by default,
you are allowed to interface with all of the resources, devices and network inside the container as you are outside the
container.

2.2.4 Compatibility with standard work-flows, pipes and IO
Singularity abstracts the complications of running an application in an environment that differs from the host. For
example, applications or scripts within a Singularity container can easily be part of a pipeline that is being executed
on the host. Singularity containers can also be executed from a batch script or other program (e.g. an HPC system’s
resource manager) natively. Some usage examples of Singularity can be seen as follows:
$ singularity exec dummy.img xterm

# run xterm from within the container

$ singularity exec dummy.img python script.py
˓→using container's python

# run a script on the host system

$ singularity exec dummy.img python < /path/to/python/script.py
˓→redirection

# do the same via

$ cat /path/to/python/script.py | singularity exec dummy.img python
˓→via a pipe

# do the same

You can even run MPI executables within the container as simply as:

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$ mpirun -np X singularity exec /path/to/container.img /usr/bin/mpi_program_inside_
˓→container (mpi program args)

2.2.5 The Singularity Process Flow
When executing container commands, the Singularity process flow can be generalized as follows:
1. Singularity application is invoked
2. Global options are parsed and activated
3. The Singularity command (subcommand) process is activated
4. Subcommand options are parsed
5. The appropriate sanity checks are made
6. Environment variables are set
7. The Singularity Execution binary is called (sexec)
8. Sexec determines if it is running privileged and calls the SUID code if necessary
9. Namespaces are created depending on configuration and process requirements
10. The Singularity image is checked, parsed, and mounted in the namespace
11. Bind mount points are setup so that files on the host are visible in the CLONE_NEWNS container
12. The namespace CLONE_FS is used to virtualize a new root file system
13. Singularity calls execvp() and Singularity process itself is replaced by the process inside the container
14. When the process inside the container exits, all namespaces collapse with that process, leaving a clean system
All of the above steps take approximately 15-25 thousandths of a second to run, which is fast enough to seem instantaneous.

2.3 The Singularity Usage Workflow
The security model of Singularity (as described above, “A user inside a Singularity container is the same user as outside
the container”) defines the Singularity workflow. There are generally two groups of actions you must implement on a
container; management (building your container) and usage.
In many circumstances building containers require root administrative privileges just like these actions would require
on any system, container, or virtual machine. This means that a user must have access to a system on which they have
root privileges. This could be a server, workstation, a laptop, virtual machine, or even a cloud instance. If you are
using OS X or Windows on your laptop, it is recommended to setup Vagrant, and run Singularity from there (there are
recipes for this which can be found at Once you have Singularity installed on your endpoint of choice, this is where
you will do the bulk of your container development. This workflow can be described visually as follows:
On the left side, you have your build environment: a laptop, workstation, or a server that you control. Here you will
(optionally):
1. develop and test containers using --sandbox (build into a writable directory) or --writable (build into a
writable ext3 image)
2. build your production containers with a squashfs filesystem.

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Fig. 1: Singularity workflow
Once you have the container with the necessary applications, libraries and data inside it can be easily shared to other
hosts and executed without requiring root access. A production container should be an immutable object, so if you
need to make changes to your container you should go back to your build system with root privileges, rebuild the
container with the necessary changes, and then re-upload the container to the production system where you wish to
run it.

2.3.1 Singularity Commands
How do the commands work?
Here is where to look for more information:
• build : Build a container on your user endpoint or build environment
• exec : Execute a command to your container
• inspect : See labels, run and test scripts, and environment variables
• pull : pull an image from Docker or Singularity Hub
• run : Run your image as an executable
• shell : Shell into your image
Image Commands
• image.import : import layers or other file content to your image
• image.export : export the contents of the image to tar or stream
• image.create : create a new image, using the old ext3 filesystem
• image.expand : increase the size of your image (old ext3)

Instance Commands
Instances were added in 2.4. This list is brief, and likely to expand with further development.
• instances : Start, stop, and list container instances
Deprecated Commands The following commands are deprecated in 2.4 and will be removed in future releases.

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• bootstrap : Bootstrap a container recipe

2.4 Support
Have a question, or need further information? Reach out to us.

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CHAPTER

THREE

INSTALLATION

This document will guide you through the process of installing Singularity from source with the version and location
of your choice.

3.1 Before you begin
If you have an earlier version of Singularity installed, you should remove it before executing the installation commands.
These instructions will build Singularity from source on your system. So you will need to have some development
tools installed. If you run into missing dependencies, try installing them like so:
$ sudo apt-get update && \
sudo apt-get install \
python \
dh-autoreconf \
build-essential \
libarchive-dev
$ sudo yum update && \
sudo yum groupinstall 'Development Tools' && \
sudo yum install libarchive-devel

3.2 Install the master branch
The following commands will install the latest version of the GitHub repo master branch to /usr/local.
$ git clone https://github.com/singularityware/singularity.git
$ cd singularity
$ ./autogen.sh
$ ./configure --prefix=/usr/local --sysconfdir=/etc
(continues on next page)

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(continued from previous page)

$ make
$ sudo make install

If you omit the --sysconfdir option , the configuration file will be installed in /usr/local/etc. If you omit
the --prefix option, Singularity will be installed in the /usr/local directory hierarchy by default. And if you
specify a custom directory with the --prefix option, all of Singularity’s binaries and the configuration file will be
installed within that directory. This last option can be useful if you want to install multiple versions of Singularity,
install Singularity on a shared system, or if you want to remove Singularity easily after installing it.

3.3 Install a specific release
The following commands will install a specific release from GitHub releases page to /usr/local.
$ VER=2.5.1
$ wget https://github.com/singularityware/singularity/releases/download/$VER/
˓→singularity-$VER.tar.gz
$ tar xvf singularity-$VER.tar.gz
$ cd singularity-$VER
$ ./configure --prefix=/usr/local --sysconfdir=/etc
$ make
$ sudo make install

3.4 Install the development branch
If you want to test a development branch the routine above should be tweaked slightly:
$ git clone https://github.com/singularityware/singularity.git
$ cd singularity
$ git fetch
$ git checkout development
$ ./autogen.sh
$ ./configure --prefix=/usr/local --sysconfdir=/etc
$ make
$ sudo make install

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3.5 Remove an old version
Let’s say that we installed Singularity to /usr/local. To remove it completely, you need to hit all of the following:
$ sudo rm -rf /usr/local/libexec/singularity
$ sudo rm -rf /usr/local/etc/singularity
$ sudo rm -rf /usr/local/include/singularity
$ sudo rm -rf /usr/local/lib/singularity
$ sudo rm -rf /usr/local/var/lib/singularity/
$ sudo rm /usr/local/bin/singularity
$ sudo rm /usr/local/bin/run-singularity
$ sudo rm /usr/local/etc/bash_completion.d/singularity
$ sudo rm /usr/local/man/man1/singularity.1

If you modified the system configuration directory, remove the singularity.conf file there as well. If you
installed Singularity in a custom directory, you need only remove that directory to uninstall Singularity. For instance if
you installed singularity with the --prefix=/some/temp/dir option argument pair, you can remove Singularity
like so:
$ sudo rm -rf /some/temp/dir

What should you do next? You can check out the quickstart guide, or learn how to interact with your container via the
shell , exec , or run commands. Or click next below to continue reading.

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CHAPTER

FOUR

BUILD A CONTAINER

build is the “Swiss army knife” of container creation. You can use it to download and assemble existing containers
from external resources like Singularity Hub and Docker Hub. You can use it to convert containers between the various
formats supported by Singularity. And you can use it in conjunction with a Singularity recipe file to create a container
from scratch and customized it to fit your needs.

4.1 Overview
The build command accepts a target as input and produces a container as output.
The target defines the method that build uses to create the container. It can be one of the following:
• URI beginning with shub:// to build from Singularity Hub
• URI beginning with docker:// to build from Docker Hub
• path to a existing container on your local machine
• path to a directory to build from a sandbox
• path to an archive in .tar or compressed .tar.gz format
• path to a Singularity recipe file
In addition build can produce containers in three different formats. Formats types can be specified by passing the
following options to build.
• compressed read-only squashfs file system suitable for production (default)
• writable ext3 file system suitable for interactive development ( --writable option )
• writable (ch)root directory called a sandbox for interactive development ( --sandbox option)
Because build can accept an existing container as a target and create a container in any of these three formats you
can convert existing containers from one format to another.
The following diagram illustrates the targets that can be supplied to build as inputs and the containers build can
produce as outputs. Green arrows represent operations that can be carried out without root privileges (though the
container may not perform properly when run as root). Red arrows represent operations that must be carried out with
root privileges.

4.2 Downloading a existing container from Singularity Hub
You can use the build command to download a container from Singularity Hub.

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Fig. 1: Singularity build process

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$ singularity build lolcow.simg shub://GodloveD/lolcow

The first argument (lolvow.simg) specifies a path and name for your container. The second argument (shub://
GodloveD/lolcow) gives the Singularity Hub URI from which to download. But default the container will be converted to a compressed, read-only squashfs file. If you want your container in a different format use the --writable
or --sandbox options.

4.3 Downloading a existing container from Docker Hub
You can use build to download layers from Docker Hub and assemble them into Singularity containers.
$ singularity build lolcow.simg docker://godlovedc/lolcow

4.4 Creating --writable images and --sandbox directories
4.4.1 --writable
If you wanted to create a writable ext3 image similar to those used by Singularity version < 2.4, you could do so with
the --writable option. You must create writable containers as root.
Extending the Singularity Hub example from above:
$ sudo singularity build --writable lolcow.img shub://GodloveD/lolcow

The resulting container is writable, but is still mounted as read-only when executed with commands such as run,
exec, and shell. To mount the container as read-write when using these commands add the --writable option
to them as well.
To ensure that you have the proper permissions to write to the container as you like, it is also a good idea to make
changes as root. For example:
$ sudo singularity shell --writable lolcow.img

4.4.2 --sandbox
If you wanted to create a container within a writable directory (called a sandbox) you could do so with the --sandbox
option. It’s possible to create a sandbox without root privileges, but to ensure proper file permissions it is recommended
to do so as root.
$ sudo singularity build --sandbox lolcow/ shub://GodloveD/lolcow

The resulting directory operates just like a container in an image file. You are permitted to make changes and write
files within the directory, but those changes will not persist when you are finished using the container. To make your
changes persistent, use the --writable flag when you invoke your container. Once again, it’s a good idea to do this
as root to ensure you have permission to access the files and directories that you want to change.
$ sudo singularity shell --writable lolcow/

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4.5 Converting containers from one format to another
If you already have a container saved locally, you can use it as a target to build a new container. This allows you convert
containers from one format to another. For example if you had a squashfs container called production.simg and
wanted to convert it to a writable ext3 container called development.img you could:
$ sudo singularity build --writable development.img production.simg

Similarly, to convert it to a writable directory (a sandbox):
$ singularity build --sandbox development/ production.simg

If you omit any options you can also convert your sandbox back to a read-only compressed squashfs image suitable
for use in a production environment:
$ singularity build production2 development/

You can convert the three supported container formats using any combination.
Use care when converting writable ext3 images or sandbox directories to the default squashfs file format. If changes
were made to the writable container before conversion, there is no record of those changes in the Singularity recipe file
rendering your container non-reproducible. It is a best practice to build your immutable production containers directly
from a Singularity recipe file instead.

4.6 Building containers from Singularity recipe files
Of course, Singularity recipe files can be used as the target when building a container. For detailed information on
writing Singularity recipe files, please see the Container Recipes docs. Let’s say you already have the following
container recipe file called Singularity , and you want to use it to build a container.
Bootstrap: docker
From: ubuntu:16.04

%post
apt-get -y update
apt-get -y install fortune cowsay lolcat

%environment
export LC_ALL=C
export PATH=/usr/games:$PATH

%runscript
fortune | cowsay | lolcat

You can do so with the following command.

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$ sudo singularity build lolcow.simg Singularity

The command requires sudo just as installing software on your local machine requires root privileges.

4.6.1 --force
You can build into the same container multiple times (though the results may be unpredictable and it is generally better
to delete your container and start from scratch).
By default if you build into an existing container, the build command will skip the steps involved in adding a new
base. You can override this default with the --force option requiring that a new base OS is bootstrapped into the
existing container. This behavior does not delete the existing OS, it just adds the new OS on top of the existing one.
Use care with this option: you may get results that you did not expect.

4.6.2 --section
If you only want to build a single section of your Singularity recipe file use the --section option. For instance, if
you have edited the %environment section of a long Singularity recipe and don’t want to completely re-build the
container, you could re-build only the %environment section like so:
$ sudo singularity build --section environment image.simg Singularity

Under normal build conditions, the Singularity recipe file is saved into a container’s meta-data so that there is a record
showing how the container was built. Using the --section option may render this meta-data useless, so use care if
you value reproducibility.

4.6.3 --notest
If you don’t want to run the %test section during the container build, you can skip it with the --notest option.
For instance, maybe you are building a container intended to run in a production environment with GPUs. But perhaps
your local build resource does not have GPUs. You want to include a %test section that runs a short validation but
you don’t want your build to exit with an error because it cannot find a GPU on your system.
$ sudo singularity build GPU.simg --notest Singularity

4.6.4 --checks
Checks are a new feature (in 2.4) that offer an easy way for an admin to define a security (or any other kind of check)
to be run on demand for a Singularity image. They are defined (and run) via different tags.
CHECKS OPTIONS:
-c|--checks

enable checks

-t|--tag

specify a check tag (not default)

-l|--low

Specify low threshold (all checks, default)

-m|--med

Perform medium and high checks

-h|--high

Perform only checks at level high

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When you add the --checks option along with applicable tags to the build command Singularity will run the
desired checks on your container at build time. See singularity check --help for available tags.

4.7 More Build topics
• If you want to customize the cache location (where Docker layers are downloaded on your system), specify
Docker credentials, or any custom tweaks to your build environment, see build environment.
• If you want to make internally modular containers, check out the getting started guide here
• If you want to build your containers on Singularity Hub, (because you don’t have root access on a Linux
machine or want to host your container on the cloud) check out this guide

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CHAPTER

FIVE

BUILD ENVIRONMENT

It’s commonly the case that you want to customize your build environment, such as specifying a custom cache directory
for layers, or sending your Docker Credentials to the registry endpoint. Here we will discuss those things

5.1 Cache Folders
To make download of layers for build and pull faster and less redundant, we use a caching strategy. By default, the
Singularity software will create a set of folders in your $HOME directory for docker layers, Singularity Hub images,
and Docker metadata, respectively:
$HOME/.singularity
$HOME/.singularity/docker
$HOME/.singularity/shub
$HOME/.singularity/metadata

Fear not, you have control to customize this behavior! If you don’t want the cache to be created (and a temporary
directory will be used), set SINGULARITY_DISABLE_CACHE to True/yes, or if you want to move it elsewhere, set
SINGULARITY_CACHEDIR to the full path where you want to cache. Remember that when you run commands as
sudo this will use root’s home at /root and not your user’s home.

5.2 Temporary Folders
Singularity also uses some temporary directories to build the squashfs filesystem, so this temp space needs to be large
enough to hold the entire resulting Singularity image. By default this happens in /tmp but can be overridden by
setting SINGULARITY_TMPDIR to the full path where you want the squashfs temp files to be stored. Since images
are typically built as root, be sure to set this variable in root’s environment.
If you are building an image on the fly, for example
singularity exec docker://busybox /bin/sh

by default a temporary runtime directory is created that looks like /tmp/.singularity-runtime.xxxxxxxx.
This can be problematic for some /tmp directories that are hosted at Jetstream/OpenStack, Azure, and possibly EC2, which are very small. If you need to change the location of this runtime, then export the variable
SINGULARITY_LOCALCACHEDIR.

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SINGULARITY_LOCALCACHEDIR=/tmp/pancakes
export SINGULARITY_LOCALCACHEDIR
singularity exec docker://busybox /bin/sh

The above runtime folder would be created under /tmp/pancakes/.singularity-runtime.xxxxxxxx

5.3 Pull Folder
For details about customizing the output location of pull, see the pull docs. You have the similar ability to set it to be
something different, or to customize the name of the pulled image.

5.4 Environment Variables
All environmental variables are parsed by Singularity python helper functions, and specifically the file defaults.py is
a gateway between variables defined at runtime, and pre-defined defaults. By way of import from the file, variables
set at runtime do not change if re-imported. This was done intentionally to prevent changes during the execution, and
could be changed if needed. For all variables, the order of operations works as follows:
1. First preference goes to environment variable set at runtime
2. Second preference goes to default defined in this file
3. Then, if neither is found, null is returned except in the case that required=True. A required=True
variable not found will system exit with an error.
4. Variables that should not be displayed in debug logger are set with silent=True, and are only reported to be
defined.
For boolean variables, the following are acceptable for True, with any kind of capitalization or not:
("yes", "true", "t", "1","y")

5.5 Cache
The location and usage of the cache is also determined by environment variables.
SINGULARITY_DISABLE_CACHE If you want to disable the cache, this means is that the layers are written to a temporary directory. Thus, if you want to disable cache and write to a temporary folder, simply set
SINGULARITY_DISABLE_CACHE to any true/yes value. By default, the cache is not disabled.
SINGULARITY_CACHEDIR Is the base folder for caching layers and singularity hub images. If not defined, it
uses default of $HOME/.singularity. If defined, the defined location is used instead.
If SINGULARITY_DISABLE_CACHE is set to True, this value is ignored in favor of a temporary directory. For specific sub-types of things to cache, subdirectories are created (by python), including $SINGULARITY_CACHEDIR/
docker for docker layers and $SINGULARITY_CACHEDIR/shub for Singularity Hub images. If the cache is not
created, the Python script creates it.
SINGULARITY_PULLFOLDER While this isn’t relevant for build, since build is close to pull, we will include it
here. By default, images are pulled to the present working directory. The user can change this variable to change that.

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SINGULARITY_TMPDIR Is the base folder for squashfs image temporary building. If not defined, it uses default
of $TEMPDIR. If defined, the defined location is used instead.
SINGULARITY_LOCALCACHEDIR Is the temporary folder (default /tmp) to generate runtime folders (containers “on the fly”) typically a run, exec , or shell or a docker:// image. This is different from where
downloaded layers are cached ($SINGULARITY_CACHEDIR) or pulled (SINGULARITY_PULLFOLDER) or where
a (non on-the-fly build) happens ( $SINGULARITY_TMPDIR ). See temporary folders above for an example. You
can generally determine the value of this setting by running a command with --debug , and seeing the last line
“Removing directory:”
singularity --debug run docker://busybox echo "pizza!"
...
DEBUG
[U=1000,P=960]
s_rmdir()
˓→directory: /tmp/.singularity-runtime.oArO0k

Removing

5.5.1 Defaults
The following variables have defaults that can be customized by you via environment variables at runtime.
5.5.1.1 Docker
DOCKER_API_BASE Set as index.docker.io, which is the name of the registry. In the first version of Singularity we parsed the Registry argument from the build spec file, however now this is removed because it can be
obtained directly from the image name (eg, registry/namespace/repo:tag). If you don’t specify a registry
name for your image, this default is used. If you have trouble with your registry being detected from the image URI,
use this variable.
DOCKER_API_VERSION Is the version of the Docker Registry API currently being used, by default now is v2.
DOCKER_OS This is exposed via the exported environment variable SINGULARITY_DOCKER_OS and pertains to
images that reveal a version 2 manifest with a manifest list. In the case that the list is present, we must choose an
operating system (this variable) and an architecture (below). The default is linux.
DOCKER_ARCHITECTURE
This
is
exposed
via
the
exported
environment
variable
SINGULARITY_DOCKER_ARCHITECTURE and the same applies as for the DOCKER_OS with regards to being used in context of a list of manifests. In the case that the list is present, we must choose an architecture (this
variable) and an os (above). The default is amd64, and other common ones include arm, arm64, ppc64le, 386,
and s390x. NAMESPACE Is the default namespace, library.
RUNSCRIPT_COMMAND Is not obtained from the environment, but is a hard coded default (“/bin/bash”). This is
the fallback command used in the case that the docker image does not have a CMD or ENTRYPOINT. TAG Is the
default tag, latest.
SINGULARITY_NOHTTPS This is relevant if you want to use a registry that doesn’t have https, and it speaks
for itself. If you export the variable SINGULARITY_NOHTTPS you can force the software to not use https when
interacting with a Docker registry. This use case is typically for use of a local registry.
5.5.1.2 Singularity Hub
SHUB_API_BASE The default base for the Singularity Hub API, which is https://singularity-hub.org/
api. If you deploy your own registry, you don’t need to change this, you can again specify the registry name in the
URI.

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5.5.2 General
SINGULARITY_PYTHREADS The Python modules use threads (workers) to download layer files for
Docker, and change permissions.
By default, we will use 9 workers, unless the environment variable
SINGULARITY_PYTHREADS is defined. SINGULARITY_COMMAND_ASIS By default, we want to make sure
the container running process gets passed forward as the current process, so we want to prefix whatever the Docker
command or entrypoint is with exec. We also want to make sure that following arguments get passed, so we append
"$@". Thus, some entrypoint or cmd might look like this:
/usr/bin/python

and we would parse it into the runscript as:
exec /usr/bin/python "$@"

However, it might be the case that the user does not want this. For this reason, we have the environmental variable
RUNSCRIPT_COMMAND_ASIS. If defined as yes/y/1/True/true, etc., then the runscript will remain as /usr/bin/
python.

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CHAPTER

SIX

CONTAINER RECIPES

A Singularity Recipe is the driver of a custom build, and the starting point for designing any custom container. It
includes specifics about installation software, environment variables, files to add, and container metadata. You can
even write a help section, or define modular components in the container called based on the Scientific Filesystem.

6.1 Overview
A Singularity Recipe file is divided into several parts:
1. Header: The Header describes the core operating system to build within the container. Here you will configure the base operating system features that you need within your container. Examples of this include, what
distribution of Linux, what version, what packages must be part of a core install.
2. Sections: The rest of the definition is comprised of sections, sometimes called scriptlets or blobs of data. Each
section is defined by a % character followed by the name of the particular section. All sections are optional.
Sections that are executed at build time are executed with the /bin/sh interpreter and can accept bin/sh
options. Similarly, sections that produce scripts to be executed at runtime can accept options intended for /
bin/sh

Please see the examples directory in the Singularity source code for some ideas on how to get started.

6.1.1 Header
The header is at the top of the file, and tells Singularity the base Operating System that it should use to build the
container. It is composed of several keywords. Specifically:
• Bootstrap: references the kind of base you want to use (e.g., docker, debootstrap, shub). For example, a
shub bootstrap will pull containers for shub as bases. A Docker bootstrap will pull docker layers to start your
image. For a full list see build
• From: is the named container (shub) or reference to layers (Docker) that you want to use (e.g., vsoch/helloworld)

Depending on the value assigned to Bootstrap, other keywords may also be valid in the header.
For example, a very minimal Singularity Hub build might look like this:

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Bootstrap: shub
From: vsoch/hello-world

A build that uses a mirror to install Centos-7 might look like this:
Bootstrap: yum
OSVersion: 7
MirrorURL: http://mirror.centos.org/centos-%{OSVERSION}/%{OSVERSION}/os/$basearch/
Include: yum

Each build base requires particular details during build time. You can read about them and see examples at the
following links:
• shub (images hosted on Singularity Hub)
• docker (images hosted on Docker Hub)
• localimage (images saved on your machine)
• yum (yum based systems such as CentOS and Scientific Linux)
• debootstrap (apt based systems such as Debian and Ubuntu)
• arch (Arch Linux)
• busybox (BusyBox)
• zypper (zypper based systems such as Suse and OpenSuse)

6.1.2 Sections
The main content of the bootstrap file is broken into sections. Different sections add different content or execute
commands at different times during the build process. Note that if any command fails, the build process will halt.
Let’s add each section to our container to see how it works. For each section, we will build the container from the
recipe (a file called Singularity) as follows:
$ sudo singularity build roar.simg Singularity

6.1.2.1 %help
You don’t need to do much programming to add a %help section to your container. Just write it into a section:
Bootstrap: docker
From: ubuntu

%help
Help me. I'm in the container.

And it will work when the user asks the container for help.

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$ singularity help roar.simg
Help me. I'm in the container.

6.1.2.2 %setup
Commands in the %setup section are executed on the host system outside of the container after the base OS has
been installed. For versions earlier than 2.3 if you need files during %post, you should copy files from your host to
$SINGULARITY_ROOTFS to move them into the container. For >2.3 you can add files to the container (added before
%post) using the %files section. We can see the difference between %setup and %post in the following asciicast:
In the above, we see that copying something to $SINGULARITY_ROOTFS during %setup was successful to move
the file into the container, but copying during %post was not. Let’s add a setup to our current container, just writing
a file to the root of the image:
Bootstrap: docker
From: ubuntu

%help
Help me. I'm in the container.

%setup
touch ${SINGULARITY_ROOTFS}/tacos.txt
touch avocados.txt

Importantly, notice that the avocados file isn’t relative to $SINGULARITY_ROOTFS, so we would expect it not to be
in the image. Is tacos there?
$ singularity exec roar.simg ls /
bin

environment

lib

mnt

root

scif

sys

boot

etc

lib64

opt

run

singularity

dev

home

media

proc

sbin

srv

usr

**tacos.txt**

var

tmp

Yes! And avocados.txt isn’t inside the image, but in our present working directory:
$ ls
avocados.txt

roar.simg

Singularity

6.1.2.3 %files
If you want to copy files from your host system into the container, you should do so using the %files section.
Each line is a pair of  and , where the source is a path on your host system, and the
destination is a path in the container.

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The %files section uses the traditional cp command, so the same conventions apply Files are copied before any
%post or installation procedures for Singularity versions >2.3. If you are using a legacy version, files are copied after
%post so you must do this via %setup. Let’s add the avocado.txt into the container, to join tacos.txt.
Bootstrap: docker
From: ubuntu

%help
Help me. I'm in the container.

# Both of the below are copied before %post
# 1. This is how to copy files for legacy < 2.3

%setup
touch ${SINGULARITY_ROOTFS}/tacos.txt
touch avocados.txt

# 2. This is how to copy files for >= 2.3

%files
avocados.txt
avocados.txt /opt

Notice that I’m adding the same file to two different places. For the first, I’m adding the single file to the root of the
image. For the second, I’m adding it to opt. Does it work?
$ singularity exec roar.simg ls /
singularity exec roar.simg ls /
**avocados.txt**
bin
boot

dev

environment
etc

home

media

proc

sbin

srv

lib

mnt

root

scif

sys

lib64

opt

run

singularity

tmp
usr

**tacos.txt**

var

$ singularity exec roar.simg ls /opt
**avocados.txt**

We have avocados!

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6.1.2.4 %labels
To store metadata with your container, you can add them to the %labels section. They will be stored in the file
/.singularity.d/labels.json as metadata within your container. The general format is a LABELNAME
followed by a LABELVALUE. Labels from Docker bootstraps will be carried forward here. Let’s add to our example:
Bootstrap: docker
From: ubuntu

%help
Help me. I'm in the container.

%setup
touch ${SINGULARITY_ROOTFS}/tacos.txt
touch avocados.txt

%files
avocados.txt
avocados.txt /opt

%labels
Maintainer Vanessasaurus
Version v1.0

The easiest way to see labels is to inspect the image:
$ singularity inspect roar.simg
{
"org.label-schema.usage.singularity.deffile.bootstrap": "docker",
"MAINTAINER": "Vanessasaurus",
"org.label-schema.usage.singularity.deffile": "Singularity",
"org.label-schema.usage": "/.singularity.d/runscript.help",
"org.label-schema.schema-version": "1.0",
"VERSION": "v1.0",
"org.label-schema.usage.singularity.deffile.from": "ubuntu",
"org.label-schema.build-date": "2017-10-02T17:00:23-07:00",
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(continued from previous page)

"org.label-schema.usage.singularity.runscript.help": "/.singularity.d/runscript.
˓→help",
"org.label-schema.usage.singularity.version": "2.3.9-development.g3dafa39",
"org.label-schema.build-size": "1760MB"
}

You’ll notice some other labels that are captured automatically from the build process. You can read more about labels
and metadata here.
6.1.2.5 %environment
As of Singularity 2.3, you can add environment variables to your Singularity Recipe in a section called
%environment. Keep in mind that these environment variables are sourced at runtime and not at build time. This
means that if you need the same variables during build time, you should also define them in your %post section.
Specifically:
• during build: the %environment section is written to a file in the container’s metadata folder. This file is not
sourced.
• during runtime: the file written to the container’s metadata folder is sourced.
Since the file is ultimately sourced, you should generally use the same conventions that you might use in a bashrc
or profile. In the example below, the variables VADER and LUKE would not be available during build, but when the
container is finished and run:
Bootstrap: docker
From: ubuntu

%help
Help me. I'm in the container.

%setup
touch ${SINGULARITY_ROOTFS}/tacos.txt
touch avocados.txt

%files
avocados.txt
avocados.txt /opt

%labels
Maintainer Vanessasaurus
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(continued from previous page)

Version v1.0

%environment
VADER=badguy
LUKE=goodguy
SOLO=someguy
export VADER LUKE SOLO

For the rationale behind this approach and why we do not source the %environment section at build time, refer to this
issue. When the container is finished, you can easily see environment variables also with inspect, and this is done by
showing the file produced above:
$ singularity inspect -e roar.simg # Custom environment shell code should follow

VADER=badguy
LUKE=goodguy
SOLO=someguy
export VADER LUKE SOLO

or in the case of variables generated at build time, you can add environment variables to your container in the %post
section (see below) using the following syntax:
%post
echo 'export JAWA_SEZ=wutini' >> $SINGULARITY_ENVIRONMENT

When we rebuild, is it added to the environment?
singularity exec roar.simg env | grep JAWA
JAWA_SEZ=wutini

Where are all these environment variables going? Inside the container is a metadata folder located at /.
singularity.d, and a subdirectory env for environment scripts that are sourced. Text in the %environment
section is appended to a file called /.singularity.d/env/90-environment.sh. Text redirected
to the SINGULARITY_ENVIRONMENT variable will added to a file called /.singularity.d/env/
91-environment.sh. At runtime, scripts in /.singularity/env are sourced in order. This means that
variables in $SINGULARITY_ENVIRONMENT take precedence over those added via %environment. Note that
you won’t see these variables in the inspect output, as inspect only shows the contents added from %environment.
See Environment and Metadata for more information about the %labels and %environment sections.
6.1.2.6 %post
Commands in the %post section are executed within the container after the base OS has been installed at build time.
This is where the meat of your setup will live, including making directories, and installing software and libraries. We

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will jump from our simple use case to show a more realistic scientific container. Here we are installing yum, openMPI,
and other dependencies for a Centos7 bootstrap:
%post
echo "Installing Development Tools YUM group"
yum -y groupinstall "Development Tools"
echo "Installing OpenMPI into container..."

# Here we are at the base, /, of the container
git clone https://github.com/open-mpi/ompi.git

# Now at /ompi
cd ompi
./autogen.pl
./configure --prefix=/usr/local
make
make install

/usr/local/bin/mpicc examples/ring_c.c -o /usr/bin/mpi_ring

You cannot copy files from the host to your container in this section, but you can of course download with commands
like git clone and wget and curl.
6.1.2.7 %runscript
The %runscript is another scriptlet, but it does not get executed during bootstrapping. Instead it gets persisted
within the container to a file (or symlink for later versions) called singularity which is the execution driver when
the container image is run (either via the singularity run command or via executing the container directly).
When the %runscript is executed, all options are passed along to the executing script at runtime, this means that
you can (and should) manage argument processing from within your runscript. Here is an example of how to do that,
adding to our work in progress:
Bootstrap: docker
From: ubuntu

%help
Help me. I'm in the container.

%setup
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(continued from previous page)

touch ${SINGULARITY_ROOTFS}/tacos.txt
touch avocados.txt

%files
avocados.txt
avocados.txt /opt

%labels
Maintainer Vanessasaurus
Version v1.0

%environment
VADER=badguy
LUKE=goodguy
SOLO=someguy
export VADER LUKE SOLO

%post
echo 'export JAWA_SEZ=wutini' >> $SINGULARITY_ENVIRONMENT

%runscript
echo "Rooooar!"
echo "Arguments received: $*"
exec echo "$@"

In this particular runscript, the arguments are printed as a single string ($*) and then they are passed to echo via a
quoted array ($@) which ensures that all of the arguments are properly parsed by the executed command. Using the
exec command is like handing off the calling process to the one in the container. The final command (the echo)
replaces the current entry in the process table (which originally was the call to Singularity). This makes it so the
runscript shell process ceases to exist, and the only process running inside this container is the called echo command.
This could easily be another program like python, or an analysis script. Running it, it works as expected:
$ singularity run roar.simg
Rooooar!
Arguments received:
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(continued from previous page)

$ singularity run roar.simg one two
Rooooar!
Arguments received: one two
one two

6.1.2.8 %test
You may choose to add a %test section to your definition file. This section will be run at the very end of the build
process and will give you a chance to validate the container during the bootstrap process. You can also execute this
scriptlet through the container itself, such that you can always test the validity of the container itself as you transport
it to different hosts. Extending on the above Open MPI %post, consider this real world example:
%test
/usr/local/bin/mpirun --allow-run-as-root /usr/bin/mpi_test

This is a simple Open MPI test to ensure that the MPI is build properly and communicates between processes as it
should. If you want to build without running tests (for example, if the test needs to be done in a different environment),
you can do so with the --notest argument:
$ sudo singularity build --notest mpirun.simg Singularity

This argument is useful in cases where you need hardware that is available during runtime, but is not available on the
host that is building the image.

6.2 Apps
What if you want to build a single container with two or three different apps that each have their own runscripts and
custom environments? In some circumstances, it may be redundant to build different containers for each app with
almost equivalent dependencies.
Starting in Singularity 2.4 all of the above commands can also be used in the context of internal modules called apps
based on the Standard Container Integration Format. For details on apps, see the apps documentation. For a quick
rundown of adding an app to your container, here is an example runscript:
Bootstrap: docker
From: ubuntu

%environment
VADER=badguy
LUKE=goodguy
SOLO=someguy
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(continued from previous page)

export VADER LUKE SOLO

%labels
Maintainer Vanessasaur

##############################
# foo
##############################

%apprun foo
exec echo "RUNNING FOO"

%applabels foo
BESTAPP=FOO
export BESTAPP

%appinstall foo
touch foo.exec

%appenv foo
SOFTWARE=foo
export SOFTWARE

%apphelp foo
This is the help for foo.

%appfiles foo
avocados.txt

##############################
# bar
##############################
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(continued from previous page)

%apphelp bar
This is the help for bar.

%applabels bar
BESTAPP=BAR
export BESTAPP

%appinstall bar
touch bar.exec

%appenv bar
SOFTWARE=bar
export SOFTWARE

Importantly, note that the apps can exist alongside any and all of the primary sections (e.g. %post or %runscript
), and the new %appinstall section is the equivalent of %post but for an app. The title sections (######) aren’t
necessary or required, they are just comments to show you the different apps. The ordering isn’t important either, you
can have any mixture of sections anywhere in the file after the header. The primary difference is now the container can
perform any of it’s primary functions in the context of an app:
What apps are installed in the container?
$ singularity apps roar.simg
bar
foo

Help me with bar!
$ singularity help --app bar roar.simg
This is the help for bar.

Run foo
singularity run --app foo roar.simg
RUNNING FOO

Show me the custom environments
Remember how we defined the same environment variable, SOFTWARE for each of foo and bar? We can execute a
command to search the list of active environment variables with grep to see if the variable changes depending on the
app we specify:

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$ singularity exec --app foo roar.simg env | grep SOFTWARE
SOFTWARE=foo
$ singularity exec --app bar roar.simg env | grep SOFTWARE
SOFTWARE=bar

6.3 Examples
For more examples, for real world scientific recipes we recommend you look at other containers on Singularity Hub.
For examples of different bases, look at the examples folder for the most up-to-date examples. For apps, including
snippets and tutorial with more walk throughs, see SCI-F Apps Home.

6.4 Best Practices for Build Recipes
When crafting your recipe, it is best to consider the following:
1. To make your container internally modular, use SCI-F apps. Shared dependencies (between app modules) can
go under %post.
2. For global installs to %post, install packages, programs, data, and files into operating system locations (e.g.
not /home, /tmp , or any other directories that might get commonly binded on).
3. Make your container speak for itself. If your runscript doesn’t spit out help, write a %help or %post or
%apphelp section. A good container tells the user how to interact with it.
4. If you require any special environment variables to be defined, add them the %environment and %appenv
sections of the build recipe.
5. Files should never be owned by actual users, they should always be owned by a system account (UID less than
500).
6. Ensure that the container’s /etc/passwd , /etc/group , /etc/shadow , and no other sensitive files have
anything but the bare essentials within them.
7. It is encouraged to build containers from a recipe instead of a sandbox that has been manually changed. This
ensures greatest possibility of reproducibility and mitigates the black box effect.
Are you a recipe pro and now ready to build? Take a look at the build documentation.

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CHAPTER

SEVEN

SINGULARITY FLOW

This document describes a suggested “best-practices” workflow for building, running, and managing your containers.
There are generally two ways to get images. You either want to pull an image file as is, or (more likely) build your
own custom image. We will start with talking about build, and the many different use cases it affords.

7.1 Building Images
If you read the quick start, you probably remember that building images from a Docker base does not require a
Singularity recipe. However, if you do want to build and customize your image, you can create a Singularity recipe
text file, which is a simple text file that describes how the container should be made.

7.1.1 The Singularity Flow
The diagram below is a visual depiction of how you can use Singularity to build images. The high level idea is that we
have two environments:
• a build environment (where you have sudo privileges) to test and build your container
• a production environment where you run your container

Fig. 1: Singularity Workflow
Singularity production images are immutable. This is a feature added as of Singularity 2.4, and it ensures a higher
level of reproducibility and verification of images. To read more about the details, check out the build docs. However,

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immutability is not so great when you are testing, debugging, or otherwise want to quickly change your image. We
will proceed by describing a typical workflow of developing first, building a final image, and using it in production.

7.1.2 1. Development Commands
If you want a writable image or folder for developing, you have two options:
• build into a directory that has writable permissions using the --sandbox option
• build into an ext3 image file, that has writable permissions with the --writable option
In both cases you will need to execute your container with the --writable option at runtime for your changes to
be persistent.
7.1.2.1 Sandbox Folder
To build into a folder (we call this a “sandbox”) just ask for it:
$ sudo singularity build --sandbox ubuntu/ docker://ubuntu
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /root/.singularity/docker
Importing: base Singularity environment
Importing: /root/.singularity/docker/
˓→sha256:9fb6c798fa41e509b58bccc5c29654c3ff4648b608f5daa67c1aab6a7d02c118.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:3b61febd4aefe982e0cb9c696d415137384d1a01052b50a85aae46439e15e49a.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:9d99b9777eb02b8943c0e72d7a7baec5c782f8fd976825c9d3fb48b3101aacc2.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:d010c8cf75d7eb5d2504d5ffa0d19696e8d745a457dd8d28ec6dd41d3763617e.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:7fac07fb303e0589b9c23e6f49d5dc1ff9d6f3c8c88cabe768b430bdb47f03a9.tar.gz
Importing: /root/.singularity/metadata/
˓→sha256:22e289880847a9a2f32c62c237d2f7e3f4eae7259bf1d5c7ec7ffa19c1a483c8.tar.gz
Building image from sandbox: ubuntu/
Singularity container built: ubuntu/

We now have a folder with the entire ubuntu OS, plus some Singularity metadata, plopped in our present working
directory.
$ tree -L 1 ubuntu
ubuntu
bin
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boot
dev
environment -> .singularity.d/env/90-environment.sh
etc
home
lib
lib64
media
mnt
opt
proc
root
run
sbin
singularity -> .singularity.d/runscript
srv
sys
tmp
usr
var

And you can shell into it just like a normal container.
$ singularity shell ubuntu
Singularity: Invoking an interactive shell within container...

Singularity ubuntu:~/Desktop> touch /hello.txt
touch: cannot touch '/hello.txt': Permission denied

You can make changes to the container (assuming you have the proper permissions to do so) but those changes will
disappear as soon as you exit. To make your changes persistent across sessions, use the --writable option. It’s
also a good practice to shell into your container as root to ensure you have permissions to write where you like.

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$ sudo singularity shell ubuntu
Singularity: Invoking an interactive shell within container...

Singularity ubuntu:/home/vanessa/Desktop> touch /hello.txt

7.1.2.2 Writable Image
If you prefer to work with a writable image file rather than a directory, you can perform a similar development build
and specify the --writable option. This will produce an image that is writable with an ext3 file system. Unlike the
sandbox, it is a single image file.
$ sudo singularity build --writable ubuntu.img docker://ubuntu
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /root/.singularity/docker
Importing: base Singularity environment
Importing: /root/.singularity/docker/
˓→sha256:9fb6c798fa41e509b58bccc5c29654c3ff4648b608f5daa67c1aab6a7d02c118.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:3b61febd4aefe982e0cb9c696d415137384d1a01052b50a85aae46439e15e49a.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:9d99b9777eb02b8943c0e72d7a7baec5c782f8fd976825c9d3fb48b3101aacc2.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:d010c8cf75d7eb5d2504d5ffa0d19696e8d745a457dd8d28ec6dd41d3763617e.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:7fac07fb303e0589b9c23e6f49d5dc1ff9d6f3c8c88cabe768b430bdb47f03a9.tar.gz
Importing: /root/.singularity/metadata/
˓→sha256:22e289880847a9a2f32c62c237d2f7e3f4eae7259bf1d5c7ec7ffa19c1a483c8.tar.gz
Building image from sandbox: /tmp/.singularity-build.VCHPpP
Creating empty Singularity writable container 130MB
Creating empty 162MiB image file: ubuntu.img
Formatting image with ext3 file system
Image is done: ubuntu.img
Building Singularity image...

Cleaning up...

Singularity container built: ubuntu.img

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You can use this image with commands like shell, exec , run , and if you want to change the image you must
use the --writable flag. As before, it’s a good idea to issue these commands as root to ensure you have the proper
permissions to write.
$ sudo singularity shell --writable ubuntu.img

Development Tip! When building containers, it often is the case that
you will have a lot of testing of installation commands, and if
building a production image, one error will stop the entire build.
If you interactively write the build recipe with one of these
writable containers, you can debug as you go, and then build the
production (squashfs) container without worrying that it will error
and need to be started again.

7.1.3 2. Production Commands
Let’s set the scene - we just finished building our perfect hello world container. It does a fantastic hello-world analysis,
and we have written a paper on it! We now want to build an immutable container - meaning that if someone obtained
our container and tried to change it, they could not. They could easily use the same recipe that you used (it is provided
as metadata inside the container), or convert your container to one of the writable formats above using build . So
your work can still be extended.
7.1.3.1 Recommended Production Build
What we want for production is a build into a squashfs image . Squashfs is a read only, and compressed filesystem,
and well suited for confident archive and re-use of your hello-world. To build a production image, just remove the
extra options:
sudo singularity build ubuntu.simg docker://ubuntu
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /root/.singularity/docker
Importing: base Singularity environment
Importing: /root/.singularity/docker/
˓→sha256:9fb6c798fa41e509b58bccc5c29654c3ff4648b608f5daa67c1aab6a7d02c118.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:3b61febd4aefe982e0cb9c696d415137384d1a01052b50a85aae46439e15e49a.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:9d99b9777eb02b8943c0e72d7a7baec5c782f8fd976825c9d3fb48b3101aacc2.tar.gz
Importing: /root/.singularity/docker/
˓→sha256:d010c8cf75d7eb5d2504d5ffa0d19696e8d745a457dd8d28ec6dd41d3763617e.tar.gz
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(continued from previous page)

Importing: /root/.singularity/docker/
˓→sha256:7fac07fb303e0589b9c23e6f49d5dc1ff9d6f3c8c88cabe768b430bdb47f03a9.tar.gz
Importing: /root/.singularity/metadata/
˓→sha256:22e289880847a9a2f32c62c237d2f7e3f4eae7259bf1d5c7ec7ffa19c1a483c8.tar.gz
Building Singularity image...
Cleaning up...
Singularity container built: ubuntu.simg

7.1.3.2 Production Build from Sandbox
We understand that it might be wanted to build a Singularity (squashfs) from a previous development image. While
we advocate for the first approach, we support this use case. To do this, given our folder called “ubuntu/” we made
above:
sudo singularity build ubuntu.simg ubuntu/

It could be the case that a cluster maintains a “working” base of container folders (with writable) and then builds and
provides production containers to its users.
If you want to go through this entire process without having singularity installed locally, or without leaving your
cluster, you can build images using Singularity Hub.

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CHAPTER

EIGHT

BIND PATHS AND MOUNTS

If enabled by the system administrator, Singularity allows you to map directories on your host system to directories
within your container using bind mounts. This allows you to read and write data on the host system with ease.

8.1 Overview
When Singularity ‘swaps’ the host operating system for the one inside your container, the host file systems becomes
inaccessible. But you may want to read and write files on the host system from within the container. To enable
this functionality, Singularity will bind directories back in via two primary methods: system-defined bind points and
conditional user-defined bind points.

8.1.1 System-defined bind points
The system administrator has the ability to define what bind points will be included automatically inside each container.
The bind paths are locations on the host’s root file system which should also be visible within the container. Some of
the bind paths are automatically derived (e.g. a user’s home directory) and some are statically defined (e.g. bind path
in the Singularity configuration file). In the default configuration, the directories $HOME , /tmp , /proc , /sys ,
/dev and are among the system-defined bind points.

8.1.2 User-defined bind points
If the system administrator has enabled user control of binds, you will be able to request your own bind points within
your container.
To mount a bind path inside the container, a bind point must be defined within the container. The bind point is a
directory within the container that Singularity can use to bind a directory on the host system. This means that if you
want to bind to a point within the container such as /global, that directory must already exist within the container.
It is, however, possible that the system administrator has enabled a Singularity feature called overlay in the Singularity
configuration file. This will cause the bind points to be created on an as-needed basis in an overlay file system so that
the underlying container is not modified. But because the overlay feature is not always enabled or is unavailable in the
kernels of some older host systems, it may be necessary for container standards to exist to ensure portability from host
to host.
8.1.2.1 Specifying Bind Paths
Many of the Singularity commands such as run, exec , and shell take the --bind / command-line option
to specify bind paths, in addition to the SINGULARITY_BINDPATH environment variable. This option’s argument
is a comma-delimited string of bind path specifications in the format src[:dest[:opts]], where src and dest
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are outside and inside paths. If dest is not given, it is set equal to src . Mount options (opts) may be specified as
ro (read-only) or rw (read/write, which is the default). The --bind/-B option can be specified multiple times, or a
comma-delimited string of bind path specifications can be used.
Here’s an example of using the -B option and binding /tmp on the host to /scratch in the container (/scratch
does not need to already exist in the container if file system overlay is enabled):
$ singularity shell -B /tmp:/scratch /tmp/Centos7-ompi.img
Singularity: Invoking an interactive shell within container...

Singularity.Centos7-ompi.img> ls /scratch
ssh-7vywtVeOez

systemd-private-cd84c81dda754fe4a7a593647d5a5765-ntpd.service-12nMO4

You can bind multiple directories in a single command with this syntax:
$ singularity shell -B /opt,/data:/mnt /tmp/Centos7-ompi.img

This will bind /opt on the host to /opt in the container and /data on the host to /mnt in the container. Using the
environment variable instead of the command line argument, this would be:
$ export SINGULARITY_BINDPATH="/opt,/data:/mnt"
$ singularity shell /tmp/Centos7-ompi.img

Using the environment variable $SINGULARITY_BINDPATH, you can bind directories even when you are running
your container as an executable file with a runscript. If you bind many directories into your Singularity containers and
they don’t change, you could even benefit by setting this variable in your .bashrc file.
8.1.2.2 Binding with Overlay
If a bind path is requested and the bind point does not exist within the container, a warning message will be displayed
and Singularity will continue trying to start the container. For example:
$ singularity shell --bind /global /tmp/Centos7-ompi.img
WARNING: Non existent bind point (directory) in container: '/global'
Singularity: Invoking an interactive shell within container...

Singularity.Centos7-ompi.img>

Even though /global did not exist inside the container, the shell command printed a warning but continued on. If
overlay is available and enabled, you will find that we no longer get the error and /global is created and accessible
as expected:
$ singularity shell --bind /global /tmp/Centos7-ompi.img
Singularity: Invoking an interactive shell within container...

Singularity.Centos7-ompi.img>

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In this case, Singularity dynamically created the necessary bind point in your container. Without overlay, you would
have needed to manually create the /global directory inside your container.

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CHAPTER

NINE

PERSISTENT OVERLAYS

Persistent overlay images are new to version 2.4! This feature allows you to overlay a writable file system on an
immutable read-only container for the illusion of read-write access.

9.1 Overview
A persistent overlay is an image that “sits on top” of your compressed, immutable squashfs container. When you
install new software or create and modify files the overlay image stores the changes.
In Singularity versions 2.4 and later an overlay file system is automatically added to your squashfs or sandbox container
when it is mounted. This means you can install new software and create and modify files even though your container
is read-only. But your changes will disappear as soon as you exit the container.
If you want your changes to persist in your container across uses, you can create a writable image to use as a persistent
overlay. Then you can specify that you want to use the image as an overlay at runtime with the --overlay option.
You can use a persistent overlays with the following commands:
• run
• exec
• shell
• instance.start

9.2 Usage
To use a persistent overlay, you must first have a container.
$ singularity build ubuntu.simg shub://GodloveD/ubuntu

Then you must create a writable, ext3 image. We can do so with the image.create command:
$ singularity image.create my-overlay.img

Now you can use this overlay image with your container. Note that it is not necessary to be root to use an overlay
partition, but this will ensure that we have write privileges where we want them.
$ sudo singularity shell --overlay my-overlay.img ubuntu.simg
Singularity ubuntu.simg:~> touch /foo
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Singularity ubuntu.simg:~> apt-get install -y vim
Singularity ubuntu.simg:~> which vim
/usr/bin/vim
Singularity ubuntu.simg:~> exit

You will find that your changes persist across sessions as though you were using a writable container.
$ sudo singularity shell --overlay my-overlay.img ubuntu.simg
Singularity ubuntu.simg:~> ls /foo
/foo
Singularity ubuntu.simg:~> which vim
/usr/bin/vim
Singularity ubuntu.simg:~> exit

If you mount your container without the --overlay option, your changes will be gone.
$ sudo singularity shell ubuntu.simg
Singularity ubuntu.simg:~> ls /foo
ls: cannot access 'foo': No such file or directory
Singularity ubuntu.simg:~> which vim
Singularity ubuntu.simg:~> exit

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CHAPTER

TEN

RUNNING SERVICES

Singularity 2.4 introduces the ability to run “container instances”, allowing you to run services (e.g. Nginx, MySQL,
etc. . . ) using Singularity. A container instance, simply put, is a persistent and isolated version of the container image
that runs in the background.

10.1 Why container instances?
that is pretty simple, I install nginx and start the service:
apt-get update && apt-get install -y nginx
service nginx start

With older versions of Singularity, if you were to do something like this, from inside the container you would happily
see the service start, and the web server running! But then if you were to log out of the container what would happen?
Orphan process within unreachable namespaces! You would lose control of the process. It would still be running, but
you couldn’t easily kill or interface with it. This is a called an orphan process. Singularity versions less than 2.4 were
not designed to handle running services properly.

10.2 Container Instances in Singularity
With Singularity 2.4 and the addition of container instances, the ability to cleanly, reliably, and safely run services in
a container is here. First, let’s put some commands that we want our instance to execute into a script. Let’s call it a
startscript. This fits into a definition file like so:
%startscript

service nginx start

Now let’s say we build a container with that startscript into an image called nginx.img and we want to run an nginx
service. All we need to do is start the instance with the instance.start command, and the startscript will run inside the
container automatically:
[command]
$ singularity instance.start

[image]

[name of instance]

nginx.img

web

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When we run that command, Singularity creates an isolated environment for the container instances’ processes/services to live inside. We can confirm that this command started an instance by running the instance.list
command like so:
$ singularity instance.list
INSTANCE NAME

PID

CONTAINER IMAGE

web

790

/home/mibauer/nginx.img

If we want to run multiple instances from the same image, it’s as simple as running the command multiple times. The
instance names are an identifier used to uniquely describe an instance, so they cannot be repeated.
$ singularity instance.start

nginx.img

web1

$ singularity instance.start

nginx.img

web2

$ singularity instance.start

nginx.img

web3

And again to confirm that the instances are running as we expected:
$ singularity instance.list
INSTANCE NAME

PID

CONTAINER IMAGE

web1

790

/home/mibauer/nginx.img

web2

791

/home/mibauer/nginx.img

web3

792

/home/mibauer/nginx.img

If the service you want to run in your instance requires a bind mount, then you must pass the -B option when calling
instance.start. For example, if you wish to capture the output of the web1 container instance which is placed
at /output/ inside the container you could do:
$ singularity instance.start -B output/dir/outside/:/output/ nginx.img

web1

If you want to poke around inside of your instance, you can do a normal singularity shell command, but give
it the instance URI:
$ singularity shell instance://web1
Singularity: Invoking an interactive shell within container...

Singularity pdf_server.img:~/>

Similarly, you can use the singularity run/exec commands on instances:
$ singularity run instance://web1
$ singularity exec instance://web1 ps -ef

When using run with an instance URI, the runscript will be executed inside of the instance. Similarly with exec,
it will execute the given command in the instance.
When you are finished with your instance you can clean it up with the instance.stop command like so:

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$ singularity instance.stop web1

If you have multiple instances running and you want to stop all of them, you can do so with a wildcard or the -a flag:
$ singularity instance.stop \*
$ singularity instance.stop -a

Note: Note that you must escape the wildcard with a backslash like this \* to pass it properly.

10.3 Nginx “Hello-world” in Singularity
Let’s take a look at setting up a sample nginx web server using instances in Singularity. First we will just create a
basic definition file:
Bootstrap: docker
From: nginx
Includecmd: no

%startscript
nginx

All this does is download the official nginx Docker container, convert it to a Singularity image, and tell it to run nginx
when you start the instance. Since we’re running a web server, we’re going to run the following commands as root.
# singularity build nginx.img Singularity
# singularity instance.start nginx.img web1

Just like that we’ve downloaded, built, and ran an nginx Singularity image. And to confirm that it’s correctly running:
$ curl localhost
127.0.0.1 - - [06/Oct/2017:21:46:43 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.47.0"
˓→"-"







Welcome to nginx!
If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.

For online documentation and support please refer to
nginx.org.

Commercial support is available at
nginx.com.

Thank you for using nginx.



10.4 Putting all together
In this section, we will demonstrate an example of packaging a service into a container and running it. The service
we will be packaging is an API server that converts a web page into a PDF, and can be found here. The final example
can be found here on GitHub. If you wish to just download the final image directly from Singularity Hub, simply run
singularity pull shub://bauerm97/instance-example.

10.4.1 Building the image
To begin, we need to build the image. When looking at the GitHub page of the url-to-pdf-api, we can see that
it is a Node 8 server that uses headless Chromium called Puppeteer. Let’s first choose a base from which to build our
container, in this case I used the docker image node:8 which comes pre-installed with Node 8:
Bootstrap: docker
From: node:8
Includecmd: no

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Puppeteer also requires a few dependencies to be manually installed in addition to Node 8, so we can add those into
the post section as well as the installation script for the url-to-pdf-api:

%post
apt-get update

˓→

apt-get install -yq gconf-service libasound2 libatk1.0-0 libc6 libcairo2
libcups2 \
libdbus-1-3 libexpat1 libfontconfig1 libgcc1 libgconf-2-4 libgdk-pixbuf2.0-0 \
libglib2.0-0 libgtk-3-0 libnspr4 libpango-1.0-0 libpangocairo-1.0-0 libstdc++6 \
libx11-6 libx11-xcb1 libxcb1 libxcomposite1 libxcursor1 libxdamage1 libxext6 \
libxfixes3 libxi6 libxrandr2 libxrender1 libxss1 libxtst6 ca-certificates \
fonts-liberation libappindicator1 libnss3 lsb-release xdg-utils wget curl
rm -r /var/lib/apt/lists/*
cd /
git clone https://github.com/alvarcarto/url-to-pdf-api.git pdf_server
cd pdf_server
npm install
chmod -R 0755 .

And now we need to define what happens when we start an instance of the container. In this situation, we want to run
the commands that starts up the url-to-pdf-api server:
%startscript
cd /pdf_server
# Use nohup and /dev/null to completely detach server process from terminal
nohup npm start > /dev/null 2>&1 < /dev/null &

Also, the url-to-pdf-api server requires environment some variables be set, which we can do in the environment section:
%environment
NODE_ENV=development
PORT=8000
ALLOW_HTTP=true
URL=localhost
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export NODE_ENV PORT ALLOW_HTTP URL

Now we can build the definition file into an image! Simply run build and the image will be ready to go:
$ sudo singularity build url-to-pdf-api.img Singularity

10.4.2 Running the Server
Now that we have an image, we are ready to start an instance and run the server:
$ singularity instance.start url-to-pdf-api.img pdf

We can confirm it’s working by sending the server an http request using curl:
$ curl -o google.pdf localhost:8000/api/render?url=http://google.com
% Total

100 51664

% Received % Xferd

100 51664

0

0

Average Speed

Time

Time

Time

Current

Dload

Total

Spent

Left

Speed

Upload

12443

0

0:00:04

0:00:04 --:--:-- 12446

If you shell into the instance, you can see the running processes:
$ singularity shell instance://pdf
Singularity: Invoking an interactive shell within container...

Singularity pdf_server.img:~/bauerm97/instance-example> ps auxf
USER

PID %CPU %MEM

VSZ

RSS TTY

STAT START

TIME COMMAND

node

87

0.2

0.0

20364

3384 pts/0

S

16:16

0:00 /bin/bash --norc

node

88

0.0

0.0

17496

2144 pts/0

R+

16:16

0:00

1904 ?

Ss

16:10

0:00 singularity-

0.4 997452 40364 ?

Sl

16:10

0:00 npm

node
13 0.0
˓→watch ./src -e j

0.0

S

16:10

0:00

node
14 0.0
˓→apps/pdf_server/p

0.4 1184492 37008 ?

Sl

16:10

0:00

node
26 0.0
˓→node src/index.js

0.0

S

16:10

0:00

node
27
˓→src/index.js

0.5 906108 43424 ?

Sl

16:10

0:00

node
1 0.0 0.0 13968
˓→instance: mibauer [pdf]
node

3

0.1

0.2

4340

4340

724 ?

804 ?

\_ ps auxf

\_ sh -c nodemon --

\_ node /scif/

\_ sh -c

\_ node

Singularity pdf_server.img:~/bauerm97/instance-example> ls
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LICENSE

README.md

Singularity

out

pdf_server.img

Singularity pdf_server.img:~/bauerm97/instance-example> exit

10.4.3 Making it Pretty
Now that we have confirmation that the server is working, let’s make it a little cleaner. It’s difficult to remember the
exact curl command and URL syntax each time you want to request a PDF, so let’s automate that. To do that, we’re
going to be using Standard Container Integration Format (SCIF) apps, which are integrated directly into singularity. If
you haven’t already, check out the Singularity app documentation to come up to speed.
First off, we’re going to move the installation of the url-to-pdf-api into an app, so that there is a designated spot to
place output files. To do that, we want to add a section to our definition file to build the server:
%appinstall pdf_server
git clone https://github.com/alvarcarto/url-to-pdf-api.git pdf_server
cd pdf_server
npm install
chmod -R 0755 .

And update our startscript to point to the app location:
%startscript
cd "${APPROOT_pdf_server}/pdf_server"
# Use nohup and /dev/null to completely detach server process from terminal
nohup npm start > /dev/null 2>&1 < /dev/null &

Now we want to define the pdf_client app, which we will run to send the requests to the server:
%apprun pdf_client
if [ -z "${1:-}" ]; then
echo "Usage: singularity run --app pdf   [output file]"
exit 1
fi

˓→

curl -o "${SINGULARITY_APPDATA}/output/${2:-output.pdf}" "${URL}:${PORT}/api/
render?url=${1}"

As you can see, the pdf_client app checks to make sure that the user provides at least one argument. Now that we
have an output directory in the container, we need to expose it to the host using a bind mount. Once we’ve rebuilt the
container, make a new directory callout out for the generated PDF’s to go. Now we simply start the instance like so:

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$ singularity instance.start -B out/:/scif/data/pdf_client/output/ url-to-pdf-api.img
˓→pdf

And to request a pdf simply do:
$ singularity run --app pdf_client instance://pdf http://google.com google.pdf

And to confirm that it worked:
$ ls out/
google.pdf

When you are finished, use the instance.stop command to close all running instances.
$ singularity instance.stop \*

10.5 Important Notes

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CHAPTER

ELEVEN

CONTAINER CHECKS

New to Singularity 2.4 is the ability to run container “checks” on demand. Checks can be anything from a filter for
sensitive information, to an analysis of installed binaries. A few default checks are installed with Singularity and
others can be added by the administrator. Users can perform checks at build time or on demand: Perform all default
checks, these are the same
$ singularity check ubuntu.img
$ singularity check --tag default ubuntu.img

Perform checks with tag “clean”
$ singularity check --tag clean ubuntu.img

11.1 Tags and Organization
Currently, checks are organized by tag and security level. If you know a specific tag that you want to use, for example
“docker” deploys checks for containers with Docker imported layers, you can specify the tag:
USAGE
-t/--tag

tag to filter checks. default is "default"
Available: default, security, docker, clean

EXAMPLE
$ singularity check --tag docker ubuntu.img

If you want to run checks associated with a different security level, you can specify with --low , --med , or --high
:
USAGE: singularity [...] check [exec options...] 
This command will run security checks for an image.
Note that some checks require sudo.

-l/--low

Specify low threshold (all checks, default)
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-m/--med

Perform medium and high checks

-h/--high

Perform only checks at level high

Note: Note that some checks will require sudo, and you will be alerted if this is the case and you didn’t use it. Finally,
if you want to run all default checks, just don’t specify a tag or level.

11.2 What checks are available?
Currently, you can view all installable checks here, and we anticipate adding an ability to view tags that are available,
along with your own custom checks. You should also ask your administration if new checks have been added not
supported by Singularity. If you want to request adding a new check, please tell us!.

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TWELVE

ENVIRONMENT AND METADATA

Singularity containers support environment variables and labels that you can add to your container during the build
process. This page details general information about defining environments and labels. If you are looking for specific
environment variables for build time, see build environment.

12.1 Environment
If you build a container from Singularity Hub or Docker Hub, the environment will be included with the container at
build time. You can also define custom environment variables in your Recipe file like so:
Bootstrap: shub
From: vsoch/hello-world

%environment
VARIABLE_NAME=VARIABLE_VALUE
export VARIABLE_NAME

You may need to add environment variables to your container during the %post section. For instance, maybe you
will not know the appropriate value of a variable until you have installed some software. To add variables to the
environment during %post you can use the $SINGULARITY_ENVIRONMENT variable with the following syntax:
%post
echo 'export VARIABLE_NAME=VARIABLE_VALUE' >>$SINGULARITY_ENVIRONMENT

Text in the %environment section will be appended to the file /.singularity.d/env/90-environment.
sh while text redirected to $SINGULARITY_ENVIRONMENT will end up in the file /.singularity.d/env/91environment.sh.
Because files in /.singularity.d/env are sourced in alpha-numerical order, this means that variables added
using $SINGULARITY_ENVIRONMENT take precedence over those added via the %environment section.
Need to define a variable at runtime? You can set variables inside the container by prefixing them with
SINGULARITYENV_. They will be transposed automatically and the prefix will be stripped. For example, let’s
say we want to set the variable HELLO to have value WORLD. We can do that as follows:
$ SINGULARITYENV_HELLO=WORLD singularity exec --cleanenv centos7.img env
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HELLO=WORLD
LD_LIBRARY_PATH=:/usr/local/lib:/usr/local/lib64
SINGULARITY_NAME=test.img
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/home/gmk/git/singularity
LANG=en_US.UTF-8
SHLVL=0
SINGULARITY_INIT=1
SINGULARITY_CONTAINER=test.img

Notice the --cleanenv in the example above? That argument specifies that we want to remove the host environment
from the container. If we remove the --cleanenv, we will still pass forward HELLO=WORLD, and the list shown
above, but we will also pass forward all the other environment variables from the host.
If you need to change the $PATH of your container at runtime there are a few environmental variables you can use:
• SINGULARITYENV_PREPEND_PATH=/good/stuff/at/beginning to prepend directories to the beginning of the
• SINGULARITYENV_APPEND_PATH=/good/stuff/at/end to append directories to the end of the
• SINGULARITYENV_PATH=/a/new/path to override the $PATH within the container

12.2 Labels
Your container stores metadata about it’s build, along with Docker labels, and custom labels that you define during
build in a %labels section.
For containers that are generated with Singularity version 2.4 and later, labels are represented using the rc1 Label
Schema. For example:
$ singularity inspect dino.img
{
"org.label-schema.usage.singularity.deffile.bootstrap": "docker",
"MAINTAINER": "Vanessasaurus",
"org.label-schema.usage.singularity.deffile": "Singularity.help",
"org.label-schema.usage": "/.singularity.d/runscript.help",
"org.label-schema.schema-version": "1.0",
"org.label-schema.usage.singularity.deffile.from": "ubuntu:latest",
"org.label-schema.build-date": "2017-07-28T22:59:17-04:00",
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˓→

"org.label-schema.usage.singularity.runscript.help": "/.singularity.d/runscript.
help",
"org.label-schema.usage.singularity.version": "2.3.1-add/label-schema.g00f040f",
"org.label-schema.build-size": "715MB"

}

You will notice that the one label doesn’t belong to the label schema, MAINTAINER . This was a user provided
label during bootstrap. Finally, for Singularity versions >= 2.4, the image build size is added as a label, org.
label-schema.build-size, and the label schema is used throughout. For versions earlier than 2.4, containers
did not use the label schema, and looked like this:
singularity exec centos7.img cat /.singularity.d/labels.json
{ "name":
"CentOS Base Image",
"build-date": "20170315",
"vendor": "CentOS",
"license": "GPLv2"
}

You can add custom labels to your container in a bootstrap file:
Bootstrap: docker
From: ubuntu: latest

%labels
AUTHOR Vanessasaur

The inspect command is useful for viewing labels and other container meta-data.

12.3 Container Metadata
Inside of the container, metadata is stored in the /.singularity.d directory. You probably shouldn’t edit any of
these files directly but it may be helpful to know where they are and what they do:
/.singularity.d/

actions
exec
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run
shell
start
test
env
01-base.sh
90-environment.sh
95-apps.sh
99-base.sh
labels.json
libs
runscript
Singularity
startscript

• actions: This directory contains helper scripts to allow the container to carry out the action commands.
• env: All *.sh files in this directory are sourced in alpha-numeric order when the container is initiated. For
legacy purposes there is a symbolic link called /environment that points to /.singularity.d/env/
90-environment.sh.
• labels.json: The json file that stores a containers labels described above.
• libs: At runtime the user may request some host-system libraries to be mapped into the container (with the
--nv option for example). If so, this is their destination.
• runscript: The commands in this file will be executed when the container is invoked with the run command or
called as an executable. For legacy purposes there is a symbolic link called /singularity that points to this
file
• Singularity: This is the Recipe file that was used to generate the container. If more than 1 Recipe file was
used to generate the container additional Singularity files will appear in numeric order in a sub-directory called
bootstrap_history
• startscript: The commands in this file will be executed when the container is invoked with the instance.
start command.

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THIRTEEN

REPRODUCIBLE SCI-F APPS

13.1 Why do we need SCI-F?
The Scientific Filesystem (SCIF) provides internal modularity of containers, and it makes it easy for the creator to
give the container implied metadata about software. For example, installing a set of libraries, defining environment
variables, or adding labels that belong to app foo makes a strong assertion that those dependencies belong to foo
. When I run foo, I can be confident that the container is running in this context, meaning with foo's custom
environment, and with foo's libraries and executables on the path. This is drastically different from serving many
executables in a single container, because there is no way to know which are associated with which of the container’s
intended functions. This documentation will walk through some rationale, background, and examples of the SCIF
integration for Singularity containers. For other examples (and a client that works across container technologies) see
the the scientific filesystem. This page will primarily cover the native Singularity SCIF integration.
To start, let’s take a look at this series of steps to install dependencies for software foo and bar.
%post

# install dependencies 1
# install software A (foo)
# install software B (bar)
# install software C (foo)
# install software D (bar)

The creator may know that A and C were installed for foo and B and D for bar , but down the road, when someone
discovers the container, if they can find the software at all, the intention of the container creator would be lost. As
many are now, containers without any form of internal organization and predictability are black boxes. We don’t know
if some software installed to /opt , or to /usr/local/bin , or to their custom favorite folder /code . We could
assume that the creator added important software to the path and look in these locations, but that approach is still akin
to fishing in a swamp. We might only hope that the container’s main function, the Singularity runscript, is enough to
make the container perform as intended.

13.1.1 Mixed up Modules
If your container truly runs one script, the traditional model of a runscript fits well. Even in the case of having two
functions like foo and bar you probably have something like this.

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%runscript
if some logic to choose foo:
check arguments for foo
run foo
else if some logic to choose bar:
run bar

and maybe your environment looks like this:
%environment
BEST_GUY=foo
export BEST_GUY

but what if you run into this issue, with foo and bar?

%environment
BEST_GUY=foo
BEST_GUY=bar
export BEST_GUY

You obviously can’t have them at separate times. You’d have to source some custom environment file (that you make
on your own) and it gets hard easily with issues of using shell and sourcing. We don’t know who the best guy is! You
probably get the general idea. Without internal organization and modularity:
• You have to do a lot of manual work to expose the different software to the user via a custom runscript (and be
a generally decent programmer).
• All software must share the same metadata, environment, and labels.
Under these conditions, containers are at best block boxes with unclear delineation between software provided, and
only one context of running anything. The container creator shouldn’t need to spend inordinate amounts of time
writing custom runscripts to support multiple functions and inputs. Each of foo and bar should be easy to define,
and have its own runscript, environment, labels, tests and help section.

13.1.2 Container Transparency
SCI-F Apps make foo and bar transparent, and solve this problem of mixed up modules. Our simple issue of mixed
up modules could be solved if we could do this:
Bootstrap:docker
From: ubuntu:16.04
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%appenv foo
BEST_GUY=foo
export BEST_GUY

%appenv bar
BEST_GUY=bar
export BEST_GUY

%apprun foo
echo The best guy is $BEST_GUY

%apprun bar
echo The best guy is $BEST_GUY

Generate the container
$ sudo singularity build foobar.simg Singularity

and run it in the context of foo and then bar
$ singularity run --app bar foobar.simg
The best guy is bar
$ singularity run --app foo foobar.simg
The best guy is foo

Using SCI-F apps, a user can easily discover both foo and bar without knowing anything about the container:
singularity apps foobar.simg
bar
foo

and inspect each one:

singularity inspect --app foo

foobar.simg

{
"SCIF_APP_NAME": "foo",
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"SCIF_APP_SIZE": "1MB"
}

13.1.3 Container Modularity
What is going on, under the hood? Just a simple, clean organization that is tied to a set of sections in the build recipe
relevant to each app. For example, I can specify custom install procedures (and they are relevant to each app’s specific
base defined under /scif/apps), labels, tests, and help sections. Before I tell you about the sections, I’ll briefly
show you what the organization looks like, for each app:
/scif/apps/

foo/
bin/
lib/
scif/
runscript.help
runscript
env/
01-base.sh
90-environment.sh

bar/
....

If you are familiar with Singularity, the above will look very familiar. It mirrors the Singularity (main container) metadata folder, except instead of .singularity.d we have scif. The name and base scif is chosen intentionally
to be something short, and likely to be unique. On the level of organization and metadata, these internal apps are like
little containers! Are you worried that you need to remember all this path nonsense? Don’t worry, you don’t. You can
just use environment variables in your runscripts, etc. Here we are looking at the environment active for lolcat:
singularity exec --app foo foobar.simg env | grep foo

Let’s talk about the output of the above in sections, you will notice some interesting things! First, notice that the app’s
bin has been added to the path, and it’s lib added to the LD_LIBRARY_PATH . This means that anything you drop
in either will automatically be added. You don’t need to make these folders either, they are created for you.
LD_LIBRARY_PATH=/scif/apps/foo/lib::/.singularity.d/libs
PATH=/scif/apps/foo/bin:/scif/apps/foo:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/
˓→bin:/sbin:/bin

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Next, notice that we have environment variables relevant to the active app’s (foo) data and metadata. They look like
this:
SCIF_APPOUTPUT=/scif/data/foo/output
SCIF_APPDATA=/scif/data/foo
SCIF_APPINPUT=/scif/data/foo/input
SCIF_APPMETA=/scif/apps/foo/scif
SCIF_APPROOT=/scif/apps/foo
SCIF_APPNAME=foo

We also have foo’s environment variables defined under %appenv foo , and importantly, we don’t see bar’s.
BEST_GUY=foo

Also provided are more global paths for data and apps:
SCIF_APPS=/scif/apps
SCIF_DATA=/scif/data

Importantly, each app has its own modular location. When you do an %appinstall foo, the commands are all
done in context of that base. The bin and lib are also automatically generated. So what would be a super simple app?
Just add a script and name it:
%appfiles foo
runfoo.sh

bin/runfoo.sh

and then maybe for install I’d make it executable
%appinstall foo
chmod u+x bin/runfoo.sh

You don’t even need files! You could just do this.
%appinstall foo
echo 'echo "Hello Foo."' >> bin/runfoo.sh
chmod u+x bin/runfoo.sh

We can summarize these observations about using apps:
• the specific environment (%appenv_foo) is active because BEST_APP is foo
• the lib folder in foo’s base is added to the LD_LIBRARY_PATH
• the bin folder is added to the path
• locations for input, output, and general data are exposed. It’s up to you how you use these, but you can predictably know that a well made app will look for inputs and outputs in it’s specific folder.
• environment variables are provided for the app’s root, it’s data, and it’s name

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13.1.4 Sections
Finding the section %appinstall , %apphelp , or %apprun is indication of an application command. The
following string is parsed as the name of the application, and this folder is created, in lowercase, under /scif/apps
if it doesn’t exist. A singularity metadata folder, .singularity.d, equivalent to the container’s main folder, is generated
inside the application. An application thus is like a smaller image inside of it’s parent. Specifically, SCI-F defines the
following new sections for the build recipe, where each is optional for 0 or more apps:
%appinstall corresponds to executing commands within the folder to install the application. These commands would
previously belong in %post, but are now attributable to the application.
%apphelp is written as a file called runscript.help in the application’s metadata folder, where the Singularity software
knows where to find it. If no help section is provided, the software simply will alert the user and show the files provided
for inspection.
%apprun is also written as a file called runscript.exec in the application’s metadata folder, and again looked for when
the user asks to run the software. If not found, the container should default to shelling into that location.
%applabels will write a labels.json in the application’s metadata folder, allowing for application specific labels.
%appenv will write an environment file in the application’s base folder, allowing for definition of application specific
environment variables.
%apptest will run tests specific to the application, with present working directory assumed to be the software module’s
folder
%appfiles will add files to the app’s base at /scif/apps/

13.1.5 Interaction
I didn’t show you the complete output of a grep to the environment when running foo in the first example - because
the remainder of variables are more fit for a discussion about app interaction. Essentially, when any app is active, we
also have named variable that can explicitly reference the environment file, labels file, runscript, lib and bin folders
for all app’s in the container. For our above Singularity Recipe, we would also find:
SCIF_APPDATA_bar=/scif/data/bar
SCIF_APPRUN_bar=/scif/apps/bar/scif/runscript
SCIF_APPROOT_bar=/scif/apps/bar
SCIF_APPLIB_bar=/scif/apps/bar/lib
SCIF_APPMETA_bar=/scif/apps/bar/scif
SCIF_APPBIN_bar=/scif/apps/bar/bin
SCIF_APPENV_bar=/scif/apps/bar/scif/env/90-environment.sh
SCIF_APPLABELS_bar=/scif/apps/bar/scif/labels.json

SCIF_APPENV_foo=/scif/apps/foo/scif/env/90-environment.sh
SCIF_APPLABELS_foo=/scif/apps/foo/scif/labels.json
SCIF_APPDATA_foo=/scif/data/foo
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SCIF_APPRUN_foo=/scif/apps/foo/scif/runscript
SCIF_APPROOT_foo=/scif/apps/foo
SCIF_APPLIB_foo=/scif/apps/foo/lib
SCIF_APPMETA_foo=/scif/apps/foo/scif
SCIF_APPBIN_foo=/scif/apps/foo/bin

This is really great because it means that we can have apps interact with one another internally. For example, let’s
modify the recipe a bit:
Bootstrap:docker
From: ubuntu:16.04

%appenv cow
ANIMAL=COW
NOISE=moo
export ANIMAL NOISE

%appenv bird
NOISE=tweet
ANIMAL=BIRD
export ANIMAL

%apprun moo
echo The ${ANIMAL} goes ${NOISE}

%appenv moo
. ${APPENV_cow}

In the above example, we have three apps. One for a cow, one for a bird, and a third that depends on the cow. We can’t
define global functions or environment variables (in %post or /environment , respectively) because they would
interfere with the third app, bird, that has equivalently named variables. What we do then, is source the environment
for “cow” in the environment for “moo” and the result is what we would want:
$ singularity run --app moo /tmp/one.simg
The COW goes moo

The same is true for each of the labels, environment, runscript, bin, and lib. The following variables are available to
you, for each app in the container, whenever any app is being run:

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• **SCIF_APPBIN_*: the path to the bin folder, if you want to add an app that isn’t active to your ‘PATH‘
• **SCIF_APPLIB_*: the path to the lib folder, if you want to add an app that isn’t active to your
‘LD_LIBRARY_PATH‘
• **SCIF_APPRUN_*: the app’s runscript (so you can call it from elsewhere)
• **SCIF_APPMETA_*: the path to the metadata folder for the app
• **SCIF_APPENV_*: the path to the primary environment file (for sourcing) if it exists
• **SCIF_APPROOT_*: the app’s install folder
• **SCIF_APPDATA_*: the app’s data folder
• **SCIF_APPLABELS_*: The path to the label.json in the metadata folder, if it exists
Singularity containers are already reproducible in that they package dependencies. This basic format adds to that by
making the software inside of them modular, predictable, and programmatically accessible. We can say confidently
that some set of steps, labels, or variables in the runscript is associated with a particular action of the container.
We can better reveal how dependencies relate to each step in a scientific workflow. Making containers is not easy.
When a scientist starts to write a recipe for his set of tools, he probably doesn’t know where to put it, perhaps that a
help file should exist, or that metadata about the software should be served by the container. If container generation
software made it easy to organize and capture container content automatically, we would easily meet these goals of
internal modularity and consistency, and generate containers that easily integrate with external hosts, data, and other
containers. These are essential components for (ultimately) optimizing the way we develop, understand, and execute
our scientific containers.

13.2 Cowsay Container
Now let’s go through the tutorial to build our cowsay container.
Warning: Important! This tutorial is for Singularity 2.4.
When you’ve installed 2.4, download the recipe, and save it to your present working directory. By the way, credit
for anything and everything lolcat and cowsay goes to GodLoveD! Here is the recipe:
wget https://raw.githubusercontent.com/singularityware/singularity/master/examples/
˓→apps/Singularity.cowsay
sudo singularity build moo.simg Singularity.cowsay

What apps are installed?
singularity apps moo.simg
cowsay
fortune
lolcat

Ask for help for a specific app!
singularity help --app fortune moo.simg
fortune is the best app

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Ask for help for all apps, without knowing in advance what they are:
for app in $(singularity apps moo.simg)
do
singularity help --app $app moo.simg
done
cowsay is the best app
fortune is the best app
lolcat is the best app

Run a particular app
singularity run --app fortune moo.simg
My dear People.
My dear Bagginses and Boffins, and my dear Tooks and Brandybucks,
and Grubbs, and Chubbs, and Burrowses, and Hornblowers, and Bolgers,
Bracegirdles, Goodbodies, Brockhouses and Proudfoots.

Also my good

Sackville Bagginses that I welcome back at last to Bag End.

Today is my

one hundred and eleventh birthday: I am eleventy-one today!"
-- J. R. R. Tolkien

Advanced running - pipe the output of fortune into lolcat, and make a fortune that is beautifully colored!
singularity run --app fortune moo.simg | singularity run --app lolcat moo.simg
You will be surrounded by luxury.

This one might be easier to see - pipe the same fortune into the cowsay app:
singularity run --app fortune moo.simg | singularity run --app cowsay moo.simg
________________________________________
/ Executive ability is prominent in your \
\ make-up.

/

---------------------------------------\
\

^__^
(oo)\_______
(__)\

)\/\
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||----w |
||

||

and the final shabang - do the same, but make it colored. Let’s even get lazy and use an environment variable for the
command:
CMD="singularity run --app"
$CMD fortune moo.simg | $CMD cowsay moo.simg | $CMD lolcat moo.simg
_________________________________________
/ Ships are safe in harbor, but they were \
\ never meant to stay there.

/

----------------------------------------\
\

^__^
(oo)\_______
(__)\

)\/\

||----w |
||

||

Yes, you need to watch the asciinema to see the colors. Finally, inspect an app:
singularity inspect --app fortune moo.simg
{
"SCIF_APP_NAME": "fortune",
"SCIF_APP_SIZE": "1MB"
}

If you want to see the full specification or create your own Scientific Filesystem integration (doesn’t have to be
Singularity, or Docker, or containers!) see the full documentation.
If you haven’t yet, take a look at these examples with the asciinema!

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FOURTEEN

SINGULARITY AND DOCKER

Singularity is good friends with Docker. The reason is because the developers use and really like using Docker, and
scientists have already put much resources into creating Docker images. Thus, one of our early goals was to support
Docker. What can you do?
• You don’t need Docker installed
• You can shell into a Singularity-ized Docker image
• You can run a Docker image instantly as a Singularity image
• You can pull a Docker image (without sudo)
• You can build images with bases from assembled Docker layers that include environment, guts, and labels

14.1 TLDR (Too Long Didn’t Read)
You can shell, import, run, and exec.
singularity shell docker://ubuntu:latest
singularity run docker://ubuntu:latest
singularity exec docker://ubuntu:latest echo "Hello Dinosaur!"

singularity pull docker://ubuntu:latest
singularity build ubuntu.img docker://ubuntu:latest

14.2 Import a Docker image into a Singularity Image
The core of a Docker image is basically a compressed set of files, a set of .tar.gz that (if you look in your Docker
image folder on your host machine, you will see. The Docker Registry, which you probably interact with via Docker
Hub, serves these layers. These are the layers that you see downloading when you interact with the docker daemon.
We are going to use these same layers for Singularity!

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14.3 Quick Start: The Docker Registry
The Docker engine communicates with the Docker Hub via the Docker Remote API, and guess what, we can too! The
easiest thing to do is create an image, and then pipe a Docker image directly into it from the Docker Registry. You
don’t need Docker installed on your machine, but you will need a working internet connection. Let’s create an ubuntu
operating system, from Docker. We will pull, then build:
singularity pull docker://ubuntu
WARNING: pull for Docker Hub is not guaranteed to produce the
WARNING: same image on repeated pull. Use Singularity Registry
WARNING: (shub://) to pull exactly equivalent images.
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /home/vanessa/.singularity/docker
[5/5] |===================================| 100.0%
Importing: base Singularity environment
Importing: /home/vanessa/.singularity/docker/
˓→sha256:9fb6c798fa41e509b58bccc5c29654c3ff4648b608f5daa67c1aab6a7d02c118.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:3b61febd4aefe982e0cb9c696d415137384d1a01052b50a85aae46439e15e49a.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:9d99b9777eb02b8943c0e72d7a7baec5c782f8fd976825c9d3fb48b3101aacc2.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:d010c8cf75d7eb5d2504d5ffa0d19696e8d745a457dd8d28ec6dd41d3763617e.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:7fac07fb303e0589b9c23e6f49d5dc1ff9d6f3c8c88cabe768b430bdb47f03a9.tar.gz
Importing: /home/vanessa/.singularity/metadata/
˓→sha256:77cece4ce6ef220f66747bb02205a00d9ca5ad0c0a6eea1760d34c744ef7b231.tar.gz
WARNING: Building container as an unprivileged user. If you run this container as root
WARNING: it may be missing some functionality.
Building Singularity image...
Cleaning up...
Singularity container built: ./ubuntu.img

The warnings mean well - it is to tell you that you are creating the image on the fly from layers, and if one of those
layers changes, you won’t produce the same image next time.

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14.4 The Build Specification file, Singularity
Just like Docker has the Dockerfile, Singularity has a file called Singularity that (currently) applications like Singularity
Hub know to sniff for. For reproducibility of your containers, our strong recommendation is that you build from these
files. Any command that you issue to change a container sandbox (building with --sandbox ) or to a build with
--writable is by default not recorded, and your container loses its reproducibility. So let’s talk about how to make
these files! First, let’s look at the absolute minimum requirement:
Bootstrap: docker
From: ubuntu

We would save this content to a file called Singularity and then issue the following commands to bootstrap the image
from the file
sudo singularity build ubuntu.img Singularity

Do you want to specify a particular tag? or version? You can just add that to the docker uri:
Bootstrap: docker
From: ubuntu:latest

Note: Note that the default is latest . If you want to customize the Registry or Namespace, just add those to the
header:
Bootstrap: docker
From: ubuntu
Registry: pancakes.registry.index.io
Namespace: blue/berry/cream

The power of build comes with the other stuff that you can do! This means running specific install commands,
specifying your containers runscript (what it does when you execute it), adding files, labels, and customizing the
environment. Here is a full Singularity file:
Bootstrap: docker
From: tensorflow/tensorflow:latest

%runscript
exec /usr/bin/python "$@"

%post
echo "Post install stuffs!"

%files
(continues on next page)

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(continued from previous page)

/home/vanessa/Desktop/analysis.py /tmp/analysis.py
relative_path.py /tmp/analysis2.py

%environment
TOPSECRET=pancakes
HELLO=WORLD
export HELLO TOPSECRET

%labels
AUTHOR Vanessasaur

In the example above, I am overriding any Dockerfile ENTRYPOINT or CMD because I have defined a %runscript
. If I want the Dockerfile ENTRYPOINT to take preference, I would remove the %runscript section. If I want to
use CMD instead of ENTRYPOINT , I would again remove the runscript, and add IncludeCmd to the header:
Bootstrap: docker
From: tensorflow/tensorflow:latest
IncludeCmd: yes

%post

echo "Post install stuffs!"

Did you know that you can commit this Singularity file to a GitHub repo and it will automatically build for you when
you push to Singularity Hub?. This will ensure maximum reproducibility of your work.

14.5 How does the runscript work?
Docker has two commands in the Dockerfile that have something to do with execution, CMD and ENTRYPOINT.
The differences are subtle, but the best description I’ve found is the following:
A CMD is to provide defaults for an executing container.
and
An ENTRYPOINT helps you to configure a container that you can run as an executable.
Given the definition, the ENTRYPOINT is most appropriate for the Singularity %runscript , and so using the
default bootstrap (whether from a docker:// endpoint or a Singularity spec file) will set the ENTRYPOINT
variable as the runscript. You can change this behavior by specifying IncludeCmd: yes in the Spec file (see
below). If you provide any sort of %runscript in your Spec file, this overrides anything provided in Docker. In
summary, the order of operations is as follows:
1. If a %runscript is specified in the Singularity spec file, this takes prevalence over all

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2. If no %runscript is specified, or if the import command is used as in the example above, the ENTRYPOINT
is used as runscript.
3. If no %runscript is specified, but the user has a Singularity spec with IncludeCmd , then the Docker
CMD is used.
4. If no %runscript is specified, and there is no CMD or ENTRYPOINT , the image’s default execution action is
to run the bash shell.

14.6 How do I specify my Docker image?
In the example above, you probably saw that we referenced the docker image first with the uri docker:// and that
is important to tell Singularity that it will be pulling Docker layers. To ask for ubuntu, we asked for docker://
ubuntu . This uri that we give to Singularity is going to be very important to choose the following Docker metadata
items:
• registry (e.g., “index.docker.io”)
• namespace (e.g., “library”)
• repository (e.g., “ubuntu”)
• tag (e.g., “latest”) OR version (e.g., “@sha256:1234. . . )
When we put those things together, it looks like this:
docker:////:

By default, the minimum requirement is that you specify a repository name (eg, ubuntu) and it will default to the
following:
docker://index.docker.io/library/ubuntu:latest

If you provide a version instead of a tag, that will be used instead:
docker://index.docker.io/library/ubuntu@sha256:1235...

You can have one or the other, both are considered a “digest” in Docker speak.
If you want to change any of those fields and are having trouble with the uri, you can also just state them explicitly:
Bootstrap: docker
From: ubuntu
Registry: index.docker.io
Namespace: library

14.7 Custom Authentication
For both import and build using a build spec file, by default we use the Docker Registry index.docker.io .
Singularity first tries the call without a token, and then asks for one with pull permissions if the request is defined.
However, it may be the case that you want to provide a custom token for a private registry. You have two options.
You can either provide a Username and Password in the build specification file (if stored locally and there is no

14.6. How do I specify my Docker image?

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need to share), or (in the case of doing an import or needing to secure the credentials) you can export these variables
to environmental variables. We provide instructions for each of these cases:

14.7.1 Authentication in the Singularity Build File
You can simply specify your additional authentication parameters in the header with the labels Username and
Password :
Username: vanessa
Password: [password]

Again, this can be in addition to specification of a custom registry with the Registry parameter.

14.7.2 Authentication in the Environment
You can export your username, and password for Singularity as follows:
export SINGULARITY_DOCKER_USERNAME=vanessasaur
export SINGULARITY_DOCKER_PASSWORD=rawwwwwr

14.7.3 Testing Authentication
If you are having trouble, you can test your token by obtaining it on the command line and putting it into an environmental variable, CREDENTIAL :
CREDENTIAL=$(echo -n vanessa:[password] | base64)
TOKEN=$(http 'https://auth.docker.io/token?service=registry.docker.io&
˓→scope=repository:vanessa/code-samples:pull' Authorization:"Basic $CREDENTIAL" | jq ˓→r '.token')

This should place the token in the environmental variable TOKEN . To test that your token is valid, you can do the
following
http https://index.docker.io/v2/vanessa/code-samples/tags/list Authorization:"Bearer
˓→$TOKEN"

The above call should return the tags list as expected. And of course you should change the repo name to be one that
actually exists that you have credentials for.

14.8 Best Practices
While most docker images can import and run without a hitch, there are some special cases for which things can go
wrong. Here is a general list of suggested practices, and if you discover a new one in your building ventures please let
us know.

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14.8.1 1. Installation to Root
When using Docker, you typically run as root, meaning that root’s home at /root is where things will install given a
specification of home. This is fine when you stay in Docker, or if the content at /root doesn’t need any kind of write
access, but generally can lead to a lot of bugs because it is, after all, root’s home. This leads us to best practice #1.
Don’t install anything to root’s home, /root.

14.8.2 2. Library Configurations
The command ldconfig is used to update the shared library cache. If you have software that requires symbolic linking
of libraries and you do the installation without updating the cache, then the Singularity image (in read only) will likely
give you an error that the library is not found. If you look in the image, the library will exist but the symbolic link will
not. This leads us to best practice #2:
Update the library cache at the end of your Dockerfile with a call to ldconfig.

14.8.3 3. Don’t install to $HOME or $TMP
We can assume that the most common Singularity use case has the $USER home being automatically mounted to
$HOME, and $TMP also mounted. Thus, given the potential for some kind of conflict or missing files, for best practice
#3 we suggest the following:
Don’t put container valuables in $TMP or $HOME
Have any more best practices? Please let us know!

14.9 Troubleshooting
Why won’t my image build work? If you can’t find an answer on this site, please ping us an issue. If you’ve found an
answer and you’d like to see it on the site for others to benefit from, then post to us here.

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TROUBLESHOOTING

A little bit of help.

15.1 No space left on device
Sometimes when you are building an image, Singularity tells you that it runs out of space on the device:
sudo singularity build fatty.simg Singularity
IOError: [Errno 28] No space left on device
ABORT: Aborting with RETVAL=255

The issue here is that during build of a squashfs image, Singularity is using the $TMPDIR . If your $TMPDIR is
overflowing (or the mount is very small!) then you would see this error. As a test, you can try building a sandbox. If
this is the issue, then the sandbox should work.
sudo singularity build --sandbox [fatty] Singularity

Solution You simply need to set the $SINGULARITY_CACHEDIR to a different location that you have more room.

15.2 Segfault on Bootstrap of Centos Image
If you are bootstrapping a centos 6 docker image from a debian host, you might hit a segfault:
$ singularity shell docker://centos:6
Docker image path: index.docker.io/library/centos:6
Cache folder set to /home/jbdenis/.singularity/docker
Creating container runtime...
Singularity: Invoking an interactive shell within container...

Segmentation fault

The fix is on your host, you need to pass the variable vsyscall=emulate to the kernel, meaning in the file /etc/
default/grub (note, this file is debian specific), add the following:

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GRUB_CMDLINE_LINUX_DEFAULT="vsyscall=emulate"

and then update grub and reboot:
update-grub && reboot

Please note that this change might have security implications that you should be aware of. For more information, see
the original issue.

15.3 How to use Singularity with GRSecurity enabled kernels
To run Singularity on a GRSecurity enabled kernel, you must disable several security features:

$ sudo sysctl -w kernel.grsecurity.chroot_caps=0
$ sudo sysctl -w kernel.grsecurity.chroot_deny_mount=0
$ sudo sysctl -w kernel.grsecurity.chroot_deny_chmod=0
$ sudo sysctl -w kernel.grsecurity.chroot_deny_fchdir=0

15.4 The container isn’t working on a different host!
Singularity by default mounts your home directory. While this is great for seamless communication between your host
and the container, it can introduce issues if you have software modules installed at $HOME. For example, we had a
user run into this issue.
Solution 1: Specify the home to mount A first thing to try is to point to some “sanitized home,” which is the purpose
of the -H or –home option. For example, here we are creating a home directory under /tmp/homie, and then telling the
container to mount it as home:
rm -rf /tmp/homie && mkdir -p /tmp/homie && \
singularity exec -H /tmp/homie analysis.img /bin/bash

Solution 2: Specify the executable to use It may be the issue that there is an executable in your host environment
(eg, python) that is being called in preference to the containers. To avoid this, in your runscript (the %runscript
section of the bootstrap file) you should specify the path to the executable exactly. This means:
%runscript

# This specifies the python in the container
exec /usr/bin/python "$@"

# This may pick up a different one
exec python "$@"

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This same idea would be useful if you are issuing the command to the container using exec. Thanks to yarikoptic for
the suggestions on this issue.

15.5 Invalid Argument or Unknown Option
When I try mounting my container with the -B or --bind option I receive an unknown option or Invalid argument
error. Make sure that you are using the most recent Singularity release to mount your container to the host system, and
that the --bind argument is placed after the execution command. An example might look like this:
$ singularity run -B $PWD:/data my_container.img

Also, make sure you are using an up-to-date Singularity to bootstrap your container. Some features (such as --bind
) will not work in earlier versions.

15.6 Error running Singularity with sudo
This fix solves the following error when Singularity is installed into the default compiled prefix of /usr/local:
$ sudo singularity instance.start container.img daemon1
sudo: singularity: command not found

The cause of the problem is that sudo sanitizes the PATH environment variable and does not include /usr/local/bin
in the default search path. Considering this program path is by default owned by root, it is reasonable to extend the
default sudo PATH to include this directory. To add /usr/local/bin to the default sudo search path, run the program
visudo which will edit the sudoers file, and search for the string ‘secure_path’. Once found, append :/usr/local/bin to
that line so it looks like this:
Defaults

secure_path = /sbin:/bin:/usr/sbin:/usr/bin:/usr/local/bin

15.7 How to resolve “Too many levels of symbolic links” error
Running singularity failed with “Too many levels of symbolic links” error
$ singularity run -B /apps container.img
ERROR : There was an error binding the path /apps: Too many levels of symbolic links
ABORT : Retval = 255

You got this error because /apps directory is an autofs mount point. You can fix it by editing singularity.conf and
adding the following directive with corresponding path:
autofs bug path = /apps

15.5. Invalid Argument or Unknown Option

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APPENDIX

16.1 build-docker-module
16.1.1 Overview
Docker images are comprised of layers that are assembled at runtime to create an image. You can use Docker layers
to create a base image, and then add your own custom software. For example, you might use Docker’s Ubuntu image
layers to create an Ubuntu Singularity container. You could do the same with CentOS, Debian, Arch, Suse, Alpine,
BusyBox, etc.
Or maybe you want a container that already has software installed. For instance, maybe you want to build a container
that uses CUDA and cuDNN to leverage the GPU, but you don’t want to install from scratch. You can start with one
of the nvidia/cuda containers and install your software on top of that.
Or perhaps you have already invested in Docker and created your own Docker containers. If so, you can seamlessly
convert them to Singularity with the docker bootstrap module.

16.1.2 Keywords
Bootstrap: docker

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.
From: //:@

The From keyword is mandatory. It specifies the container to use as a base. registry is optional and defaults to
index.docker.io. namespace is optional and defaults to library. This is the correct namespace to use for
some official containers (ubuntu for example). tag is also optional and will default to latest
See Singularity and Docker for more detailed info on using Docker registries.
Registry: http://custom_registry

The Registry keyword is optional. It will default to index.docker.io.
Namespace: namespace

The Namespace keyword is optional. It will default to library.
IncludeCmd: yes

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The IncludeCmd keyword is optional. If included, and if a %runscript is not specified, a Docker CMD will take
precedence over ENTRYPOINT and will be used as a runscript. Note that the IncludeCmd keyword is considered
valid if it is not empty! This means that
IncludeCmd: yes and IncludeCmd: no are identical. In both cases the IncludeCmd keyword is not empty, so the Docker CMD will take precedence over an ENTRYPOINT.
See Singularity and Docker for more info on order of operations for determining a runscript.

16.1.3 Notes
Docker containers are stored as a collection of tarballs called layers. When building from a Docker container the layers
must be downloaded and then assembled in the proper order to produce a viable file system. Then the file system must
be converted to squashfs or ext3 format.
Building from Docker Hub is not considered reproducible because if any of the layers of the image are changed, the
container will change. If reproducibility is important to you, consider hosting a base container on Singularity Hub and
building from it instead.
For detailed information about setting your build environment see Build Customization.

16.2 build-shub
16.2.1 Overview
You can use an existing container on Singularity Hub as your “base,” and then add customization. This allows you
to build multiple images from the same starting point. For example, you may want to build several containers with
the same custom python installation, the same custom compiler toolchain, or the same base MPI installation. Instead
of building these from scratch each time, you could create a base container on Singularity Hub and then build new
containers from that existing base container adding customizations in %post , %environment, %runscript, etc.

16.2.2 Keywords
Bootstrap: shub

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.
From: shub:////:@digest

The From keyword is mandatory. It specifies the container to use as a base. registry is optional and
defaults to ``singularity-hub.org. tag and digest are also optional. tag defaults to latest and
digest can be left blank if you want the latest build.

16.2.3 Notes
When bootstrapping from a Singularity Hub image, all previous definition files that led to the creation of the current
image will be stored in a directory within the container called /.singularity.d/bootstrap_history. Singularity will also alert you if environment variables have been changed between the base image and the new image
during bootstrap.

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16.3 build-localimage
This module allows you to build a container from an existing Singularity container on your host system. The name is
somewhat misleading because your container can be in either image or directory format.

16.3.1 Overview
You can use an existing container image as your “base,” and then add customization. This allows you to build multiple
images from the same starting point. For example, you may want to build several containers with the same custom
python installation, the same custom compiler toolchain, or the same base MPI installation. Instead of building these
from scratch each time, you could start with the appropriate local base container and then customize the new container
in %post, %environment, %runscript, etc.

16.3.2 Keywords
Bootstrap: localimage

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.
From: /path/to/container/file/or/directory

The From keyword is mandatory. It specifies the local container to use as a base.

16.3.3 Notes
When building from a local container, all previous definition files that led to the creation of the current container will
be stored in a directory within the container called /.singularity.d/bootstrap_history. Singularity will
also alert you if environment variables have been changed between the base image and the new image during bootstrap.

16.4 build-yum
This module allows you to build a Red Hat/CentOS/Scientific Linux style container from a mirror URI.

16.4.1 Overview
Use the yum module to specify a base for a CentOS-like container. You must also specify the URI for the mirror you
would like to use.

16.4.2 Keywords
Bootstrap: yum

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.
OSVersion: 7

The OSVersion keyword is optional. It specifies the OS version you would like to use. It is only required if you have
specified a %{OSVERSION} variable in the MirrorURL keyword.
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MirrorURL: http://mirror.centos.org/centos-%{OSVERSION}/%{OSVERSION}/os/$basearch/

The MirrorURL keyword is mandatory. It specifies the URL to use as a mirror to download the OS. If you define the
OSVersion keyword, than you can use it in the URL as in the example above.
Include: yum

The Include keyword is optional. It allows you to install additional packages into the core operating system. It is a
best practice to supply only the bare essentials such that the %post section has what it needs to properly complete the
build. One common package you may want to install when using the yum build module is YUM itself.

16.4.3 Notes
There is a major limitation with using YUM to bootstrap a container. The RPM database that exists within the container
will be created using the RPM library and Berkeley DB implementation that exists on the host system. If the RPM
implementation inside the container is not compatible with the RPM database that was used to create the container,
RPM and YUM commands inside the container may fail. This issue can be easily demonstrated by bootstrapping an
older RHEL compatible image by a newer one (e.g. bootstrap a Centos 5 or 6 container from a Centos 7 host).
In order to use the debootstrap build module, you must have yum installed on your system. It may seem counterintuitive to install YUM on a system that uses a different package manager, but you can do so. For instance, on Ubuntu
you can install it like so:
$ sudo apt-get update && sudo apt-get install yum

16.5 build-debootstrap
This module allows you to build a Debian/Ubuntu style container from a mirror URI.

16.5.1 Overview
Use the debootstrap module to specify a base for a Debian-like container. You must also specify the OS version
and a URI for the mirror you would like to use.

16.5.2 Keywords
Bootstrap: debootstrap

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.
OSVersion: xenial

The OSVersion keyword is mandatory. It specifies the OS version you would like to use. For Ubuntu you can use code
words like trusty (14.04), xenial (16.04), and yakkety (17.04). For Debian you can use values like stable,
oldstable, testing, and unstable or code words like wheezy (7), jesse (8), and stretch (9).
MirrorURL:

http://us.archive.ubuntu.com/ubuntu/

The MirrorURL keyword is mandatory. It specifies a URL to use as a mirror when downloading the OS.

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Include: somepackage

The Include keyword is optional. It allows you to install additional packages into the core operating system. It is a
best practice to supply only the bare essentials such that the %post section has what it needs to properly complete the
build.

16.5.3 Notes
In order to use the debootstrap build module, you must have debootstrap installed on your system. On Ubuntu
you can install it like so:
$ sudo apt-get update && sudo apt-get install debootstrap

On CentOS you can install it from the epel repos like so:
$ sudo yum update && sudo yum install epel-release && sudo yum install debootstrap.
˓→noarch

16.6 build-arch
This module allows you to build a Arch Linux based container.

16.6.1 Overview
Use the arch module to specify a base for an Arch Linux based container. Arch Linux uses the aptly named the
pacman package manager (all puns intended).

16.6.2 Keywords
Bootstrap: arch

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.
The Arch Linux bootstrap module does not name any additional keywords at this time. By defining the arch module,
you have essentially given all of the information necessary for that particular bootstrap module to build a core operating
system.

16.6.3 Notes
Arch Linux is, by design, a very stripped down, light-weight OS. You may need to perform a fair amount of configuration to get a usable OS. Please refer to this README.md and the Arch Linux example for more info.

16.7 build-busybox
This module allows you to build a container based on BusyBox.

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16.7.1 Overview
Use the busybox module to specify a BusyBox base for container. You must also specify a URI for the mirror you
would like to use.

16.7.2 Keywords
Bootstrap: busybox

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.
MirrorURL: https://www.busybox.net/downloads/binaries/1.26.1-defconfig-multiarch/
˓→busybox-x86_64

The MirrorURL keyword is mandatory. It specifies a URL to use as a mirror when downloading the OS.

16.7.3 Notes
You can build a fully functional BusyBox container that only takes up ~600kB of disk space!

16.8 build-zypper
This module allows you to build a Suse style container from a mirror URI.

16.8.1 Overview
Use the zypper module to specify a base for a Suse-like container. You must also specify a URI for the mirror you
would like to use.

16.8.2 Keywords
Bootstrap: zypper

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.
OSVersion: 42.2

The OSVersion keyword is optional. It specifies the OS version you would like to use. It is only required if you have
specified a %{OSVERSION} variable in the MirrorURL keyword.
Include: somepackage

The Include keyword is optional. It allows you to install additional packages into the core operating system. It is a
best practice to supply only the bare essentials such that the %post section has what it needs to properly complete the
build. One common package you may want to install when using the zypper build module is zypper itself.

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16.9 Singularity Action Flags
For each of exec, run, and shell, there are a few important flags that we want to note for new users that have
substantial impact on using your container. While we won’t include the complete list of run options (for this complete
list see singularity run --help or more generally singularity  --help) we will review
some highly useful flags that you can add to these actions.
• –contain: Contain suggests that we want to better isolate the container runtime from the host. Adding the
--contain flag will use minimal
/dev and empty other directories (e.g., /tmp).
• –containall: In addition to what is provided with --contain (filesystems) also contain PID, IPC, and environment.
• –cleanenv: Clean the environment before running the container.
• –pwd: Initial working directory for payload process inside the container.
This is not a complete list! Please see the singularity  help for an updated list.

16.9.1 Examples
Here we are cleaning the environment. In the first command, we see that the variable PEANUTBUTTER gets passed
into the container.
PEANUTBUTTER=JELLY singularity exec Centos7.img env | grep PEANUT
PEANUTBUTTER=JELLY

And now here we add --cleanenv to see that it doesn’t.
PEANUTBUTTER=JELLY singularity exec --cleanenv Centos7.img env | grep PEANUT

Here we will test contain. We can first confirm that there are a lot of files on our host in /tmp, and the same files are
found in the container.
# On the host
$ ls /tmp | wc -l
17

# And then /tmp is mounted to the container, by default
$ singularity exec Centos7.img

ls /tmp | wc -l

# ..but not if we use --contain
$ singularity exec --contain Centos7.img

ls /tmp | wc -l

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16.10 Commands
16.10.1 Command Usage
16.10.1.1 The Singularity command
Singularity uses a primary command wrapper called singularity. When you run singularity without any
options or arguments it will dump the high level usage syntax.
The general usage form is:
$ singularity (opts1) [subcommand] (opts2) ...

If you type singularity without any arguments, you will see a high level help for all arguments. The main options
include: Container Actions
• build : Build a container on your user endpoint or build environment
• exec : Execute a command to your container
• inspect : See labels, run and test scripts, and environment variables
• pull : pull an image from Docker or Singularity Hub
• run : Run your image as an executable
• shell : Shell into your image
Image Commands
• image.import : import layers or other file content to your image
• image.export : export the contents of the image to tar or stream
• image.create : create a new image, using the old ext3 filesystem
• image.expand : increase the size of your image (old ext3)
Instance Commands
Instances were added in 2.4. This list is brief, and likely to expand with further development.
• instances : Start, stop, and list container instances
Deprecated Commands The following commands are deprecated in 2.4 and will be removed in future releases.
• bootstrap : Bootstrap a container recipe
For the full usage, see the bottom of this page
16.10.1.1.1 Options and argument processing
Because of the nature of how Singularity cascades commands and sub-commands, argument processing is done with
a mandatory order. This means that where you place arguments is important! In the above usage example,
opts1 are the global Singularity run-time options. These options are always applicable no matter what subcommand
you select (e.g. --verbose or --debug ). But subcommand specific options must be passed after the relevant
subcommand.
To further clarify this example, the exec Singularity subcommand will execute a program within the container and
pass the arguments passed to the program. So to mitigate any argument clashes, Singularity must not interpret or
interfere with any of the command arguments or options that are not relevant for that particular function.

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16.10.1.1.2 Singularity Help
Singularity comes with some internal documentation by using the help subcommand followed by the subcommand
you want more information about. For example:
$ singularity help create
CREATE OPTIONS:
-s/--size

Specify a size for an operation in MiB, i.e. 1024*1024B
(default 768MiB)

-F/--force

Overwrite an image file if it exists

EXAMPLES:

$ singularity create /tmp/Debian.img
$ singularity create -s 4096 /tmp/Debian.img

For additional help, please visit our public documentation pages which are
found at:

https://www.sylabs.io/docs/

16.10.1.2 Commands Usage
USAGE: singularity [global options...]  [command options...] ...

GLOBAL OPTIONS:
-d|--debug

Print debugging information

-h|--help

Display usage summary

-s|--silent

Only print errors

-q|--quiet

Suppress all normal output

--version
-v|--verbose

Show application version
Increase verbosity +1

-x|--sh-debug Print shell wrapper debugging information

GENERAL COMMANDS:
help

Show additional help for a command or container
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selftest

Run some self tests for singularity install

CONTAINER USAGE COMMANDS:
exec

Execute a command within container

run

Launch a runscript within container

shell

Run a Bourne shell within container

test

Launch a testscript within container

CONTAINER MANAGEMENT COMMANDS:
apps

List available apps within a container

bootstrap

*Deprecated* use build instead

build

Build a new Singularity container

check

Perform container lint checks

inspect

Display a container's metadata

mount

Mount a Singularity container image

pull

Pull a Singularity/Docker container to $PWD

COMMAND GROUPS:
image

Container image command group

instance

Persistent instance command group

CONTAINER USAGE OPTIONS:
see singularity help 

For any additional help or support visit the Singularity
website: https://www.sylabs.io/contact/

16.10.1.3 Support
Have a question, or need further information? Reach out to us.

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16.10.2 build
Use build to download and assemble existing containers, convert containers from one format to another, or build a
container from a Singularity recipe.
16.10.2.1 Overview
The build command accepts a target as input and produces a container as output. The target can be a Singularity
Hub or Docker Hub URI, a path to an existing container, or a path to a Singularity Recipe file. The output container
can be in squashfs, ext3, or directory format.
For a complete list of build options type singularity help build. For more info on building containers see
Build a Container.
16.10.2.2 Examples
16.10.2.2.1 Download an existing container from Singularity Hub or Docker Hub
$ singularity build lolcow.simg shub://GodloveD/lolcow
$ singularity build lolcow.simg docker://godlovedc/lolcow

16.10.2.2.2 Create –writable images and –sandbox directories
$ sudo singularity build --writable lolcow.img shub://GodloveD/lolcow
$ sudo singularity build --sandbox lolcow/ shub://GodloveD/lolcow

16.10.2.2.3 Convert containers from one format to another
You can convert the three supported container formats using any combination.
$ sudo singularity build --writable development.img production.simg
$ singularity build --sandbox development/ production.simg
$ singularity build production2 development/

16.10.2.2.4 Build a container from a Singularity recipe
Given a Singularity Recipe called Singularity :
$ sudo singularity build lolcow.simg Singularity

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16.10.3 exec
The exec Singularity sub-command allows you to spawn an arbitrary command within your container image as if it
were running directly on the host system. All standard IO, pipes, and file systems are accessible via the command
being exec’ed within the container. Note that this exec is different from the Docker exec, as it does not require a
container to be “running” before using it.
16.10.3.1 Examples
16.10.3.1.1 Printing the OS release inside the container
$ singularity exec container.img cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 8 (jessie)"
NAME="Debian GNU/Linux"
VERSION_ID="8"
VERSION="8 (jessie)"
ID=debian
HOME_URL="http://www.debian.org/"
SUPPORT_URL="http://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"
$

16.10.3.1.2 Printing the OS release for a running instance
Use the instance:// syntax like so:
$ singularity exec instance://my-instance cat /etc/os-release

16.10.3.1.3 Runtime Flags
If you are interested in containing an environment or filesystem locations, we highly recommend that you look at the
singularity run help and our documentation on flags to better customize this command.
16.10.3.1.4 Special Characters
And properly passing along special characters to the program within the container.
$ singularity exec container.img echo -ne "hello\nworld\n\n"
hello
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world
$

And a demonstration using pipes:
$ cat debian.def | singularity exec container.img grep 'MirrorURL'
MirrorURL "http://ftp.us.debian.org/debian/"
$

16.10.3.1.5 A Python example
Starting with the file hello.py in the current directory with the contents of:
#!/usr/bin/python

import sys
print("Hello World: The Python version is %s.%s.%s" % sys.version_info[:3])

Because our home directory is automatically bound into the container, and we are running this from our home directory,
we can easily execute that script using the Python within the container:
$ singularity exec /tmp/Centos7-ompi.img /usr/bin/python hello.py
Hello World: The Python version is 2.7.5

We can also pipe that script through the container and into the Python binary which exists inside the container using
the following command:
$ cat hello.py | singularity exec /tmp/Centos7-ompi.img /usr/bin/python
Hello World: The Python version is 2.7.5

For demonstration purposes, let’s also try to use the latest Python container which exists in DockerHub to run this
script:
$ singularity exec docker://python:latest /usr/local/bin/python hello.py
library/python:latest
Downloading layer:
˓→sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
Downloading layer:
˓→sha256:fbd06356349dd9fb6af91f98c398c0c5d05730a9996bbf88ff2f2067d59c70c4
Downloading layer:
˓→sha256:644eaeceac9ff6195008c1e20dd693346c35b0b65b9a90b3bcba18ea4bcef071
Downloading layer:
˓→sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
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Downloading layer:
˓→sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
Downloading layer:
˓→sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
Downloading layer:
˓→sha256:766692404ca72f4e31e248eb82f8eca6b2fcc15b22930ec50e3804cc3efe0aba
Downloading layer:
˓→sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
Downloading layer:
˓→sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
Downloading layer:
˓→sha256:6a3d69edbe90ef916e1ecd8d197f056de873ed08bcfd55a1cd0b43588f3dbb9a
Downloading layer:
˓→sha256:ff18e19c2db42055e6f34323700737bde3c819b413997cddace2c1b7180d7efd
Downloading layer:
˓→sha256:7b9457ec39de00bc70af1c9631b9ae6ede5a3ab715e6492c0a2641868ec1deda
Downloading layer:
˓→sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
Downloading layer:
˓→sha256:6a5a5368e0c2d3e5909184fa28ddfd56072e7ff3ee9a945876f7eee5896ef5bb
Hello World: The Python version is 3.5.2

16.10.3.1.6 A GPU example
If your host system has an NVIDIA GPU card and a driver installed you can leverage the card with the --nv option.
(This example requires a fairly recent version of the NVIDIA driver on the host system to run the latest version of
TensorFlow.
$ git clone https://github.com/tensorflow/models.git
$ singularity exec --nv docker://tensorflow/tensorflow:latest-gpu \
python ./models/tutorials/image/mnist/convolutional.py
Docker image path: index.docker.io/tensorflow/tensorflow:latest-gpu
Cache folder set to /home/david/.singularity/docker
[19/19] |===================================| 100.0%
Creating container runtime...
Extracting data/train-images-idx3-ubyte.gz
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Extracting data/train-labels-idx1-ubyte.gz
Extracting data/t10k-images-idx3-ubyte.gz
Extracting data/t10k-labels-idx1-ubyte.gz
2017-08-18 20:33:59.677580: W tensorflow/core/platform/cpu_feature_guard.cc:45] The
˓→TensorFlow library wasn't compiled to use SSE4.1 instructions, but these are
˓→available on your machine and could speed up CPU computations.
2017-08-18 20:33:59.677620: W tensorflow/core/platform/cpu_feature_guard.cc:45] The
˓→TensorFlow library wasn't compiled to use SSE4.2 instructions, but these are
˓→available on your machine and could speed up CPU computations.
2017-08-18 20:34:00.148531: I tensorflow/stream_executor/cuda/cuda_gpu_executor.
˓→cc:893] successful NUMA node read from SysFS had negative value (-1), but there
˓→must be at least one NUMA node, so returning NUMA node zero
2017-08-18 20:34:00.148926: I tensorflow/core/common_runtime/gpu/gpu_device.cc:955]
˓→Found device 0 with properties:
name: GeForce GTX 760 (192-bit)
major: 3 minor: 0 memoryClockRate (GHz) 0.8885
pciBusID 0000:03:00.0
Total memory: 2.95GiB
Free memory: 2.92GiB
2017-08-18 20:34:00.148954: I tensorflow/core/common_runtime/gpu/gpu_device.cc:976]
˓→DMA: 0
2017-08-18 20:34:00.148965: I tensorflow/core/common_runtime/gpu/gpu_device.cc:986]
˓→0:
Y
2017-08-18 20:34:00.148979: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1045]
˓→Creating TensorFlow device (/gpu:0) -> (device: 0, name: GeForce GTX 760 (192-bit),
˓→pci bus id: 0000:03:00.0)
Initialized!
Step 0 (epoch 0.00), 21.7 ms
Minibatch loss: 8.334, learning rate: 0.010000
Minibatch error: 85.9%
Validation error: 84.6%
Step 100 (epoch 0.12), 20.9 ms
Minibatch loss: 3.235, learning rate: 0.010000
Minibatch error: 4.7%
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Validation error: 7.8%
Step 200 (epoch 0.23), 20.5 ms
Minibatch loss: 3.363, learning rate: 0.010000
Minibatch error: 9.4%
Validation error: 4.2%
[...snip...]
Step 8500 (epoch 9.89), 20.5 ms
Minibatch loss: 1.602, learning rate: 0.006302
Minibatch error: 0.0%
Validation error: 0.9%
Test error: 0.8%

16.10.4 inspect
How can you sniff an image? We have provided the inspect command for you to easily see the runscript, test script,
environment, help, and metadata labels.
This command is essential for making containers understandable by other tools and applications.
16.10.4.1 JSON Api Standard
For any inspect command, by adding --json you can be assured to get a JSON API standardized response, for
example:
singularity inspect -l --json ubuntu.img
{
"data": {
"attributes": {
"labels": {
"SINGULARITY_DEFFILE_BOOTSTRAP": "docker",
"SINGULARITY_DEFFILE": "Singularity",
"SINGULARITY_BOOTSTRAP_VERSION": "2.2.99",
"SINGULARITY_DEFFILE_FROM": "ubuntu:latest"
}
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},
"type": "container"
}
}

16.10.4.2 Inspect Flags
The default, if run without any arguments, will show you the container labels file
$ singularity inspect ubuntu.img
{
"SINGULARITY_DEFFILE_BOOTSTRAP": "docker",
"SINGULARITY_DEFFILE": "Singularity",
"SINGULARITY_BOOTSTRAP_VERSION": "2.2.99",
"SINGULARITY_DEFFILE_FROM": "ubuntu:latest"
}

and as outlined in the usage, you can specify to see any combination of --labels , --environment ,
--runscript , --test , and --deffile. The quick command to see everything, in json format, would be:
$ singularity inspect -l -r -d -t -e -j -hf ubuntu.img
{
"data": {
"attributes": {
"test": null,
"help": "This is how you run the image!\n",
"environment": "# Custom environment shell code should follow\n\n",
"labels": {
"SINGULARITY_DEFFILE_BOOTSTRAP": "docker",
"SINGULARITY_DEFFILE": "Singularity",
"SINGULARITY_BOOTSTRAP_VERSION": "2.2.99",
"SINGULARITY_DEFFILE_FROM": "ubuntu:latest"
},
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"deffile": "Bootstrap:docker\nFrom:ubuntu:latest\n",
"runscript": "#!/bin/sh\n\nexec /bin/bash \"$@\""
},
"type": "container"
}
}

16.10.4.2.1 Labels
The default, if run without any arguments, will show you the container labels file (located at /.singularity.d/
labels.json in the container. These labels are the ones that you define in the %labels section of your bootstrap
file, along with any Docker LABEL that came with an image that you imported, and other metadata about the bootstrap.
For example, here we are inspecting labels for ubuntu.img
$ singularity inspect ubuntu.img
{
"SINGULARITY_DEFFILE_BOOTSTRAP": "docker",
"SINGULARITY_DEFFILE": "Singularity",
"SINGULARITY_BOOTSTRAP_VERSION": "2.2.99",
"SINGULARITY_DEFFILE_FROM": "ubuntu:latest"
}

This is the equivalent of both of:
$ singularity inspect -l ubuntu.img
$ singularity inspect --labels ubuntu.img

16.10.4.2.2 Runscript
The commands --runscript or --r will show you the runscript, which also can be shown in --json:
$ singularity inspect -r -j ubuntu.img{
"data": {
"attributes": {
"runscript": "#!/bin/sh\n\nexec /bin/bash \"$@\""
},
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"type": "container"
}
}

or in a human friendly, readable print to the screen:
$ singularity inspect -r ubuntu.img

##runscript
#!/bin/sh

exec /bin/bash "$@"

16.10.4.2.3 Help
The commands --helpfile or --hf will show you the runscript helpfile, if it exists. With --json you can also
see it as such:
singularity inspect -hf -j dino.img
{
"data": {
"attributes": {
"help": "\n\n\nHi there! This is my image help section.
\n\nUsage:\n\nboobeep doo doo\n\n --arg/a arrrrg I'm a pirate!\n --boo/b eeeeeuzzz
˓→where is the honey?\n\n\n"

˓→

},
"type": "container"
}
}

or in a human friendly, readable print to the screen, don’t use -j or --json:
$ singularity inspect -hf dino.img

Hi there! This is my image help section.

Usage:

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boobeep doo doo

--arg/a arrrrg I'm a pirate!
--boo/b eeeeeuzzz where is the honey?

16.10.4.2.4 Environment
The commands --environment and -e will show you the container’s environment, again specified by the
%environment section of a bootstrap file, and other ENV labels that might have come from a Docker import.
You can again choose to see --json :
$ singularity inspect -e --json ubuntu.img
{
"data": {
"attributes": {
"environment": "# Custom environment shell code should follow\n\n"
},
"type": "container"
}
}

or human friendly:
$ singularity inspect -e ubuntu.img

##environment
# Custom environment shell code should follow

The container in the example above did not have any custom environment
variables set.
16.10.4.2.5 Test
The equivalent --test or -t commands will print any test defined for the container, which comes from the %test
section of the bootstrap specification Singularity file. Again, we can ask for --json or human friendly (default):
$ singularity --inspect -t --json ubuntu.img
{
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"data": {
"attributes": {
"test": null
},
"type": "container"
}
}

$ singularity inspect -t

ubuntu.img

{
"status": 404,
"detail": "This container does not have any tests defined",
"title": "Tests Undefined"
}

16.10.4.2.6 Deffile
Want to know where your container came from? You can see the entire Singularity definition file, if the container was
created with a bootstrap, by using --deffile or -d:
$ singularity inspect -d

ubuntu.img

##deffile
Bootstrap:docker
From:ubuntu:latest

or with --json output.
$ singularity inspect -d --json ubuntu.img
{
"data": {
"attributes": {
"deffile": "Bootstrap:docker\nFrom:ubuntu:latest\n"
},
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"type": "container"
}
}

The goal of these commands is to bring more transparency to containers, and to help better integrate them into common
workflows by having them expose their guts to the world! If you have feedback for how we can improve or amend
this, please let us know!

16.10.5 pull
Singularity pull is the command that you would want to use to communicate with a container registry. The command
does exactly as it says - there exists an image external to my host, and I want to pull it here. We currently support pull
for both Docker and Singularity Hub images, and will review usage for both.
16.10.5.1 Singularity Hub
Singularity differs from Docker in that we serve entire images, as opposed to layers. This means that pulling a
Singularity Hub means downloading the entire (compressed) container file, and then having it extract on your local
machine. The basic command is the following:
singularity pull shub://vsoch/hello-world
Progress |===================================| 100.0%
Done. Container is at: ./vsoch-hello-world-master.img

16.10.5.1.1 How do tags work?
On Singularity Hub, a tag coincide with a branch. So if you have a repo called vsoch/hello-world , by
default the file called Singularity (your build recipe file) will be looked for in the base of the master branch. The
command that we issued above would be equivalent to doing:
singularity pull shub://vsoch/hello-world:master

To enable other branches to build, they must be turned on in your collection. If you then put another Singularity file in
a branch called development, you would pull it as follows:
singularity pull shub://vsoch/hello-world:development

The term latest in Singularity Hub will pull, across all of your branches, the most recent image. If development
is more recent than master, it would be pulled, for example.
16.10.5.1.2 Image Names
As you can see, since we didn’t specify anything special, the default naming convention is to use the username,
reponame, and the branch (tag). You have three options for changing this:

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PULL OPTIONS:
-n/--name

Specify a custom container name (first priority)

-C/--commit Name container based on GitHub commit (second priority)
-H/--hash

Name container based on file hash (second priority)

16.10.5.1.3 Custom Name
singularity pull --name meatballs.img shub://vsoch/hello-world
Progress |===================================| 100.0%
Done. Container is at: ./meatballs.img

16.10.5.1.4 Name by commit
Each container build on Singularity Hub is associated with the GitHub commit of the repo that was used to build it.
You can specify to name your container based on the commit with the --commit flag, if, for example, you want to
match containers to their build files:
singularity pull --commit shub://vsoch/hello-world
Progress |===================================| 100.0%
Done. Container is at: ./4187993b8b44cbfa51c7e38e6b527918fcdf0470.img

16.10.5.1.5 Name by hash
If you prefer the hash of the file itself, you can do that too.
singularity pull --hash shub://vsoch/hello-world
Progress |===================================| 100.0%
Done. Container is at: ./4db5b0723cfd378e332fa4806dd79e31.img

16.10.5.1.6 Pull to different folder
For any of the above, if you want to specify a different folder for your image, you can define the variable
SINGULARITY_PULLFOLDER. By default, we will first check if you have the SINGULARITY_CACHEDIR defined, and pull images there. If not, we look for SINGULARITY_PULLFOLDER. If neither of these are defined, the
image is pulled to the present working directory, as we showed above. Here is an example of pulling to /tmp .
SINGULARITY_PULLFOLDER=/tmp
singularity pull shub://vsoch/hello-world
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Progress |===================================| 100.0%
Done. Container is at: /tmp/vsoch-hello-world-master.img

16.10.5.1.7 Pull by commit
You can also pull different versions of your container by using their commit id ( version ).
singularity pull shub://vsoch/hello-world@42e1f04ed80217895f8c960bdde6bef4d34fab59
Progress |===================================| 100.0%
Done. Container is at: ./vsoch-hello-world-master.img

In this example, the first build of this container will be pulled.
16.10.5.2 Docker
Docker pull is similar (on the surface) to a Singularity Hub pull, and we would do the following:
singularity pull docker://ubuntu
Initializing Singularity image subsystem
Opening image file: ubuntu.img
Creating 223MiB image
Binding image to loop
Creating file system within image
Image is done: ubuntu.img
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /home/vanessa/.singularity/docker
Importing: base Singularity environment
Importing: /home/vanessa/.singularity/docker/
˓→sha256:b6f892c0043b37bd1834a4a1b7d68fe6421c6acbc7e7e63a4527e1d379f92c1b.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:55010f332b047687e081a9639fac04918552c144bc2da4edb3422ce8efcc1fb1.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:2955fb827c947b782af190a759805d229cfebc75978dba2d01b4a59e6a333845.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:3deef3fcbd3072b45771bd0d192d4e5ff2b7310b99ea92bce062e01097953505.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:cf9722e506aada1109f5c00a9ba542a81c9e109606c01c81f5991b1f93de7b66.tar.gz
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Importing: /home/vanessa/.singularity/metadata/
˓→sha256:fe44851d529f465f9aa107b32351c8a0a722fc0619a2a7c22b058084fac068a4.tar.gz
Done. Container is at: ubuntu.img

If you specify the tag, the image would be named accordingly (eg, ubuntu-latest.img). Did you notice that the
output looks similar to if we did the following?
singularity create ubuntu.img
singularity import ubuntu.img docker://ubuntu

this is because the same logic is happening on the back end. Thus, the pull command with a docker uri also supports
arguments --size and --name . Here is how I would pull an ubuntu image, but make it bigger, and name it
something else.
singularity pull --size 2000 --name jellybelly.img docker://ubuntu
Initializing Singularity image subsystem
Opening image file: jellybelly.img
Creating 2000MiB image
Binding image to loop
Creating file system within image
Image is done: jellybelly.img
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /home/vanessa/.singularity/docker
Importing: base Singularity environment
Importing: /home/vanessa/.singularity/docker/
˓→sha256:b6f892c0043b37bd1834a4a1b7d68fe6421c6acbc7e7e63a4527e1d379f92c1b.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:55010f332b047687e081a9639fac04918552c144bc2da4edb3422ce8efcc1fb1.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:2955fb827c947b782af190a759805d229cfebc75978dba2d01b4a59e6a333845.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:3deef3fcbd3072b45771bd0d192d4e5ff2b7310b99ea92bce062e01097953505.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:cf9722e506aada1109f5c00a9ba542a81c9e109606c01c81f5991b1f93de7b66.tar.gz
Importing: /home/vanessa/.singularity/metadata/
˓→sha256:fe44851d529f465f9aa107b32351c8a0a722fc0619a2a7c22b058084fac068a4.tar.gz
Done. Container is at: jellybelly.img

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16.10.6 run
It’s common to want your container to “do a thing.” Singularity run allows you to define a custom action to be taken
when a container is either run or executed directly by file name. Specifically, you might want it to execute a command,
or run an executable that gives access to many different functions for the user.
16.10.6.1 Overview
First, how do we run a container? We can do that in one of two ways - the commands below are identical:
$ singularity run centos7.img
$ ./centos7.img

In both cases, we are executing the container’s “runscript” (the executable /singularity at the root of the image)
that is either an actual file (version 2.2 and earlier) or a link to one (2.3 and later). For example, looking at a 2.3 image,
I can see the runscript via the path to the link:
$ singularity exec centos7.img cat /singularity
#!/bin/sh

exec /bin/bash "$@"

or to the actual file in the container’s metadata folder, /.singularity.d
$ singularity exec centos7.img cat /.singularity.d/runscript
#!/bin/sh

exec /bin/bash "$@"

Notice how the runscript has bash followed by \$@ ? This is good practice to include in a runscript, as any arguments
passed by the user will be given to the container.
16.10.6.2 Runtime Flags
If you are interested in containing an environment or filesystem locations, we highly recommend that you look at the
singularity run help and our documentation on flags to better customize this command.
16.10.6.3 Examples
In this example the container has a very simple runscript defined.
$ singularity exec centos7.img cat /singularity
#!/bin/sh

echo motorbot

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$ singularity run centos7.img
motorbot

16.10.6.3.1 Defining the Runscript
When you first create a container, the runscript is defined using the following order of operations:
1. A user defined runscript in the %runscript section of a bootstrap takes preference over all
2. If the user has not defined a runscript and is importing a Docker container, the Docker ENTRYPOINT is used.
3. If a user has not defined a runscript and adds IncludeCmd:
the ENTRYPOINT

yes to the bootstrap file, the CMD is used over

4. If the user has not defined a runscript and the Docker container
doesn’t have an ENTRYPOINT, we look for CMD, even if the user hasn’t asked for it.
1. If the user has not defined a runscript, and there is no ENTRYPOINT or CMD (or we aren’t importing Docker at
all) then we default to /bin/bash
Here is how you would define the runscript section when you build an image:
Bootstrap: docker
From: ubuntu:latest

%runscript
exec /usr/bin/python "$@"

and of course python should be installed as /usr/bin/python. The addition of $@ ensures that arguments are passed
along from the user. If you want your container to run absolutely any command given to it, and you want to use run
instead of exec, you could also just do:
Bootstrap: docker
From: ubuntu:latest

%runscript
exec "$@"`

If you want different entrypoints for your image, we recommend using the %apprun syntax (see apps). Here we have
two entrypoints for foo and bar:
%runscript
exec echo "Try running with --app dog/cat"

%apprun dog
exec echo Hello "$@", this is Dog
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%apprun cat
exec echo Meow "$@", this is Cat

and then running (after build of a complete recipe) would look like:
sudo singularity build catdog.simg Singularity

$ singularity run catdog.simg
Try running with --app dog/cat

$ singularity run --app cat catdog.simg
Meow , this is Cat
$ singularity run --app dog catdog.simg
Hello , this is Dog

Generally, it is advised to provide help for your container with %help or %apphelp. If you find it easier, you can
also provide help by way of a runscript that tells your user how to use the container, and gives access to the important
executables. Regardless of your strategy. a reproducible container is one that tells the user how to interact with it.

16.10.7 shell
The shell Singularity sub-command will automatically spawn an interactive shell within a container. As of v2.3 the
default that is spawned via the shell command is /bin/bash if it exists otherwise /bin/sh is called.
$ singularity shell
USAGE: singularity (options) shell [container image] (options)

Here we can see the default shell in action:
$ singularity shell centos7.img
Singularity: Invoking an interactive shell within container...

Singularity centos7.img:~> echo $SHELL
/bin/bash

Additionally any arguments passed to the Singularity command (after the container name) will be passed to the called
shell within the container, and shell can be used across image types. Here is a quick example of shelling into a
container assembled from Docker layers. We highly recommend that you look at the singularity shell help
and our documentation on flags to better customize this command.

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16.10.7.1 Change your shell
The shell sub-command allows you to set or change the default shell using the --shell argument. As of Singularity version 2.2, you can also use the environment variable SINGULARITY_SHELL which will use that as your
shell entry point into the container.
16.10.7.1.1 Bash
The correct way to do it:
export SINGULARITY_SHELL="/bin/bash --norc"
singularity shell centos7.img Singularity: Invoking an interactive shell within
˓→container...
Singularity centos7.img:~/Desktop> echo $SHELL
/bin/bash --norc

Don’t do this, it can be confusing:
$ export SINGULARITY_SHELL=/bin/bash
$ singularity shell centos7.img
Singularity: Invoking an interactive shell within container...

# What? We are still on my Desktop? Actually no, but the uri says we are!
vanessa@vanessa-ThinkPad-T460s:~/Desktop$ echo $SHELL
/bin/bash

Depending on your shell, you might also want the --noprofile flag. How can you learn more about a shell? Ask
it for help, of course!
16.10.7.2 Shell Help
$ singularity shell centos7.img --help
Singularity: Invoking an interactive shell within container...

GNU bash, version 4.2.46(1)-release-(x86_64-redhat-linux-gnu)
Usage:

/bin/bash [GNU long option] [option] ...

/bin/bash [GNU long option] [option] script-file ...
GNU long options:
--debug
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--debugger
--dump-po-strings
--dump-strings
--help
--init-file
--login
--noediting
--noprofile
--norc
--posix
--protected
--rcfile
--rpm-requires
--restricted
--verbose
--version
Shell options:
-irsD or -c command or -O shopt_option

(invocation only)

-abefhkmnptuvxBCHP or -o option
Type `/bin/bash -c "help set"' for more information about shell options.
Type `/bin/bash -c help' for more information about shell builtin commands.

And thus we should be able to do:
$ singularity shell centos7.img -c "echo hello world"
Singularity: Invoking an interactive shell within container...

hello world

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16.11 Image Command Group
16.11.1 image.export
Export is a way to dump the contents of your container into a .tar.gz, or a stream to put into some other place. For
example, you could stream this into an in memory tar in python. Importantly, this command was originally intended
for Singularity version less than 2.4 in the case of exporting an ext3 filesystem. For Singularity greater than 2.4, the
resulting export file is likely to be larger than the original squashfs counterpart. An example with an ext3 image is
provided.
Here we export an image into a .tar file:
singularity image.export container.img > container.tar

We can also specify the file with --file
singularity image.export --file container.tar container.img

And here is the recommended way to compress your image:
singularity image.export container.img | gzip -9 > container.img.tar.gz

16.11.2 image.expand
While the squashfs filesystem means that you typically don’t need to worry about the size of your container being
built, you might find that if you are building an ext3 image (pre Singularity 2.4) you want to expand it.
16.11.2.1 Increasing the size of an existing image
You can increase the size of an image after it has been instantiated by using the image.expand Singularity subcommand. In the example below, we:
1. create an empty image
2. inspect it’s size
3. expand it
4. confirm it’s larger
$ singularity image.create container.img
Creating empty 768MiB image file: container.imglarity image.create container.im
Formatting image with ext3 file system
Image is done: container.img

$ ls -lh container.img
-rw-rw-r-- 1 vanessa vanessa 768M Oct

2 18:48 container.img

$ singularity image.expand container.img
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Expanding image by 768MB
Checking image's file system
e2fsck 1.42.13 (17-May-2015)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
container.img: 11/49152 files (0.0% non-contiguous), 7387/196608 blocks
Resizing image's file system
resize2fs 1.42.13 (17-May-2015)
Resizing the filesystem on container.img to 393216 (4k) blocks.
The filesystem on container.img is now 393216 (4k) blocks long.
Image is done: container.img

$ ls -lh container.img
-rw-rw-r-- 1 vanessa vanessa 1.5G Oct

2 18:48 container.img

Similar to the create sub-command, you can override the default size increase (which is 768MiB) by using the --size
option.

16.11.3 image.import
Singularity import is essentially taking a dump of files and folders and adding them to your image. This works for
local compressed things (e.g., tar.gz) but also for docker image layers that you don’t have on your system. As of
version 2.3, import of docker layers includes the environment and metadata without needing sudo. It’s generally very
intuitive.
As an example, here is a common use case: wanting to import a Docker image:
singularity image.import container.img docker://ubuntu:latest

16.11.4 image.create
A Singularity image, which can be referred to as a “container,” is a single file that contains a virtual file system.
As of Singularity 2.4, we strongly recommend that you build (create and install) an image using build. If you have
reason to create an empty image, or use create for any other reason, the original create command is replaced with a

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more specific image.create. After creating an image you can install an operating system, applications, and save
meta-data with it.
Whereas Docker assembles images from layers that are stored on your computer (viewed with the docker history
command), a Singularity image is just one file that can sit on your Desktop, in a folder on your cluster, or anywhere.
Having Singularity containers housed within a single image file greatly simplifies management tasks such as sharing,
copying, and branching your containers. It also means that standard Linux file system concepts like permissions,
ownership, and ACLs apply to the container (e.g. I can give read only access to a colleague, or block access completely
with a simple chmod command).
16.11.4.1 Creating a new blank Singularity container image
Singularity will create a default container image of 768MiB using the following command:
singularity image.create container.img
Creating empty 768MiB image file: container.img
Formatting image with ext3 file system
Image is done: container.img

How big is it?
$ du -sh container.img
29M

container.img

Create will make an ext3 filesystem. Let’s create and import a docker base (the pre-2.4 way with two
commands), and then compare to just building (one command) from the same base.
singularity create container.img
sudo singularity bootstrap container.img docker://ubuntu

...

$ du -sh container.img
769M

Prior to 2.4, you would need to provide a --size to change from the default:
$ singularity create --size 2048 container2.img
Initializing Singularity image subsystem
Opening image file: container2.img
Creating 2048MiB image
Binding image to loop
Creating file system within image
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Image is done: container2.img

$ ls -lh container*.img
-rwxr-xr-x 1 user group 2.1G Apr 15 11:34 container2.img
-rwxr-xr-x 1 user group 769M Apr 15 11:11 container.img

Now let’s compare to if we just built, without needing to specify a size.
sudo singularity build container.simg docker://ubuntu

...

du -sh container.simg
45M container.simg

Quite a difference! And one command instead of one.
16.11.4.1.1 Overwriting an image with a new one
For any commands that If you have already created an image and wish to overwrite it, you can do so with
the --force option.
$ singularity image.create container.img
ERROR: Image file exists, not overwriting.

$ singularity image.create --force container.img
Creating empty 768MiB image file: container.img
Formatting image with ext3 file system
Image is done: container.img

@GodLoveD has provided a nice interactive demonstration of creating an image (pre 2.4).

16.12 Instance Command Group
16.12.1 instance.start
New in Singularity version 2.4 you can use the instance command group to run instances of containers in the
background. This is useful for running services like databases and web servers. The instance.start command
lets you initiate a named instance in the background.

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16.12.1.1 Overview
To initiate a named instance of a container, you must call the instance.start command with 2 arguments: the
name of the container that you want to start and a unique name for an instance of that container. Once the new instance
is running, you can join the container’s namespace using a URI style syntax like so:
$ singularity shell instance://

You can specify options such as bind mounts, overlays, or custom namespaces when you initiate a new instance of a
container with instance.start. These options will persist as long as the container runs.
For a complete list of options see the output of:
singularity help instance.start

16.12.1.2 Examples
These examples use a container from Singularity Hub, but you can use local containers or containers from Docker
Hub as well. For a more detailed look at instance usage see Running Instances.
16.12.1.2.1 Start an instance called cow1 from a container on Singularity Hub
$ singularity instance.start shub://GodloveD/lolcow cow1

16.12.1.2.2 Start an interactive shell within the instance that you just started
$ singularity shell instance://cow1
Singularity GodloveD-lolcow-master.img:~> ps -ef
UID

PID

PPID

C STIME TTY

TIME CMD

ubuntu

1

0

0 20:03 ?

00:00:00 singularity-instance: ubuntu [cow1]

ubuntu

3

0

0 20:04 pts/0

00:00:00 /bin/bash --norc

ubuntu

4

3

0 20:04 pts/0

00:00:00 ps -ef

Singularity GodloveD-lolcow-master.img:~> exit

16.12.1.2.3 Execute the runscript within the instance
$ singularity run instance://cow1
_________________________________________
/ Clothes make the man. Naked people have \
| little or no influence on society.

|
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|

|

\ -- Mark Twain

/

----------------------------------------\
\

^__^
(oo)\_______
(__)\

)\/\

||----w |
||

||

16.12.1.2.4 Run a command within a running instance
$ singularity exec instance://cow1 cowsay "I like blending into the background"
_____________________________________
< I like blending into the background >
------------------------------------\
\

^__^
(oo)\_______
(__)\

)\/\

||----w |
||

||

16.12.2 instance.list
New in Singularity version 2.4 you can use the instance command group to run instances of containers in the
background. This is useful for running services like databases and web servers. The instance.list command
lets you keep track of the named instances running in the background.
16.12.2.1 Overview
After initiating one or more named instances to run in the background with the instance.start command you
can list them with the instance.list command.
16.12.2.2 Examples
These examples use a container from Singularity Hub, but you can use local containers or containers from Docker
Hub as well. For a more detailed look at instance usage see Running Instances.
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16.12.2.2.1 Start a few named instances from containers on Singularity Hub
$ singularity instance.start shub://GodloveD/lolcow cow1
$ singularity instance.start shub://GodloveD/lolcow cow2
$ singularity instance.start shub://vsoch/hello-world hiya

16.12.2.2.2 List running instances
$ singularity instance.list
DAEMON NAME

PID

CONTAINER IMAGE

cow1

20522

/home/ubuntu/GodloveD-lolcow-master.img

cow2

20558

/home/ubuntu/GodloveD-lolcow-master.img

hiya

20595

/home/ubuntu/vsoch-hello-world-master.img

16.12.3 instance.stop
New in Singularity version 2.4 you can use the instance command group to run instances of containers in the
background. This is useful for running services like databases and web servers. The instance.stop command
lets you stop instances once you are finished using them
16.12.3.1 Overview
After initiating one or more named instances to run in the background with the instance.start command you
can stop them with the instance.stop command.
16.12.3.2 Examples
These examples use a container from Singularity Hub, but you can use local containers or containers from Docker
Hub as well. For a more detailed look at instance usage see Running Instances.
16.12.3.2.1 Start a few named instances from containers on Singularity Hub
$ singularity instance.start shub://GodloveD/lolcow cow1
$ singularity instance.start shub://GodloveD/lolcow cow2
$ singularity instance.start shub://vsoch/hello-world hiya

16.12.3.2.2 Stop a single instance

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$ singularity instance.stop cow1
Stopping cow1 instance of /home/ubuntu/GodloveD-lolcow-master.img (PID=20522)

16.12.3.2.3 Stop all running instances
$ singularity instance.stop --all
Stopping cow2 instance of /home/ubuntu/GodloveD-lolcow-master.img (PID=20558)
Stopping hiya instance of /home/ubuntu/vsoch-hello-world-master.img (PID=20595)

16.13 Deprecated
16.13.1 bootstrap
Bootstrapping was the original way (for Singularity versions prior to 2.4) to install an operating system and then
configure it appropriately for a specified need. Bootstrap is very similar to build, except that it by default uses an ext3
filesystem and allows for writability. The images unfortunately are not immutable in this way, and can degrade over
time. As of 2.4, bootstrap is still supported for Singularity, however we encourage you to use build instead.
16.13.1.1 Quick Start
A bootstrap is done based on a Singularity recipe file (a text file called Singularity) that describes how to specifically
build the container. Here we will overview the sections, best practices, and a quick example.
$ singularity bootstrap
USAGE: singularity [...] bootstrap  

The  is the path to the Singularity image file, and the  is the location
of the definition file (the recipe) we will use to create this container. The process of building a container should always
be done by root so that the correct file ownership and permissions are maintained. Also, so installation programs check
to ensure they are the root user before proceeding. The bootstrap process may take anywhere from one minute to one
hour depending on what needs to be done and how fast your network connection is.
Let’s continue with our quick start example. Here is your spec file, Singularity ,
Bootstrap:docker
From:ubuntu:latest

You next create an image:
$ singularity image.create ubuntu.img
Initializing Singularity image subsystem
Opening image file: ubuntu.img
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Creating 768MiB image
Binding image to loop
Creating file system within image
Image is done: ubuntu.img

and finally run the bootstrap command, pointing to your image (  ) and the file Singularity (
 ).
$ sudo singularity bootstrap ubuntu.img Singularity
Sanitizing environment
Building from bootstrap definition recipe
Adding base Singularity environment to container
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /root/.singularity/docker
[5/5] |===================================| 100.0%
Exploding layer:
˓→sha256:b6f892c0043b37bd1834a4a1b7d68fe6421c6acbc7e7e63a4527e1d379f92c1b.tar.gz
Exploding layer:
˓→sha256:55010f332b047687e081a9639fac04918552c144bc2da4edb3422ce8efcc1fb1.tar.gz
Exploding layer:
˓→sha256:2955fb827c947b782af190a759805d229cfebc75978dba2d01b4a59e6a333845.tar.gz
Exploding layer:
˓→sha256:3deef3fcbd3072b45771bd0d192d4e5ff2b7310b99ea92bce062e01097953505.tar.gz
Exploding layer:
˓→sha256:cf9722e506aada1109f5c00a9ba542a81c9e109606c01c81f5991b1f93de7b66.tar.gz
Exploding layer:
˓→sha256:fe44851d529f465f9aa107b32351c8a0a722fc0619a2a7c22b058084fac068a4.tar.gz
Finalizing Singularity container

Notice that bootstrap does require sudo. If you do an import, with a docker uri for example, you would see a similar
flow, but the calling user would be you, and the cache your $HOME.
$ singularity image.create ubuntu.img
singularity import ubuntu.img docker://ubuntu:latest
Docker image path: index.docker.io/library/ubuntu:latest
Cache folder set to /home/vanessa/.singularity/docker
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Importing: base Singularity environment
Importing: /home/vanessa/.singularity/docker/
˓→sha256:b6f892c0043b37bd1834a4a1b7d68fe6421c6acbc7e7e63a4527e1d379f92c1b.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:55010f332b047687e081a9639fac04918552c144bc2da4edb3422ce8efcc1fb1.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:2955fb827c947b782af190a759805d229cfebc75978dba2d01b4a59e6a333845.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:3deef3fcbd3072b45771bd0d192d4e5ff2b7310b99ea92bce062e01097953505.tar.gz
Importing: /home/vanessa/.singularity/docker/
˓→sha256:cf9722e506aada1109f5c00a9ba542a81c9e109606c01c81f5991b1f93de7b66.tar.gz
Importing: /home/vanessa/.singularity/metadata/
˓→sha256:fe44851d529f465f9aa107b32351c8a0a722fc0619a2a7c22b058084fac068a4.tar.gz

For details and best practices for creating your Singularity recipe, read about them here.

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