Lab Manual 2

User Manual: Pdf

Open the PDF directly: View PDF .
Page Count: 16

Operating Systems Lab Manual 02

1 | P a g e

National University of Computer and Emerging

Sciences Operating

System Lab - 02

Lab Manual

Objective

This lab is all about running commands in Ubuntu Terminal and compiling C program in

Ubuntu

Table of Content

Objective ...........................................................................................................................................1

Table of Content...............................................................................................................................1

Shell ...................................................................................................................................................2

Commands in Linux .........................................................................................................................2

Patterns and Wildcards....................................................................................................................9

Pipe in Linux..................................................................................................................................... 10

Compile C program in Linux .......................................................................................................... 10

Introduction to Shell Scripting ........................................................................................................ 11

Lab Activity ....................................................................................................................................... 12

Operating Systems Lab Manual 02

2 | P a g e

Shell

Fortunately, or unfortunately, a computer can only understand binary language and humans

can easily understand English language or equivalent high level language and therefore it is

difficult to interpret and understand with the computer system. In order to ward off this

difficulty every operating system has got an inbuilt interpreter(Shell). A shell accepts

instructions or commands fed by user in user understandable language and translate it to

binary language which a computer can easily understand. So in short a Shell is a language

translator and in this lab is all about introducing Shell of the Linux and the commands that

are most commonly used.

Figure below will make the above paragraph more meaningful and reader can understand it

better.

Figure 1 Shell - A diagrammatic representation

Commands in Linux

From here the reader is exposed to the basic Linux commands. All the commands have

to be tried in the terminal. Throughout the lab manuals Ubuntu will be used for explaining

the concepts. To know how to start a Terminal please see Lab Manual 01 – Introduction

to Terminal. The commands with their usage and example is given in the table below:

NOTE: All Linux commands are case sensitive i.e. ‘cp’ is not equivalent to ‘CP’. Also, all the

files and directories in linux are case sensitive so for example ‘/etc/hosts’ is not equivalent

to ‘/etc/Hosts’ and so hosts and Hosts are two different files in the same directory.

Command

Switch

Description

Example

Output

BASIC COMMANDS

Manual/Help for any command

man

None

Gives manual for the

specified command

man mkdir

Opens manual in

terminal, press ‘h’

for help or ‘q’ to quit

and get back to

terminal

User Input

(

Commands

)

Shell

English to

Binary

Conversation

Yes, Boss I understand

you request and will

execute it.

Operating Systems Lab Manual 02

3 | P a g e

Command

Switch

Description

Example

Output

Date and Time Commands

date

None

Displays the system date

date

Sun Jan 19 22:11:00

MST 2014

-u, –utc,

--universal

Displays the universal

coordinated time

date -u

Mon Jan 20 16:09:20

UTC 2014

-d, --date

Displays the date

specified by string

date –d

“12/02/2014”

Wed Dec 3 00:00:00

GMT 2014

-s

Sets the date specified by

the string

date –s “20 JAN

2014

18:00:00”

Mon Jan 20 18:00:00

GMT 2014

+%d

Displays the day

date +%d

+%m

Displays the month

date +%m

+%y

Displays the year

date +%y

2014

+%D

Displays the date in

mm/dd/yyyy format

date +%D

20/01/2014

+%H

Displays the hour in 24

hour format

date +%H

+%M

Displays the minute

date +%M

+%S

Displays the second

date +%S

+%T

Displays the time in

HH:MM:SS in 24 hour

format

date +%T

15:20:20

+%a

Displays the abbreviated

weekday

date +%a

Mon

+%A

Displays the full weekday

name

date +%A

Monday

+%b

Displays the abbreviated

month

date +%b

Jan

+%B

Displays the full month

name

date +%B

January

+%c

Displays the local system

date and time

date +%c

Mon 20 Jan 2014

06:05:06 PM GMT

+%C

Displays century

date +%C

+%r

Displays the time in

HH:MM:SS in 12 hour

format followed by AM or

date +%r

06:05:49 PM

Managing Users and Groups in Linux (root user only)

useradd

None

Creates a new user

profile or update

useradd abc

User Created

Operating Systems Lab Manual 02

4 | P a g e

existing user

information

addgroup

None

Add a group to the system

addgroup

example

Adding group

`example' (GID 1003)

...

Done.

adduser

None

Creates a user account

that can be used for login

adduser

username

Ask for password

and some data

along with

confirmation and

creates the account

--ingroup

Creates user account and

add that user in a group

specified

adduser --

ingroup sudo

abc

Same as adduser

<username> and

also it adds the user

to the group

usermod

-a -G

Modify an existing user

Usermod –a –G

sudo abc

Add already existing

user to already

existing group

Command

Switch

Description

Example

Output

deluser

None

Deletes the user from the

system

deluser abc

Removing user `abc'

... Done.

--group

Deletes the group from

the system

deluser --group

example

Removing group

`example' ...

Done.

removehome

Removes the user along

with its home folder

directory

ls -a

<content of current

directory>

-h

Displays the content in

human readable form

ls -h

Operating Systems Lab Manual 02

8 | P a g e

-R

Displays the content in

recursive order (it list file

and directories along

with files and

subdirectories of

subdirectories and so

on)

ls -R

File/Directory Permissions and Ownerships

Every file created in file system has an owner and permissions associated with it. There are

basically three kinds of user available in Linux

1. Owner (User who created the file/directory)

2. Group

3. Other Users/Groups

Each of the above-mentioned user will have access permissions. Following are the three

permissions associated with all the files.

1. Read (Denoted by r)

2. Write (Denoted by w)

3. Execute (Denoted by x)

These permissions can be visualized by ‘ls -l <file/directory name>’

Let us examine ‘-rwxr-x---‘ the first ‘-‘ represent that it’s a file ‘d’ would represent that it’s a

directory, the next 3 characters ‘rwx‘ are the rights for the owner, next three are the

permissions of the group and last three characters are the permissions for the other

users/group.

The third column represents states the user who is the owner of the file. Now the question

is: can I change the permission or ownership of a file or directory. The answer is ‘yes!’

Operating Systems Lab Manual 02

9 | P a g e

Chmod can be issued in two different ways, First method is 4 2 1 code in digital electronics

1 or 0

This is really simple, if a user has to be assign with all permission (Read, Write and Execute),

1 has to be applied in all the permissions that are required: 1(r) + 1(w) + 1(x) = 1(4) + 1(2) +

1(1) = 7 so 7 is the number that will fetch all the permissions for that file or folder.

Owner

Group

Other

Assuming that all the users get rwx permission so 4+2+1 = 7 will get mathematically 777.

Below table shows the syntax and example of using chmod command and also how to

change the owner of the file i.e. chown command.

Command

Switch

Description

Example

Output

chmod

None

Changes permissions of a file

chmod 700 file1

None

-v

Output a diagnostic for every file

processed

chmod -v 650

file1

mode of 'file1'

changed from 0700

(rwx------) to 0650

(rw-r-x---)

-R

Changes permissions files and

directories recursively

chmod -R 760

dir1

None

chown

None

Change the ownership of a file

chown username

filename

None

-R

Change the ownership files and

directories recursively

chown -R user

dir1

None

Operating Systems Lab Manual 02

10 | P a g e

Other Useful Commands in Linux

Command

Switch

Description

Example

Output

grep

None

Search pattern in a given

file

grep ‘hellow’

file1.txt

-i

Search given pattern in a

file ignoring case

Grep -i ‘hEllow’

file1.txt

-r

Search given pattern in

all the files in a directory

recursively

grep -r ‘helllow’

dir1

-w

Search words only not

strings

grep –w hello

cricket.txt

-c

Show match count for

pattern

grep -c hello

cricket.txt

-n

Show line number for the

matching pattern in file

grep -n hello

/home/cricket.txt

-v

Prints match inverse, i.e.

prints all those lines

which do not contain the

pattern.

grep -v hello

/home/cricket.txt

cal

None

Get the calender of the

current or specified

month and year (only

month will not do)

Cal

<calendar of current month

and year>

cal 9 2020

<calendar of September

2020>

cal 2020

whatis

None

Gives a brief description

of command

whatis ls

ls (1) - list directory

contents

whereis

None

Gives the path of the

Command

whereis ls

ls: /bin/ls

/usr/share/man/man1/ls.1.gz

Operating Systems Lab Manual 02

11 | P a g e

ifconfig

-a

To know the status and

configurations of

network interfaces

ifconfig -a

finger

None

To know about user

account in Linux Users

finger username

None

Show snapshot of

running processes

-A

Show all the processes

ps -A

kill

None

Kills the process with

specified process id

kill 1434

None

alias

None

Renames a command

alias l=’ls -al’

None

unalias

None

Undo renaming a

command

unalias l

None

Shows detail of disk

usage. df works by

examining a directory

entry, which generally are

updated only when a file is

closed.

Filesystem 1K-blocks

Used Available Use%

Mounted on …

None

Estimates file space

usage. Output the

summary of disk usages

of every file hierarchically

i.e. recursively

mount

None

It is use to mound a file

system that do not mound

itself

mount /dev/sda5

mount /dev/usb

None

sudo

None

Runs the command as

root/super

user/administrator

sudo cp

~/Desktop/file

/usr

None

-i

sudo -i

None

Change username or

become a super user

su username

Operating Systems Lab Manual 02

12 | P a g e

Patterns and Wildcards

Patterns aka regular expression uses wildcards to represent unknown values. Wildcards

helps the user to perform certain operations with specifying filename or text pattern. There

are three special characters basically made available for this purpose. There are:

1. * - will match against none or one or a string of more than a character

2. ? - can be used to match one character

3. [] - matches one specified character out of a group of characters

All the characters are discussed in detail below:

WildCard ‘*’

• ‘$ ls file*’ - list all the files in current directory starting with filename ‘file’.

• ‘$ ls *2.txt’ - list all the files in current directory ending with ‘2.txt’

WildCard ‘?’

• ‘$ ls file.tx?’ - list all the files that begins with ‘file.tx’

WildCard ‘[]’

• ‘$ ls rmt[12345]’ - list all the file that begins with ‘rmt’ and has a 1,2,3,4 or 5 after it.

Operating Systems Lab Manual 02

13 | P a g e

Pipe in Linux

If a user in Linux likes to combine two or more commands, pipes is the option. Example “ ls

-al | grep ‘mp3’ ” many options can be tried easily. Pipe is represented by the symbol ‘|’. Let

us look at the example below:

$ cat file1.txt | grep ‘world populations’

First the command cat file1.txt is executed and then the output from that command is fed to

the second command as an input. Likewise, many other combinations can be tried.

$ ls | grep ‘mp3’ | sort -r

First ls command will grab the list of files and directories in the current relative directory

whose output will be fed to grep command, that will pick out all the line containing ‘mp3’

pattern which will be fed to sort command and this will print the output in reverse order as

per the -r switch.

Compile C program in Linux

In future lab manuals, you will need to write programs and run them. You will write programs

in C programming language and this session will show how to write a C program, compile

the program and how to execute it using terminal.

1. Open the terminal and create a file with ‘c’ extension.

$ nano hello.c

2. Write the following text to the file:

#include<stdio.h>

Int main() {

printf(“hellow world from Cprogram”);

return 0;

}

3. Compile the file and create an executable object file

$ gcc -o Hello hello.c

4. Run the newly created object file

$ ./Hello

Operating Systems Lab Manual 02

14 | P a g e

The snapshot of the terminal as below:

Introduction to Shell Scripting

This section covers an introduction to Lab Manual 03. We have already learned that Shell is

a program which provides CLI to the OS. Shell scripting is used when there is a sequence

of commands that is needed to be executed frequently. These commands can be written in

a shell script file ‘.sh’ and that file can be executed. This makes the execution much simpler.

Examples of usage of Shell Script is below:

1. To create a number of user by system administrator.

2. To search for a pattern in file or group of files available in some directories.

Advantage of using Shell Script is that It is easy to write, run and debug and disadvantage

is that requirements of high complexity cannot be programmed in Shell.

Operating Systems Lab Manual 02

15 | P a g e

Lab Activity

1) User Account

a. Create a group name ‘OSLAB02’

b. Create a user account ‘OSUser1’ and ‘OSUser2’ and add it to the group which

is created in ‘a’

c. Also add the newly created user to group ‘sudo’

d. Login in to that user using terminal

2) Create the following directories with one command. dirOSLAB -> subDir ->

subsubdir -> OSLAB2

3) Write 2 C program one prints “I love Operating System” and other prints “I love

Linux”. Compile and Run both programs and print the output to two different files.

After then combine both the files in one new file using a single command.

4) Perform the following activity

a. Create user ‘abc’

b. Create a file ‘file1.txt’

c. Change the owner of the file to newly created user “abc”

d. Rename a file ‘file1.txt’

e. Create a file with timestamp

f. Make a copy of /proc directory

g. Write a command to delete empty

h. Write a command to delete non-empty directories

i. Create a dummy file using vi editor and then try search a specific word.

j. Create a dummy file and then change the ownership of the dummy file.

k. Determine the process id of the user from which you are logged in and then

terminate that process. What happens after terminating the particular process

id?

l. List all files in system having string ‘lab’ in their filenames.

m. Determine the storage capacity utilized in system.

5) Perform the following

a. List the files in the directory "/bin" that end in "sh".

b. On one line, use the "cd" command to first go to your home directory then to

the "<rollnumber>" subdirectory. [Ans: cd /home; cd <rollnumber>]

c. What command lists the files in the current directory that begin with upper

case letters?

d. If they do not already exist, create three new directories "Letters", "Programs",

and "Misc" using a single command

Operating Systems Lab Manual 02

16 | P a g e

e. Copy all files in the current directory whose names contain the character string

"let" into the subdirectory "Letters".

f. Copy all files in the current directory whose names end in ".c" or ".h" into the

subdirectory "Programs".

g. Copy all files in the current directory whose names contain the character

strings "notes" or "misc" into the subdirectory "Misc".

h. Copy all files which begin with "copy.me" into the "OS" subdirectory. Move all

files which begin with "move.me" into the "OS" subdirectory.

i. Delete all files which contain the sequence "del".

Lab Manual 2

Navigation menu

Versions of this User Manual:

Views

Navigation