Rhcsa7 Study Guide 1520876655
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Study Guide Linux Academy RHCSA 7 Prep Contents Basic Commands 1 Input-Output Redirection 1 File System Hierarchy Standard 2 Grep and Regular Expressions 2 Access Remote Systems Using SSH 3 Log In and Switch Users in Multi-User Targets 3 Archive and Compress Using tar, star, gzip and bzip2 4 Create and Edit Files 5 Create, Delete, Copy and Move Files and Directories 5 Create Hard and Soft Links 6 List, Set and Change Standard Permissions 6 Locate, Read and Use System Documentation 7 Boot, Reboot and Shut Down a System 8 Boot Into Different Targets Manually 8 Interrupt Boot Process to Access System 9 Identify CPU/Memory Intensive Processes, Adjust Priority, Kill Processes 10 Locate and Interpret System Log Files and Journals 12 List, Create and Delete Partitions 12 Create and Remove Physical Volumes, Logical Volumes 13 LVM Set Up 13 Configure System to Mount File System at Boot 13 Schedule Tasks Using at and cron 14 Configure System to Use Time Services 15 Install and Update Software Packages 15 Enable Third-Party Repositories 16 RPM 17 Create, Delete and Modify Local User Accounts Change Password and Password Aging Create, Delete and Modify Groups 17 18 18 Create, Mount, Unmount and Use VFAT, EXT4 and XFS File Systems 18 RHCSA 7 Prep Linux Academy Basic Commands • pwd • Show current working directory path • cd • Change directory • ls • List • sudo • Allows a super user to run a command with root priviledges • mkdir • Create new directory contents of directory »» -p • Create parent directories, if do not already exist • rmdir • Remove • rm -rf • Force • touch • Create directory remove a directory, recursively (includes all files inside) new, empty files Input-Output Redirection • > • Redirect standard output to file »» echo "test" > file.txt »» Replaces file, if already exists • >> • Redirects and appends standard output »» echo "test" >> file.txt »» Adds text to bottom of file • | • Chain scripts, files and commands together by the STDOUT as STDIN for the next command »» cat /etc/passwd | grep root • 2> • Redirect standard error • 2>> • Redirect • /dev/null • Data sent to /dev/null is lost • 2>&1 • Redirect STDERR to STDOUT • < • Accept and append standard error input from file »» mysql < filedump.sql • less • File viewing application and STDOUT can often piped into for ease of reading -1- RHCSA 7 Prep • Linux Academy head • Show first ten lines of file »» -n • Define number of lines • tail • Show last ten lines of file »» -n • Define number of lines File System Hierarchy Standard • /etc • Contains • /var • Variable data specific to system. This data should not be removed or changed when the system reboots. Logs files tend to be stored within the /var directory • /run • Runtime • /home • Location the system configuration files for programs and packages data for processes since last boot of home directories; used for storing personal documents and information on • /root • root • /tmp • Files are removed after ten days; universal read/write permissions • /boot • Files needed to start the system boot process • /dev • Contains user home directory information on essential devices Grep and Regular Expressions • grep • Prints lines that match defined pattern »» grep pattern file.txt »» -i • Case insensative »» -v • Shows lines not containing pattern • Examples including regex: »» grep linuxacademy filename • Search for linuxacademy in filename »» grep "^linuxacademy" filename • Search for lines starting with linuxacademy »» grep "linuxacademy$" filename • Search for lines ending with linuxacademy »» grep "^[abd]" filename • Search for characters not contained in brackets »» grep [lL]inuxacademy filename • Search for pattern starting with either capital or lowercase L -2- RHCSA 7 Prep Linux Academy »» grep "^$" filename • Search for empty lines »» grep -v ^# filename • Search for uncommented lines • egrep • Same • fgrep • Interpret as grep, but using extended regular expressions pattern as list of fixed strings Access Remote Systems Using SSH • Password authentication • Allows user to log in with only a password; considered to be less secure than using key-based authentication • ssh user@server • Connect • ssh server command • Issue • scp filename user@server:~/ • Secure • sftp user@server • Secure to remote host command on remote host without connecting copy file to server File Transfer Protocol »» ? • Display all options »» ls • List files »» cd • Mode directories »» get • Download »» quit • Exit sftp Log In and Switch Users in Multi-User Targets • Target • Systemd configuration files used for grouping resources • Interactive shell • Any shell that has a prompt for user interaction • su • Log in as another user »» su user • Log in to an interactive, non-login shell »» su - user • Log in to a login shell • GNU Bourne-Again Shell • Bash »» Interactive shell uses either $ (user) or # (root) prompt »» Takes commands, which run programs -- Made up of three parts: -3- RHCSA 7 Prep Linux Academy Command name Options or flags to pass into the command Arguments Archive and Compress Using tar, star, gzip and bzip2 • tar • Archive files; does not handle compression »» -c • Create new archive »» -t • List contents of archive »» -x • Extract files from archive »» -z • Compress or uncompress file in gzip »» -v • Verbose »» -j • Compress or uncompress file in bzip2 »» -f • Read archive from or to file »» Examples -- • tar -cf helloworld.tar hello world • Archive helloworld.tar archive hello and world files into -- tar -tvf helloworld.tar • List -- tar -xf helloworld.tar • Extract -- tar -czvf helloworld.tar.gz hello world • Archive and compress gzip) hello and world files into helloworld.tar.gz archive -- tar -zxvf helloworld.tar.gz • Uncompress archive star • Archiving and searching all files in helloworld.tar archive files in archive (using (in gzip) and extract files from utility generally used to archive large sets of data; includes pattern-matching »» -c • Create archive file »» -v • Verbose output »» -n • Show results of running command, without executing the actions »» -t • List contents of file -4- RHCSA 7 Prep Linux Academy »» -x • Extract file »» --diff • Show difference between files »» -C • Change to specified directory »» -f • Specify file name »» Examples” -- • star -c f=archive.tar file1 file2 • Archive archive file1 and file2 into archive.tar -- star -c -C /home/user/ -f=archive.tar file1 file2 • Move -- star -x -f=archive.tar • Extract archive.tar -- star -t -f=archive.tar • List to /home/user and archive file1 and file2 from that directory into archive.tar contents of archive.tar gzip • Compression utility used to reduce file sized; files are unavailable until unpacked; generally used with tar »» -d • Decompress files »» -l • List compression information »» Examples: -- gzip file1 • Compress -- gzip -d file1.gz • Unpack -- gunzip filename • Unpack file1 into file1.gz file1 filename Create and Edit Files • vi • Text editor that is always installed and useable; replaced vim • vim • Vi iMproved; full-featured version of vi • nano • Simple text editor • touch • Create empty file Create, Delete, Copy and Move Files and Directories • mkdir • Make directory -5- RHCSA 7 Prep Linux Academy »» -p • Create parent directories, if not already created • cp • Copy files and directories »» -R • Copy directory recursively • mv • Move • rm • Remove files and directories files and directories »» -r/-R • Remove recursively »» -f • Force remove »» -i • Prompt before removal Create Hard and Soft Links • ln • Create links between files »» Without the -s flag, creates a hard link »» -s • Symlink files • symlinks • Soft links that connects one file to another, symbolically; if the target file moves to changes, the symlink continues to try use the previous location and must be updated • Hard link • Links directly to an inode to create a new entry referencing an existing file on the system List, Set and Change Standard Permissions • Two ways to define permissions on a standard Linux system: »» Using symbolic characters, such as u, g, o, r, w and x »» Using octal bits »» The RHCSA only requires knowledge of the symbolic • chmod • Change mode; set the permissions for a file or directory »» u • User »» g • Group »» o • Other »» a • All »» r • Read -6- RHCSA 7 Prep Linux Academy »» w • Write »» x • Execute »» s • Set UID or GID »» t • Set sticky bit »» -X • Indicate the execute permissions should only affect directories and not regular files »» Octal bits: • -- 1 • Execute -- 2 • Write -- 4 • Read chown • Change owner and group permissions »» chown user:group filename »» -R • Set ownership recursively • chgrp • Change • setuid • Set user ID permissions on executable file • setgid • Set group ID permissions on executable file • umask • Set default permissions for new directories and files group ownership Locate, Read and Use System Documentation • command --help • info • Read • which • Show • whatis • Display • locate • Locate • updatedb • Update locate command • man • Documentation information files; provides more information than man full path of command; useful for scripting manual page descriptions files on system by name databases »» Nine sections: -- 1 • Executable programs and shell commands -- 2 • System calls -7- RHCSA 7 Prep • Linux Academy -- 3 • Library calls -- 4 • Special files -- 5 • File formats -- 6 • Games -- 7 • Miscellaneous -- 8 • root user commands -- 9 • Kernel routines apropos • Search man pages and descriptions for text Boot, Reboot and Shut Down a System • Reboot: »» reboot »» systemctl reboot »» shutdown -r now • Shutdown: »» No power off »» systemctl halt »» halt »» shutdown -h now »» init 0 • Power off: »» systemctl poweroff »» poweroff »» shutdown -P Boot Into Different Targets Manually • A target is a Systemd unit of configuration that defines a grouping of services and configuration files the must be started when the system moves into the defined target. »» A grouping of dependencies starts when a target is called -8- RHCSA 7 Prep Linux Academy • systemctl list-units --type=target • View all targets on system • systemctl list-units --type=target --all • View • Common targets: all targets on disk »» emergency.target • su login; mounts only the root filesystem, which is read-only »» multi-user.target • Support concurrent log ins of multiple users »» rescue.target • su login; basic Systemd init »» graphical.target • Support concurrent log ins of multiple users on a graphical interface • systemctl get-default • Show • systemctl set-default • Set • Configuration files: default target default target »» /usr/lib/systemd/system »» /etc/systemd/system • systemctl -t help • View • systemctl status service • Find status of service • systemctl --type=service • List configuration files of active services • systemctl enable service • Enable • systemctl --failed • List • Select a different target at boot: unit configuration types service configuration to start at boot failed services »» Reboot system »» At Grub menu, press E to edit entry »» Go to linux16 kernel and press CTRL+E »» Add systemd.unit=target.target »» CTRL+X Interrupt Boot Process to Access System • Start or reboot system • Stop Grub autoselection • Ensure the appropriate kernel is highlighted and press E to edit -9- RHCSA 7 Prep Linux Academy • Navigate to the linux16 line, press E • Add line rd.break • CTRL+X • System boots into emergency mode • Mount /sysroot with read and write permissions »» mount -oremount, rw /sysroot • Switch into chroot jail: »» chroot /sysroot • Reset root password • Clean up »» touch /.autorelabel • exit • exit Identify CPU/Memory Intensive Processes, Adjust Priority, Kill Processes • top »» k • Kill process »» q • Quit »» r • Renice »» s • Change update rate »» P • Sort by CPU usage »» M • Sort by memory usage »» l • Toggle load average »» t • Toggle task display »» m • Toggle memory display »» B • Bold display »» u • Filter by username - 10 - RHCSA 7 Prep Linux Academy »» -b • Start in batch mode »» -n • Number of updates before exiting »» Columns: • -- PID • Process ID -- USER -- PR • Priority -- RES • Non-swap memory -- SHR • Shared memory size -- %CPU • Task’s share of elapsed CPU time -- %MEM • Current amount of used memory -- TIME+ • CPU time minus the total CPU time the task has used since starting Nice priority: »» -20 • Highest priority »» 19 • Lowest priority »» Any user can make a task lower priority • pgrep • Search processes »» -u • Username »» -l • Display process name »» -t • Define tty ID »» -n • Sort by newest • pkill • Kill process »» -u • Kill process for defined user »» -t • Kill process for defined terminal • Kill signals: »» 1 • SIGHUP • Configure reload without termination; also used to report termination of controlling process »» 2 • SIGINT • Cause program to terminate »» 3 • SIGQUIT • When user requests to quit a process - 11 - RHCSA 7 Prep Linux Academy »» 9 • SIGKILL • Immediately terminate process »» 15 • SIGTERM • Send request to terminate process; request can be interpreted or ignored »» 18 • SIGCONT • Restart previously stopped process »» 19 • SIGSTOP • Stop a process for later resumption »» 20 • SIGTSTP • Send by terminal to request a temporary stop • ps • Process status Locate and Interpret System Log Files and Journals • journald • Responsible for event logging; records events from log files, kernel messages, etc. »» Data does not persist after reboot »» Can be configured for persistence in /etc/journald.conf »» Temporary log location: /run/log/journal »» Persistent log location: /var/log/journal • journalctl »» -n • Set number of lines to show »» -x • Provide explanation text, if available »» -f • Show last ten events; continues listening »» -b • Show messages from current boot only »» -p • Show message priority type »» _SYSTEM_UNIT=service • Get events related to service »» --since=yesterday • Get events since defined time »» --until=00:00:00 • Get event from before defined time • Find information about system boot: »» systemd-analyze »» systemd-analyze blame List, Create and Delete Partitions - 12 - RHCSA 7 Prep Linux Academy • fdisk • Used to create master boot record-based partitions • gdisk • Used to create GPT-based partitions Create and Remove Physical Volumes, Logical Volumes • Physical volume • The physical disk or disks; can be a partition or whole volume • Volume group • A combination of physical volumes that work as a logical volume, with pooled space LVM Set Up • pvcreate • Create physical volume • pvdisplay • Show available physical volumes • vgcreate name /dev/disks • Create • vgdisplay • Show available volume groups • lvcreate • Create logical volume volume group »» -n • Volume »» -L • Size in bytes • lvremove /dev/vg/volume • Remove • pvremove /dev/disk • Remove volume physical volume Configure System to Mount File System at Boot • mkfs -t xfs /dev/xvdf1 • Make file system • blkid • List available block devices on system • lsblk • List all attached block devices • mount /dev/disk /mnt/mountlocation • Non-persistent mount »» Mounting with the UUID ensures the appropriate mount is used »» Add to /etc/fstab to mount persistently • tune2fs -L labelname /dev/disk • Mount • e2label /dev/disk labelname • Mount with file system label (ext) with file system label (ext) - 13 - RHCSA 7 Prep • • Linux Academy xfs_admin -L labelname /dev/disk • Mount with file system label (XFS) mount LABEL=labelname /mnt/mountlocation defaults 1 1 • Mount non-persistent; edit /etc/fstab for persistence • mount -a • Mount • umount -a • Unmount with label, all file systems in /etc/fstab all file systems in /etc/fstab Schedule Tasks Using at and cron • at • Execute command at a later time »» /etc/at.allow • Configure users permitted to use at command »» /etc/at.deny • Configure users not permitted to use at command »» Accepts following time/date formats: -- hh:mm -- midnight -- noon -- teatime (16:00) -- am/pm -- Full dates -- now + time • atrm • Remove • anacron • Execute pending at task commands periodically »» -f • Force execution, ignoring timestamps »» -u • Upload timestamps of all jobs; does not run jobs »» -n • Run jobs immediately, ignoring delays »» -t • Use specified configuration file, instead of default »» -h • Show help »» /etc/anacrontab • Configuration file »» /var/spool/anacron • Shows all timestamps for jobs »» Only root and superusers can use acacron - 14 - RHCSA 7 Prep Linux Academy »» Syntax: -- period in days • Frequency of execution -- delay in minutes • Number of minutes to wait before job execution -- job-identifier • Unique name of job used in log files -- command • Command to execute -- start_hours_range • Time frame when jobs can be run -- random_day • Stagger job starts at random times Configure System to Use Time Services • timedatectl list-timezones • List all available time zones • tzselect • Select • timedatectl set-timezone zone/location • Set • timedatectl set-time YYYY-MM-DD hh:mm:ss • Set • timedatectl set-ntp true • Use • NTP can be managed by either ntpd or chronyd appropriate time zone time zone time and date Network Time Protocol »» Generally, ntpd is for servers, and chronyd is for systems with frequent restarts »» chronyd is the default for RHEL7 Install and Update Software Packages • yum • Package management tool »» install packagename • Install package »» search string • Search packages »» search all string • Searches name, description and summary »» list • List installed packages »» list all • Listed installed and available packages »» list installed • List installed and available packages »» check-update • Lists packages with available updates »» update packagename • Update defined package - 15 - RHCSA 7 Prep Linux Academy »» update • Update all packages with available updates »» info package • Provide information about package »» provides /some/directory • Displays packages that match path »» list kernel • List installed and available kernels »» remove packagename • Removes defined package »» history • Display summary of installations and removes »» history undo idnumber • Reverse a transaction »» Working with groups (packages of software): -- yum grouplist • Show -- grouplist hidden • Show -- groupinstall groupname • Install defined group -- groupinfo groupname • Display all packages to be installed with the group available groups to install all available groups - • Package is not installed and will not be installed = • Package is installed as part of group + • Package is not installed, but will be installed at next update No symbol means that the package is installed, but was not installed as part of the group »» /var/log/yum • Log file Enable Third-Party Repositories • yum repolist • List repository ID, name and number of packages available »» -v • List more information about repos »» all • Show all repos • yum repoinfo • Show • /etc/yum.repos.d/reponame.repo • Location of repositories • yum-config-manager • Set information about both enabled and disabled repos repositories »» --enable reponame • Enable repo »» --disable reponame • Disable repo »» --add-repo repourl • Add repository from defined URL - 16 - RHCSA 7 Prep Linux Academy RPM • RPM Package Manager • Always use yum when possible • rpm »» -i • Install »» -v • Verbose »» -e • Remove package »» -h • Use hashmarks for progress »» -U • Upgrade to install package »» -F • Upgrade already-installed package »» -q • Query for a package »» -a • Display all packages »» -qa • Display installed files »» -ql • List files in installed package »» -qd • List documentation for package »» -qpl • List files in RPM package Create, Delete and Modify Local User Accounts • id • Print user and group IDs • UID ranges: »» 0 • root »» 1-200 • System users for Red Hat processes »» 201-999 • System users for processed that do not own files »» 1000+ • Regular users • /etc/passwd • User login and password information • /etc/shadow • User login and password hash information • Primary group • The main group for a user; all files created by a user are set under this group - 17 - RHCSA 7 Prep Linux Academy • /etc/groups • Group member information • getent group username • Show • useradd • Create • usermod • Modify • userdel • Delete all groups for a user user user user Change Password and Password Aging • chage • Modify amount of days between password changes »» -d • Number of days since 1970-01-01 to define password change »» -E • Set password expiration date »» -I • Number of days of inactivity before password expiration »» -l • Show account aging information »» -m • Minimum number of days between password changes »» -M • Maximum number of days between password changes »» -W • Days of warning before password change Create, Delete and Modify Groups • groupadd • Add a group »» -g • Group ID »» -r • Create system group • groupmod • Modify group »» -g • New group ID »» -n • New group name • groupdel • Delete • chmod g+s directoryname • Set group group permissions for directory, and all files created in that directory have the same permissions Create, Mount, Unmount and Use VFAT, EXT4 and XFS File Systems - 18 - RHCSA 7 Prep • Linux Academy VFAT • Extension of FAT file system, allowing log file names; often used in SAMBA shares or when sharing files between Linux and Windows computers »» mkfs.ext /dev/xvdf1 • Create VFAT file system at location »» mount /dev/xvdf1 /mnt/location • Mount file system »» fsck.vfat /dev/xvdf1 • Check for file system consistency • EXT4 • Common among Linux systems; journaling-based file system that can support up to 16TBs on Red Hat and up to 50TB in file system size »» mkfs.ext4 /dev/xvdf1 • Create EXT4 file system on device »» mount /dev/xvdf1 /mnt/location • Mount the file system at location »» fsck /dev/xvdf1 • Check for file system consistency »» dumpe2fs /dev/xvdf1 • Get details of file system »» tune2fs /L labelname /dev/xvdf1 • Label the device • XFS • Known for parallel processing and high I/O throughput; journaled file system that supports up to 500TB file size on Red Hat 7 with 500TB in file system size »» mkfs.xfs /dev/xvdf1 • Create XFS file system on device »» mount /dev/xvdf1 /mnt/location • Mount file system at location »» xfs_repair /dev/xvdf1 • Check for file system consistency »» xfs_info /dev/xvdf1 • Get details of file system »» xfs_admin /L labelname /dev/xdf1 • Label the device - 19 -
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