💻 ++101 Linux commands Open-source eBook

This is an open-source eBook with 101 Linux commands that everyone should know. No matter if you are a DevOps/SysOps engineer, developer, or just a Linux enthusiast, you will most likely have to use the terminal at some point in your career.

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Content

• Basics
  • File Hierarchy Standard (FHS)
  • Commands
• Disk and File System Management
  • General Disk Manipulation (non-LVM)
  • Globs (Wildcards)
  • Regex
  • Stream redirection
• Text Readers & Editors
  • Less
  • VI
• User and Group Management
• File System Permissions
• SSH
• Cronjobs
• Package Management
  • RPM
  • YUM
• 📃 List of commands by category:
  • Directory Navigation
  • File Commands
  • File and Directory Manipulation
  • Package archive and compression tools
  • System commands
  • Networking Commands
  • Package Management
  • User Information commands
  • Session commands
  • Getting Help
  • Applications
• 📃 List of commands by chapter:
• 🔗Links
• 📖Other eBooks
• 🤲Contributing

Basics

File Hierarchy Standard (FHS)

Commands

File System Commands

File Manipulation

Archiving

Disk and File System Management

General Disk Manipulation (non-LVM)

Creating physical partitions is not required! You can create PVs directly!

Other

Globs (Wildcards)

The dot . in front of hidden items is ignored by glob patterns!

Regex

Bash itself does not know regex. Use programs like grep, sed, awk.

Control characters

Grep

Stream redirection

• > overwrite
• >> append

Text Readers & Editors

Less

VI

VI/VIM Editing

To leave editing mode press ESC.

Navigation

Navigate as usual with arrow keys, home, end, pg up, pg dn.

Other

User and Group Management

UID

User Database

User info without passwords is stored in /etc/passwd.

Group Database

Group info with secondary group members are stored in /etc/group. Primary group members are identified by GID in user database.

Password Database

Hashed user passwords are stored in /etc/shadow. Password encryption is configured in /etc/login.defs.

PW:

• [hash] Encrypted test password
• ! [hash] Account locked
• !! or * Account locked, no password set

Commands

File System Permissions

Permissions can be set on:

• User (owner)
• Group (owner)
• Others

Only root can change User. User can change Group.

Basic permissions (Add binary flags to combine):

Advanced permissions (place in front of basic permissions: chmod 1777 shared).:

Advanced permissions replace the x when using ls -l. Lower case if x is set, upper case if x is not set.

Read permission on a directory only allows to see the directory itself but not it's contents. Use execute permission to show contents.

Commands

SSH

SSH Configuration is done in /etc/ssh/sshd_config.

Reload SSH service with systemctl reload sshd to apply changes!

DenyUsers, AllowUsers, DenyGroups, AllowGroups override each other and are applied in the order listed above.

Cronjobs

Crontab

Cronjobs are configured in crontab files. Do not edit these files directly. Use crontab -e instead. This runs all required actions to activate a cronjob after saving the edited crontab. The locations are as follows:

• /var/spool/cron/username user specific
• /etc/crontab system wide crontab

The format of the files is (user specific crontabs do not have the column user-name):

Example of job definition:
.---------------- minute (0 - 59 | */5 [every 5 minutes])
|  .------------- hour (0 - 23)
|  |  .---------- day of month (1 - 31)
|  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
|  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
|  |  |  |  |
*  *  *  *  * user-name  command to be executed

Script folders

Scripts in one of the following directories will be executed at the interval specified by the directory's name:

• /etc/cron.hourly
• /etc/cron.daily
• /etc/cron.weekly
• /etc/cron.monthly

Allow / Deny usage

Add user names one per line to the following files:

• /etc/cron.allow Whitelist
• /etc/cron.deny Blacklist

If none of the files exists, all users are allowed.

Logs and Results

Execution of cronjobs is logged in /var/log/cron. Results are sent to the users mail /var/spool/mail/username.

Package Management

RPM

RPM

YUM

YUM is configured in /etc/yum.conf

Repos are configured in /etc/yum.repos.d/

Log is in /var/log/yum.log

📃 List of commands by category:

If you want to contribute, feel free to pick up a topic marked as TODO and submit a pull request 🙌

Feel free to add new topics in case that you don't find one that you like from the current list.

Directory Navigation

• cd - change working directory
• ls - list directory contents
• dir - directory listing, columnar format
• pwd - return working directory name
• tree - list subdirectories in a tree structure

File Commands

• cat/tac - concatenate and print files
• diff/sdiff - compare files line by line
• find - search for files
• grep - file pattern matcher
• head - display the first lines of a file
• locate - find files and directories
• stat - display file status
• tail - display the last lines of a file
• uniq - report or filter out repeated lines in a file

File and Directory Manipulation

• awk - pattern-directed scanning and processing language
• chmod - change permissions
• chown - change file owner and group
• cp - copy files and directories
• cut - remove sections from files
• mkdir - make a new directory
• mv - move files and directories
• nano - text editor
• rm - delete files and directories
• rmdir - remove directory
• paste - merge corresponding or subsequent lines of file
• rsync - remote copy files
• scp - secure copy
• basename - strips directory information and suffixes from file path
• sed - text transformation tool
• sort - arrange or merge lines of files
• split - split a file into pieces
• touch - change file access and modification times
• vim - text editor

Package archive and compression tools

• bzip2 - block-sorting file compressor
• gzip - compression tool
• gunzip - decompression tool
• tar - create, extract and manipulate archives
• zip - package and compress files
• unzip - list, test, extract compressed ZIP files

System commands

• crontab - maintain individual tables used to drive the cron daemon
• df - display free disk space
• du - display disk usage statistics
• free - show memory usage information
• hostname - set or print name of current host system
• hostnamectl - change hostname settings
• ionice - get/set I/O process priority
• iostat - I/O statistics
• kill - terminate or signal a process by id
• killall - kill processes by name
• lsblk - display block and loop devices
• lsof - list open files
• mpstat - CPU statistics
• ncdu - curses-based disk usage
• ps - display process status
• pstree - show processes in tree format
• reboot - restart the system
• service - run an init script
• shutdown - close down the system at a specific time
• top/htop - display process information
• uname - prints operating system details
• useradd - add/update user accounts
• userdel - delete user account
• usermod - modify user properties
• vmstat - virtual memory statistics
• whereis - locate programs

Networking Commands

• dig - DNS lookup utility
• ifconfig - configure network interface parameters
• ip - perform network administration tasks
• iptable - configure IPv4 network firewall
• lscpu - display CPU architecture information
• netstat - show network status
• ping - check network connectivity
• whois - information about Internet domain names and network numbers

Package Management

• apt - Debian package management
• rpm - RPM package manager (RedHat)
• yum - package manager for RedHat Linux

User Information commands

For user modification, see useradd, userdel, usermod under System commands

• groups - show group memberships
• finger - shows information about users
• last - displays most recent user logins
• passwd - modify a user's password
• w - display who is logged in and what they are doing
• who - display who is logged in
• whoami - display effective user id

Session commands

• clear - clear terminal screen
• env - display environment variables, or set variables for command execution
• exit - close the active session/shell
• printenv - print specified environment variables
• history - display the command history
• login - login and initiate a user session
• nohup - invoke a utility immune to hangups
• sleep - suspend execution for a time interval
• ssh - secure shell login
• su - substitute user identity
• sudo - execute a command as another user
• screen - start a screen session

Getting Help

• man - format and display online manual pages
• help - displays help about basic commands not covered by 'man'
• whatis - display one-line command descriptions

Applications

• bc - basic calculator
• cal - displays a calendar
• cmatrix - enter the Matrix
• curl - transfer data to or from a server
• echo - display interpreted arguments
• factor - prints prime factors of numbers
• printf - format output
• sl - runs a steam locomotive across your terminal
• wget - non-interactive web file download
• xargs - construct argument lists and execute utility
• yes - print continous output stream
• banner - Writes ASCII character strings in large letters to standard output.
• aplay - aplay is a command-line to play audio files.
• spd-say - plays the given text as the sound from the command line.

📃 List of commands by chapter:

If you want to contribute, feel free to pick up a topic, update it with New Examples | [Options]and submit a pull request 🙌

Feel free to add new topics in case that you don't find one that you like from the current list.

• 001-the-ls-command.md
• 002-the-cd-command.md
• 003-the-cat-tac-command.md
• 004-the-head-command.md
• 005-the-tail-command.md
• 006-the-pwd-command.md
• 007-the-touch-command.md
• 008-the-cal-command.md
• 009-the-bc-command.md
• 010-the-df-command.md
• 011-the-help-command.md
• 012-the-factor-command.md
• 013-the-uname-command.md
• 014-the-mkdir-command.md
• 015-the-gzip-command.md
• 016-the-whatis-command.md
• 017-the-who-command.md
• 018-the-free-command.md
• 019-the-top-htop-command.md
• 020-the-sl-command.md
• 021-the-echo-command.md
• 022-the-finger-command.md
• 023-the-groups-command.md
• 024-the-man-command.md
• 025-the-passwd-command.md
• 026-the-w-command.md
• 027-the-whoami-command.md
• 028-the-history-command.md
• 029-the-login-command.md
• 030-the-lscpu-command.md
• 031-the-cp-command.md
• 032-the-mv-command.md
• 033-the-ps-command.md
• 034-the-kill-command.md
• 035-the-killall-command.md
• 036-the-env-command.md
• 037-the-printenv-command.md
• 038-the-hostname-command.md
• 039-the-nano-command.md
• 040-the-rm-command.md
• 041-the-ifconfig-command.md
• 042-the-ip-command.md
• 043-the-clear-command.md
• 044-the-su-command.md
• 045-the-wget-command.md
• 046-the-curl-command.md
• 047-the-yes-command.md
• 048-the-last-command.md
• 049-the-locate-command.md
• 050-the-iostat-command.md
• 051-the-sudo-command.md
• 052-the-apt-command.md
• 053-the-yum-command.md
• 054-the-zip-command.md
• 055-the-unzip-command.md
• 056-the-shutdown-command.md
• 057-the-dir-command.md
• 058-the-reboot-command.md
• 059-the-sort-command.md
• 060-the-paste-command.md
• 061-the-exit-command.md
• 062-the-diff-sdiff-command.md
• 063-the-tar-command.md
• 064-the-gunzip-command.md
• 065-the-hostnamectl-command.md
• 066-the-iptable-command.md
• 067-the-netstat-command.md
• 068-the-lsof-command.md
• 069-the-bzip2-command.md
• 070-the-service-command.md
• 071-the-vmstat-command.md
• 072-the-mpstat-command.md
• 073-the-ncdu-command.md
• 074-the-uniq-command.md
• 075-the-rpm-command.md
• 076-the-scp-command.md
• 077-the-sleep-command.md
• 078-the-split-command.md
• 079-the-stat-command.md
• 080-the-useradd-command.md
• 081-the-userdel-command.md
• 082-the-usermod-command.md
• 083-the-ionice-command.md
• 084-the-du-command.md
• 085-the-ping-command.md
• 086-the-rsync-command.md
• 087-the-dig-command.md
• 088-the-whois-command.md
• 089-the-ssh-command.md
• 090-the-awk-command.md
• 091-the-crontab-command.md
• 092-the-xargs-command.md
• 093-the-nohup-command.md
• 094-the-pstree-command.md
• 095-the-tree-command.md
• 096-the-whereis-command.md
• 097-the-printf-command.md
• 098-the-cut-command.md
• 099-the-sed-command.md
• 100-the-vim-command.md
• 101-the-chown-command.md
• 102-the-find-command.md
• 103-the-rmdir-command.md
• 104-the-lsblk-command.md
• 105-the-cmatrix-command.md
• 106-the-chmod-command.md
• 107-the-grep-command.md
• 108-the-screen-command.md
• 109-the-nc-command.md
• 110-the-make-command.md
• 111-the-basename-command.md
• 112-the-banner-command.md
• 113-the-alias-command.md
• 114-the-which-command.md
• 115-the-date-command.md
• 116-the-mount-command.md
• 117-the-nice-command.md
• 118-the-wc-command.md
• 119-the-tr-command.md
• 120-the-fdisk-command.md
• 121-the-wait-command.md
• 122-the-zcat-command.md
• 123-the-fold-command.md
• 124-the-quota-command.md
• 125-the-aplay-command.md
• 126-the-spd-say-command.md
• 127-the-xeyes-command.md
• 128-the-parted-command.md
• 129-the-nl-command.md
• 130-the-pidof-command.md
• 131-the-shuf-command.md
• 132-the-less-command.md
• 133-the-nslookup-command.md
• 134-the-cmp-command.md
• 135-the-expr-command.md

🔗Links

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📖Other eBooks

• Introduction to SQL
• Introduction to Git and GitHub
• Introduction to Bash Scripting
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🤲Contributing

If you are contributing 🍿 please read the contributing file before submitting your pull requests.