#_ Essential Linux Commands [+100 ]
1. File Operations:
● ls: Lists all files and directories in the present working
directory
● ls -R: Lists files in sub-directories as well
● ls -a: Shows hidden files
● ls -al: Lists files and directories with detailed information like
permissions, size, owner, etc.
● cd directoryname: Changes the directory
● cd ..: Moves one level up
● pwd: Displays the present working directory
● cat > filename: Creates a new file
● cat filename: Displays the file content
● cat file1 file2 > file3: Joins two files (file1 and file2) and stores
the output in a new file (file3)
● touch filename: Creates or modifies a file
● rm filename: Deletes a file
● cp source destination: Copies files from the source path to the
destination path
● mv source destination: Moves files from the source path to the
destination path
● find / -name filename: Finds a file or a directory by its name
starting from root
● file filename: Determines the file type
● less filename: Views the file content page by page
● head filename: Views the first ten lines of a file
● tail filename: Views the last ten lines of a file
● lsof: Shows which files are opened by which process.
● du -h --max-depth=1: Shows the size of each directory. Use
--max-depth=1 to limit the output to the current directory and its
immediate children.
● fdisk: Disk partition manipulation command.
By: Waleed Mousa
2. Directory Operations:
● mkdir directoryname: Creates a new directory in the present
working directory
● rmdir directoryname: Deletes a directory
● cp -r source destination: Copies directories recursively
● mv olddir newdir: Renames directories
● find / -type d -name directoryname: Finds a directory starting from
root
3. Process Operations:
● ps: Displays your currently active processes
● top: Displays all running processes
● kill pid: Kills the process with given pid
● pkill name: Kills the process with the given name
● bg: Resumes suspended jobs without bringing them to foreground
● fg: Brings the most recent job to foreground
● fg n: Brings job n to the foreground
● renice +n [pid]: Change the priority of a running process.
● &>filename: Redirects both the stdout and the stderr to the file
filename.
● 1>filename: Redirect the stdout to file filename.
● 2>filename: Redirect stderr to file filename.
4. File Permissions:
● chmod octal filename: Change the permissions of file to octal,
which can be between 0 (no permissions) to 7 (full permissions)
● chown ownername filename: Change file owner
● chgrp groupname filename: Change group owner
By: Waleed Mousa
5. Networking:
● ping host: Ping a host and outputs results
● whois domain: Get whois information for domain
● dig domain: Get DNS information for domain
● netstat -pnltu: Display various network related information such
as network connections, routing tables, interface statistics etc.
● ifconfig: Displays IP addresses of all network interfaces
● ssh user@host: Remote login into the host as user
● scp: Transfers files between hosts over ssh
● wget url: Download files from the web
● curl url: Sends a request to a URL and returns the response
● traceroute domain: Prints the route that a packet takes to reach
the domain.
● mtr domain: mtr combines the functionality of the traceroute and
ping programs in a single network diagnostic tool.
● ss: Another utility to investigate sockets. It's a more modern
alternative to netstat.
● nmap: Network exploration tool and security scanner.
6. Archives and Compression:
● tar cf file.tar files: Create a tar named file.tar containing files
● tar xf file.tar: Extract the files from file.tar
● gzip file: Compresses file and renames it to file.gz
● gzip -d file.gz: Decompresses file.gz back to file
● zip -r file.zip files: Create a zip archive named file.zip
● unzip file.zip: Extract the contents of a zip file
7. Text Processing:
● grep pattern files: Search for pattern in files
● grep -r pattern dir: Search recursively for pattern in dir
By: Waleed Mousa
● command | grep pattern: Pipe the output of command to grep for
searching
● echo 'text': Prints text
● sed 's/string1/string2/g' filename: Replaces string1 with string2
in filename
● diff file1 file2: Compares two files and shows the differences
● wc filename: Count lines, words, and characters in a file
● awk: A versatile programming language for working on files.
● sed -i 's/string1/string2/g' filename: Replace string1 with string2
in filename. The -i option edits the file in-place.
● cut -d':' -f1 /etc/passwd: Cut out the first field of each line in
/etc/passwd, using colon as a field delimiter.
8. Disk Usage:
● df: Shows disk usage
● du: Shows directory space usage
● free: Show memory and swap usage
● whereis app: Show possible locations of app
9. System Info:
● date: Show the current date and time
● cal: Show this month's calendar
● uptime: Show current uptime
● w: Display who is online
● whoami: Who you are logged in as
● uname -a: Show kernel information
● df -h: Disk usage in human readable format
● du -sh: Disk usage of current directory in human readable format
● free -m: Show free and used memory in MB
By: Waleed Mousa
10. Package Installations:
● sudo apt-get update: Updates package lists for upgrades
● sudo apt-get upgrade: Upgrades all upgradable packages
● sudo apt-get install pkgname: Install pkgname
● sudo apt-get remove pkgname: Removes pkgname
11. Others (mostly used in scripts):
● command1 ; command2: Run command1 and then command2
● command1 && command2: Run command2 if command1 is successful
● command1 || command2: Run command2 if command1 is not successful
● command &: Run command in background
12. Version Control (Git commands):
● git init: Initialize a local git repository
● git clone url: Create a local copy of a remote repository
● git add filename: Add a file to the staging area
● git commit -m "Commit message": Commit changes with a message
● git status: Check the status of the working directory
● git pull: Pull latest changes from the remote repository
● git push: Push changes to the remote repository
● git branch: List all local branches
● git branch branchname: Create a new branch
● git checkout branchname: Switch to a branch
● git merge branchname: Merge a branch into the active branch
● git stash: Stash changes in a dirty working directory
● git stash apply: Apply changes from a stash
● git log: View commit history
● git reset: Reset your HEAD pointer to a previous commit
● git rm filename: Remove a file from version control
● git rebase: Reapply commits on top of another base tip.
By: Waleed Mousa
● git revert: Create a new commit that undoes all of the changes
made in a particular commit, then apply it to the current branch.
● git cherry-pick commitID: Apply the changes introduced by some
existing commits.
13. Environment Variables:
● env: Display all environment variables
● echo $VARIABLE: Display the value of an environment variable
● export VARIABLE=value: Set the value of an environment variable
● alias new_command='old_command options': Create a new command that
executes the old command with the specified options.
● echo $PATH: Print the PATH environment variable.
● export PATH=$PATH:/new/path: Add /new/path to the PATH.
14. Job Scheduling (Cron Jobs):
● crontab -l: List all your cron jobs
● crontab -e: Edit your cron jobs
● crontab -r: Remove all your cron jobs
● crontab -v: Display the last time you edited your cron jobs
● crontab file: Install a cron job from a file
● @reboot command: Schedule a job to run at startup
15. Package Installations (using pip, a Python package installer):
● pip install packagename: Install a Python package.
● pip uninstall packagename: Uninstall a Python package.
● pip freeze > requirements.txt: Freeze the installed packages into
a requirements file.
● pip install -r requirements.txt: Install packages from a
requirements file.
By: Waleed Mousa
16. Shell Scripting:
● #!/bin/bash: Shebang line to specify the script interpreter.
● $0, $1, ..., $9, ${10}, ${11}: Script arguments.
● if [condition]; then ... fi: if statement in bash scripts.
● for i in {1..10}; do ... done: for loop in bash scripts.
● while [condition]; do ... done: while loop in bash scripts.
● function name() {...}: Define a function.
17. System Monitoring and Performance:
● iostat: Reports Central Processing Unit (CPU) statistics and
input/output statistics for devices, partitions, and network
filesystems.
● vmstat: Reports information about processes, memory, paging, block
IO, traps, disks, and CPU activity.
● htop: An interactive process viewer for Unix systems. It's a more
user-friendly alternative to top.
10. Search and Find:
● locate filename: Find a file by its name. The database updated by
updatedb command.
● whereis programname: Locate the binary, source, and manual page
files for a command.
● which commandname: Shows the full path of (shell) commands.
11. Compression / Archives:
● tar -cvf archive.tar dirname/: Create a tar archive.
● tar -xvf archive.tar: Extract a tar archive.
● tar -jcvf archive.tar.bz2 dirname/: Create a compressed bz2
archive.
● tar -jxvf archive.tar.bz2: Extract a bz2 archive.
By: Waleed Mousa
12. Disk Usage:
● dd if=/dev/zero of=/tmp/output.img bs=8k count=256k: Create a file
of a certain size for testing disk speed.
● hdparm -Tt /dev/sda: Measure the read speed of your hard drive.
13. Others:
● yes > /dev/null &: Use this command to push a system to its limit.
● :(){ :|:& };:: A fork bomb – handle with care. Do not run this
command on a production system.
Remember, you can always use the man command (e.g. man ls) to get more
information about each command.
By: Waleed Mousa
