1. File Operations:

• ls: Lists all fles and directories in the present working directory

• ls -R: Lists fles in sub-directories as well

• ls -a: Shows hidden fles

• ls -al: Lists fles 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 fle

• cat filename: Displays the fle content

• cat file1 file2 > file3: Joins two fles (fle1 and fle2) and stores the output in a new fle (fle3)

• touch filename: Creates or modifes a fle

• rm filename: Deletes a fle

• cp source destination: Copies fles from the source path to the destination path

• mv source destination: Moves fles from the source path to the destination path

• find / -name filename: Finds a fle or a directory by its name starting from root

• file filename: Determines the fle type

• less filename: Views the fle content page by page

• head filename: Views the frst ten lines of a fle

• tail filename: Views the last ten lines of a fle

• lsof: Shows which fles 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.

1. 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

1. 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 fle flename.

• 1>filename: Redirect the stdout to fle flename.

• 2>filename: Redirect stderr to fle flename.

1. File Permissions:

• chmod octal filename: Change the permissions of fle to octal, which can be between 0 (no permissions) to 7 (full permissions)

• chown ownername filename: Change fle owner

• chgrp groupname filename: Change group owner

1. 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 fles between hosts over ssh

• wget url: Download fles 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.

1. Archives and Compression:

• tar cf file.tar files: Create a tar named fle.tar containing fles

• tar xf file.tar: Extract the fles from fle.tar

• gzip file: Compresses fle and renames it to fle.gz

• gzip -d file.gz: Decompresses fle.gz back to fle

• zip -r file.zip files: Create a zip archive named fle.zip

• unzip file.zip: Extract the contents of a zip fle

1. Text Processing:

• grep pattern files: Search for pattern in fles

• grep -r pattern dir: Search recursively for pattern in dir

• 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 flename

• diff file1 file2: Compares two fles and shows the differences

• wc filename: Count lines, words, and characters in a fle

• awk: A versatile programming language for working on fles.

• sed -i 's/string1/string2/g' filename: Replace string1 with string2 in flename. The -i option edits the fle in-place.

• cut -d':' -f1 /etc/passwd: Cut out the frst feld of each line in /etc/passwd, using colon as a feld delimiter.

1. Disk Usage:

• df: Shows disk usage

• du: Shows directory space usage

• free: Show memory and swap usage

• whereis app: Show possible locations of app

1. 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

1. 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

1. 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

1. 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 fle 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 fle from version control

• git rebase: Reapply commits on top of another base tip.

• 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.

1. 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 specifed options.

• echo $PATH: Print the PATH environment variable.

• export PATH=$PATH:/new/path: Add /new/path to the PATH.

1. 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 fle

• @reboot command: Schedule a job to run at startup

1. 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 fle.

• pip install -r requirements.txt: Install packages from a requirements fle.

1. 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() {...}: Defne a function.

1. System Monitoring and Performance:

• iostat: Reports Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions, and network flesystems.

• 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.

1. Search and Find:

• locate filename: Find a fle by its name. The database updated by updatedb command.

• whereis programname: Locate the binary, source, and manual page fles for a command.

• which commandname: Shows the full path of (shell) commands.

1. 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.

1. Disk Usage:

• dd if=/dev/zero of=/tmp/output.img bs=8k count=256k: Create a fle of a certain size for testing disk speed.

• hdparm -Tt /dev/sda: Measure the read speed of your hard drive.

1. Others:

• yes > /dev/null &: Use this command to push a system to its limit.

Remember, you can always use the man command (e.g. man ls) to get more information about each command.