Linux Cheat Sheet

Linux Cheat Sheet

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Rajat Chauhan

Basic Commands

Navigation

  • pwd: Print the current working directory.

  • cd [dir]: Change directory to [dir]. Use cd .. to go up one level.

  • ls: List directory contents.

    • ls -l: List in long format.

    • ls -a: List all files including hidden files (those starting with a dot).

    • ls -lh: Long format with human-readable file sizes.

File Operations

  • touch [file]: Create an empty file or update the timestamp of the file.

  • cp [source] [destination]: Copy file or directory.

    • cp -r [source] [destination]: Copy directories recursively.

  • mv [source] [destination]: Move or rename file or directory.

  • rm [file]: Remove file.

    • rm -r [dir]: Remove directory and its contents recursively.

    • rm -i [file]: Remove with a prompt before every removal.

File Viewing

  • cat [file]: Concatenate and display file content.

  • less [file]: View file content one screen at a time.

  • more [file]: View file content, similar to less.

  • head [file]: Display the first 10 lines of a file.

    • head -n [num] [file]: Display the first [num] lines of a file.

  • tail [file]: Display the last 10 lines of a file.

    • tail -n [num] [file]: Display the last [num] lines of a file.

    • tail -f [file]: Follow the file content as it grows.

File Permissions

  • chmod [permissions] [file]: Change the file permissions.

    • chmod 755 [file]: Set permissions to rwxr-xr-x.

    • chmod u+x [file]: Add execute permission for the owner.

  • chown [owner]:[group] [file]: Change file owner and group.

  • chgrp [group] [file]: Change group ownership.

File Permissions Symbols

  • r: Read permission.

  • w: Write permission.

  • x: Execute permission.

  • -: No permission.

Access Control Lists (ACL)

  • getfacl [file]: Get ACL of a file.

  • setfacl -m u:[user]:[permissions] [file]: Set ACL for a user.

  • setfacl -m g:[group]:[permissions] [file]: Set ACL for a group.

  • setfacl -x u:[user] [file]: Remove ACL for a user.

Process Management

  • ps: Display current processes.

    • ps aux: Display detailed information about all running processes.

  • top: Display dynamic real-time view of running processes.

  • htop: Enhanced version of top (needs to be installed).

  • kill [pid]: Terminate process with process ID [pid].

    • kill -9 [pid]: Forcefully terminate process with process ID [pid].

  • killall [process_name]: Terminate all processes with the specified name.

  • bg: Resume a suspended job in the background.

  • fg: Bring a background job to the foreground.

  • jobs: List all background jobs.

Disk Usage

  • df: Report file system disk space usage.

    • df -h: Human-readable format.

  • du [file/dir]: Estimate file space usage.

    • du -sh [file/dir]: Display summary in human-readable format.

Networking

  • ping [host]: Check the network connection to a server.

  • ifconfig: Configure network interfaces (deprecated; use ip).

  • ip addr: Show IP addresses and network interfaces.

  • netstat: Network statistics.

    • netstat -tuln: List all listening ports.

  • wget [url]: Download files from the web.

  • curl [url]: Transfer data from or to a server.

Searching

  • grep [pattern] [file]: Search for a pattern in a file.

    • grep -r [pattern] [dir]: Search recursively in a directory.

    • grep -i [pattern] [file]: Case-insensitive search.

  • find [dir] -name [pattern]: Find files by name.

  • locate [name]: Find files by name (uses a database, needs to be updated with updatedb).

Archiving and Compression

  • tar -cvf [archive.tar] [file/dir]: Create a tar archive.

  • tar -xvf [archive.tar]: Extract a tar archive.

  • tar -czvf [archive.tar.gz] [file/dir]: Create a compressed tar archive with gzip.

  • tar -xzvf [archive.tar.gz]: Extract a compressed tar archive with gzip.

  • zip [archive.zip] [file/dir]: Create a zip archive.

  • unzip [archive.zip]: Extract a zip archive.

Package Management

  • Debian/Ubuntu:

    • apt update: Update package lists.

    • apt upgrade: Upgrade installed packages.

    • apt install [package]: Install a package.

    • apt remove [package]: Remove a package.

    • apt autoremove: Remove unnecessary packages.

  • Red Hat/CentOS:

    • yum update: Update package lists and upgrade packages.

    • yum install [package]: Install a package.

    • yum remove [package]: Remove a package.

    • yum autoremove: Remove unnecessary packages.

Service Management

  • Systemd:

    • systemctl start [service]: Start a service.

    • systemctl stop [service]: Stop a service.

    • systemctl restart [service]: Restart a service.

    • systemctl status [service]: Check the status of a service.

    • systemctl enable [service]: Enable a service to start on boot.

    • systemctl disable [service]: Disable a service from starting on boot.

User Management

  • adduser [username]: Add a new user.

  • passwd [username]: Change user password.

  • deluser [username]: Remove a user.

  • usermod -aG [group] [username]: Add a user to a group.

  • groups [username]: List the groups a user is in.

Shell Scripting

  • Basic Structure:

      #!/bin/bash
  echo "Hello, World!"

  • Variables:

      NAME="John"
  echo "Hello, $NAME"

  • Conditional Statements:

      if [ condition ]; then
    # Commands
  elif [ condition ]; then
    # Commands
  else
    # Commands
  fi

  • Loops:

      for i in {1..5}; do
    echo "Iteration $i"
  done

  while [ condition ]; do
    # Commands
  done

Additional Useful Commands

  • echo [text]: Display text.

  • date: Display or set the system date and time.

  • uptime: Show how long the system has been running.

  • who: Show who is logged on.

  • uname -a: Show system information.

  • history: Show command history.

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