Linux Cheat Sheet

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.