1. Navigation Commands
pwd: Prints the current working directory (shows where you are in the system).cd <directory>: Changes the current directory to the specified one.ls: Lists the files and directories in the current directory.ls -l: Lists files in long format (includes permissions, ownership, size, and modification time).ls -a: Lists all files, including hidden ones (those starting with a dot).
cd ..: Moves up one directory level.
2. File and Directory Operations
touch <file>: Creates an empty file with the specified name.mkdir <directory>: Creates a new directory.rm <file>: Removes (deletes) a file.rm -r <directory>: Removes a directory and its contents recursively.rm -f <file>: Forces removal without asking for confirmation.
cp <source> <destination>: Copies a file or directory to another location.cp -r <source> <destination>: Copies a directory recursively.
mv <source> <destination>: Moves or renames a file or directory.
3. Viewing Files
cat <file>: Displays the contents of a file.more <file>: Displays file contents one screen at a time.less <file>: Similar tomorebut allows scrolling both forward and backward.head <file>: Shows the first 10 lines of a file.tail <file>: Shows the last 10 lines of a file.tail -f <file>: Displays the last 10 lines and updates as the file changes (useful for logs).
4. File Permissions
chmod <permissions> <file>: Changes file permissions (e.g.,chmod 755 file).chown <user>:<group> <file>: Changes the ownership of a file or directory.
5. Searching
find <directory> -name <filename>: Searches for files in a directory.grep <pattern> <file>: Searches for a specific pattern inside a file.grep -r <pattern> <directory>: Recursively searches in all files within a directory.
6. System Monitoring
top: Displays real-time system resource usage (CPU, memory, processes).df: Shows the disk space usage of file systems.df -h: Shows disk space in a human-readable format (e.g., GB, MB).
free: Displays memory usage.ps: Lists running processes.ps aux: Lists all running processes with detailed information.
7. File Compression/Decompression
tar -czvf <archive.tar.gz> <directory>: Compresses a directory into a tarball (.tar.gz).tar -xzvf <archive.tar.gz>: Extracts a tarball (.tar.gz) archive.zip <archive.zip> <file(s)>: Compresses files into a .zip archive.unzip <archive.zip>: Extracts a .zip archive.
8. Networking
ping <hostname>: Tests connectivity to another system.ifconfig(orip a): Displays network interface configurations.curl <url>: Fetches data from a URL (useful for checking web pages, APIs, etc.).ssh <user>@<hostname>: Connects to a remote system via SSH.scp <file> <user>@<hostname>:<path>: Copies a file to/from a remote server using SSH.
9. Package Management (for distributions like Ubuntu/Debian)
sudo apt update: Updates the list of available packages.sudo apt install <package>: Installs a package.sudo apt upgrade: Upgrades all installed packages.sudo apt remove <package>: Removes a package.
10. Process Management
kill <PID>: Terminates a process by its Process ID (PID).killall <process_name>: Terminates all processes with a given name.bg: Resumes a suspended process in the background.fg: Brings a background process to the foreground.
11. System Shutdown and Reboot
shutdown -h now: Shuts down the system immediately.reboot: Reboots the system.
12. User Management (Admin)
whoami: Displays the current logged-in user.useradd <username>: Creates a new user.passwd <username>: Changes the password for a user.sudo <command>: Executes a command with superuser (root) privileges.