A-Z Linux Commands Reference Guide

A

• a2enmod / a2dismod: Enable or disable Apache2 modules.

• a2ensite / a2dissite: Enable or disable Apache2 virtual hosts.

• alias: Create a shortcut for a long command.

  • alias ll='ls -la'

• apt / apt-get: Package management tools for Debian/Ubuntu.

• awk: Pattern scanning and text processing language.

B

• bash: The default command-line shell.

• bg: Sends a process to the background.

• bzip2: Compresses or expands .bz2 files.

C

• cat: Display file contents or combine files.

• cd: Change directory.

  • cd /var/www

• chmod: Change file/directory permissions (e.g., 755, 644).

• chown: Change file/directory owner and group.

• clear: Clear the terminal screen.

• cp: Copy files or directories (-r for recursive).

• curl: Transfer data from or to a server (supports HTTP, FTP, etc.).

• crontab: Schedule recurring tasks.

D

• date: Display or set system date and time.

• dd: Convert and copy a file (commonly used to create bootable USBs).

• df: Display free disk space on the filesystem.

• diff: Compare two files line by line.

• dig: DNS lookup utility.

• du: Estimate file space usage (disk usage).

E

• echo: Print text to the terminal.

• exit: Close the current terminal or logout.

• export: Set environment variables.

F

• fdisk: Partition table manipulator for Linux.

• find: Search for files in a directory hierarchy.

• free: Display amount of free and used memory (RAM).

G

• grep: Search for patterns inside text/files. (Crucial)

  • grep "error" log.txt

• gzip / gunzip: Compress or decompress .gz files.

H

• head: Output the first part of files (default 10 lines).

• history: Display the command history list.

• hostname: Show or set the system's host name.

I

• ifconfig / ip: Configure network interfaces ( ip a is the modern version).

• iptables: Administration tool for IPv4 packet filtering and NAT (Firewall).

J

• jobs: List active jobs in the current shell.

• journalctl: Query and display logs from the systemd journal.

K

• kill: Terminate a process using its PID.

  • kill -9 1234

L

• ls: List directory contents.

  • ls -lh

• ln: Create links between files (use -s for symbolic links).

• locate: Find files by name (faster than find, uses a database).

M

• man: An interface to the system reference manuals (Help).

• mkdir: Create a new directory.

• mv: Move or rename files/directories.

N

• nano / vi / vim: Command-line text editors.

• netstat: Print network connections, routing tables, etc.

P

• passwd: Change user password.

• ping: Send ICMP ECHO_REQUEST to network hosts.

• ps: Report a snapshot of the current processes.

• pwd: Print Working Directory (shows where you are).

R

• rm: Remove files or directories (rm -rf to force delete).

• rmdir: Remove empty directories.

S

• scp: Securely copy files between hosts over SSH.

• sed: Stream editor for filtering and transforming text.

• ssh: Secure Shell client (remote login).

• sudo: Execute a command as another user (usually root).

T

• tail: Output the last part of files (use -f to follow live logs).

• tar: Archiving utility (tape archiver).

  • tar -cvzf archive.tar.gz /path

• top: Display Linux processes (interactive task manager).

• touch: Create an empty file or update timestamps.

U

• uname: Print system information (uname -a).

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

W

• w / who: Show who is logged on and what they are doing.

• wget: Non-interactive network downloader.

Z

• zip / unzip: Package and compress (archive) files.