Common Linux commands (ls, cd, cp, mv, rm, etc.)

1. Basic Linux Commands

ls	List files in a directory
cd	Change directory
pwd	Show current directory =path
cp	Copy files or directories
mv	Move or rename files
rm	Remove files or =directories
mkdir	Create a new directory
rmdir	Remove empty directory
touch	Create empty file
cat	View contents of a file
nano / vim	Text editors in terminal
chmod	Change file permissions
chown	Change file owner
find	Find files by name or type
grep	Search text in files
df -h	Disk usage summary (human-readable)
du -sh	Directory size
ps aux	List running processes
top / htop	Real-time system monitoring
kill	Kill a process by PID
man	View manual pages for commands
clear	Clear terminal screen
exit	Close terminal session

2. File permissions & ownership

ls -l	Lists files with permissions, ownership, size, and modification date.
chmod [options] mode file	Changes permissions of a file or directory.
chmod 755 script.sh	Sets read, write, and execute for owner; read and execute for group and others.
chmod u+x file	Adds execute permission to the user (owner).
chmod g-w file	Removes write permission from the group.
chmod o=r file	Sets read-only for others.

Group Management  

chgrp group file	Changes the group ownership of a file.
groups	Lists groups the current user belongs to.
usermod -aG group user	Adds a user to a group (requires root).

permissions

read+write+execute(rwx)=7

read+write(rw-)=6

read+execute(r-x)=5

read(r–)=4

write(-w-)=2

execute(–x)=1

no permission(—)=0

3. File compression or Archive

a. Creating Archives  

tar -cf archive.tar file1 file2	Create an uncompressed archive from file1 and file2.
tar -cvf archive.tar dir/	Create archive from a directory with verbose output.
tar -czf archive.tar.gz dir/	Create a gzip-compressed archive.
tar -cjf archive.tar.bz2 dir/	Create a bzip2-compressed archive.
tar -caf archive.tar.xz dir/	Create an archive and compress it with xz.
tar -czvf archive.tar.gz *	Archive and compress all files in the current directory.

b. Extracting Archives

tar -xf archive.tar	Extract contents of a .tar file.
tar -xvf archive.tar	Same as above, with verbose output.
tar -xzf archive.tar.gz	Extract a .tar.gz archive.
tar -xjf archive.tar.bz2	Extract a .tar.bz2 archive.
tar -xvf archive.tar -C /target/dir/	Extract to a specific directory.
tar -xvf archive.tar file1 file2	Extract specific files from the archive.

4. packages management command   

a. APT (Debian, Ubuntu and derivatives)  

sudo apt update	Refreshes package lists from repositories.
sudo apt upgrade	Installs the newest versions of all upgradable packages.
sudo apt install package	Installs a package.
sudo apt remove package	Removes a package but leaves config files.
sudo apt purge package	Removes a package and its configuration files.
sudo apt autoremove	Removes unnecessary dependencies.
apt list –installed	Lists all installed packages.
apt show package	Displays details about a package.

b. YUM / DNF (CentOS, RHEL, Fedora)  

sudo yum update / sudo dnf update	Updates all packages to the latest version.
sudo yum install package	Installs a package.
sudo yum remove package	Removes a package.
sudo yum info package	Displays package information.
yum list installed	Lists installed packages.
yum clean all	Clears cache to free up space.

5. rpm packages management command

rpm -ivh package.rpm	Installs a package (-i = install, -v = verbose, -h = show hash/progress).
rpm -Uvh package.rpm	Upgrades a package (installs if not present, replaces if already installed).
rpm -Fvh package.rpm	Freshens a package (only upgrades if already installed).
rpm -e package	Erases (removes) a package.
rpm -q package	Queries if a package is installed.
rpm -qa	Lists all installed packages.
rpm -qi package	Displays detailed info about an installed package.
rpm -ql package	Lists all files installed by the package.
rpm -qf /path/to/file	Finds which package a particular file belongs to.
rpm -K package.rpm	Verifies the signature of a package file.

6. ssh & remote Access

ssh user@hostname	Connect to a remote server via SSH (replace user with the username and hostname with the IP or domain).
ssh -p 2222 user@hostname	Connect using a custom port (e.g., 2222). Useful if SSH is not on the default port (22).
ssh -i /path/to/key.pem user@hostname	Connect using a private key file (common for AWS and cloud VMs).
exit	Log out from the SSH session.
ssh-copy-id user@hostname	Copy your public key to a server for passwordless login.
scp file.txt user@hostname:/path/	Copy a local file to a remote server using SCP.
scp user@hostname:/path/file.txt ./	Download a file from the remote server to the local machine.
rsync -avz file.txt user@hostname:/path/	Efficient file sync to a remote server using SSH.

7. user management

a. User Account Commands  

adduser username	Adds a new user and prompts for password and user info (Debian/Ubuntu friendly).
useradd username	Adds a new user (lower-level; doesn’t prompt for password).
passwd username	Sets or changes the password for a user.
id username	Displays the user’s UID, GID, and group membership.
whoami	Shows the current logged-in username.
users	Shows a list of users currently logged into the system.
deluser username	Deletes a user account and optionally its home directory (Debian-based).
userdel username	Deletes a user account (more low-level, used in Red Hat-based distros).
userdel -r username	Deletes a user and their home directory.

b. Group Management Commands  

groupadd groupname	Creates a new group.
groupdel groupname	Deletes an existing group.
usermod -aG groupname username	Adds a user to a group (append). Important: don’t forget the -a.
groups username	Lists the groups that the user belongs to.
gpasswd -d username groupname	Removes a user from a group.

c. Modifying Users  

usermod -l newname oldname	Renames a user account.
usermod -d /new/home username	Changes the user’s home directory (use -m to move files).
usermod -s /bin/bash username	Changes the user’s default shell.
chage -l username	Displays password aging information (password expiration policy).
chage -E 2025-12-31 username	Set account expiration date.

d.  Locking and Disabling Users  

passwd -l username	Locks a user account (can’t login).
passwd -u username	Unlocks a user account.
usermod -L username	Another way to lock the account.
usermod -U username	Unlock the account.

8. network command

a. Interface & Configuration  

ifconfig	Displays or configures network interfaces (older systems; superseded by ip command).
ip addr	Shows detailed network interface information (IP addresses, MAC, etc.).
ip link	Displays interface link status (up/down).
ip a	Short form of ip addr.
ip route	Shows current routing table.
nmcli device status	Displays network interface statuses (NetworkManager-managed systems).
ethtool interface	Displays or changes interface properties (e.g., speed/duplex).
hostname -I	Displays the system’s IP addresses (excluding loopback).
nmcli connection show	Lists network connections.

b. Testing Connectivity  

ping hostname/IP	Tests connectivity to a host (ICMP packets). Use -c 4 to limit number of pings.
traceroute hostname/IP	Displays route packets take to reach a host.
mtr hostname/IP	Combines ping and traceroute for advanced route analysis (real-time).
curl -I http://example.com	Fetches HTTP headers to verify website/server responses.
wget example.com	Downloads files over HTTP/HTTPS (useful for testing connectivity).
nc -zv hostname port	Checks if a specific port is open (port scanning).
telnet hostname port	Tests network connectivity to a specific port (if Telnet is installed).

c. Ports & Services  

ss -tuln	Lists listening ports and associated services (replaces netstat).
ss -plnt	Displays processes using TCP ports.
netstat -tulnp	Displays active connections and port usage (older; requires net-tools).
lsof -i	Lists open network connections with associated processes.
nmap hostname/IP	Scans remote host/network for open ports (requires nmap installation).

d. DNS & Host Resolution  

dig domain.com	Queries DNS records for a domain (A, MX, TXT, etc.).
nslookup domain.com	Basic DNS lookup (older but still widely used).
host domain.com	Performs DNS lookups for a domain/IP.
resolvectl status	Displays DNS resolver status (Systemd-based systems).