Basic Linux Commands

🐧 Linux Basic Commands — Quick Reference

A comprehensive yet compact beginner's guide to Linux file system, commands, permissions, networking, users, and more.

📘 Why Learn Linux?

Linux powers everything from servers and clouds to IoT devices. Whether you’re a developer, sysadmin, or cloud engineer, Linux skills are essential.

  • Works seamlessly with Windows and macOS.
  • Hosts most cloud workloads and containers.
  • Open source, modular, and secure.
📂 1. Linux File System Hierarchy 
/
├── bin
├── boot
├── dev
├── etc
├── home
│   ├── alice
│   ├── bob
│   └── eve
├── root
├── run
├── sbin
├── tmp
├── usr
│   ├── bin
│   ├── local
│   │   ├── bin
│   │   ├── sbin
│   └── sbin
└── var
  • /boot – Kernel & bootloader files
  • /etc – System configuration
  • /home – User directories
  • /usr – Installed software
  • /var – Logs, spools
  • /tmp – Temporary data
📁 2. File Management & Navigation

Absolute vs Relative Paths

  • Absolute: /var/log/syslog
  • Relative: log/syslog (from /var)
pwd                 # Print working directory
ls                  # List files
cd /etc             # Change directory
mkdir ProjectX      # Create folder
cp file1 file2      # Copy
mv file target/     # Move
rm file.txt         # Delete
📝 3. Create, View, and Edit Text Files (Vim)

Launch Vim: vim file.txt

  • Modes: Normal, Insert (i), Visual (v), Command (:)
  • Save & Exit: :wq, :q!
  • Edit: dd delete line, yy copy, p paste
  • Search: /word, n next
Tip: Add set number and syntax on in ~/.vimrc for better coding experience.
👤 4. UID & GID (User & Group IDs)
  • UID → User ID, GID → Group ID
  • Root = 0, System = 1–999, Normal = 1000+
id username
cat /etc/passwd
groups user
👥 5. Manage Users and Groups

User Commands:

sudo adduser user1
sudo passwd user1
sudo usermod -aG sudo user1
sudo deluser user1 --remove-home

Group Commands:

sudo addgroup devteam
sudo usermod -aG devteam user1
sudo delgroup devteam
🔐 6. File Permissions & Ownership 
-rwxr-xr--
u=rwx (owner) g=rx (group) o=r (others)

Change permissions:

chmod 755 script.sh
chown user:group file.txt

Sticky bit (t): Only file owner can delete (used in /tmp)
⚙️ 7. Process Management 
ps aux          # List processes
top / htop      # Monitor
kill -9 PID     # Kill
nice -n 10 cmd  # Start with priority
pstree          # View process tree
jobs, fg, bg    # Manage background jobs
🧩 8. Manage Services (systemctl) 
systemctl start nginx
systemctl enable nginx
systemctl status nginx
systemctl list-units --type=service

Check logs with: journalctl -u nginx
🔑 9. Configure and Secure SSH 
sudo apt install openssh-server
sudo systemctl enable --now ssh
sudo nano /etc/ssh/sshd_config

Important settings:

  • PermitRootLogin no
  • PasswordAuthentication no
  • AllowUsers youruser
📜 10. Log Analysis & Monitoring 
cat /var/log/syslog
journalctl -b
grep "error" /var/log/auth.log
sudo logrotate -f /etc/logrotate.conf

Use logwatch or goaccess for analysis.

🌐 11. Manage Networking 
ip a                # Show interfaces
ip route             # View routes
ping google.com      # Test connectivity
sudo nano /etc/resolv.conf
nameserver 8.8.8.8

Use nmcli for NetworkManager-managed systems.
📦 12. Archive & Transfer Files 
tar -czvf backup.tar.gz folder/
scp file user@ip:/path/
rsync -av --delete src/ dest/
sftp user@ip
🧰 13. Package Management

APT (Ubuntu/Debian)

sudo apt update
sudo apt install nginx
sudo apt remove nginx

DNF/YUM (RHEL/Fedora)

sudo dnf install httpd
sudo dnf remove httpd
💾 14. Access Linux File Systems 
df -h
lsblk -f
sudo mount /dev/sdb1 /mnt
sudo umount /mnt
sudo fsck /dev/sdb1

Auto-mount: edit /etc/fstab carefully.

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