Linux Commands

Linux Administration Guide

This page serves as a comprehensive guide to Linux system administration, including essential commands, system management, and upgrade procedures.

Essential Linux Commands

File and Directory Management

• ls -l - List files with details
• cd /path/to/directory - Change directory
• mkdir directory_name - Create a new directory
• rm -rf file_or_directory - Remove files/directories
• cp -r source destination - Copy files and directories
• mv source destination - Move or rename files

User and Group Management

• whoami - Show the current user
• id username - Show user ID and group ID
• sudo useradd -m username - Add a new user
• sudo passwd username - Change user password
• sudo userdel -r username - Delete a user and their home directory
• sudo groupadd groupname - Create a new group
• sudo usermod -aG groupname username - Add a user to a group

Process Management

• ps aux - List all running processes
• top - Show real-time system processes
• htop - Interactive process viewer (if installed)
• kill -9 PID - Forcefully terminate a process
• pkill process_name - Kill a process by name
• nohup command & - Run a command in the background

System Monitoring

• df -h - Show disk usage
• du -sh /path - Show directory size
• free -m - Show memory usage
• uptime - Show system uptime
• vmstat - Show system performance stats
• iostat - Show CPU and disk usage

Networking

• ip a - Show IP addresses
• ip route - Show routing table
• ping -c 4 google.com - Send ICMP packets
• netstat -tulnp - Show active network connections
• ss -tulnp - Alternative to netstat
• nslookup domain.com - Query DNS information
• traceroute google.com - Trace packet route

Package Management

Debian-based (Ubuntu, Debian)

• sudo apt update - Update package lists
• sudo apt upgrade - Upgrade installed packages
• sudo apt install package_name - Install a package
• sudo apt remove package_name - Remove a package
• sudo apt autoremove - Remove unused packages

RHEL-based (CentOS, Fedora, RHEL)

• sudo yum update - Update system packages
• sudo yum install package_name - Install a package
• sudo yum remove package_name - Remove a package
• sudo dnf update - (Fedora) Update packages

File Permissions and Ownership

• chmod 755 file - Change file permissions
• chown user:group file - Change file ownership
• ls -lah - List file permissions
• umask - Show default permissions

Services and Daemons

• systemctl start service - Start a service
• systemctl stop service - Stop a service
• systemctl restart service - Restart a service
• systemctl enable service - Enable service at boot
• systemctl status service - Check service status

Logs and Debugging

• journalctl -xe - Show system logs
• tail -f /var/log/syslog - Follow system log
• grep "error" /var/log/messages - Search logs for errors
• dmesg | less - Kernel message log

Upgrading Linux

Checking System Version

• lsb_release -a - Show OS version (Debian/Ubuntu)
• cat /etc/os-release - Show OS release info
• uname -r - Show kernel version

Upgrading Ubuntu/Debian

1. Update package lists: sudo apt update 2. Upgrade all installed packages: sudo apt upgrade -y 3. Upgrade distribution: sudo apt dist-upgrade -y 4. Clean up unused packages: sudo apt autoremove -y 5. If upgrading to a new release: sudo do-release-upgrade

Upgrading CentOS/RHEL

1. Update packages: sudo yum update -y 2. Upgrade system: sudo yum upgrade -y 3. If using DNF (Fedora): sudo dnf upgrade --refresh 4. If upgrading to a new version, use: sudo dnf system-upgrade

Kernel Upgrade

• Check available kernel versions: sudo apt-cache search linux-image
• Install new kernel: sudo apt install linux-image-version
• Update GRUB bootloader: sudo update-grub
• Reboot to apply changes: sudo reboot

Summary

This guide covers essential Linux administration tasks, including user management, networking, services, and system upgrades. For in-depth troubleshooting, refer to system logs and package-specific documentation.