Linux System Administration

Introduction

Linux system administration involves managing, maintaining, and securing Linux-based systems and networks.

Core Responsibilities

System maintenance
User management
Security administration
Backup and recovery
Performance monitoring

Essential Commands

System Information


# System info
uname -a         # System/kernel information
lsb_release -a   # Distribution information
df -h           # Disk usage
free -h         # Memory usage
top             # Process information
htop            # Interactive process viewer

# User Management
useradd         # Add new user
usermod         # Modify user
userdel         # Delete user
passwd          # Change password
id              # User/group info

# File Operations
ls -la          # List files with details
chmod           # Change permissions
chown           # Change ownership
find            # Search files
tar             # Archive files

System Management

Package Management

APT (Debian/Ubuntu):

apt update
apt upgrade
apt install
apt remove

Service Management

Systemd:

systemctl start
systemctl stop
systemctl enable
systemctl disable

Network Management

Commands:

ifconfig/ip
netstat/ss
ping
traceroute

Security Best Practices

Regular system updates
Strong password policies
Firewall configuration
SSH hardening
Regular security audits

File System Management

Directory Structure

/etc - Configuration files
/var - Variable data
/home - User homes
/usr - User programs
/boot - Boot files

File Permissions


# Permission Types
r (read)    = 4
w (write)   = 2
x (execute) = 1

# Common Permission Sets
chmod 755   # rwxr-xr-x
chmod 644   # rw-r--r--
chmod 700   # rwx------

Common Issues

Disk space problems
Permission errors
Service failures
Network connectivity
Resource exhaustion

Monitoring and Maintenance

Regular Tasks

System updates
Log monitoring
Backup verification
Disk space checks
Security audits
Performance monitoring

Useful Scripts


#!/bin/bash
# System health check
echo "Disk Usage:"
df -h
echo -e "\nMemory Usage:"
free -h
echo -e "\nSystem Load:"
uptime
echo -e "\nActive Services:"
systemctl list-units --type=service --state=running