linux

# Linux Administration ## What I Do I am Linux, the open-source Unix-like operating system powering servers, cloud infrastructure, and embedded devices worldwide. I provide a robust, secure, and efficient platform for running applications and services. I offer multiple distributions (Ubuntu, RHEL, Debian, CentOS, Alpine) with different package managers and configurations. My command-line interface provides powerful tools for system administration, automation, and troubleshooting. I support multi-user environments, advanced permissions, and enterprise-grade security features. I integrate seamlessly with cloud platforms and container runtimes like Docker and Kubernetes. ## When to Use Me - Web server and application hosting - Database server management - Container orchestration platforms - CI/CD pipeline infrastructure - Network services (DNS, DHCP, VPN) - File and print services - Security and monitoring systems - Embedded and IoT devices ## Core Concepts **Processes and Services**: Managing background tasks with systemd, process signals, and scheduling. **File System Hierarchy**: Understanding /bin, /etc, /var, /home, /tmp, /proc directories. **User Management**: Users, groups, sudo privileges, and access control. **Package Management**: apt, yum/dnf, zypper for software installation. ** systemd**: Service management, journalctl logging, and timers. **Permissions**: chmod, chown, ACLs, and SELinux/AppArmor. **Networking**: ip, netstat, ss, firewall-cmd for network configuration. ## Code Examples ### Example 1: System Administration Script (Bash) ```bash #!/bin/bash set -euo pipefail # Linux System Administration Toolkit readonly LOG_FILE="/var/log/admin-toolkit.log" readonly BACKUP_DIR="/var/backups" log() { echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*" | tee -a "$LOG_FILE" } error() { echo "[ERROR] $*" | tee -a "$LOG_FILE" exit 1 } check_root() { if [[ $EUID -ne 0 ]]; then error "This script must be run as root" fi } # System Information get_system_info() { log "Gathering system information..." cat << EOF === System Information Report === Generated: $(date) Hostname: $(hostname) Kernel: $(uname -r) Uptime: $(uptime -p 2>/dev/null || uptime) CPU: $(nproc) cores Memory: $(free -h | awk '/^Mem:/ {print $2}') Disk Usage: $(df -h | grep -vE '^Filesystem|tmpfs|devtmpfs') Load Average: $(awk '{print $1, $2, $3}' /proc/loadavg) EOF } # User Management list_users() { echo "=== System Users ===" awk -F: '($3 >= 1000) && ($3 != 65534) {print $1 ":" $5}' /etc/passwd } create_user() { local username="$1" local password="${2:-}" if id "$username" &>/dev/null; then log "User $username already exists" return 1 fi useradd -m -s /bin/bash -c "Created by admin toolkit" "$username" if [[ -n "$password" ]]; then echo "$username:$password" | chpasswd fi log "Created user: $username" } manage_groups() { local action="$1" local group="$2" local users="${3:-}" case "$action" in create) groupadd "$group" 2>/dev/null || log "Group $group already exists" ;; add) for user in $users; do usermod -aG "$group" "$user" log "Added $user to group $group" done ;; list) getent group "$group" ;; esac } # Service Management manage_service() { local service="$1" local action="$2" if ! systemctl is-active "$service" &>/dev/null && [[ "$action" == "stop" ]]; then log "Service $service not active, skipping" return 0 fi case "$action" in start|stop|restart|reload|status) systemctl "$action" "$service" log "Service $service: $action" ;; enable|disable) systemctl "$action" "$service" log "Service $service: $action (boot)" ;; *) error "Unknown action: $action" ;; esac } # Firewall Management (ufw) configure_firewall() { local action="$1" local port="$2" local protocol="${3:-tcp}" case "$action" in allow) ufw allow "$port/$protocol" log "Allowed port $port/$protocol" ;; deny) ufw deny "$port/$protocol" log "Denied port $port/$protocol" ;; status) ufw status numbered ;; esac } # Disk Management check_disk_usage() { echo "=== Disk Usage Report ===" df -h | awk ' NR==1 {print; next} /^\/dev/ { usage = $5 + 0 if (usage >= 80) print "\033[31m" $0 "\033[0m" else if (usage >= 70) print "\033[33m" $0 "\033[0m" else print }' } analyze_inodes() { echo "=== Inode Usage ===" df -i | awk ' NR==1 {print; next} /^\/dev/ { usage = $5 + 0 if (usage >= 80) print "\033[31m" $0 "\033[0m" else print }' } # Process Management find_top_processes() { echo "=== Top CPU Processes ===" ps aux --sort=-%cpu | head -11 echo "" echo "=== Top Memory Processes ===" ps aux --sort=-%mem | head -6 } kill_process_by_name() { local name="$1" local pids=$(pgrep -x "$name" 2>/dev/null) if [[ -z "$pids" ]]; then log "No process found: $name" return 1 fi echo "Killing processes: $pids" kill $pids 2>/dev/null log "Sent kill signal to $name" } # Network Tools network_diagnostics() { echo "=== Network Diagnostics ===" echo "Hostname: $(hostname)" echo "IP Addresses:" ip -br addr | grep -v "^lo" | awk '{print " " $1 ": " $3}' echo "" echo "Routing Table:" ip route show echo "" echo "DNS Resolution:" cat /etc/resolv.conf | grep nameserver echo "" echo "Active Connections:" ss -tunp | head -10 } test_connectivity() { local host="${1:-8.8.8.8}" echo "Testing connectivity to $host..." if ping -c 4 "$host" &>/dev/null; then echo "✓ ICMP: OK" else echo "✗ ICMP: FAILED" fi if timeout 5 bash -c "echo > /dev/tcp/$host/443" 2>/dev/null; then echo "✓ Port 443: OPEN" fi if timeout 5 getent hosts "$host" &>/dev/null; then echo "✓ DNS: RESOLVED" fi } # Log Analysis analyze_logs() { local logfile="${1:-/var/log/syslog}" local pattern="${2:-ERROR}" if [[ ! -f "$logfile" ]]; then error "Log file not found: $logfile" fi echo "=== Log Analysis: $logfile ===" echo "Total lines: $(wc -l < "$logfile")" echo "Error lines: $(grep -c "$pattern" "$logfile" 2>/dev/null || echo 0)" echo "" echo "Recent errors:" grep "$pattern" "$logfile" | tail -10 } # Backup Management create_backup() { local source="$1" local destination="${2:-$BACKUP_DIR}" local timestamp=$(date +%Y%m%d_%H%M%S) if [[ ! -d "$destination" ]]; then mkdir -p "$destination" fi local basename=$(basename "$source") local archive="$destination/${basename}_${timestamp}.tar.gz" log "Creating backup: $archive" tar -czf "$archive" "$source" 2>/dev/null if [[ $? -eq 0 ]]; then log "Backup created: $archive ($(du -h "$archive" | cut -f1))" ls -lh "$destination" | grep "$basename" else error "Backup failed" fi } # Security Hardening security_audit() { echo "=== Security Audit ===" echo "" echo "1. User Accounts:" awk -F: '($3 == 0) {print " Root user: " $1}' /etc/passwd echo "" echo "2. Password Policy:" grep -E "^PASS_MAX_DAYS|^PASS_MIN_DAYS|^PASS_WARN_AGE" /etc/login.defs echo "" echo "3. SSH Configuration:" if [[ -f /etc/ssh/sshd_config ]]; then echo " PermitRootLogin: $(grep ^PermitRootLogin /etc/ssh/sshd_config 2>/dev/null || echo not set)" echo " PasswordAuth: $(grep ^PasswordAuthentication /etc/ssh/sshd_config 2>/dev/null || echo not set)" fi echo "" echo "4. Failed Login Attempts:" lastb | head -5 2>/dev/null || echo " (lastb not available)" echo "" echo "5. SUID/SGID Files:" find /usr -type f \( -perm -4000 -o -perm -2000 \) -exec ls -ld {} \; 2>/dev/null | head -5 } # Main menu show_menu() { cat << EOF === Linux System Administration Toolkit === 1. System Information 2. User Management 3. Service Management 4. Firewall Configuration 5. Disk Usage 6. Process Management 7. Network Diagnostics 8. Log Analysis 9. Backup Creation 10. Security Audit 11. Exit EOF } main() { mkdir -p "$BACKUP_DIR" while true; do show_menu read -p "Select option: " choice case "$choice" in 1) get_system_info ;; 2) echo "a) List Users b) Create User c) Group Management" read -p "Select: " sub case "$sub" in a) list_users ;; b) read -p "Username: " user; create_user "$user" ;; c) read -p "Action (create/add/list): " act read -p "Group: " grp read -p "Users: " users manage_groups "$act" "$grp" "$users" ;; esac ;; 3) read -p "Service: " svc read -p "Action (start/stop/restart/status): " act manage_service "$svc" "$act" ;; 4) read -p "Action (allow/deny/status): " act read -p "Port: " port configure_firewall "$act" "$port" ;; 5) check_disk_usage ;; 6) find_top_processes ;; 7) network_diagnostics ;; 8) read -p "Log file: " logf read -p "Pattern: " pat analyze_logs "$logf" "$pat" ;; 9) read -p "Source path: " src create_backup "$src" ;; 10) security_audit ;; 11) exit 0 ;; esac echo "" read -p "Press Enter to continue..." clear done } # Run main function main "$@" ``` ### Example 2: Systemd Service File ```ini [Unit] Description=Application Service Documentation=https://example.com/docs After=network.target Wants=network-online.target [Service] Type=notify User=appuser Group=appgroup WorkingDirectory=/opt/app ExecStart=/opt/app/bin/server ExecReload=/bin/kill -HUP $MAINPID Restart=on-failure RestartSec=5 TimeoutStartSec=300 TimeoutStopSec=30 # Environment Environment=NODE_ENV=production EnvironmentFile=/etc/default/app EnvironmentFile=/run/secrets/app # Security hardening NoNewPrivileges=true ProtectSystem=strict ProtectHome=true PrivateTmp=true ReadOnlyPaths=/etc /var ExecStartPre=/bin/mkdir -p /var/log/app