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Lab 8.1 - Managing systemd Services

Objectives​

By the end of this lab, you will be able to:

  • Use systemctl to manage services
  • Understand service states
  • Start, stop, restart services
  • Enable/disable services at startup
  • View service logs

Prerequisites​

  • Ubuntu 24.04 installed
  • Sudo access
  • Terminal open

Exercise 1: Basic Commands​

Step 1: View the Status of a Service​

# Service status
systemctl status sshd
# or
systemctl status ssh

# Short status
systemctl is-active sshd
systemctl is-enabled sshd
systemctl is-failed sshd

Step 2: List Services​

# All services
systemctl list-units --type=service

# Active services
systemctl list-units --type=service --state=running

# Inactive services
systemctl list-units --type=service --state=inactive

# Failed services
systemctl list-units --type=service --state=failed

Exercise 2: Service Control​

Step 1: Start/Stop​

# Start a service
sudo systemctl start sshd

# Stop a service
sudo systemctl stop sshd

# Restart
sudo systemctl restart sshd

# Reload configuration (if supported)
sudo systemctl reload sshd

Step 2: Enable at Startup​

# Enable (automatic startup)
sudo systemctl enable sshd

# Disable
sudo systemctl disable sshd

# Enable and start
sudo systemctl enable --now sshd

Step 3: Mask a Service​

# Mask (prevents manual start too)
sudo systemctl mask sshd

# Unmask
sudo systemctl unmask sshd

Exercise 3: Service Logs​

Step 1: journalctl​

# Service logs
sudo journalctl -u sshd

# Last lines
sudo journalctl -u sshd -n 50

# Follow in real-time
sudo journalctl -u sshd -f

# Logs from today
sudo journalctl -u sshd --since today

# Logs from a period
sudo journalctl -u sshd --since "2024-12-01" --until "2024-12-31"

Step 2: Log Levels​

# By priority
sudo journalctl -u sshd -p err
sudo journalctl -u sshd -p warning

# Combinations
sudo journalctl -u sshd -p err --since "1 hour ago"

Exercise 4: System Services​

Step 1: Essential Services​

# View system services
systemctl list-units --type=service | grep systemd

# systemd status
systemctl status

# Critical services
systemctl list-units --type=service --state=failed

Step 2: Analyze Dependencies​

# Dependencies of a service
systemctl list-dependencies sshd

# Services depending on sshd
systemctl list-dependencies --reverse sshd

Exercise 5: Practice with nginx​

Step 1: Installation and Configuration​

# Install nginx
sudo apt update
sudo apt install -y nginx

# Check status
systemctl status nginx

# Start
sudo systemctl start nginx

# Enable at startup
sudo systemctl enable nginx

Step 2: Management​

# Restart
sudo systemctl restart nginx

# Reload configuration
sudo systemctl reload nginx

# View logs
sudo journalctl -u nginx -f

Step 3: Test​

# Test the service
curl http://localhost

# View processes
ps aux | grep nginx

Exercise 6: Management Script​

Step 1: Basic Script​

# Script to manage a service
cat > manage-service.sh << 'EOF'
#!/bin/bash
SERVICE=$1
ACTION=$2

if [ -z "$SERVICE" ] || [ -z "$ACTION" ]; then
    echo "Usage: $0 service {start|stop|restart|status|enable|disable}"
    exit 1
fi

case $ACTION in
    start)
        sudo systemctl start "$SERVICE"
        ;;
    stop)
        sudo systemctl stop "$SERVICE"
        ;;
    restart)
        sudo systemctl restart "$SERVICE"
        ;;
    status)
        systemctl status "$SERVICE"
        ;;
    enable)
        sudo systemctl enable "$SERVICE"
        ;;
    disable)
        sudo systemctl disable "$SERVICE"
        ;;
    *)
        echo "Unknown action: $ACTION"
        exit 1
        ;;
esac
EOF

chmod +x manage-service.sh

# Use
./manage-service.sh nginx status
./manage-service.sh nginx restart

Verification​

Checklist​

Check that you can:

  • View service status (systemctl status)
  • List services (list-units)
  • Start/stop services
  • Enable/disable at startup
  • View logs (journalctl)
  • Analyze dependencies
  • Manage common services (nginx, sshd)

Reflection Questions​

  1. What is the difference between start and enable?

    • start: Starts now
    • enable: Activates at system startup

  2. When to use reload vs restart?

    • reload: Reloads config without interruption
    • restart: Completely restarts (interruption)

  3. Why use journalctl instead of /var/log?

    • journalctl: Centralized systemd logs, more modern
    • /var/log: Traditional logs, always available

Next Steps​

  • Lab 8.2: Custom Services
  • Lab 8.3: Advanced Cron and systemd Timers
  • Chapter 8.1: Managing systemd Services

Lab created on: December 2024 - Tested on Ubuntu 24.04