Managing systemd Services: systemctl Commands, Custom Unit Files, and Checking Logs with journalctl

# Check status
systemctl status nginx

# Start / stop / restart
systemctl start  nginx
systemctl stop   nginx
systemctl restart nginx
systemctl reload nginx      # Reload configuration only (no downtime)

# Enable/disable start on boot
systemctl enable  nginx
systemctl disable nginx

# Enable and start immediately (in one step)
systemctl enable --now nginx

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

# Check failed services
systemctl --failed

# Analyze boot time
systemd-analyze blame | head -20

# /etc/systemd/system/myapp.service

[Unit]
Description=My Node.js Application
After=network.target

[Service]
Type=simple
User=deploy
WorkingDirectory=/opt/myapp
ExecStart=/usr/bin/node /opt/myapp/server.js
Restart=on-failure
RestartSec=5
StandardOutput=journal
StandardError=journal
Environment=NODE_ENV=production PORT=3000

[Install]
WantedBy=multi-user.target

systemctl daemon-reload          # Always run this after changing a unit file
systemctl enable --now myapp

journalctl -u nginx                    # Full logs for the nginx service
journalctl -u nginx -f                 # Follow in real time
journalctl -u nginx --since "1 hour ago"
journalctl -u nginx -n 50             # Last 50 lines
journalctl -u nginx -p err            # Errors only
journalctl --disk-usage               # Log disk usage
journalctl --vacuum-time=7d           # Delete logs older than 7 days

# /etc/systemd/system/backup.timer
[Unit]
Description=Daily Backup Timer

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target

systemctl enable --now backup.timer
systemctl list-timers