systemd

Overview

systemd manages Linux services — start, stop, restart, enable on boot, and monitor processes. It replaces init scripts with declarative unit files. Handles dependencies, auto-restart, logging (journald), resource limits, and timers (cron replacement).

Instructions

Step 1: Create a Service

# /etc/systemd/system/myapp.service — Node.js app as a system service
[Unit]
Description=My Node.js Application
After=network.target postgresql.service
Wants=postgresql.service

[Service]
Type=simple
User=deploy
Group=deploy
WorkingDirectory=/opt/myapp
ExecStart=/usr/bin/node dist/server.js
Restart=always
RestartSec=5
Environment=NODE_ENV=production
Environment=PORT=3000
EnvironmentFile=/opt/myapp/.env

# Security hardening
NoNewPrivileges=true
ProtectSystem=strict
ProtectHome=true
ReadWritePaths=/opt/myapp/uploads

# Resource limits
MemoryMax=512M
CPUQuota=80%

[Install]
WantedBy=multi-user.target

Step 2: Manage Service

sudo systemctl daemon-reload          # reload after editing unit files
sudo systemctl enable myapp            # start on boot
sudo systemctl start myapp             # start now
sudo systemctl status myapp            # check status
sudo systemctl restart myapp           # restart
sudo systemctl stop myapp              # stop
journalctl -u myapp -f                 # view live logs
journalctl -u myapp --since "1 hour ago"  # recent logs

Step 3: Timer (Cron Replacement)

# /etc/systemd/system/backup.timer — Run backup daily at 3 AM
[Unit]
Description=Daily Backup Timer

[Timer]
OnCalendar=*-*-* 03:00:00
Persistent=true

[Install]
WantedBy=timers.target

# /etc/systemd/system/backup.service — The actual backup job
[Unit]
Description=Database Backup

[Service]
Type=oneshot
User=deploy
ExecStart=/opt/scripts/backup.sh

sudo systemctl enable --now backup.timer
systemctl list-timers                    # list active timers

Guidelines

• Always run daemon-reload after changing unit files.
• Use Restart=always for production services — systemd auto-restarts on crash.
• journalctl -u service -f is the primary log viewer — replaces checking log files.
• Timers are better than cron: persistent (catch up missed runs), dependency-aware, logged.