systemd Unit Files#

Service unit skeleton#

# /etc/systemd/system/myapp.service
[Unit]
Description=My Application
After=network.target
Wants=network.target

[Service]
Type=simple
User=myapp
Group=myapp
WorkingDirectory=/opt/myapp
ExecStart=/opt/myapp/bin/myapp --config /etc/myapp/config.toml
ExecReload=/bin/kill -HUP $MAINPID
Restart=on-failure
RestartSec=5s
StandardOutput=journal
StandardError=journal
Environment="NODE_ENV=production"
EnvironmentFile=-/etc/myapp/env   # dash = ignore if missing

[Install]
WantedBy=multi-user.target

Timer unit (cron replacement)#

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

[Timer]
OnCalendar=*-*-* 02:30:00
Persistent=true   # run missed timers on next boot

[Install]
WantedBy=timers.target

# /etc/systemd/system/backup.service  (paired service)
[Unit]
Description=Run backup

[Service]
Type=oneshot
ExecStart=/usr/local/bin/backup.sh

Essential commands#

# Reload unit files after editing
systemctl daemon-reload

# Enable + start
systemctl enable --now myapp.service

# Status / logs
systemctl status myapp.service
journalctl -u myapp.service -f          # follow
journalctl -u myapp.service --since "1 hour ago"
journalctl -u myapp.service -n 50 --no-pager

# Restart / reload
systemctl restart myapp.service
systemctl reload myapp.service          # sends SIGHUP (if ExecReload set)

# List timers
systemctl list-timers --all

# Show unit dependencies
systemctl list-dependencies myapp.service

# Check why a unit failed
systemctl status myapp.service
journalctl -xe

Service types#