Managing Services with systemd: Start, Auto-Start on Boot, and Read Logs

Most modern Linux distributions (Ubuntu, Debian, CentOS, and others) use systemd to manage background services. Learn two commands, systemctl and journalctl, and you can start, stop, auto-start, and troubleshoot almost any service on your VPS.

The Basics: Start, Stop, Restart

We'll use Nginx as an example, but swap nginx for your own service name. These actions change the system, so they usually need sudo.

sudo systemctl start nginx      # start it
sudo systemctl stop nginx       # stop it
sudo systemctl restart nginx    # stop, then start again
sudo systemctl reload nginx     # re-read config without dropping connections (if supported)

After editing a config file, reach for reload first; fall back to restart only when the service doesn't support reloading.

Checking Status

systemctl status nginx

A few lines matter most: Active: active (running) means it's up; the word enabled or disabled at the end of the Loaded line tells you whether it starts on boot; and the last few log lines are shown right there, which is handy for debugging. Checking status normally doesn't need sudo.

Auto-Start on Boot: enable and disable

start only runs the service right now — it won't come back after a reboot. To have a service launch automatically at boot, use enable:

sudo systemctl enable nginx          # start automatically on boot
sudo systemctl enable --now nginx    # enable on boot AND start it now
sudo systemctl disable nginx         # don't start on boot
systemctl is-enabled nginx           # check whether it's set to auto-start

Keep the two ideas separate: enable controls whether it starts at boot, while start controls whether it's running right now.

Reading Logs: journalctl

systemd collects service logs in one place; read them with journalctl:

journalctl -u nginx              # all logs for this service
journalctl -u nginx -n 50        # the last 50 lines
journalctl -u nginx -f           # follow live (like tail -f)
journalctl -u nginx --since today          # today's logs only
journalctl -u nginx -p err                 # errors only

When a service won't start, check status for the summary, then run journalctl -u <service> -n 50 to see recent entries — the reason is almost always in there.

Writing a Minimal Service Unit

To hand your own program over to systemd, create a .service file under /etc/systemd/system/, for example myapp.service:

[Unit]
Description=My App
After=network.target

[Service]
ExecStart=/usr/local/bin/myapp
Restart=on-failure
User=www-data

[Install]
WantedBy=multi-user.target

Use an absolute path in ExecStart, and Restart=on-failure will bring the program back if it crashes. Whenever you add or change a unit file, reload systemd before enabling it:

sudo systemctl daemon-reload
sudo systemctl enable --now myapp

Summary

• One-off control: start / stop / restart / reload.
• Use status for a quick health check and journalctl -u <service> for the full logs.
• enable sets auto-start on boot, disable turns it off — independent of whether it's running now.
• For a custom service, drop in a .service file, then run daemon-reload followed by enable --now.