What Is systemd? Services, systemctl and journalctl for Beginners

systemd is the system and service manager on most Linux distributions — Ubuntu, Debian, Fedora and others. It's the first program the kernel starts, and it starts and looks after everything else: the web server, the database, SSH, and (if you set it up) your app. (What is Linux?)

Why you'll meet it

On a server, you want your app to:

• start automatically when the server boots,
• restart if it crashes,
• keep its logs somewhere you can read them.

systemd does all three. Things it manages are called units; the ones that run programs are services (files ending in .service).

systemctl: controlling services

sudo systemctl status nginx      # is it running? recent log lines
sudo systemctl start nginx       # start now
sudo systemctl stop nginx        # stop now
sudo systemctl restart nginx     # stop and start
sudo systemctl reload nginx      # reload config without stopping (if supported)

sudo systemctl enable nginx      # start automatically on boot
sudo systemctl disable nginx     # don't start on boot
sudo systemctl enable --now nginx   # enable and start in one go

start affects now; enable affects future boots. Forgetting enable is why an app is mysteriously gone after a server restart.

List what's running, and what's broken:

systemctl list-units --type=service --state=running
systemctl --failed

Reading status

● myapp.service - My Node app
     Loaded: loaded (/etc/systemd/system/myapp.service; enabled)
     Active: active (running) since Thu 2026-10-01 09:12:44 UTC; 1 day ago
   Main PID: 1234 (node)

• Loaded … enabled — the unit file exists and will start on boot.
• Active: active (running) — it's up. Other values: inactive (stopped), failed (crashed and gave up), activating (starting or restarting).

journalctl: reading the logs

systemd captures everything services print to stdout/stderr in the journal:

journalctl -u myapp              # all logs for a service
journalctl -u myapp -f           # follow live
journalctl -u myapp -n 100       # last 100 lines
journalctl -u myapp --since "1 hour ago"
journalctl -b                    # everything since the last boot
journalctl -p err -b             # only errors since boot

When an app won't start, journalctl -u myapp -n 50 almost always shows why — a missing environment variable, a port in use, a crash. (How to read an error message)

Running your own app as a service

A minimal unit file at /etc/systemd/system/myapp.service:

[Unit]
Description=My Node app
After=network.target

[Service]
User=app
WorkingDirectory=/srv/myapp
ExecStart=/usr/bin/node server.js
Restart=always
EnvironmentFile=/srv/myapp/.env

[Install]
WantedBy=multi-user.target

Then:

sudo systemctl daemon-reload     # pick up the new/changed file
sudo systemctl enable --now myapp

Restart=always brings it back after crashes. For the full set of options — memory limits, hardening, graceful shutdown — see the systemd service file guide.

systemd vs PM2

PM2 is a Node.js-specific process manager that does similar things with a friendlier interface. systemd is built into the OS, works for any language, and needs nothing extra installed. (PM2 vs systemd)

Timers: systemd's cron

systemd can also run things on a schedule with timers, an alternative to cron with better logging. (Cron expressions explained)

Quick reference

Task	Command
Is it running?	systemctl status name
Start / stop / restart	systemctl start / stop / restart name
Start on boot	systemctl enable name
After editing a unit file	systemctl daemon-reload
Logs	journalctl -u name -f
What failed?	systemctl --failed

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Related: Writing a systemd Service File · PM2 vs systemd · Basic Linux Commands · Deploy a Node.js App to a VPS