Service Management with systemd

You will manage existing services and author a custom systemd unit that restarts automatically on failure. By the end you will have a resilient daemon with logs in journald and a clean enable-on-boot configuration.

Learning Objectives

Start, stop, enable, and inspect services with systemctl.
Write a custom unit with automatic restart.
Read service logs with journalctl.
Time: ~2 hours · Difficulty: Intermediate · Prereqs: a systemd-based Linux server.

Architecture Overview

Environment Setup

You will need: a Linux server with systemd and a simple program or script to run as a service.

Before you begin: confirm systemd is the init system with systemctl --version.

Step-by-Step Execution

Inspect an existing service

Understanding state and dependencies is the basis of all service management.

systemctl status ssh --no-pager && systemctl list-dependencies ssh

Author a custom unit with auto-restart

The Restart directive makes the daemon self-heal after a crash, key for reliability.

printf '[Unit]\nDescription=My App\n[Service]\nExecStart=/usr/local/bin/app\nRestart=on-failure\nRestartSec=3\n[Install]\nWantedBy=multi-user.target\n' | sudo tee /etc/systemd/system/app.service

[ROOT REQUIRED] Creates a restart-on-failure service unit.

Reload, enable, and start

sudo systemctl daemon-reload && sudo systemctl enable --now app.service

Read the logs

# journalctl -u app.service -n 5 --no-pager

Jun 17 09:02 srv01 systemd[1]: Started My App. Jun 17 09:02 srv01 app[5123]: listening on :8080

Progress So Far

graph LR A[01 Inspect] -->|done| B[02 Write unit] B -->|done| C[03 Enable + start] C -->|done| D[04 Read logs] style A fill:#1a4a1a,stroke:#00ff00,color:#fff style B fill:#1a4a1a,stroke:#00ff00,color:#fff style C fill:#1a4a1a,stroke:#00ff00,color:#fff style D fill:#1a4a1a,stroke:#00ff00,color:#fff

Testing & Validation

sudo kill -9 $(systemctl show -p MainPID --value app.service); sleep 4; systemctl is-active app.service

After killing the process you should see active again within seconds, proving auto-restart works.

Troubleshooting

Unit not found: run systemctl daemon-reload after creating the file.
Service flaps: add StartLimitIntervalSec/StartLimitBurst to avoid restart loops.
No logs: ensure the program writes to stdout/stderr, which journald captures.

Extension Ideas

Pair the service with a systemd timer for scheduled runs.
Sandbox it with directives like ProtectSystem=strict.
Forward journald to a central log host (see Log Management).

Key Results

Authored a custom unit that auto-restarts within ~3 seconds of failure.
Enabled the service to start on boot reliably.
Captured all service output in journald.
Proved self-healing with a kill-and-recover test.

Service Management with systemd: Units, Logs, and Auto-Restart