linuxexpert-practice-labs/labs/lfcs/4-2-services/README.md

LFCS 4.2: Creating and configuring services

Writing a service unit, giving it an environment file, overriding a packaged unit with a drop-in, and fixing a broken unit from its logs.

Before you start

The lab installs ticker.service, which runs /usr/local/bin/ticker as system user ticker. Someone broke its unit file: it fails to start. For the program in task 1, a script that loops forever writing the date to its output works.

Tasks

1. Write a service heartbeat that runs a script as a new system user heartbeat, restarts on failure after 5 seconds, and starts at boot.
2. Make the service read a variable INTERVAL from /etc/default/heartbeat and use it (for example, as the number of seconds between lines).
3. Make the packaged chrony service restart always, in a way that survives package updates. Install chrony if it's missing; the unit is chronyd on RHEL and chrony on Debian and Ubuntu.
4. ticker.service has a wrong ExecStart path and a user that doesn't exist. Find and fix both from the logs, so that it runs and starts at boot.

Hints

• useradd -r, a unit in /etc/systemd/system/, Restart=, RestartSec=, systemctl daemon-reload, systemctl enable --now. sudo systemctl kill -s KILL heartbeat tests the restart.
• EnvironmentFile=, systemctl show heartbeat -p EnvironmentFiles.
• systemctl edit, systemctl cat, systemctl show -p Restart.
• systemctl status ticker, journalctl -u ticker, systemd-analyze verify ticker.service.