linuxexpert-practice-labs/labs/linux-plus/2-5-1-systemd-units/README.md

Linux+ 2.5.1: systemd units

A service with a timer, masking and unmasking a unit, and overriding a vendor unit with a drop-in.

Before you start

The lab installs at (for atd.service) and stops and disables atd. Leave your work in place for grading: le-lab reset removes the timer and reverts atd.

Tasks

1. Write labbeat.service, a oneshot service that runs /usr/bin/logger -t labbeat "still here", and labbeat.timer, which runs it every 2 minutes. Enable and start the timer, and watch the messages arrive in the journal.
2. Mask atd.service and see that starting it is refused. Then unmask it, and make it run now and at every boot.
3. With a drop-in made by systemctl edit, run atd at nice level 5. Check it with systemctl cat and systemctl show -p Nice. (The chapter then reverts it with systemctl revert atd; leave it in place here.)

Hints

• Unit files go in /etc/systemd/system/; OnCalendar=*:0/2, AccuracySec=1s, WantedBy=timers.target; systemctl daemon-reload, systemctl list-timers, journalctl -t labbeat.
• systemctl mask, systemctl unmask, systemctl enable --now.
• systemctl edit atd: [Service] and Nice=5; restart atd so the running process picks it up.