linuxexpert-practice-labs/labs/lpic-1/107-2-scheduling-jobs/README.md

LPIC-1 107.2: Scheduling jobs

A user crontab, one-off jobs with at, who may use cron, and the same job as a systemd timer.

Before you start

The lab creates user alice (password Lab-Pass-1) and makes sure cron is installed and running. at isn't set up: installing it and starting atd is part of task 2. Tasks 1 and 2 need a few minutes of waiting.

Tasks

1. As alice, add a crontab entry that appends the output of date to ~/date.log every two minutes. Wait until the file has a line or two, then remove the entry.
2. Queue a job with at now + 2 minutes that writes first to /var/tmp/at-first. List it with atq, read it with at -c, and let it run. Then queue another that would write second to /var/tmp/at-second, write its job number to /root/lab-answers/2, and remove it with atrm.
3. Put alice in /etc/cron.deny and try crontab -e as her. Then create /etc/cron.allow without her name, and try again.
4. Turn the two-minute job into datelog.service and datelog.timer: the service runs as alice and appends date to /home/alice/date.log, and the timer runs it with OnCalendar=*:0/2. Enable and start the timer, and watch systemctl list-timers and journalctl -u datelog.

Hints

• crontab -e, crontab -l, */2 * * * *; crontab -r or edit the line out.
• The at package and its atd service; atq, at -c, atrm.
• /etc/cron.deny, /etc/cron.allow; crontab -l as alice shows the refusal.
• [Service] with Type=oneshot, User=alice, and a shell for the >>: ExecStart=/bin/sh -c '...'. [Timer] and [Install] WantedBy=timers.target. systemd-analyze calendar '*:0/2'.