linuxexpert-practice-labs/labs/rhcsa/7-1-scheduling-tasks/README.md

RHCSA 7.1: Scheduling tasks: at, cron and systemd timers

A crontab for another user, a systemd timer that runs every 15 minutes, and one-off jobs with at.

Before you start

The lab creates user alice (password Lab-Pass-1) with an empty crontab, makes sure cron is running, and removes /tmp/at-ran. at isn't set up; installing it and starting its service is part of task 3.

Tasks

1. As root, schedule a job for user alice that runs /usr/bin/logger hello every weekday at 14:30.
2. Make a systemd timer that runs a script every 15 minutes and survives a reboot. After a reboot, systemctl list-timers lists it with a next run at most 15 minutes away; wait until it has fired once.
3. Use at to create a file /tmp/at-ran two minutes from now. Then schedule another job and cancel it.

Hints

• crontab -u alice -e, crontab -l -u alice; fields are minute, hour, day of month, month, day of week.
• A script (chmod +x), a .service with Type=oneshot and ExecStart=, and a .timer with OnCalendar=*:0/15 (or OnUnitActiveSec=15min with OnBootSec=) in /etc/systemd/system/; systemctl daemon-reload, systemctl enable --now NAME.timer; journalctl -u NAME.service.
• dnf install at, systemctl enable --now atd; at now + 2 minutes, atq, atrm.