linuxexpert-practice-labs/labs/linux-terminal/2-3-crontab/README.md

Using Linux Terminal 2.3: Crontab format and location

A user crontab with a repeating job and a boot job, a system job in /etc/cron.d, and keeping one user away from crontab.

Before you start

The lab creates users student and alice (password Lab-Pass-1), puts a harmless script at /usr/local/bin/cleanup, and makes sure cron is running. It saves /etc/cron.allow and /etc/cron.deny (if they exist) and puts them back on reset. Task 1 needs a few minutes of waiting and a reboot.

Tasks

1. As student (sudo -iu student), add a cron job that appends the date to ~/ticks.log every two minutes, and one that writes booted to ~/boot.log at every boot. Wait until ~/ticks.log has a date or two, then reboot and look at ~/boot.log.
2. Make a system job that runs /usr/local/bin/cleanup as root at 3:15 am on the first day of every month, in its own file under /etc/cron.d.
3. Stop alice from using crontab, without touching anyone else: her crontab -l says she isn't allowed, and student's still works.

Hints

• crontab -e, crontab -l; */2 * * * * and @reboot; >> appends, > overwrites.
• Files in /etc/cron.d have a user field after the five time fields, and cron skips files whose names contain a dot.
• /etc/cron.deny lists users who may not use crontab; a cron.allow would shut out everyone it doesn't list.