Scheduling tasks

Some work repeats on a clock: clearing temporary files, backing up a database, refreshing the package list. Running it by hand every day wastes time and is a sure way to forget. Linux gives you two tools that do it for you: the old cron and systemd timers.

Start with cron. It is a service that wakes up once a minute and checks whether something is due to run. Your personal list of jobs lives in a file called the crontab. You do not edit it directly; there is a separate command.

$ crontab -e      # open your crontab in an editor
$ crontab -l      # show what is in it now
$ crontab -r      # erase the whole crontab (careful, no confirmation)

Each job line is five time fields and a command. The fields go left to righ