Cron and Crontabs

The cron daemon manages the global cron tables and users typically ar not allowed to use them.

On some systems users are allowed to have per user cron tables which mimic the format of the global ones except for the user field.

--> crontab(5)

Showing and manipulating user crontabs is done ia an own command of the same name.

--> crontab(1)

The main surprise could be lines in crontabs misbehaving when a % occurs. crontab(5) should explain this.

1. Hitchhiker 25:
   (41) Deep Thought paused for a moment's reflection.
   (42) "Tricky," he said finally.

Test/Create your Crontab

Use crontab -e and add a line like:

* * * * * >>/tmp/crontest.$USER python3%import time%print(time.time())

After saving cron will execute this every minute. To disable it, disarm it by turning it into a comment by a leading # or delete that line completely.

Myth

Cron is too dumb for complex events.

Delegate complex stuff to the command part and something to "fire" on each last day of a month, on every even Thursday, on the 256th day of the year, ... and much more is doable even as oneliner.

Examples may or may not show up later.

1. Hitchhiker 25:
   (59) Scarcely pausing for breath, Vroomfondel shouted, "We don't demand solid facts! What we demand is a total absence of solid facts. I demand that I may or may not be Vroomfondel!"

This is a stub

...and needs to be extended by a lot.

For now testing whether this will appear after committing is more important than an epic collection of examples.

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