Merge pull request 'started user-crontabs.md' (#8) from yeti/institute__wiki:trunk into trunk HEAD trunk

Reviewed-on: https://tildegit.org/institute/wiki/pulls/8
Reviewed-by: gbmor <ben@gbmor.org>

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+<!--
+title: User Crontabs
+description: Using crontabs as user on tilde.institute
+author: yeti
+-->
+
+# 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.
+
+
+[back](/)