[Gllug] Advanced versions of cron for scheduling

[James McGuigan]

Richard Jones wrote:

> (2) Run a job continually - after it finishes, schedule it to run
> again.
> 
> A shell script, while true; do ... done, solves this, but there are
> maintainability concerns (eg for one, how to start the script when the
> machine boots, from a non-root user account, without requiring root
> access?).

If you want to keep all the config in the crontab file, then maybe a put 
a comment at the end of the line with the word "bootup" (or any other 
unique keyword) and have a small boot time script that reads the 
relevant parts from the crontab.

#!/bin/bash
cat /etc/crontab | grep bootup | \
awk '/.*/ {print $7 $8 $9 $10 $11 $12}' > cronboot.sh;
bash cronboot.sh


As for running as a non-root user, is getting root to sudo to another 
user a valid option.
sudo -u nonrootuser beep
su nonrootuser -c  'beep'

> (4) Running jobs regularly, but at odd intervals.
> 
> For example, one request I've had was to run a job every 45 minutes.
> This isn't easy to express in a crontab.

Not sure if this will work, but 60*24 / 45 minutes is 1/32 of a day:

# min hour day   month dow user command
   *   *    */32  *     *   root /usr/local/bin/do-something.pl # bootup

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