[plug] automating tasks

[Ryan]

>If I wanted to,say execute a command on a daily basis like "vacuumdb -a" 
>at 3.21am, how would I do this?
>
>What if I wanted to restart a daemon on a weekly basis?

Firstly have a look at: man 5 crontab

That should be all I need to say :)   however if you are feeling lazy or it 
is too early in the morning, read the rest ...

Once you have that under your belt, have a look at your /etc/crontab file, 
it, along with the crontab(5) manpage should have enough examples to get 
you going, the first comment line says it all:

#m h dom mon dow user   command
25 6  *   *   *  root   test -e /usr/sbin/anacron || run-parts --report 
/etc/cron.daily
47 6  *   *   7  root   test -e /usr/sbin/anacron || run-parts --report 
/etc/cron.weekly
52 6  1   *   *  root   test -e /usr/sbin/anacron || run-parts --report 
/etc/cron.monthly

So to do what you asked in a crude and non-error checking way:

21 3  *   *   *  foo vacuumdb -a
01 6  *   *   7  root /etc/init.d/some_service restart

Alternatively for the weekly one you can create an executable script in 
/etc/cron.weekly/ - cron will execute all scripts in that directory on a 
weekly basis as stated in the crontab file example above (6:47AM on the 7th 
day of the week).  Likewise for the daily script if you don't want to 
control the EXACT time it gets run at.

If the commands you run output to STDOUT, that output will normally get 
emailed to you.  If you don't want this you can redirect the command to 
/dev/null and then you'll only get emailed drastic STDERR stuff.

And remember to restart cron once you've made changes.

HTH,

Ryan