When does crontab starts?

Question

I'm having lots of problems with my Ubuntu 10.04 in AWS and init scripts. I have my rc.local with some mounts, mkdirs & more but they don't do everything as expected, just a few of them and not always the same.

I'm learning puppet, but until I'll be prepared to get my machine remotely configured I'm trying to do something more ugly. I thought to do a cronjob every 3 minutes to configure all the system and save a flag file in my /dev/shm. When my instance get rebooted or something worse, this file will be deleted and my script will attempt to init the server again.

Do you have something more clever?

Thanks in advance!

Answer 1

You don't need to mess with flag files – cron already does that for you. You can schedule a @reboot job which will be run exactly once every time the instance starts:

In a user crontab:

@reboot /my/script

In a system-wide /etc/crontab:

@reboot root /my/script

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And of course, simply adding commands to /etc/rc.local will have the same effect, since rc.local is only run when booting (though a little later than @reboot cronjobs).