CentOS 6 upstart overrides: How to make something happen before something else

I have generic users that are logged in automatically since they’re not allowed user prefs anyway, and it would be more of a hindrance in their environment.

I use puppet to manage a staging directory that has the home directory as I want it to be, and use tmpfs for the user’s actual $HOME. In order for this to work, the staged default home needs to be copied onto the tmpfs mount before Xwindows starts.

All this means that I can’t do it in rc.local as that’s run simultaneous to the prefdm upstart job, creating a race condition.

To resolve the problem, I learned about upstart override configuration. It turns out you can create a .override and override any stanza in the packaged upstart job configuration. In my case I created the following:

/etc/prefdm.override

# homedir - sets up the home directory of the auto-logged-in user
#

pre-start script
    /usr/bin/puppet agent --onetime --no-daemonize >/var/log/prestart.log
    /usr/bin/rsync -av /home/thinguest.orig/ /home/thinguest/ >>/var/log/prestart.log
    /sbin/restorecon -rv /home/thinguest >> /var/log/prestart.log
end script

This overrides the non-existent pre-start stanza in prefdm.conf with that script, ensuring those things are done before /etc/X11/prefdm -nodaemon is executed.

This is actually true, of course, for all the EL6 based distros, and also is true for Ubuntu/Debian.