on Red Hat Enterprise and CentOS, what is creating /var/run/reboot-required?

Solution 1:

This file isn't referred to in any package script, nor any rpm macro (see /usr/lib/rpm/**/macros.*).

I suspect this came from a non-official package, based on a common practice in the Debian and Ubuntu communities.

There, it can be created by http://packages.debian.org/squeeze/update-notifier.

Solution 2:

This was something I created on my own. I had a script that was tracking versions of packages (eg linux kernel), and when those changed it would create "/var/run/reboot-required". It was created as a chef recipe, so it's probably not relevant to others, nor easy to reproduce unless you are using chef.