You have patches to apply, we all know that if there are kernel patches that you need to (or at least should) restart/reboot the server. But what about other packages? There are a few non-kernel patches which can cause havoc if you spply them and do not reboot the server. The biggest package that most people miss are libraries, specifically libraries used by the system, like glibc. When the system is running it loads the libraries it needs into memory, updating does not force a reload of those libraries. Therefore after patching you will have the old version in memory and the new version on disk. When a new subroutine or kernel process is called it will load the new version into memory, this is where the fun can start. I say fun because you can see some really strange behavior. Perhaps you have and in frustration rebooted, problem solved but you are perplexed, well now you know.
Since I deal mostly with Redhat these days here are the packages that require/highly recommend a reboot of the server. (Caveat: If you can reload what is in memory you do not need to reboot. This is what we do with services like tomcat or apache after a patch and that removes the old packages from memory and loads the new.)
While we all want to avoid interruptions to system uptime, when updating these packages a reboot is required. Remember to use your own discretion as this list is provided as an informational guide only. Redhat could introduce changes that increase or decrease this list. You may be using packages not considered or functionality not examined.
Red Hat Enterprise Linux 5:
Red Hat Enterprise Linux 6:
Red Hat Enterprise Linux 7:
Remember if you don’t have to reboot you should restart the updated service. Good Luck.