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I'm aware that it is good to run yum update from time to time to keep my Centos server updated, and I even see that there is way to automate this update. My question is, is it necessary to restart the server after the update? Is it a good idea? What happens if I keep updating and never restart?


So from the answers, I believe it is correct to say that I need to restart the server if the Kernel, libc, glibc has been updated. Alternatively use KSplice.

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You don't have to restart the server unless you are getting a message (from yum) that explicitly encourages you to do so.

But you can't use the new kernel that was updated until you restart the system (unless you are using something like Ksplice, which is a technology that switches the old kernel with the new one without the need for a reboot).

So in the end, it's your decision if you want to reboot. I would suggest that unless there's a major security update for the kernel you shouldn't reboot during work hours. Otherwise, if the server is idle (and you don't need it for the next 30 minutes or so, because in some rare circumstances updates could interfere with the boot process), I would suggest you reboot it.

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If kernel has updated, yes it is a good idea to reboot because new kernel will be used only after reboot. other packages will be updated in place, no need to reboot.

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updates to libc without reboot can give issues –  Folkert van Heusden Jan 2 '12 at 9:42
    
that is not correct, there are a number of other packages that require a reboot to be updated correctly, as pointed out above libc is one, there are others (systemd/init) –  totaam Jan 2 '12 at 14:25
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To say it more clean than Folkert: You should also reboot after a glibc update. –  Nils Jan 2 '12 at 21:58
    
@Nils You don't need to reboot; it's enough to restart all the services which you want to switch to run against the new libc. –  Gilles Jan 2 '12 at 23:43
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@Nils On most systems, all services are linked against libc. There's no automatic way to know which ones must be restarted: only the ones that are affected by whatever bug the upgrade fixes are important. –  Gilles Jan 3 '12 at 20:37
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I have a fully automated server that gets its daily updates via yum-cron and I let it reboot every weekend (via root-crontab).

This has been working well for more than three years now.

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I like this solution. –  Phil Jan 5 '12 at 3:49
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