[CentOS] when to reboot after updates

Scott Silva ssilva at sgvwater.com
Thu Apr 9 17:41:11 UTC 2009

on 4-9-2009 10:07 AM Les Mikesell spake the following:
> Scott Silva wrote:
>>>>> You only *really* need to reboot if/when you update the kernel. Yum/RPM
>>>>> takes care of restarting daemons, etc. during the update process.  This
>>>>> is NOT MS-Windows....
>>>> Yes, but any program that is already running will keep using the old 
>>>> versions of the program, libraries, open files, etc., retaining the disk 
>>>> space and not sharing the in-memory copy with new instances that start 
>>>> after the update.  And since modern programs like to dynamically load 
>>>> library modules as needed while running you can get a strange mix of 
>>>> old/new versions running at once.
>>> Generally, this is not as bad as it seems.  In some cases, some updates
>>> do restart critical daemons (rpm -hUv glibc... will restart sshd for
>>> example). Also, since most critical library updates also imply a similar
>>> update for the deamons/programs that use those libraries and since the
>>> rpms for the deamon programs do restart the deamon they install/update,
>>> in most cases the deamons do get restarted at some point during the
>>> update process -- that is, since httpd (Apache) depends on apr and when apr
>>> gets a critical update, it is very likely that the httpd program would
>>> also be rebuilt as well, so that both rpms are updated in the repo.  A
>>> 'yum update' will install the new apr rpm, then the new httpd rpm and at
>>> that point restart httpd, this picking up the new apr library.
>> Sometimes you just have to know your system. Like if you update a sendmail
>> milter, you would need to restart sendmail also, but if the rpm developer
>> didn't write that into the %post section you would want to do it yourself.
> You have some chance of 'knowing' the server side of things - a lot less 
> about what other users might be running.  What should you expect if you 
> have logged in users over freenx, remote X or at the console running 
> (say) firefox through an update?  Or other long running applications, 
> especially in languages likely to dynamically load new components.
> And in one case, I got kicked off of my ssh connection in mid-update. 
> I'm still not sure what happened there but I had to install yum-utils 
> and run yum-recover-transaction to continue.
I always run my updates through screen. That way disconnects aren't a problem.
During major updates I also usually run yum with the --downloadonly option so
I can have most of the files local when I am ready.

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