[CentOS] when to reboot after updates

Les Mikesell lesmikesell at gmail.com
Thu Apr 9 17:07:53 UTC 2009

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.

   Les Mikesell
     lesmikesell at gmail.com

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