[CentOS] when to reboot after updates

[Scott Silva]

on 4-9-2009 9:01 AM Robert Heller spake the following:
> At Thu, 09 Apr 2009 10:38:08 -0500 CentOS mailing list <centos-IFYaIzF+flcdnm+yROfE0A at public.gmane.org> wrote:
> 
>> Robert Heller wrote:
>>> At Thu, 09 Apr 2009 07:49:30 -0400 CentOS mailing list <centos-IFYaIzF+flcdnm+yROfE0A at public.gmane.org> wrote:
>>>
>>>> What is the rule of thumb for reboots after updates...
>>>>
>>>> Certainly if I update from 5.2 to 5.3 I reboot.
>>>>
>>>> But if you update something like krb5 or pam
>>>> does that require a reboot? Does the "fix" get automatically loaded and used
>>>> or do you just do a reboot always?
>>> 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.

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