[CentOS] when to reboot after updates

Robert Heller heller at deepsoft.com
Thu Apr 9 17:01:38 UTC 2009


At Thu, 09 Apr 2009 10:38:08 -0500 CentOS mailing list <centos at centos.org> wrote:

> 
> Robert Heller wrote:
> > At Thu, 09 Apr 2009 07:49:30 -0400 CentOS mailing list <centos at centos.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.

> 

-- 
Robert Heller             -- 978-544-6933
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heller at deepsoft.com       -- http://www.deepsoft.com/ModelRailroadSystem/
                                                                                                                 


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