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Re: [LUG] OS Architecture

 

David Bell wrote:
> On Wednesday 22 November 2006 13:43, Ben Goodger wrote:
>> 
>> Er, no... the norm has always been to reload the service that was updated
>> (usually done by APT) and then continue. In the world of Joe User, this
>> should be constrained to logging in and out again if the update is
>> major-ish, or just carrying on as normal otherwise.
> 
> No - the norm, as far as I'm concerned (as I said above) is to reboot.
> Thus agreeing with Simon ;)

Ben is right that often all that is needed is the service restart, and
that "apt" usually does this. Indeed the libc upgrade in the Sarge to
Etch upgrade is very good on explaining this, and offering to restart
relevant services. Although it specifically leaves some services, and
suggests you reboot/restart them after the upgrade is complete, but then
you get a kernel update as well with Etch.

I found I had "stale libraries" in use with Postfix, which in Debian is
run chrooted, and needs to be restarted for the scripts to automatically
maintain the chroot jailed versions of libraries.

But not all Debian scripts which update libraries reliably restart all
the services that depend on them. Indeed these relationships can be
quite subtle, with multiple versions of various applications (apache,
postfix) and applications with different ways of working (xinetd/inetd,
versus standalone).

For the desktop the situation is messy, because we are seeing apps
appearing that don't terminate when a user logs out, and so can keep
stale libraries open even between restarts of the window manager.

But for server type environments, we have long running processes and
scripts, which usually run 24x7 and I get paged if they stop. There are
tools around for Debian (and not doubt elsewhere) to help spot when such
applications are using stale libraries, but for many users it is simply
easier to reboot. Indeed making sure everything still works correctly
with the new libraries is probably more crucial than the vague security
vulnerabilities being patched.

But my main message is that one can over value uptime, over good
maintenance. Rebooting after upgrades is also a good way to make sure
the upgrade won't stop the machine coming up later when you get the
inevitable power interruption or need to power down when the upgrade is
long forgotten except for the administrator diary or notes.

The other lesson I learnt the hard way, is when working on machines you
don't know well it can pay to reboot and make sure it comes up clean
before applying any changes. Otherwise you'll assume you broken
something, which was in fact already broken.

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