Re: [Xen-users] Patching a Xen PV environment

[Simon Hobson <simon@xxxxxxxxxxxxxxxx>]

Bear in mind that I'm only a user, I really don't follow all the deeply 
technical details. Stands ready to be corrected ...


Christopher Myers <cmyers@xxxxxxxxxxxx> wrote:

> Just to make sure, when installing OS patches on a PV Xen environment, do you 
> basically patch the Dom0 first and then patch the DomU's?

To a large extent, it doesn't matter. Dom0 and the DomUs are separate systems - 
and need to be patched separately. One thing you DO needs to do is to make sure 
that each DomU boots from the correct images, more about this below ...

> Just for giggles, last night I did an "apt-get upgrade" on a DomU before 
> running it on the Dom0 (without actually installing the patches on the DomU) 
> to compare the patch list before and after installing them on the Dom0. 
> Before installing patches on the Dom0, there were a number of updates listed 
> for the DomU, and after patching the Dom0, there weren't any. So my 
> assumption is that in that particular case, patching the Dom0 pushed patches 
> to the DomU as well.

Ordinarily patching Dom0 should not have affected DomU. However there are ways 
of having stuff in Dom0 affect a DomU - for example, by sharing a kernel and 
intird image in Dom0's /boot. Another would be if you had some sort of shared 
root filesystem - eg "/" on NFS ?

So I've always just treated Dom0 and each DomU as a separate system - updating 
them separately as downtime has permitted. With the proviso that for those 
DomUs where I could not get pygrub to work, I needed to copy any 
upgraded/updated kernel image and initrd to the Dom0 (and update the config 
accordingly if the names had changed, eg DomU kernel update.)


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