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Re: [Xen-users] dom0 reboot like domU

To: <xen-users@xxxxxxxxxxxxxxxxxxx>, "ccmail111" <ccmail111@xxxxxxxxx>
Subject: Re: [Xen-users] dom0 reboot like domU
From: "Nick Couchman" <Nick.Couchman@xxxxxxxxx>
Date: Mon, 19 Apr 2010 12:07:48 -0600
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No, and the option you reference has nothing to do with the question you ask.  
Rebooting dom0 reboots Xen.  There are a few reasons why this does not work.  
The primary one is that, unless you're using stubdoms to assign physical 
resources to your domUs, dom0 is responsible for providing things like network 
and disk access to your domUs.  If you reboot dom0, all of your domUs lose all 
of their connectivity to network, disk, console, and serial resources, which 
would lock up the domains.  Stubdoms may be an attempt to allow this, but 
you're faced with the same problem with the stubdoms, as well - at some point, 
you have to be able to reboot the domains providing these resources, and that's 
going to interrupt domU service.

The noreboot option simply prevents Xen from automatically resetting the 
computer when something bad happens to the Xen kernel.  Most often this is at 
boot time - Xen attempts to boot but runs into an issue with the processors, 
acpi, etc., and reboots.  Adding noreboot allows you to see what's causing it 
to fail before it reboots.  Furthermore, regardless of having the noreboot 
option specified at boot time, when Xen detects that dom0 is down, it will 
either shut down or reboot, depending on the requested action passed to it from 
dom0.  noreboot is for debugging errors, it does not affect what Xen considers 
to be "normal" behavior.

Why are you asking?  Why do you want to reboot dom0 without affecting domUs?  
And, if you're looking for high availability, how about live migration?


>>> On 2010/04/16 at 15:39, ccmail111 <ccmail111@xxxxxxxxx> wrote: 

> Question:
> can dom0 in Xen4.0 be rebooted (from domU or from within dom0) anytime 
> without loosing anything ?
> If so, please provide details. If not, does Xen.org have this in roadmap ?
> The closest posting I found (old one) is:
> http://lists.xensource.com/archives/html/xen-devel/2005-07/msg00885.html
> The option is parameter as below (but this grub conf)
> noreboot 
> Debugging
> Requests that the machine not be automatically rebooted in the case of fatal 
> errors.
> Thanks !
> SV

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