Re: [Xen-users] Kernel panics

[Martin Goldstone <m.j.goldstone@xxxxxxxxxxxxxxx>]

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Yves Dorfsman wrote:
> 
> Hi,

Hi

> 
> I'm knwe to XEN, and having the usual panic problem.
> XEN (3.0.4.1) loads, then the kernel loads, then it says:
> "Please append a correct "root=" boot option"
> "Not syncying VFS unable to mount root fs on unknown-block(2,0)"
> (sort of, I'm catching this just before it reboots !).
> 
> I've googled, and it seems that the typical two sources of this problems
> are invalid initrd and/or missing drivers in the kernel. So before I
> turn mad, I've got a bunch of questions I'd be very happy if somebody
> could help me with:

I'm assuming you've already got a root= entry, but I've noticed
sometimes that what works as the root= under a regular kernel doesn't
under Xen (I've noticed this mainly on RHEL systems, they have a
tendency to use root=LABEL=/, and under certain Xen kernels (though not
on the 2.6.18 that comes with the Xen 3.1 binary) I've had to point it
to the correct device (though to be fair, it could have been my initrd).

> 
> Do you HAVE to have an initrd, or if you managed to put all the
> necessary drivers in the kernel, you should be able to boot without an
> initrd ?

As long as you have all the driver's needed to boot the kernel, you
should be fine without an initrd

> 
> My root partition is formated with JFS. Can this be an issue, or as long
> as I have the JFS drivers in the kernel I should be fine ?

Again, as long as you have you have either the driver in the kernel or
the module in the initrd, this should be fine.  I've not come across any
xen issues when using non ext3 fs's myself, but I haven't tried JFS.  I
can't see why it would make a difference.

> 
> Is there a way to capture the console output, short of using the serial
> line (or a digital camera :-) ?

Sadly not as far as I know.  Using a serial console is probably the best
way.

> 
> Or a way to make it stop and wait for a key to be pressed before it
> reboots ?

I add noreboot to the end of the dom0 kernel's module line in grub (not
the kernel line, as that's Xen, but usually the line below it.

> 
> When I do use an initrd, I get a segfault from the linuxrc.
> Depending what version of mkinitrd I use I get different results, a lot
> of the time I can't even mount the gunzip resulting file, and when I can
> mount it, I get a lot of empty directories.... Is there a better way of
> producing the initrd ?
> 

I always use mkinitrd, and I've not had a problem like this before.
What distro are you using?  Do you put anything weird in your initrd?
Are you using the stock binaries from the Xen site, or are you rolling
your own?  Is mkinitrd returning any errors?


Martin
> 
> Thanks.
> 
> 
> Yves.
> ----
> Yves Dorfsman                                             yves@xxxxxxxxx
>                                                    http://www.SollerS.ca
> 
> 
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> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
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