fix kernel on Xen Server hypervisor vps

Question

I have a cloud server hosted at Rackspace, and they use Xen Server hypervisor. I was running Ubuntu 12.04, and really messed up by attempting to do a release upgrade manually.

The hypervisor apparently doesn't get along with the changes made to GRUB (I think; there could be more) and thus does not reboot; it gets stuck at the initramfs stage of booting:

I've been speaking with a tech for a long time. We're rather undecided on what to do; would it make sense to provision a new server, grab that kernel / GRUB config, and drop it on the current server? Or to try and roll back the changes / downgrade?

If you have any suggestions, they would be greatly appreciated.

Alien Life Form · Answer 1 · 2013-05-11T09:33:42.910

2

Not really a xen thing. The operative bit is /dev/disk-by-uuid/dev/xvda1 does not exist.

Access grub.conf by standard means (e.g. boot rescue or mount the partition/file/whatever)
see if thingies like root=UUID=/dev/xvda1 appear and change them to root=/dev/xvda1
check that /etc/fstab also complies e.g it reads:

/dev/xvda1 / ext3 defaults,errors=remount-ro 0 1

and not:

UUID=/dev/xvda1 /   ext3 defaults,errors=remount-ro 0       1

That should be it.

Hint: unless the "tech" you are talking with has already tried this, he/she is out of his/her depth. This is in Google's first page, and it's Rackspace related to boot ;-) Cheers, alf

EDIT

Having seen your (grub2) config I would try to replace it with something along the lines of:

timeout=5


menuentry 'Ubuntu, with Linux 3.2.0-24-generic' {
#not sure about the following line
root=xvda,1
linux   /boot/vmlinuz-3.2.0-24-generic root=/dev/xvda1 ro console=hvc0
initrd  /boot/initrd.img-3.2.0-24-generic
}

And then, I'd get down to find out a way to make it permanent, because, on the next upgrade grub-mkconfig will hose your config again. Here you find a different strategy which might also work not to mention advice that should probably be heeded.

edited May 11 '13 at 09:33

answered May 10 '13 at 07:46

Alien Life Form

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Do you mean `/boot/grub/grub.cfg`? – tekknolagi May 10 '13 at 14:12
Also, there's no such line in the grub conf. I can upload mine / take a screenshot if you like. – tekknolagi May 10 '13 at 14:14
Are these lines related? http://pastebin.com/my5KqSmG – tekknolagi May 10 '13 at 14:18
If yours is called grub.cfg, then we're likely dealing with grub2 (which I do not know much, or at all). Seeing your cfg would help and ye, the lines you posted are probably involved. – Alien Life Form May 10 '13 at 14:47
I shall post my config promptly, then. Do you think you can help? – tekknolagi May 10 '13 at 21:01
http://pastebin.com/Nf92G4Q5 – tekknolagi May 10 '13 at 21:46
I edited my answer above. – Alien Life Form May 13 '13 at 16:44
So that should be my entire grub? And I don't plan on updating again after this -.- – tekknolagi May 13 '13 at 22:14
That is what I'd try can't be worse than it's now, right? ;-) The root= stuff may need to be different. – Alien Life Form May 14 '13 at 07:10
Now I get this http://i.imgur.com/KCwzj1M.png when I try and VNC in from Rackspace control panel. – tekknolagi May 14 '13 at 19:48
That appears to be a different kettle of fish. I'd say that the DomU may have started, but yo do not have a graphical console because...(some weird Xen reason thate needs to be fixed by even weirder boot time kernel options). But, given CLI access, you should be able to get to the text mode console with xm console – Alien Life Form May 15 '13 at 13:04

score 0 · Accepted Answer · answered May 15 '13 at 17:39

0

So the problem wasn't particularly correctly analyzed by anyone here, but the higher-tier Linux Admins at Rackspace were instrumental in solving this problem.

I replaced my GRUB2 conf with what Alien Life Form gave me, but changed the root line to:

set root=(hd0)

Then, in my menu.lst, I removed the by-uuid line, so that it could find my drive.

From there, it booted properly.

Thank you all!

answered May 15 '13 at 17:39

tekknolagi

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Good tip. It could help our situation: http://askubuntu.com/questions/572446/xen-vm-stuck-at-grub-prompt in which root=/dev/xvda1 is correct but /dev/xvda seems to be unavailabe for selection by grub2 repair tools. – Marcos Jan 11 '15 at 16:49

fix kernel on Xen Server hypervisor vps

2 Answers2