wrong ownership on /dev/kvm (Maverick)

[Marco Davids]

Binary package hint: qemu-kvm

Installed qemu-kvm, but it was *very* slow (while using virt-manager). Looked in /var/log/libvirt/qemu/xxxx.log and noticed that user libvirt-qemu had no access to /dev/kvm (access denied error) and that it was unable to use the KVM full virtualization support. Placing user libvirt-qemu in the kvm group did not solve the issue.

Looked at /dev/kvm an noticed it was own by root.

Changed group ownership to kvm and, in combination with libvirt-qemu being in the kvm-group, this dramatically increased the performance!

ls -al /dev/ | grep kvm
crw-rw---- 1 root kvm 10, 232 2011-01-15 22:06 kvm

lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 10.10
Release: 10.10
Codename: maverick

[Marco Davids (mdavids)]

Okay, the error came back... (can't go unnoticed, it was painfully slow again)

open /dev/kvm: Permission denied
Could not initialize KVM, will disable KVM support

Turns out that the ownership is reset after 'qemu-kvm' is restarted. As a workaround I added 'chgrp kvm /dev/kvm' in the 'pre-start script' section of /etc/init/qemu-kvm.conf.

[Dustin Kirkland  (kirkland)]

Hmm, I could not reproduce this...

kirkland@x201:~$ ls -halF /dev/kvm
crw-rw----+ 1 root kvm 10, 232 2011-01-15 17:23 /dev/kvm
kirkland@x201:~$ sudo service qemu-kvm stop
[sudo] password for kirkland:
qemu-kvm stop/waiting
kirkland@x201:~$ ls -halF /dev/kvm
ls: cannot access /dev/kvm: No such file or directory
kirkland@x201:~$ sudo service qemu-kvm start
qemu-kvm start/running
kirkland@x201:~$ ls -halF /dev/kvm
crw-rw----+ 1 root kvm 10, 232 2011-01-16 09:16 /dev/kvm

Can you give specific instructions to reproducing this?

[Marco Davids (mdavids)]

This is weird, can't reproduce it myself anymore either...
I went back to an older version of qemu-kvm en re-installed the current one again, after that, the issue seems to have disappeared. Don't have a clue why.

I do run into quite some other problems now, however....

They are related to this:
http://ubuntuforums.org/showthread.php?t=1621431

(But that is an entire other story, that should be in it's own bug-report, I suppose)

[Dustin Kirkland  (kirkland)]

Okay, thanks for following up.

In this case, I'm going to close this bug for now. Please do re-open it if you figure out how to reproduce it. Cheers.