Comment 6 for bug 527875

ok, you're going to hate me for this, I know it. As if I've not input enough. I did do a separate install of karmic,
and I reproduced this state. I installed a 64 version.

I installed, prepared the kernel for karmic. Unless I missed it, Ubuntu didn't provide a xen kernel for karmic. I provided my own, and it's run lenny 64, karmic 32, now karmic 64, gentoo 32 and gentoo 64. It may not be perfect. Anyway, having booted into xen.

idella@karmic64:~$ sudo libvirtd
[sudo] password for idella:
22:58:12.769: error : qemudWritePidFile:457 : Failed to open pid file '/var/run/libvirtd.pid' : File exists
idella@karmic64:~$ ls /var/run/libvirt
qemu
idella@karmic64:~$ sudo rm /var/run/libvirtd.pid
idella@karmic64:~$ sudo libvirtd
libvir: Network Config error : cannot enable /proc/sys/net/ipv6/conf/virbr0/disable_ipv6: No such file or directory
23:00:47.610: warning : qemudStartup:521 : Unable to create cgroup for driver: No such device or address
Segmentation fault
idella@karmic64:~$ ls /var/run/libvirt
qemu
idella@karmic64:~$ uname -a
Linux karmic64 2.6.31-xen-r10-AMD-64 #19 SMP Sun Feb 28 21:28:33 WST 2010 x86_64 GNU/Linux

More of the same. Installed virt-manager, try connecting to xen by gui,

Unable to open connection to hypervisor URI 'xen:///':
<class 'libvirt.libvirtError'> unable to connect to '/var/run/libvirt/libvirt-sock': No such file or directory

I booted into the freshly installed server kernel, and

idella@karmic64:~$ sudo libvirtd
[sudo] password for idella:
Sorry, try again.
[sudo] password for idella:
22:39:18.849: error : qemudWritePidFile:457 : Failed to open pid file '/var/run/libvirtd.pid' : File exists
idella@karmic64:~$ sudo rm /var/run/libvirtd.pid
idella@karmic64:~$ sudo libvirtd
22:39:39.118: warning : qemudStartup:521 : Unable to create cgroup for driver: No such device or address
22:39:39.204: warning : lxcStartup:1460 : Unable to create cgroup for driver: No such device or address
WARNING: Unhandled message: interface=org.freedesktop.DBus.Introspectable, path=/, member=Introspect

^X^Z
[1]+ Stopped sudo libvirtd
idella@karmic64:~$ sudo libvirtd
22:40:21.411: error : qemudWritePidFile:457 : Failed to open pid file '/var/run/libvirtd.pid' : File exists
idella@karmic64:~$ ls /var/run/libvirt
libvirt-sock libvirt-sock-ro network qemu
idella@karmic64:~$ uname -a
Linux karmic64 2.6.31-19-server #56-Ubuntu SMP Thu Jan 28 03:40:48 UTC 2010 x86_64 GNU/Linux

Those elusive sockets libvirt-sock libvirt-sock-ro are there, in an environment absent of xen.

Yes well, I fear this may lead nowhere if you can't reproduce. What kernel would you use??