[Lxc-users] Failed to access console after launching LXC through libvirt

[Serge Hallyn]

Quoting unicell (unicell at gmail.com):
> On Fri, Nov 9, 2012 at 12:09 AM, unicell <unicell at gmail.com> wrote:
> 
> > Hi,
> >
> > I'm trying to manage LXC instances through OpenStack, which use libvirt as
> > a virtualization driver layer. After launching LXC instance, I simply could
> > not attach to the console.
> >
> > virsh # list
> >  Id Name                 State
> > ----------------------------------
> > 14366 instance-00000078    running
> >
> > virsh # console 14366
> > Connected to domain instance-00000078
> > Escape character is ^]
> >
> >
> > And it keeps stuck here.
> >
> > Initially I thought it could be a cgroup device config issue, and tried to
> > "echo ‘c 5:1 rwm'
> > >/cgroup/devices/libvirt/lxc/instance-00000078/devices.allow“, to add
> > /dev/console access right to the container. But it does not work, console
> > stilll not working.
> >
> > Before the cgroup tweaking, devices.list are as follows
> >
> > [root at localhost libvirt]# cat
> > /cgroup/devices/libvirt/lxc/instance-0000007a/devices.list
> >
> > c 1:3 rwm
> > c 1:5 rwm
> > c 1:7 rwm
> > c 1:8 rwm
> > c 1:9 rwm
> > c 5:0 rwm
> > c 5:2 rwm
> > c 136:* rwm
> >
> >
> > I'm not quite sure what kind of issue could possibly cause this console
> > access issue. Cause I'm now using two different guest OS templates on two

Just a few things to help you look around:

Both lxc and libvirt-lxc provide consoles by creating a pty on the host
and bind-mounting that onto /dev/ttyN in the guest before starting init.

Ubuntu on the host passes 'container=lxc' (or 'container=libvirt') to
the container, which tells ubuntu in the container to not do some things
(look for 'container' in /etc/init/*;  also things like mountall accept
that they should not do some things in containers).

You can investigate /dev/ttyN and /dev/console in your container by
looking at the pid of init in the container, and looking at
	/proc/$pid/root/dev/{console,tty*}

That *should* show 136:* devices, but I assume that in the cases where
it is not working it will show 4:* for ttyN.  If you look at
	cat /proc/$pid/root/proc/1/mounts
I expect you'll see a /dev is mounted in the container.  Which hides the
bind mounts which (libvirt-)lxc has set up.

-serge