[lxc-users] lxc-console produces no output

[Dwight Engen]

On Fri, 9 May 2014 00:18:13 -0400
Robert Pendell <shinji at elite-systems.org> wrote:

> On Fri, May 9, 2014 at 12:12 AM, Robert Pendell
> <shinji at elite-systems.org> wrote:
> > On Thu, May 8, 2014 at 10:56 PM, Serge Hallyn
> > <serge.hallyn at ubuntu.com> wrote:
> >> Quoting Robert Pendell (shinji at elite-systems.org):
> >>> OS: Ubuntu 14.04 LTS x86_64
> >>> Kernel: Host-Supplied 3.14.1
> >>> Provider: Linode
> >>> Host Virtualization: Xen Paravirtualized
> >>> LXC Version: 1.0.3-0ubuntu3
> >>> Guest: CentOS 6 i386
> >>>
> >>> I know I've seen this issue crop up before however I don't know
> >>> how it has been fixed and the solution may vary.
> >>>
> >>> I'm using a standard Centos template created using the download
> >>> type. It is running in unprivileged mode and for some reason
> >>> lxc-console isn't producing any output when I attempt to connect
> >>> to it.
> >>>
> >>> Here is what I get:
> >>> shinji at icarus:~$ sudo lxc-console -n gateone
> >>>
> >>> Connected to tty 1
> >>> Type <Ctrl+a q> to exit the console, <Ctrl+a Ctrl+a> to enter
> >>> Ctrl+a itself
> >>
> >> Before you run lxc-console, find the host pid of the mingetty on
> >> pts/1, and strace -f -p that one.
> >>
> >
> > Heh... I tried and it keeps telling me the process id doesn't exist
> > then I noticed that the pid is changing so I went into the guest and
> > looked at the messages log and it is being spammed with this...
> >
> > May  8 23:54:17 localhost init: tty (/dev/tty1) main process (2335)
> > terminated with status 1
> > May  8 23:54:17 localhost init: tty (/dev/tty1) main process ended,
> > respawning May  8 23:54:17 localhost /sbin/mingetty[2348]: tty1:
> > vhangup() failed
> >
> > *a few minutes later*
> > Found the fix.  This might have to go into the prep script for
> > CentOS as it seems to happen for others as well.  It seems the
> > folks working on the Oracle image figured this out.
> >
> > https://github.com/lxc/lxc/blob/master/templates/lxc-oracle.in
> > Line 368 comments about how vhangup fails with userns.  It probably
> > is related to unprivileged containers only although I have not
> > checked with privileged so don't quote me on that last bit.  All I
> > know is it fixed the issue for me.  Others may gain usefulness in
> > this.
> >
> > Basically I edited the /etc/init/tty.conf script and added
> > --nohangup to the mingetty exec command in the script.
> >
> > It became this: exec /sbin/mingetty $TTY --nohangup
> >
> > This will propagate to /dev/console as well due to the way that it
> > is being created during boot (it calls the tty init using
> > TTY=console as a parameter).
> 
> Adding to my last message:
> https://github.com/lxc/lxc/commit/2e83f7201c5d402478b9849f0a85c62d5b9f1589
> "This is needed when using the user namespace since the kernel check
> does not allow user_ns root to successfully call vhangup(2), and
> mingetty will quit in this case."
> 
> So it does appear to only affect unprivileged containers.

Hi Robert, yes its only when using user_ns. I added this as a
workaround because we never did figure out vhangup in a user_ns. See 
http://comments.gmane.org/gmane.linux.kernel.containers.lxc.devel/2632
for the original discussion.

> _______________________________________________
> lxc-users mailing list
> lxc-users at lists.linuxcontainers.org
> http://lists.linuxcontainers.org/listinfo/lxc-users