[lxc-users] lxc-console produces no output

[CDR]

I detected an issue with all Fedora 20 containers that may benefit
from --nohangup workaround
If I start the container without the "-d" flag, then I cannot enter
the container via the console, later.
If I start the container without the "-d" flag, it works, bu then I
cannot get out.

So how do I try this workaround? If you give me precise instructions I
will try it.
Note: I have containers of 3 types, Debian, SLES and Fedora, only
Fedora has the issue.

Philip

On Fri, May 9, 2014 at 9:56 AM, Dwight Engen <dwight.engen at oracle.com> wrote:
> 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.
>
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