Re: [libvirt] lxc: setsid() usage
Am 22.06.2015 um 16:51 schrieb Daniel P. Berrange:
On Mon, Jun 22, 2015 at 04:40:37PM +0200, Richard Weinberger wrote:
> Hi!
>
> Why is libvirt-lxc issuing a setsid() in lxcContainerSetupFDs()?
> To me it seems like a hack to have a controlling TTY if PID 1 is /bin/bash.
I honestly can't remember the reason. It might have been to ensure we have
separation from the libvirt_lxc session.
Hm, can be.
> If one runs a sysv init style distro (like Debian) in libvirt-lxc
the setsid() has
> a major downside, when getty spawns a login shell on /dev/tty1 it cannot become
> the controlling tty. Hence, if one presses ctrl-c in such a session, the container
will
> reboot.
Is that problem due to the fact we call setsid(), or due to use calling
ioctl(TIOCSCTTY) ?
If I remove the TIOCSCTTY nothing changes.
Without setsid() libvirt is unable to start the container at all.
So, I fear you're right that it has something do to with the libvirt session.
> Interestingly it does not happen when a systemd distro is used.
> Maybe because systemd completely closes and reopens the TTY?
I have a feeling it does close & reopen the tty, but i dunno if
that has an impact on the ability to set the controlling tty ?
My TTY-fu is not strong enough to answer that question.
Also note systemd uses the device via /dev/console, not /dev/tty1
and with 'container_ttys' we've told it not to use /dev/tty1 for
gettys. So maybe it deals with /dev/console in a different way
than it would if it were /dev/tty1
This can also be. If I change Debian's getty to use /dev/console instead
of /dev/tty1 it is still unable to spwan a controlling tty.
Thanks,
//richard