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