[Bug 832123] Re: when booting oneiric cloud-images under libvirt, no pty is available

[Serge Hallyn]

Diagnosis:  udev looks through /dev, making sure all devices have the
expected device type and permissions.  If not, it replaces them.

lxc creates /dev/ptmx and bind mounts /dev/pts/ptmx on top of it, so it
has the expected device type.

libvirt creates /dev/ptmx as a symlink to /dev/pts/ptmx.  This is not
the expected device type, so udev replaces it.  A bare ptmx device is
not usable in the container as it is tied to the initial devpts
namespace.

There are three ways to solve this.  One is a small patch to libvirt to
do the same thing lxc does.  Another is to patch udev to allow ptmx to
be a symlink.  The third is to have another upstart job shipped with the
lxcguest package, which starts on starting udev and replaces ptmx with a
bind mount.

Since a bind mount from /dev/pts/ptmx is always correct (with any modern
kernel), I suppose a fourth solution would be to have
/etc/init/udev.conf create the expected ptmx as a bind mount from
/dev/pts/ptmx unconditionally, even if it is not a container.

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https://bugs.launchpad.net/bugs/832123

Title:
  when booting oneiric cloud-images under libvirt, no pty is available

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