Got this on your xen domU when trying to ssh?
There are 2 possible fixes (prolly even more, but ill show you 2 easy ones)
Fix 1: (Needs reboot)
apt-get install udev && reboot
Fix 2: (Needs no reboot)
Add to fstab:
none /dev/pts devpts defaults 0 0
Then do a couple of commands:
rm -rf /dev/ptmx
mknod /dev/ptmx c 5 2
chmod 666 /dev/ptmx
umount /dev/pts
rm -rf /dev/pts
mkdir /dev/pts
mount /dev/pts
/etc/init.d/ssh restart
World domination!