Bug#998051: initscripts: /dev/ptmx and /dev/pts/ptmx have wrong permissions after boot in lxc container

[Mark Hindley]

I am no lxc expert, but there is a (fairly recent) suggested fix here[1]. 

  I found this line in /etc/fstab in the container’s rootfs: devpts /dev/pts
  devpts nosuid,noexec,gid=tty,mode=620 0 0 After I added ptmxmode=666 to mount
  options, /dev/ptmx became 666.

Does that help?

Mark

[1]  https://discuss.linuxcontainers.org/t/dev-ptmx-permission-issue/15509