The "Permission denied" error suggests the apparmor profile, or whatever else lightdm is doing special to the guest session, is the reason for this failure.
Can you check in syslog if you have a DENIED message from apparmor? ** Also affects: lightdm (Ubuntu) Importance: Undecided Status: New ** Changed in: unity8 (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1644237 Title: unity8 fails to start as guest user To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1644237/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs