20

After a recent package update, the guest session feature is no longer available on Ubuntu 16.10 and 17.04. What happened?

3
  • if that applies like that to 18.04 can we add tags to that version please.
    – TiloBunt
    Jun 18, 2018 at 20:41
  • @TiloBunt: Thanks for pointing it out. It does apply to all versions later than 16.04 which use LightDM, so I dropped the version tags instead and changed the title. Default display manager for standard Ubuntu as from 17.10 is GDM, which does not carry a guest session feature at all. Jun 18, 2018 at 21:11

1 Answer 1

17

The guest session was intentionally disabled by default due to a security issue, where the guest session was not contained by the AppArmor profile that usually limits guest sessions. This AppArmor profile, among other things, prevents a guest user from using su to switch to other users, or viewing other users' home directories.

You can enable it, if you consider the issue to be manageable on your system, as explained in comment #24 of the bug report or by using this one liner:

sudo sh -c 'printf "[Seat:*]\nallow-guest=true\n" >/etc/lightdm/lightdm.conf.d/40-enable-guest.conf'

To reverse it back to the disabled state, simply do:

sudo rm /etc/lightdm/lightdm.conf.d/40-enable-guest.conf
18
  • Is 16.04 unaffected by this?
    – Anwar
    May 15, 2017 at 15:45
  • @Anwar: No it's not. It's a systemd thing. May 15, 2017 at 15:49
  • 1
    @Anwar: The latter (I think - please see the bug report). May 15, 2017 at 15:54
  • 2
    @GunnarHjalmarsson It's not a big deal, but a) su doesn't use sudoers, and b) AppArmor apparently prevents su and sudo from functioning properly for guests (so sudoers doesn't even enter the picture). A user would need to know a valid user's password, but on an otherwise locked down system without access to TTYs, it does open a hole.
    – muru
    May 15, 2017 at 16:24
  • 1
    @GunnarHjalmarsson I don't really keep anything on my internal hard drive, so I'm not worried about that. Thanks for the information.
    – Olliver K
    Jun 24, 2020 at 21:49

Not the answer you're looking for? Browse other questions tagged or ask your own question.