gdm3 doesn't start with disable-user-list=true option enabled

[fprietog]

See comment #9 for how to correctly set this option.

Original Bug Report
===================
Ubuntu 17.10 final
gdm3 package version is 3.26.1-3ubuntu2

Problem details:
----------------
The file /etc/gdm3/greeter.dconf-defaults got this option commented by default:

# disable-user-list=true

I've used this option with Ubuntu 17.04 (GNOME session) in order to not show any profile in greeter, as a security measure.

But with Ubuntu 17.10, if you uncomment that line Ubuntu will not boot (really will not start gdm3, so no greeter is shown).

How to reproduce the problem:
- Fresh install Ubuntu 17.10 desktop (for instance, in a virtual machine).
- Uncomment the line "# disable-user-list=true" in file "/etc/gdm3/greeter.dconf-defaults".
- Reboot...

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Eike (e-h-juerrens)]

In addition, using dconf-editor for changing this setting does not work, too.

System:

$ lsb_release -a
Distributor ID: Ubuntu
Description: Ubuntu 17.10
Release: 17.10
Codename: artful

$ gdm3 --version
GDM 3.26.1

see https://askubuntu.com/questions/979743/ubuntu-17-10-disable-user-list-in-gdm

[Joris Le Blansch (j-leblansch)]

Affects 18.04 as well.

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu Bionic Beaver (development branch)
Release: 18.04
Codename: bionic

$ gdm3 --version
GDM 3.28.0

1. Setting

# disable-user-list=true

to

disable-user-list=true

in

/usr/share/gdm/greeter.dconf-defaults

has no effect.

2. Using dconf-editor GUI to set /org/gnome/login-screen/disable-user-list to ON has no effect.

After reboot userlist is shown as before.

[Sebastien Bacher (seb128)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. The issue you are reporting is an upstream one and it would be nice if somebody having it could send the bug to the developers of the software by following the instructions at https://wiki.ubuntu.com/Bugs/Upstream/GNOME. If you have done so, please tell us the number of the upstream bug (or the link), so we can add a bugwatch that will inform us about its status. Thanks in advance.

[fprietog (fprietog)]

I managed to get some journalctl entries related with the gdm starting error:

abr 09 20:54:01 testuser-VirtualBox generate-config[699]: warning: Failed to read keyfile '/usr/share/gdm/dconf/90-debian-settings': Key file does not start with a group
abr 09 20:54:01 testuser-VirtualBox systemd[1]: gdm.service: Control process exited, code=exited status=1
abr 09 20:54:01 testuser-VirtualBox systemd[1]: gdm.service: Failed with result 'exit-code'.
abr 09 20:54:01 testuser-VirtualBox systemd[1]: Failed to start GNOME Display Manager.

The file '/usr/share/gdm/dconf/90-debian-settings' is an softlink to the file '/etc/gdm3/greeter.dconf-defaults' and suddenly I realized that this is not a bug: it's my fault from the beginning!!! :(

There is another line that must be also uncommented in order to get it to run, the previous 'group one':

   #[org/gnome/login-screen]

and

   # disable-user-list=true

After uncommented both lines the greeter works as expected in Ubuntu 18.04 beta 2: asking for the user instead of showing a list.

But in Ubuntu 17.10 it's still showing the users list. So I think it's fixed in Ubuntu 18.04 Beta 2.

Sorry for the inconveniences.

[fprietog (fprietog)]

BTW: as Joris Le Blansch wrote, using dconf-editor GUI to set /org/gnome/login-screen/disable-user-list to ON has no effect and after reboot userlist is shown as before.

So, at this point:

1. Manually changing the file '/etc/gdm3/greeter.dconf-defaults' uncommenting the lines:
     #[org/gnome/login-screen]
       and
     # disable-user-list=true
   Work in Ubuntu 18.04 Beta 2 but doesn't work in Ubuntu 17.10.

2. Using dconf-editor GUI to set '/org/gnome/login-screen/disable-user-list' to ON just doesn't work...

[fprietog (fprietog)]

And the 2nd point is also an "user" problem.

When we use the dconf-editor GUI we are changing the dconf keys for the user that executes the command, usually your personal user. So changing it from there has no effect because the user that launches the greeter is different; 'gdm'.

So the solution is change the dconf key for the user 'gdm'.

I don't know how to do it from the dconf-editor GUI so I give the old fashion way:

Using root:

- Create a file named '/etc/dconf/profile/gdm' with this contents:

  user-db:user
  system-db:gdm

- Create a file named '/etc/dconf/db/gdm.d/50-disable-user-list' with this content:

  [org/gnome/login-screen]
  disable-user-list=true

- Execute the command 'sudo dconf update'

And that's all. It changes the dconf setting for user 'gdm' and after reboot the greeter works as expected: asking for the user instead of showing the users list.

And this solution works in both Ubuntu 17.10 and Ubuntu 18.04 Beta 2!!!

[Tomas (xhudik)]

this is happaning also in Ubuntu 18.04 - once user list is disbaled gdm3 (sudo systemctl restart gdm3) crashes

[Jeremy Bícha (jbicha)]

I am closing this bug. I believe the problem was that you didn't uncomment the [org/gnome/login-screen] line.

To disable the user list on the login screen in Ubuntu 18.04 and newer:
1. Edit /etc/gdm3/greeter.dconf-defaults

You can use your preferred editor, but I suggest:

gedit admin:///etc/gdm3/greeter.dconf-defaults

2. Remove the # from the front of these two lines to uncomment them:
[org/gnome/login-screen]
 disable-user-list=true

3. Save the file

4. Reboot your computer.
On Ubuntu 18.10 and newer, you can probably skip rebooting and just run this command:

sudo systemctl reload gdm

[Jeremy Bícha (jbicha)]

Ok, I'm reopening this because the default could be better. I have filed a Debian bug for input.

Unfortunately, my initial thinking is that it will cause too much disruption to change the way this file works in stable Ubuntu releases.