Comment 7 for bug 1724944

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!!!