Ask for username and password on 18's login screen [duplicate]

Settings for gdm3 are done in /usr/share/gdm/greeter.dconf-defaults.

Uncomment these 2 lines:

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

(Only un-commenting the 2nd line will crash your login: bugreport confirming it works for 18.04) and restart the login manager with

sudo dpkg-reconfigure gdm3

and reboot (or restart with sudo systemctl stop gdm and log out).

Make a backup 1st so in case something get messed up and you can not log in you can use tty3 to redo your changes. edit: this wont work; gdm also takes care of the tty sessions so tty3 is dead too... you will need to user a live session or grub rescue prompt.

Another way that works for 17.10 and 18.04 (from comment #7 by fprietog in the bug report):

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