Locked out of logging in through GUI on Ubuntu

Question

When I installed Ubuntu on my laptop, I chose "Automatic login" so that I was not asked for a username and password everytime I switched on.

I later wanted to change the settings.

So I went to:

Systems > Administration > Login window > Security

From there I disabled automatic login and rebooted the computer. Now the GUI does not allow me to enter username and password.

The following displays on the login screen:

Authentication failed

Please help me.

Answer 1

First off, you can try booting into single user mode. Interrupt the boot process at the GRUB loader screen by pressing 'enter'. Then edit the booting line, and put the word 'single' at the end of that kernel line. Then boot, and it will give you a login prompt. Plug in your root credentials, and that will give you a shell.

The GUI screen you were modifying makes changes in /etc/gdm/custom.conf. So check that file once you have access. You may need to make sure "AllowRoot" is undefined, or set to 'true', so that the root user can login. There's also "AutomaticLoginEnabled" which is set to 'true' if automatic logins are in use.

Answer 2

Press CTRL+ALT+F1 and enter your username and password, it will give you a shell. Then type:

nano /etc/gdm/custom.conf

And replace the content with:

[daemon]
AutomaticLoginEnable=false

Then restart.