Cannot login after enabling "don't ask for password on login"

[ouroumov]

Try this:
Power on the PC, hold SHIFT till you see the GRUB menu.
Go to "Other Options for Ubuntu" or equivalent.
Boot last kernel in recovery mode.
Select 'root' to perform admin tasks.
Once in the root shell, issue the command:

mount -o remount,rw /

Then use the command:

passwd you

(Where 'you' is your user name on the machine)
You'll be asked twice for the new password, and won't see stars echoed back to you as you type - this is normal.

Then reboot using:

init 6

Edit: advising this because of this comment from @lah7

Turn Login screen back on

Possibly a tad bit unnecessary, I’ve found that a new password needs to be set when toggling the “Don’t ask for password at login”.

Edit: also see this:

Disable auto login

Open a terminal. sudo nano /etc/lightdm/lightdm.conf It displays some text as follows: [SeatDefaults] greeter-session=lightdm-gtk-greeter user-session=mate autologin-user=username Solution This would be your particular user name that is automatically logged in with or without password. Delete this username and type in the administrative username or leave it blank. Shut down the system. It will go back to the login selection screen. Just power down the system and put it on again.