How to turn off Automatic Login

Question

I have turned on Automatic Login in Ubuntu 14.04. Now I cant install any updates as I cannot authorize. I tried to turn off Automatic Login, using the User Accounts screen in System Settings. But to make any changes I need to unlock it. When I press the Unlock button I am again asked for an authorization password. How do I fix this?

Answer 1

I assume you're using an administrative account. (By which I don't mean root) Then you just enter your password you supplied when you installed Ubuntu.

If you, however, have no administrative account and don't know the root password, you need to ask a person who owns an administrative account to give you the password or to fix this for you.

This whole situation comes up because user and password information is stored in files only root has access to. Thus, these changes can only be accomplished by root or an account which can give root execution rights to a program, in which case an authentication password is asked to prevent abuse. (and sometimes foolishness of users like me)

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As you disabled your password when enabling autologin, here's the way to reset it:

1. Reboot your computer to GRUB menu (Hold Ctrl or Shift on boot)
2. If 1. doesn't work, hit Ctrl+Alt+Del during boot. Your computer will immediately reboot to GRUB menu.
3. Select the Recovery Mode option.
4. Select the Root shell entry (I think it's at the bottom). Now Ubuntu will boot into a root terminal.
5. Remount the system as RW: mount -o rw,remount /.
6. Set your new password: passwd yourusername.
7. Set the root password: passwd.
8. Reboot: reboot.