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My Ubuntu machine has suddenly started asking for a username and password when it starts up but does not accept the details I enter. When i go into terminal however, it seems to work fine. I have tried using the

passwd <user>

change thing but get authentication error. I know i am definately entering the correct details as I always use the same ones.

How can I change the password?

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You need to change password for your username.

Enter command like below,


and make sure that you are logging in using the username you entered earlier.

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This is not different from passwd. Running passwd as $USER is equivalent to running passwd $USER as $USER. (Running sudo passwd is different.) Also, passwd YOUR_USERNAME is what the OP ran, but the question's formatting was broken so it didn't appear. – Eliah Kagan Jul 11 '12 at 19:33

Try running passwd as root. When you run passwd as root, unlike when you run it as yourself, you do have to specify the user whose password you want to change:

sudo passwd $USER

Either keep $USER as it is (it will expand to your username), or replace it with your username.

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