authentication failure

[porsher_puddles]

chas@chas-laptop:~$ su
Password:
su: Authentication failure
Sorry.
chas@chas-laptop:~$
on linux mint when i try to log in as su or root i get this, my password is correct, why?

[objuan]

Hi have you updated any packages like kdm gdm or any core packages for
kde or gnome.

[Cabhan]

What distro are you using? Some (Ubuntu amongst them) do not use su, and use sudo instead. For su, you need to enter the root user's password, not your regular user password.

If you are using a distro that uses sudo, you use it like so:

$ sudo cat /etc/shadow

It will ask you for a password, and you use your user's password.

If you've used su before, it's possible, I suppose, that you accidentally changed your root password. If this is the case, we can certainly help you fix that.