debian: cannot change password

Solution 1:

You have another authentication method (kerberos) in use than a standard linux account - chances are the pam module is unable to write/update passwords. Doing so from root confuses the module because root is truly a local account and not in the other service's user list.

Look for some hints to what pam modules are in use look in /etc/pam.conf and in the dir: /etc/pam.d - /etc/nsswitch.conf may also provide hints, but debian uses compat which doesn't really help in specifying what is in use obviously.

If kerberos is indeed in use, you can't update the password using passwd

Solution 2:

Run "pam-auth-update"

It'll prompt.

Debian has been really annoying and added kerberos by default during apt-get upgrade(s).