Getting an "Authentication token manipulation" error when trying to change my user password

Do these two things just to make sure:

mount -o remount,rw /

This first part remounts the root partition as read/write since it was only in read mode. It actually dismounts the root partition and then mounts it again as read/write.

Then do this:

chmod 640 /etc/shadow

Then do the sudo passwd USER. It should work after that. This part gives the correct permissions to the shadow file.

If you insert the wrong passwd

$ passwd
Changing password for rinzwind.
(current) UNIX password: 
passwd: Authentication token manipulation error
passwd: password unchanged

you get this error. If you are sure that you inserted the correct one, this error might also show up if you are using shadowed password files and the shadow doesn’t have an entry for this user (basically/etc/passwd has an entry for this user, but /etc/shadow does not).

In order to fix this, you can either add the entry manually (make a backup first!!!) or recreate the shadow file with pwconv (Manpage).

pam-auth-update

fixed my messed /etc/pam.d/common-password