I would recommend examining your PAM configuration files in /etc/pam.d/, especially the common-* files. You may want to try reinstalling pam to see if it warns you about changed configuration files too:
sudo apt-get --reinstall install libpam-runtime
The stock versions of these files are in /usr/share/pam/common-*
I would recommend examining your PAM configuration files in /etc/pam.d/, especially the common-* files. You may want to try reinstalling pam to see if it warns you about changed configuration files too:
sudo apt-get --reinstall install libpam-runtime
The stock versions of these files are in /usr/share/ pam/common- *