I think I've got it... my /etc/shadow file was owned by root:root, not root:shadow. Anyway, here's my /etc/pam.d/common-auth, if you're still interested. ** Attachment added: "/etc/pam.d/common-auth" http://librarian.launchpad.net/4932209/common-auth -- Can't Unlock GNOME Screensaver https://launchpad.net/bugs/67767