Comment 27 for bug 259867

cp: cannot stat `/etc/pam.d/common-session': No such file or directory

This is a cosmetic error only, which I'll fix in the next version.

Copying /usr/share/pam/common-session to /etc/pam.d/common-session is /not/ correct, and will also give you authentication errors. The file in /usr/share/pam is a template that needs to be processed by pam-auth-update before it can be used; this is precisely what the instructions I offered do for you.