pam_shells man page
pam_shells — PAM module to check for valid login shell
pam_shells is a PAM module that only allows access to the system if the user's shell is listed in /etc/shells.
It also checks if /etc/shells is a plain file and not world writable.
This module does not recognise any options.
Module Types Provided
The auth and account module types are provided.
Access to the system was denied.
The user's login shell was listed as valid shell in /etc/shells.
The module was not able to get the name of the user.
auth required pam_shells.so
shells(5), pam.conf(5), pam.d(5), pam(8)
pam_shells was written by Erik Troan <email@example.com>.