The directory /etc/pam.d/ contains the
PAM configuration files for each PAM-aware application. In earlier
versions of PAM, the file /etc/pam.conf
was used, but this file is now deprecated and is only used if the
/etc/pam.d/ directory does not exist.
Each PAM-aware application or service
has a file within the /etc/pam.d/
directory. Each file within this directory bears the name of the
service for which it controls access.
It is up to the PAM-aware program to define its service name and
install its own PAM configuration file in the /etc/pam.d/ directory. For example, the login program defines its service name as login and
installs the /etc/pam.d/login PAM