/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.
16.2.1. PAM Service Files
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 configuration file.