More flexible than the single configuration file is it to
      configure libpam via the contents of the
      /etc/pam.d/ directory. In this case the
      directory is filled with files each of which has a filename
      equal to a service-name (in lower-case): it is the personal
      configuration file for the named service.
    
      The syntax of each file in /etc/pam.d/ is similar to that of the
      /etc/pam.conf file and is made up of lines
      of the following form:
    
type  control  module-path  module-arguments
    
      The only difference being that the service-name is not present. The
      service-name is of course the name of the given configuration file.
      For example, /etc/pam.d/login contains the
      configuration for the login service.