The purpose of this PAM configuration file is to provide a common place for all PAM modules which should be called after the stack configured in system-auth or the other common PAM configuration files.
The postlogin configuration file is included from all individual service configuration files that provide login service with shell or file access.
The modules in the postlogin configuration file are executed regardless of the success or failure of the modules in the system-auth configuration file.
Sometimes it would be useful to be able to skip the postlogin modules in case the substack of the system-auth modules failed. Unfortunately the current Linux-PAM library does not provide any way how to achieve this.
pam(8), config-util(5), system-auth(5)
The three Linux-PAM Guides, for system administrators, module developers, and application developers.