pam_close_session() is used to indicate that an authenticated session has ended. It is used to inform the module that the user is exiting a session. It should be possible for the PAM library to open a session and close the same session from different applications.
flags may have the value
PAM_SILENT to indicate that no output
should be generated as a result of this function call.
One of the required loaded modules was unable to close a session for the user.