pam_nologin.so  [
        file=/path/nologin
      ] [
        successok
      ]
      pam_nologin is a PAM module that prevents users from logging into
      the system when /var/run/nologin or
      /etc/nologin exists. The contents
      of the file are displayed to the user. The pam_nologin module
      has no effect on the root user's ability to log in.
    
            Use this file instead the default
            /var/run/nologin or
            /etc/nologin.
          
Return PAM_SUCCESS if no file exists, the default is PAM_IGNORE.
            The user is not root and /etc/nologin
            exists, so the user is not permitted to log in.
          
Memory buffer error.
This is the default return value.
Success: either the user is root or the nologin file does not exist.
User not known to the underlying authentication module.