x                  Pointer to a group structure, if successful.
    NULL               Indicates that an error occurred. The function
                       sets errno to one of the following values:

                       o  EACCES - The user process does not have
                          appropriate privileges enabled to access
                          the user authorization file.

                       o  EINTR - A signal was intercepted during the
                          operation.

                       o  EIO - Indicates that an I/O error occurred.

                       o  EMFILE - OPEN_MAX file descriptors are
                          currently open in the calling process.

                       o  ENFILE - The maximum allowable number of
                          files is currently open in the system.