Return_Values

   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.