n                  The number of elements stored in the array
                       pointed to by the grouplist parameter.
    -1                 Indicates failure. errno might be set to one
                       of the following values:

                       o  EFAULT - The gidsetsize and grouplist
                          parameters specify an array that is
                          partially or completely outside of the
                          allocated address space of the process.

                       o  EINVAL - The gidsetsize parameter is
                          nonzero and smaller than the number of
                          supplementary group IDs.