Description

   The getgroups function gets the current supplementary group IDs
   of the calling process. The list is stored in the array pointed
   to by the grouplist parameter. The gidsetsize parameter indicates
   the number of entries that can be stored in this array.

   The getgroups function never returns more IDs than the value
   indicated by the sysconf parameter _SC_NGROUPS_MAX.

   See also getgid and setsid.