With POSIX IDs disabled, setgid is implemented for program
    portability and serves no function. It returns 0 (to indicate
    success).

    With POSIX IDs enabled, setgid sets the group IDs.

    Format

      #include  <types.h>

      #include  <unistd.h>

      int setgid  (__gid_t gid); (_DECC_V4_SOURCE)

      int setgid  (gid_t gid); (not _DECC_V4_SOURCE)