process.c:1720
static VALUE
proc_initgroups(obj, uname, base_grp)
    VALUE obj, uname, base_grp;
{
#ifdef HAVE_INITGROUPS
    if (initgroups(StringValuePtr(uname), (gid_t)NUM2INT(base_grp)) != 0) {
	rb_sys_fail(0);
    }
    return proc_getgroups(obj);
#else
    rb_notimplement();
    return Qnil;
#endif
}
