ruby.c:1027
static void
forbid_setid(s)
    const char *s;
{
    if (euid != uid)
        rb_raise(rb_eSecurityError, "No %s allowed while running setuid", s);
    if (egid != gid)
        rb_raise(rb_eSecurityError, "No %s allowed while running setgid", s);
    if (rb_safe_level() > 0)
        rb_raise(rb_eSecurityError, "No %s allowed in tainted mode", s);
}
