add: if (*flags) exit_error(PARAMETER_PROBLEM, "Can't specify TTL option twice"); *flags = 1;
context: static int parse(int c, char **argv, int invert, unsigned int *flags,		const struct ipt_entry *entry, unsigned int *nfcache,		struct ipt_entry_match **match){	struct ipt_ttl_info *info = (struct ipt_ttl_info *) (*match)->data;	u_int8_t value;	check_inverse(optarg, &invert, &optind, 0);	value = atoi(argv[optind-1]);	if (*flags) 		exit_error(PARAMETER_PROBLEM, 				"Can't specify TTL option twice");	if (!optarg)		exit_error(PARAMETER_PROBLEM,				"ttl: You must specify a value");	switch (c) {		case '2':			if (invert)				info->mode = IPT_TTL_NE;			else				info->mode = IPT_TTL_EQ;			/* is 0 allowed? */			info->ttl = value;			*flags = 1;			break;		case '3':			if (invert) 				exit_error(PARAMETER_PROBLEM,						"ttl: unexpected `!'");			info->mode = IPT_TTL_LT;			info->ttl = value;			*flags = 1;			break;		case '4':			if (invert)				exit_error(PARAMETER_PROBLEM,						"ttl: unexpected `!'");			info->mode = IPT_TTL_GT;			info->ttl = value;			*flags = 1;			break;		default:			return 0;	}	return 1;}