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/******************************************************************************
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* Program: DNS plugin for Nagios
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* Copyright (c) 1999 Ethan Galstad (nagios@nagios.org)
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* Last Modified: $Date: 2003/05/31 14:39:33 $
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* - Safe popen added by Karl DeBisschop 9-11-99
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* - expected-address parameter added by Alex Chaffee - 7 Oct 2002
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* Command line: (see print_usage)
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* This program will use the nslookup program to obtain the IP address
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* for a given host name. A optional DNS server may be specified. If
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* no DNS server is specified, the default server(s) for the system
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* OK The DNS query was successful (host IP address was returned).
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* WARNING The DNS server responded, but could not fulfill the request.
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* CRITICAL The DNS server is not responding or encountered an error.
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* License Information:
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*****************************************************************************/
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const char *progname = "check_dns";
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#define REVISION "$Revision: 1.8.2.3 $"
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#define COPYRIGHT "2000-2002"
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int process_arguments (int, char **);
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int validate_arguments (void);
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void print_usage (void);
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void print_help (void);
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int error_scan (char *);
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#define ADDRESS_LENGTH 256
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char query_address[ADDRESS_LENGTH] = "";
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char dns_server[ADDRESS_LENGTH] = "";
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char ptr_server[ADDRESS_LENGTH] = "";
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char expected_address[ADDRESS_LENGTH] = "";
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int match_expected_address = FALSE;
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main (int argc, char **argv)
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char *command_line = NULL;
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char input_buffer[MAX_INPUT_BUFFER];
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char *temp_buffer = NULL;
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int result = STATE_UNKNOWN;
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/* Set signal handling and alarm */
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if (signal (SIGALRM, popen_timeout_alarm_handler) == SIG_ERR) {
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printf ("Cannot catch SIGALRM");
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if (process_arguments (argc, argv) != OK) {
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/* get the command to run */
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asprintf (&command_line, "%s %s %s", NSLOOKUP_COMMAND, query_address, dns_server);
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alarm (timeout_interval);
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printf ("%s\n", command_line);
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child_process = spopen (command_line);
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if (child_process == NULL) {
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printf ("Could not open pipe: %s\n", command_line);
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return STATE_UNKNOWN;
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child_stderr = fdopen (child_stderr_array[fileno (child_process)], "r");
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if (child_stderr == NULL)
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printf ("Could not open stderr for %s\n", command_line);
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while (fgets (input_buffer, MAX_INPUT_BUFFER - 1, child_process)) {
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printf ("%s\n", input_buffer);
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if (strstr (input_buffer, ".in-addr.arpa")) {
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if ((temp_buffer = strstr (input_buffer, "name = ")))
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address = strscpy (address, temp_buffer + 7);
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output = strscpy (output, "Unknown error (plugin)");
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result = STATE_WARNING;
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/* the server is responding, we just got the host name... */
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if (strstr (input_buffer, "Name:")) {
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/* get the host address */
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if (!fgets (input_buffer, MAX_INPUT_BUFFER - 1, child_process))
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printf ("%s\n", input_buffer);
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if ((temp_buffer = index (input_buffer, ':'))) {
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/* Strip leading spaces */
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for (; *temp_buffer != '\0' && *temp_buffer == ' '; temp_buffer++)
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address = strdup (temp_buffer);
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if (address==NULL || strlen(address)==0)
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terminate (STATE_CRITICAL,
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"DNS CRITICAL - '%s' returned empty host name string\n",
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output = strdup ("Unknown error (plugin)");
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result = STATE_WARNING;
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result = error_scan (input_buffer);
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if (result != STATE_OK) {
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output = strscpy (output, 1 + index (input_buffer, ':'));
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while (fgets (input_buffer, MAX_INPUT_BUFFER - 1, child_stderr)) {
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if (error_scan (input_buffer) != STATE_OK) {
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result = max_state (result, error_scan (input_buffer));
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output = strscpy (output, 1 + index (input_buffer, ':'));
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(void) fclose (child_stderr);
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if (spclose (child_process)) {
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result = max_state (result, STATE_WARNING);
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if (!strcmp (output, ""))
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output = strscpy (output, "nslookup returned error status");
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/* If we got here, we should have an address string,
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and we can segfault if we do not */
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if (address==NULL || strlen(address)==0)
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terminate (STATE_CRITICAL,
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"DNS CRITICAL - '%s' output parsing exited with no address\n",
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/* compare to expected address */
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if (result == STATE_OK && match_expected_address && strcmp(address, expected_address)) {
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result = STATE_CRITICAL;
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asprintf(&output, "expected %s but got %s", expected_address, address);
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(void) time (&end_time);
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if (result == STATE_OK)
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printf ("DNS ok - %d seconds response time, Address(es) is/are %s\n",
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(int) (end_time - start_time), address);
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else if (result == STATE_WARNING)
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printf ("DNS WARNING - %s\n",
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!strcmp (output, "") ? " Probably a non-existent host/domain" : output);
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else if (result == STATE_CRITICAL)
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printf ("DNS CRITICAL - %s\n",
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!strcmp (output, "") ? " Probably a non-existent host/domain" : output);
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printf ("DNS problem - %s\n",
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!strcmp (output, "") ? " Probably a non-existent host/domain" : output);
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error_scan (char *input_buffer)
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/* the DNS lookup timed out */
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if (strstr (input_buffer,
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"Note: nslookup is deprecated and may be removed from future releases.")
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|| strstr (input_buffer,
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"Consider using the `dig' or `host' programs instead. Run nslookup with")
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|| strstr (input_buffer,
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"the `-sil[ent]' option to prevent this message from appearing."))
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/* the DNS lookup timed out */
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else if (strstr (input_buffer, "Timed out"))
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return STATE_WARNING;
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/* DNS server is not running... */
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else if (strstr (input_buffer, "No response from server"))
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return STATE_CRITICAL;
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/* Host name is valid, but server doesn't have records... */
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else if (strstr (input_buffer, "No records"))
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return STATE_WARNING;
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/* Host or domain name does not exist */
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else if (strstr (input_buffer, "Non-existent"))
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return STATE_CRITICAL;
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else if (strstr (input_buffer, "** server can't find"))
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return STATE_CRITICAL;
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else if(strstr(input_buffer,"NXDOMAIN")) /* 9.x */
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return STATE_CRITICAL;
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/* Connection was refused */
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else if (strstr (input_buffer, "Connection refused"))
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return STATE_CRITICAL;
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/* Network is unreachable */
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else if (strstr (input_buffer, "Network is unreachable"))
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return STATE_CRITICAL;
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/* Internal server failure */
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else if (strstr (input_buffer, "Server failure"))
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return STATE_CRITICAL;
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/* DNS server refused to service request */
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else if (strstr (input_buffer, "Refused"))
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return STATE_CRITICAL;
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else if (strstr (input_buffer, "Format error"))
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return STATE_WARNING;
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/* process command-line arguments */
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process_arguments (int argc, char **argv)
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static struct option long_opts[] = {
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{"help", no_argument, 0, 'h'},
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{"version", no_argument, 0, 'V'},
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{"verbose", no_argument, 0, 'v'},
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{"timeout", required_argument, 0, 't'},
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{"hostname", required_argument, 0, 'H'},
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{"server", required_argument, 0, 's'},
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{"reverse-server", required_argument, 0, 'r'},
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{"expected-address", required_argument, 0, 'a'},
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for (c = 1; c < argc; c++)
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if (strcmp ("-to", argv[c]) == 0)
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strcpy (argv[c], "-t");
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c = getopt_long (argc, argv, "hVvt:H:s:r:a:", long_opts, &opt_index);
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c = getopt (argc, argv, "hVvt:H:s:r:a:");
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if (c == -1 || c == EOF)
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case '?': /* args not parsable */
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printf ("%s: Unknown argument: %s\n\n", progname, optarg);
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exit (STATE_UNKNOWN);
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case 'V': /* version */
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print_revision (progname, REVISION);
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case 'v': /* version */
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case 't': /* timeout period */
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timeout_interval = atoi (optarg);
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case 'H': /* hostname */
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if (is_host (optarg) == FALSE) {
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printf ("Invalid host name/address\n\n");
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exit (STATE_UNKNOWN);
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if (strlen (optarg) >= ADDRESS_LENGTH)
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terminate (STATE_UNKNOWN, "Input buffer overflow\n");
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strcpy (query_address, optarg);
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case 's': /* server name */
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if (is_host (optarg) == FALSE) {
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printf ("Invalid server name/address\n\n");
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exit (STATE_UNKNOWN);
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if (strlen (optarg) >= ADDRESS_LENGTH)
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terminate (STATE_UNKNOWN, "Input buffer overflow\n");
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strcpy (dns_server, optarg);
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case 'r': /* reverse server name */
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if (is_host (optarg) == FALSE) {
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printf ("Invalid host name/address\n\n");
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exit (STATE_UNKNOWN);
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if (strlen (optarg) >= ADDRESS_LENGTH)
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terminate (STATE_UNKNOWN, "Input buffer overflow\n");
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strcpy (ptr_server, optarg);
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case 'a': /* expected address */
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if (is_dotted_quad (optarg) == FALSE) {
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printf ("Invalid expected address\n\n");
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exit (STATE_UNKNOWN);
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if (strlen (optarg) >= ADDRESS_LENGTH)
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terminate (STATE_UNKNOWN, "Input buffer overflow\n");
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strcpy (expected_address, optarg);
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match_expected_address = TRUE;
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if (strlen(query_address)==0 && c<argc) {
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if (is_host(argv[c])==FALSE) {
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printf ("Invalid name/address: %s\n\n", argv[c]);
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if (strlen(argv[c])>=ADDRESS_LENGTH)
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terminate (STATE_UNKNOWN, "Input buffer overflow\n");
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strcpy (query_address, argv[c++]);
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if (strlen(dns_server)==0 && c<argc) {
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if (is_host(argv[c]) == FALSE) {
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printf ("Invalid name/address: %s\n\n", argv[c]);
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if (strlen(argv[c]) >= ADDRESS_LENGTH)
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terminate (STATE_UNKNOWN, "Input buffer overflow\n");
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strcpy (dns_server, argv[c++]);
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return validate_arguments ();
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validate_arguments ()
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if (query_address[0] == 0)
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printf ("Usage: %s -H host [-s server] [-a expected-address] [-t timeout]\n" " %s --help\n"
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" %s --version\n", progname, progname, progname);
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print_revision (progname, REVISION);
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printf ("Copyright (c) 1999 Ethan Galstad (nagios@nagios.org)\n\n");
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"-H, --hostname=HOST\n"
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" The name or address you want to query\n"
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"-s, --server=HOST\n"
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" Optional DNS server you want to use for the lookup\n"
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"-a, --expected-address=IP-ADDRESS\n"
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" Optional IP address you expect the DNS server to return\n"
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"-t, --timeout=INTEGER\n"
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" Seconds before connection times out (default: %d)\n"
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" Print detailed help\n"
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" Print version numbers and license information\n"
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"This plugin uses the nslookup program to obtain the IP address\n"
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"for the given host/domain query. A optional DNS server to use may\n"
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"be specified. If no DNS server is specified, the default server(s)\n"
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"specified in /etc/resolv.conf will be used.\n", DEFAULT_SOCKET_TIMEOUT);