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Nagios check_http mod
Posted on 04-22-2005 15:11:00 UTC | Updated on 04-22-2005 15:11:00 UTC
Section: /software/nagios/ | Permanent Link

I was setting up Nagios to monitor some systems and finally got to the printers. Well, some one made a HP plugin for Nagios to check the laserjets status (toner low, ok, etc). This was great because we have 11 HP lasers but we also have 4 Xerox Phaser 7300's. There was of course no plugin to tell us of toner was low and such for this printer. Well cool thing is the printer runs a webpage that has a page where you can see the status of either OK, LOW, or Empty on the toner and fusers. I needed to check if the page says "Empty". If it said "Empty" we need a "Critical" state if not then we are good and give a "OK" state. Well Nagios has a plugin that can check strings on a webpage. I thought fantastic I'll just check for "Empty" and if so set it to give give a critical.

Well thing is the check_http program can check for a string on a webpage but when it finds it it gives an "OK" response. This postive response "OK" is good for when a string you looking for is supposed to be there but not good if you want a negitave response "Critical" if the string is there. Well, check_http did not have that function it only gave positive responses to finding the string. So I've heard that C is like Perl in some ways so I should be able to put a "!" in front of the string check in the source code to have it give a negative response if the string is on the page.

Well lucky me C and Perl share many of the same operators and the work the same. I made a new variable, added in a new switch at the top for my negitave response string check, and slapped in another "If" statement with the negitave check, and added the string output to the --help command line. Recompiled. And walla! Works like a charm! Now we can check our Xerox printers and see if they are out of supplies.

So if it were not for Open Source I would not be able to add my own needed features. I've always thought it was cool but it never hit home like this before.

The diff for the check_http is below. It was done on version 1.4.3 of Nagios Plugins.

85a86
> char string_noexpect[MAX_INPUT_BUFFER] = "";
172a174
>     {"nostring", required_argument, 0, 'g'},
207c209
<     c = getopt_long (argc, argv, "Vvh46t:c:w:A:k:H:P:T:I:a:e:p:s:R:r:u:f:C:nlLSm:M:N", longopts, &option);
---
>     c = getopt_long (argc, argv, "Vvh46t:c:w:A:k:H:P:T:I:a:e:g:p:s:R:r:u:f:C:nlLSm:M:N", longopts, &option);
327a330,333
>     case 'g': /* string or substring */
>       strncpy (string_noexpect, optarg, MAX_INPUT_BUFFER - 1);
>       string_noexpect[MAX_INPUT_BUFFER - 1] = 0;
>       break;
994a1001,1017
>
>    if (strlen (string_noexpect)) {
>             if (!strstr (page, string_noexpect)) {
>                     printf (_("HTTP OK %s - %.3f second response time %s%s|%s %s\n"),
>                             status_line, elapsed_time,
>                             timestamp, (display_html ? "</A>" : ""),
>                             perfd_time (elapsed_time), perfd_size (pagesize));
>                     exit (STATE_OK);
>             }
>             else {
>                     printf (_("CRITICAL - string found%s|%s %s\n"),
>                             (display_html ? "</A>" : ""),
>                             perfd_time (elapsed_time), perfd_size (pagesize));
>                     exit (STATE_CRITICAL);
>             }
>     }
>
1259a1283,1284
>  -g, --nostring\n\
>    String not to expect in the content\n\
1344c1369
<   printf ("       [-s string] [-l] [-r <regex> | -R <case-insensitive regex>] [-P string]\n");
---
>   printf ("       [-s string] [-g string] [-l] [-r <regex> | -R <case-insensitive regex>] [-P string]\n");

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