Check_Http Host vs URL Question... SOLVED


Hey guys, I have a question regarding a possible workaround or maybe even a misconfiguration on my behalf.
I am trying to monitor a URL and associate it with a Host.
However the URL is calling the page from another host.

Host IP is (Host I am tyring to associate service with)
URL is….

define service{
use content-service ; Inherit default values from a template
host_name mecprvagswebw01
_type ContentCheck
service_description MECPRVAGSWEBW01_90_00PopC_US2_Sp
check_command check_http! -s -H -u ‘’ -w 15 -c 20 --string=PASS

I get a 404 error

I was able to get around this content check by changing the Host IP under 'Host Definintion" to the address.

Is there any way to get around this? I want the host definintion to have the correct IP ( but have the check_http url stay the same.

Hope that makes sense. Thanks!



try dropping the -H part.

the service has to be associated to the host you want it to appear as in Nagios, nagios doesn’t care WHAT host you are checking…


Hi Luca, Thanks for you reply.

I tried what you suggested and Nagios threw an output of:

check_http: You must specify a server address or host name
Usage: check_http -H | -I -u ] -p ]
-w ] -c ] -t ] -L]
-a auth] -f <ok | warn | critcal | follow | sticky | stickyport>]
-e ] -s string] -l] -r | -R ]
-P string] -m <min_pg_size>:<max_pg_size>] -4|-6] -N] -M ]
-A string] -k string] -S] -C ] -T ] -j method]

So I changed the -H to -I and there was still a 404 error:

HTTP WARNING: HTTP/1.1 404 Not Found - 1799 bytes in 0.150 second response time |time=0.149694s;15.000000;20.000000;0.000000 size=1799B;;;0

I tried removing the post string (-s), just to test the URL availability and still got the above message.

It seems that Nagios just refuses to monitor the URL if the Host or IP does not match the URL.
This Monitor does work if I put the IP of the URL as Host (-H) or IP (-I)

What I was thinking of doing is defining the Host 2x. Once with the correct IP address for system monitoring, and the other with the URL IP for http content monitoring. But that would be too redundant and would crowd the Dashboard. Also, I have like 100+ servers to configure like these, each with 70+ content check monitors. This is why I gotta try to figure this out before I populate Nagios.



 -s, --string=STRING
    String to expect in the content
 -P, --post=STRING
    URL encoded http POST data

i wanted to try that but they are private addresses so i can’t :slight_smile:
If you open a browser window and copy your URL does it work?


Aw yes Luca, they are private addresses used for internal monitoring.
How its set up to run is, the URL is called from a custom SOAP monitoring application server ( as configured in the URL.
It then calls the application SOAP url from the monitored server ( and instead of returning the extremely long SOAP results, it has its own logic to compare the results and either return a “PASS” or “FAIL” response. This is how we do most of our content checks. We configure our monitors in our primary monitoring tool (EM7) to look for the string “PASS”.

So to answer you question, YES. If I paste the URL in a browser it works fine. It comes up with a PASS.

Should I be possible to monitor this kind of URL?

I tried to make is as basic as possible to see if Nagios will even return an OK status for the URL. No luck.
Like I said… it works, but only if the Host definition is set for the address, and not the address that the host actually has.

Weird huh! LOL!

Thanks for your help Luca.



Here is a simple example of works for me, and what doesnt. The only difference… the host IP address. (-I)

This works!

./check_http -I ** **-u ‘’ -w 15 -c 20

HTTP OK: HTTP/1.1 200 OK - 2552 bytes in 0.558 second response time |time=0.558224s;15.000000;20.000000;0.000000 size=2552B;;;0

This does not work! (This is what I want to try to make work)

./check_http -I ‘’ -w 15 -c 20

HTTP WARNING: HTTP/1.1 **404 Not Found **- 1799 bytes in 0.184 second response time |time=0.183842s;15.000000;20.000000;0.000000 size=1799B;;;0


if you use the -u option… why do you need -I ?
Isn’t -u enough?


Ya Luca, thats what I thought too… however if I remove it, here is what I get.

./check_http -u ‘’ -w 15 -c 20

check_http: You must specify a server address or host name
Usage: check_http -H | -I -u ] -p ]
-w ] -c ] -t ] -L]
-a auth] -f <ok | warn | critcal | follow | sticky | stickyport>]
-e ] -s string] -l] -r | -R ]
-P string] -m <min_pg_size>:<max_pg_size>] -4|-6] -N] -M ]
-A string] -k string] -S] -C ] -T ] -j method]

All of this is being done from command line on Nagios host.


in this case going back to your two examples above… why would you want to use an IP address (-I) different than the one in the -u option ? :slight_smile:

use -I $HOSTNAME$ -u $ARG1$ and you should be ok. or not?


Luca, thanks for all of your help.

I contacted one of our Linux guys here and he helped me to solve the issue.

After some troubleshooting, he told me to use both the -H and -I options.
The -H to define the actual host name of the server I am monitoring, and the -I option to define the SOAP monitoring server. See below.

*./check_http -s **-H mecprvagswebw01 **-I -u ‘’ -w 15 -c 20 --string=PASS

HTTP OK: HTTP/1.1 200 OK - 2554 bytes in 2.006 second response time |time=2.005849s;15.000000;20.000000;0.000000 size=2554B;;;0*

To answer your last question. Our setup here is a unique one. We use that custom application server (SOAP) to check the application on our systems instead of going directly to the server. From the web page ( there is a list of all of our servers, each with 70+ content check links. We just click the specific link for the server we want to check, in this case (ESRI_00-08PopGrwth_US_2D), it goes out to that server and returns a Pass or Fail.
I wanted to figure this out so that on the Nagios GUI, I can have all of the content checks listed under each server.

I appreciate your help. You really helped me to get my creative juices flowing, which helped the Linux guy figure it out.



your not working example earlier still doesn’t make sense to me, but it’s ok :slight_smile:
Just glad it worked :smiley: