check_dhcp permissions issue even when run as root

[Maxwell Carey]

On 06/05/2013 10:01 AM, Maxwell Carey wrote:
> When I run check_dhcp as the nagios user, I get the following error:
>
> $ /usr/local/nagios/libexec/check_dhcp
> Error: Could not bind socket to interface eth0.  Check your privileges...
>
> Even when I run the plugin as the root user, I get the same error, so I
> suspect this is not really a file permissions issue.
As I suspected, this had nothing to do with file permissions. I was 
misled by the second part of the error message, when I should have paid 
closer attention to the "Could not bind socket to interface eth0" part. 
Our Nagios host doesn't have an interface named eth0. Doh! When I add 
the -i <interface> flag, I can run the plugin successfully from the 
command line as root and as nagios.

But as it turns out, I diagnosed the initial issue incorrectly. Nagios 
was actually running check_dhcp with the correct interface name, but 
still spitting out an error about permissions. The cause? I recently 
upgraded Nagios by installing the new version in a new directory and 
copying over the config files from the old version (I did not do an 
in-place upgrade). When I turned on debugging I could see that all of 
the plugins being used were from the old install, where apparently SUID 
was not set correctly on check_dhcp. When I copied over the config 
files, I didn't update resource.cfg, which contains the definition of 
$USER1$ and was still pointing to the old directory. Problem solved (and 
some good lessons learned to boot).

--Max Carey

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