FAQ - Frequently Asked Questions

Q: Since I began using check_mk my Nagios logfile is rapidly growing. Why?

A: For each check Nagios sends an external command to Nagios with a passive service check. This is a speciality of check_mk. If you have enabled log messages for these two events, you'll get two logfile entries per check per check interval. Solution: turn off logging for passive checks and external commands in your Nagios configuration:

log_external_commands=0
log_passive_checks=0

Q: I tried the check_mk_agent.exe for Windows but it always crashes at the first usage.

A: This seems due to a problem with the MinGW-cross compiler. Please use the Agent of version 1.0.28 or later.

Q: The memory check says that 120% of my RAM are used. How can that be?

A: The amount of memory used up by processes includes the used swap space. Consider you have 1 GB RAM and 2 GB swap space. Your processes use 1.2 GB virtual memory - some of that in RAM and some in swap. Then check_mk reports a memory usage of 120% - in relation to your RAM. Because that is what counts with respect to performance.

Q: Why does service_groups in main.mk not create Nagios service groups?

A: service_groups only assigns services to existing Nagios' service groups. The sourcegroup definitions for Nagios have to be done manually by you. That is not a bug but indended to be so. It makes you more flexible. You can use all Nagios configuration variables for the service groups. Also you can give your service groups nice descriptions. A simple definition for a service group in Nagios looks like this:

define servicegroup {
   servicegroup_name  db
   alias              Database Services
}

Q: How can I just create the service definitions for Nagios - and leave out the host definitions?

A: Just call check_mk with the options -S and -C instead of -U (the option -U combines -S, -H and -C). You can let check_mk create the service definitions directly into your Nagios configuration directory:

root@linux# check_mk -C
root@linux# check_mk -S > /etc/nagios/conf.d/check_mk_services.cfg

Q: How can I write my own checks with check_mk?

A:Try out the Local checks. They are an easy way to integrate custom checks into check_mk without knowning about the internals of check_mk.

Q: My virus scanner detects a virus or rootkit in check_mk_agent.exe. Does the agent really conain a virus?

A:We are not aware that our agent has ever been affected by any malware. But there are some scanners out there that seem to find code created by MinGW suspicious. We are using MinGW for compiling the agent, since that compiler is freely available under GPL on Windows and the binaries it produces do not need any special DLL.

If you do not trust our precompiled agent, you can compile it yourself from the sources. MinGW is available on its homepage. On your Nagios host where you installed check_mk you'll find the source code check_mk_agent.cc and a Makefile in /usr/share/check_mk/agents. Copy the two files into your MinGW home directory on windows and simply type make.

Q: I have problems installing the agent on Windows Vista.

A:You might have to deactivate the UAC (User Account Control) while installing the agent. Once it is installed and running you can reactivate it.

Q: Does the windows agent also have a "magic number" for filesystems?

A:Yes. The magic number - as described in "How to check filesystems" applies to all agents providing a <<<df>>> section. Currently these are Linux, Windows and UNIX.

Q: How can I prevent some network interfaces from being checked?

A:Hide the according services from inventory as described in "Inventory". This can be done by putting one line into ignored_services. The following example will ignore all interfaces that contain vif:

ignored_services = [
  ( ALL_HOSTS, [ "NIC .*vif.*" ] )
]