FAQ - Frequently Asked Questions

Q: Since I'm using MK Livestatus Nagios sometimes stops to execute checks. What's wrong here?

A: That is due to a non thread safe implemention of how Nagios sets environment macros. You need to disable them in nagios.cfg:

enable_environment_macros=0

If you are using those macros (e.g. in notification scripts), you have to rewrite them using arguments and normal macros, such as $HOSTADDRESS$.

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: 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: The service_groups only assigns services to existing Nagios' service groups. The creation of sourcegroup definitions for Nagios is an optional feature. You can activate it by setting:

define_servicegroups = True

The same holds true for host groups and contact groups.

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

A: Simply set generate_hostconf to False in main.mk:

generate_hostconf = False

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. If you want to write native checks like this shipped with Check_MK, please have a look into our tutorial for writing checks.

Q: My virus scanner detects a virus or rootkit in check_mk_agent.exe. Does the agent really contain 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.*" ] )
]

Q: I cannot get Livestatus to run on FreeBSD. What's up here?

A:On FreeBSD Nagios seem to disable the event broker per default. You have to make shure that it is enabled when compiling Nagios. Add --enable-event-broker to your call of ./configure.

Q: The Windows agent hangs and cannot be restarted. But I cannot reboot the whole server. What now?

A:This can happen when you use your own local checks or plugins on windows. In some cases Windows opens a window on the server console. Sometimes this is nodepad.exe. Close that window and the agent will be fine again.