Check_MK and OMD

OMD - The Open Monitoring Distribution

OMD - The Open Monitoring Distribution - is a successful project started in 2010 by Mathias Kettner. It is a distribution of several monitoring cores (Nagios, Icinga, Shinken) and addons the makes open source monitoring a lot easier while at the same time keeping all the flexibility that friends of Nagios & Co are used to.

OMD ist not a Linux distribution but just ships the components of the actual monitoring software. It comes as one single package. The official project homepage is omdistro.org. We also offer a subscription to a download of pre-built packages of OMD for more than a dozend Linux distributions bundled with all available Check_MK versions.

Check_MK is part of OMD. This article describes some of the specialities when using Check_MK within OMD.

Directories and files: what is where?

While manual installations of Check_MK have individual settings of all relevant directories and file paths, OMD uses non-configurable standardized paths. If you are new to OMD you might think that this is a drawback. But soon you will realize the advantages of this approach. One of them is that paths used in this article are valid for all OMD installations 'round the world.

Since we have one variable component in all paths - the name of your site - we will assume that:

• Your site has the name mysite
• We use ~ to abbreviate the sites home directory /omd/sites/mysite.

Paths used by Check_MK within OMD

~/etc/mk-livestatus/nagios.cfg	Configuration of Livestatus and Livecheck. This file is referred to by a symlink in ~/etc/nagios/nagios.d and will be included in nagios.cfg (OMD uses a modular nagios.cfg).
~/etc/mk-livestatus/xinetd.cfg	Configuration for Livestatus via TCP. This file is being used, when you have enabled LIVESTATUS_TCP via omd config. The most common change here is the setting for only_from.
~/etc/check_mk	Base directory for the configuration of Check_MK and Multisite. Here you will find main.mk and multisite.mk.
~/etc/check_mk/defaults	Installation settings of all components of Check_MK. This file is being created and dealt with by OMD. Do not change anything here.
~/var/check_mk	Variable data that is persisted over a reboot. Please note that OMD make consequent use of a memory based filesystem (tmpfs) in order to minimize IO. Some directories usually put below /var/lib/check_mk in manual installations are missing here.
~/tmp/check_mk/cache	Cached agent output from hosts
~/tmp/check_mk/counters	Current values of performance counters from hosts (needed by checks for computing rates and averages)
~/share/check_mk	Installation of Check_MK software (checks, modules, web pages, etc.)
~/share/check_mk/agents	Agents for the various operating systems
~/lib/mk-livestatus/livestatus.o	Livestatus broker module
~/lib/mk-livestatus/livecheck	Livecheck helper

The local-Hierarchy

One main difference of using Check_MK in OMD as opposed to a manual installation is the availability of the local hierarchy. It is a directory structure within each site that is used for (your) local extensions of Check_MK. You can install your own checks, Multisite-Plugins and other things directly into a site without modifying OMD and without root permissions. You can even override static files (images, stylesheets) for the web application by simply putting them into the correct directory.

Directories below ~/local/share/check_mk:

checks	Your own Check_MK checks
checkman	Man-pages for your checks
pnp-templates	Your own templates for PNP4Nagios
web/	Base directory for extensions and overrides of the Multisite GUI
web/htdocs/images	Put your versions of Multisite icons and images here
web/plugins	Base directory for various Multisite plugins:
web/plugins/dashboard	Definitions for your own dashboards
web/plugins/icons	Icon plugins for custom icons in Multisite views in the columns Host/Service-Icons
web/plugins/pages	Definitions for your own web applications that use the Multisite framework
web/plugins/perfometer	Your own Perf-O-Meters
web/plugins/sidebar	You own sidebar snapins
web/plugins/views	Plugins for Multisite views like own columns, filters, layouts, sorters and builtin views
web/plugins/wato	Plugins for WATO

Using MKPs in OMD

Check_MK has its own packager for managing extensions (like collections of own checks). Check_MK packages are calles MKPs and are easy to create and install. When you install an MKP within an OMD site then the file will automatically be put into the local structure of the site. You do not need root-permissions for installing MKPs. Please note, that MKPs are always local to one site.