Munin and Nagios

Munin integrates perfectly with Nagios. There are, however, a few things of which to take notice. This article shows example configurations and explains the communication between the systems.

Setting up Nagios passive checks

Receiving messages in Nagios

First you need a way for Nagios to accept messages from Munin. Nagios has exactly such a thing, namely the NSCA which is documented here: NSCA.

NSCA consists of a client (a binary usually named send_nsca and a server usually run from inetd. We recommend that you enable encryption on NSCA communication.

You also need to configure Nagios to accept messages via NSCA. NSCA is, unfortunately, not very well documented in Nagios’ official documentation. We’ll cover writing the needed service check configuration further down in this document.

Configuring Nagios

In the main config file, make sure that the command_file directive is set and that it works. See External Command File for details.

Below is a sample extract from nagios.cfg:


The /var/run/nagios directory is owned by the user nagios runs as. The nagios.cmd is a named pipe on which Nagios accepts external input.

Configuring NSCA, server side

NSCA is run through some kind of (x)inetd.

Using inetd

the line below enables NSCA listening on port 5667:

5667            stream  tcp     nowait  nagios  /usr/sbin/tcpd  /usr/sbin/nsca -c /etc/nsca.cfg --inetd

Using xinetd

the lines below enables NSCA listening on port 5667, allowing connections only from the local host:

# description: NSCA (Nagios Service Check Acceptor)
service nsca
 flags           = REUSE
 type    = UNLISTED
 port    = 5667
 socket_type     = stream
 wait            = no

 server          = /usr/sbin/nsca
 server_args     = -c /etc/nagios/nsca.cfg --inetd
 user            = nagios
 group           = nagios

 log_on_failure  += USERID

 only_from       =


The file /etc/nsca.cfg defines how NSCA behaves. Check in particular the nsca_user and command_file directives, these should correspond to the file permissions and the location of the named pipe described in nagios.cfg.


Configuring NSCA, client side

The NSCA client is a binary that submits to an NSCA server whatever it received as arguments. Its behaviour is controlled by the file /etc/send_nsca.cfg, which mainly controls encryption.

You should now be able to test the communication between the NSCA client and the NSCA server, and consequently whether Nagios picks up the message. NSCA requires a defined format for messages. For service checks, it’s like this:


Below is shown how to test NSCA.

$ echo -e "\ttest\t0\t0" | /usr/sbin/send_nsca -H localhost -c /etc/send_nsca.cfg
1 data packet(s) sent to host successfully.

This caused the following to appear in /var/log/nagios/nagios.log:

[1159868622] Warning:  Message queue contained results for service 'test' on host ''.  The service could not be found!

Sending messages from Munin

Messages are sent by munin-limits based on the state of a monitored data source: OK, Warning, Critical and Unknown (O/W/C/U).

Configuring munin.conf

Nagios uses the above mentioned send_nsca binary to send messages to Nagios. In /etc/munin/munin.conf, enter this:

contacts nagios
contact.nagios.command /usr/bin/send_nsca -H -c /etc/send_nsca.cfg


Be aware that the -H switch to send_nsca appeared sometime after send_nsca version 2.1. Always check send_nsca --help!

Configuring Munin plugins

Lots of Munin plugins have (hopefully reasonable) values for Warning and Critical levels. To set or override these, you can change the values in munin.conf.

Configuring Nagios services

Now Nagios needs to recognize the messages from Munin as messages about services it monitors. To accomplish this, every message Munin sends to Nagios requires a matching (passive) service defined or Nagios will ignore the message (but it will log that something tried).

A passive service is defined through these directives in the proper Nagios configuration file:

active_checks_enabled           0
passive_checks_enabled          1

A working solution is to create a template for passive services, like the one below:

define service {
        name                            passive-service
        active_checks_enabled           0
        passive_checks_enabled          1
        parallelize_check               1
        notifications_enabled           1
        event_handler_enabled           1
        register                        0
        is_volatile                     1

When the template is registered, each Munin plugin should be registered as per below:

define service {
        use                             passive-service
        host_name                       foo
        service_description             bar
        check_period                    24x7
        max_check_attempts              3
        normal_check_interval           3
        retry_check_interval            1
        contact_groups                  linux-admins
        notification_interval           120
        notification_period             24x7
        notification_options            w,u,c,r
        check_command                   check_dummy!0


  • host_name is either the FQDN of the host_name registered to the Nagios plugin, or the host alias corresponding to Munin’s notify_alias directive. The host_name must be registered as a host in Nagios.
  • service_description must correspond to the plugin’s name, and for Nagios to be happy it shouldn’t have any special characters. If you’d like to change the service description from Munin, use notify_alias on the data source. Available in Munin-1.2.5 and later.

A working example is shown below:

        df.notify_alias Filesystem usage
        # The above changes from Munin's default "Filesystem usage (in %)"

What characters are allowed in a Nagios service definition?

service_description: This directive is used to define the description of the service, which may contain spaces, dashes, and colons (semicolons, apostrophes, and quotation marks should be avoided). No two services associated with the same host can have the same description. Services are uniquely identified with their host_name and service_description directives.


This means that lots of Munin plugins will not be accepted by Nagios. This limitation impacts every plugin with special characters in them, e.g. ‘(’, ‘)’, and ‘%’. Workarounds are described in ticket #34 and the bug has been fixed in the Munin code in changeset 1081.

Alternatively you can use to gather fresh data from nagios instead of check_dummy.

Sample munin.conf

To illustrate, a (familiar) sample munin.conf configuration file shows the usage:

contact.nagios.command /usr/local/nagios/bin/send_nsca -c /usr/local/nagios/etc/send_nsca.cfg -to 60

contacts none                  # Disables warning on a system-wide basis.

  contacts nagios              # Enables warning through the "nagios" contact for the group

  address localhost
  contacts none                # Disables warning for all plugins on the host

  df.contacts none             # Disables warning on the df plugin only.
  df.notify_alias Disk usage   # Uses the title "Disk usage" when sending warnings through munin-limits
                               # Useful if the receiving end does not accept all kinds of characters
                               # NB: Only available in Munin-1.2.5 or with the patch described in ticket 34.

Setting up Nagios active checks

Use check_munin.p to get data from munin-node directly into nagios and then use it as a regular check plugin. Basically munin-node become a kind of snmp agent with a lot of preconfigured plugins.