Tag: munin

One Possible Reason for Missing Munin Graphs

We’re currently expanding our munin reporting cluster at Derdubor, but after installing munin-node on one of our servers we never got any graphs. The only section available on the munin server was “Other”, and that didn’t contain any information at all (which indicates that you’re not getting any response from the server).

The first step I make when trying to debug a munin connection is to telnet into the munin port, as this confirms that the two servers are able to talk to each other and that the munin daemon listens to the correct interface and port.

# telnet localhost 4949
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Connection closed by foreign host.
#

The connection was established, but then munin closed the connection as soon as it was created. This usually means one thing: the host you’re connecting from isn’t added to the cidr_allow list or the allow list, or in the denied hosts list. This time it meant neither, the host was added and we didn’t have any denied hosts list.

The next step was to take a look at the munin-node.log in /var/log/munin (at least under under debian).

The last message was:


User "ejabberd" in configuration file "/etc/munin/plugin-conf.d/munin-node" nonexistant. Skipping plugin. at /usr/sbin/munin-node line 615, line 83.
Something wicked happened while reading "/etc/munin/plugins/munin-node". Check the previous log lines for spesifics. at /usr/sbin/munin-node line 261, line 83.

We don’t have ejabberd installed, but the ejabberd config reference was apparently added to the configuration file in /etc/munin/plugin-conf.d/munin-node. This made our version of munin-node barf, as the user it reference wasn’t available.

Next step was to remove the section from the file and restarting munin-node:

/etc/init.d/munin-node restart

After restarting munin, I did the telnet check again:

# telnet localhost 4949
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
# munin node at example.com
.
fetch load
load.value 0.02
.
quit
Connection closed by foreign host.
#

Wait 10 – 15 minutes and you should start seeing graphs again – if this actually were your problem. Probably not (and then you should probably read Debuggning Munin Plugins and other documentation on the Wiki). But if it were, you’ll be happy happy joy joy now.

Writing a Munin Plugin

I have to admit something. I’ve become addicted.

One of the things I finally got around to doing while living the quiet life over the christmas holiday was to dive a bit further into Munin – a simple framework for collecting information from your computers and servers and making nice graphs that you can watch while you’re bored.

I’m not going to write a lot about how you can create your own Munin plugin to create your own graphs, as they have a very simple tutorial giving you all the basics about writing Munin plugins themselves. The only thing you need to remember are these two tidbits:

  1. When Munin first registers your plugin, it runs your script with config as the only argument. This provides Munin with the name of the graph, the labels and names (keys) of the graphs you’re providing values for, information about the axis, etc.
  2. When Munin runs your script without the config argument, it expects you to give it values for the keys you provided it in the configuration.

You enable and disable plugins by creating symlinks in /etc/munin/plugins (at least under debian / ubuntu), and plugins are usually stored in /usr/share/munin/plugins.

I keep my plugins archived together with the rest of the repository for my web projects, and then either symlink the content into the plugins-directory or create a simple wrapper script that changes the current directory to the location of the script and then invokes it (to make the current working directory be correct).

A very simple bash script that does this – and passes through any parameters given to the script:

#!/bin/bash
cd  && php ./