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MuninLite

MuninLite is a standalone shell script implementing the Munin protocol and containing a few basic plugins out of the box.

It can run as an inetd-based service over TCP or a simple executable script communicating via stdin/stdout. The latter does not require root privileges.

Project scope

MuninLite is supposed to be a minimal portable and shell-based implementation of munin-node. It provides a small set of essential plugins suitable for basic monitoring of a host. Additionally external plugins can be used. Only essential tools (e.g. the ones provided by busybox) should be required for MuninLite.

Missing features (by design)

The following features of the official munin-node implementation are not included (see "Project scope" above):

  • no configuration per plugin (e.g. environment variables or reduced privileges)
  • no host-based access control for incoming requests (may be configured via /etc/hosts.allow or firewall rules)
  • no advanced plugin state tracking (e.g. killing a plugin process after a timeout)

Installation

Build requirements

  • Make
  • Perl

Installation

Download source and unpack it.

Assemble the MuninLite shell script by running make:

$ make

You may assemble a reduced script by including only specific plugins:

$ make PLUGINS="cpu load uptime"

Run make install or simply copy muninlite to a suitable location.

make install

Two typical ways of using MuninLite as a munin-node replacement are:

  • direct execution: suitable for remote hosts lacking root access (e.g. shared host)
  • TCP service via inetd/xinetd: providing a service that is accessible via TCP (like munin-node)

Both approaches are detailed below.

Installation for direct execution

Configure the address setting of the node in the master's configuration with a suitable transport, e.g.:

[some.host.tld]
    address ssh://node-a.example.org/usr/local/bin/muninlite

The above example causes the master to connect to the node via ssh and to execute the MuninLite script directly. The running script responds to request from standard input just like it would do as a TCP service via inetd/xinetd.

Installation as a TCP service (inetd/xinetd)

Add munin port to /etc/services (in case it is missing):

echo "munin           4949/tcp        lrrd            # Munin" >>/etc/services

Configure inetd or xinetd to fork this script for request on the munin port (4949).

Sample configuration for xinetd is located in examples/xinetd.d/munin:

cp examples/xinetd.d/munin /etc/xinetd.d
killall -HUP xinetd

Sample configuration for inetd is located in examples/inetd.conf:

cat examples/inetd.conf >> /etc/inetd.conf
killall -HUP inetd

Restrict access to munin port using hosts.allow and hosts.deny or add a rule to your favorite firewall config. Examples of hosts.allow/deny settings is provided in the examples directory.

Iptables might be set with something like this:

iptables -A INPUT -p tcp --dport munin --source 10.42.42.25 -j ACCEPT

Test

To test the script, just run it (/usr/local/bin/muninlite):

$ /usr/local/bin/muninlite
# munin node at localhost.localdomain
help
# Unknown command. Try list, nodes, config, fetch, version or quit
list
df cpu if_eth0 if_eth1 if_err_eth0 if_err_eth1 load memory
version
munins node on example.org version: 0.0.5 (muninlite)
quit

An (x)inetd setup can be tested via telnet or netcat:

# telnet localhost 4949
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
# munin node at localhost.localdomain
help
# Unknown command. Try list, nodes, config, fetch, version or quit
list
df cpu if_eth0 if_eth1 if_err_eth0 if_err_eth1 load memory
version
munins node on example.org version: 0.0.5 (muninlite)
quit
Connection closed by foreign host.

Configuration

Plugin configuration

MuninLite does not support explicit configurations per plugin (as munin-node does).

But the file /etc/munin/muninlite.conf (if it exists) is sourced as a shell script during the execution of MuninLite.

This optional configuration file allows a variety of customizations:

  • override integrated plugins (by redefining their functions, e.g. config_if and fetch_if)
  • disable integrated plugins (e.g. PLUGINS=${PLUGINS/ wireless / })
  • overwrite configuration variables for integrated plugins (e.g. NTP_PEER or DF_IGNORE_FILESYSTEM_REGEX)
  • specify configuration settings required for external plugins (provided in /etc/munin/plugins/): export FOO_SERVICE=http://localhost:7123

External plugins

MuninLite includes a set of integrated plugins. In addition it is possible to expose additional plugins (just like the official munin-node implementation). By default all executables files (or symlinks) below the directory /etc/munin/plugins are treated as plugins.

Munin master configuration

Configure /etc/munin/munin.conf on you munin master as you would for a regular munin-node. If you configured MuninLite as a TCP service (e.g. via inetd/xinetd):

[some.host.tld]
    address 10.42.42.25
    use_node_name yes

In case of direct execution of MuninLite on the remote host (without a TCP service), you need to configure a transport and execute the script directly:

[some.host.tld]
    address ssh://10.42.42.25/usr/local/bin/muninlite
    use_node_name yes

The ssh transport obviously requires the use of authorized_keys on the host running MuninLite.

License and copyright

MuninLite is released under GPLv2 (see LICENSE file).