NAME

collectd-lua - Documentation of collectd's "Lua plugin"

SYNOPSIS

  LoadPlugin lua
  # ...
  <Plugin lua>
    BasePath "/path/to/your/lua/scripts"
    Script "script1.lua"
    Script "script2.lua"
  </Plugin>

DESCRIPTION

The "Lua plugin" embeds a Lua interpreter into collectd and provides an interface to collectd's plugin system. This makes it possible to write plugins for collectd in Lua. This is a lot more efficient than executing a Lua script every time you want to read a value with the "exec plugin" (see collectd-exec(5)) and provides a lot more functionality, too.

The minimum required Lua version is 5.1.

CONFIGURATION

LoadPlugin Lua: Loads the Lua plugin.
BasePath Name: The directory the "Lua plugin" looks in to find script Script. If set, this is also prepended to package.path.
Script Name: The script the "Lua plugin" is going to run. If BasePath is not specified, this needs to be an absolute path.

WRITING YOUR OWN PLUGINS

Writing your own plugins is quite simple. collectd manages plugins by means of dispatch functions which call the appropriate callback functions registered by the plugins. Any plugin basically consists of the implementation of these callback functions and initializing code which registers the functions with collectd. See the section "EXAMPLES" below for a really basic example. The following types of callback functions are implemented in the Lua plugin (all of them are optional):

read functions: These are used to collect the actual data. It is called once per interval (see the Interval configuration option of collectd). Usually it will call collectd.dispatch_values to dispatch the values to collectd which will pass them on to all registered write functions. If this function does not return 0, interval between its calls will grow until function returns 0 again. See the MaxReadInterval configuration option of collectd.
write functions: These are used to write the dispatched values. They are called once for every value that was dispatched by any plugin.

FUNCTIONS

The following functions are provided to Lua modules:

register_read(callback): Function to register read callbacks. The callback will be called without arguments. If this callback function does not return 0 the next call will be delayed by an increasing interval.
register_write(callback): Function to register write callbacks. The callback function will be called with one argument passed, which will be a table of values. If this callback function does not return 0 next call will be delayed by an increasing interval.
log_error, log_warning, log_notice, log_info, log_debug(message): Log a message with the specified severity.

EXAMPLES

A very simple read function might look like:

  function read()
    collectd.log_info("read function called")
    t = {
        host = 'localhost',
        plugin = 'myplugin',
        type = 'counter',
        values = {42},
    }
    collectd.dispatch_values(t)
    return 0
  end

A very simple write function might look like:

  function write(vl)
    for i = 1, #vl.values do
      collectd.log_info(vl.host .. '.' .. vl.plugin .. '.' .. vl.type .. ' ' .. vl.values[i])
    end
    return 0
  end

To register those functions with collectd:

  collectd.register_read(read)     -- pass function as variable
  collectd.register_write("write") -- pass by global-scope function name

AUTHOR

The "Lua plugin" has been written by Julien Ammous <j.ammous at gmail.com>, Florian Forster <octo at collectd.org> and Ruben Kerkhof <ruben at rubenkerkhof.com>.

This manpage has been written by Ruben Kerkhof <ruben at rubenkerkhof.com>. It is based on the collectd-perl(5) manual page by Florian Forster <octo at collectd.org> and Sebastian Harl <sh at tokkee.org>.