Manpage `collectd-perl(5)`

NAME
SYNOPSIS
DESCRIPTION
CONFIGURATION
WRITING YOUR OWN PLUGINS
DATA TYPES
METHODS
GLOBAL VARIABLES
EXPORTS
EXAMPLES
NOTES
CAVEATS
KNOWN BUGS
SEE ALSO
AUTHOR

NAME

collectd-perl - Documentation of collectd's perl plugin

SYNOPSIS

  LoadPlugin perl
  # ...
  <Plugin perl>
    IncludeDir "/path/to/perl/plugins"
    BaseName "Collectd::Plugin"
    EnableDebugger ""
    LoadPlugin "FooBar"
  </Plugin>

DESCRIPTION

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

CONFIGURATION

LoadPlugin Plugin: Loads the Perl plugin Plugin. This does basically the same as use would do in a Perl program. As a side effect, the first occurrence of this option causes the Perl-interpreter to be initialized.
BaseName Name: Prepends Name:: to all plugin names loaded after this option. This is provided for convenience to keep plugin names short.
EnableDebugger Package[=option,...]: Run collectd under the control of the Perl source debugger. If Package is not the empty string, control is passed to the debugging, profiling, or tracing module installed as Devel::Package. A comma-separated list of options may be specified after the ``='' character. Please note that you may not leave out the Package option even if you specify ``''. This is the same as using the -d:Package command line option.; See perldebug for detailed documentation about debugging Perl.; This option does not prevent collectd from daemonizing, so you should start collectd with the -f command line option. Else you will not be able to use the command line driven interface of the debugger.
IncludeDir Dir: Adds Dir to the @INC array. This is the same as using the -IDir command line option or use lib Dir in the source code. Please note that it only has effect on plugins loaded after this option.

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 known to collectd (all of them are optional):

init functions: This type of functions is called once after loading the module and before any calls to the read and write functions. It should be used to initialize the internal state of the plugin (e. g. open sockets, ...). If the return value evaluates to false, the plugin will be disabled.
read functions: This type of function is used to collect the actual data. It is called once per interval (see the Interval configuration option of collectd). Usually it will call plugin_dispatch_values to dispatch the values to collectd which will pass them on to all registered write functions. If the return value evaluates to false the plugin will be skipped for an increasing amount of time until it returns true again.
write functions: This type of function is used to write the dispatched values. It is called once for each call to plugin_dispatch_values.
flush functions: This type of function is used to flush internal caches of plugins. It is usually triggered by the user only. Any plugin which caches data before writing it to disk should provide this kind of callback function.
log functions: This type of function is used to pass messages of plugins or the daemon itself to the user.
notification function: This type of function is used to act upon notifications. In general, a notification is a status message that may be associated with a data instance. Usually, a notification is generated by the daemon if a configured threshold has been exceeded (see the section ``THRESHOLD CONFIGURATION'' in collectd.conf(5) for more details), but any plugin may dispatch notifications as well.
shutdown functions: This type of function is called once before the daemon shuts down. It should be used to clean up the plugin (e.g. close sockets, ...).

Any function (except log functions) may set the $@ variable to describe errors in more detail. The message will be passed on to the user using collectd's logging mechanism.

See the documentation of the plugin_register method in the section ``METHODS'' below for the number and types of arguments passed to each callback function. This section also explains how to register callback functions with collectd.

To enable a plugin, copy it to a place where Perl can find it (i. e. a directory listed in the @INC array) just as any other Perl plugin and add an appropriate LoadPlugin option to the configuration file. After restarting collectd you're done.

DATA TYPES

The following complex types are used to pass values between the Perl plugin and collectd:

Data-Set

A data-set is a list of one or more data-sources. Each data-source defines a name, type, min- and max-value and the data-set wraps them up into one structure. The general layout looks like this:

  [{
    name => 'data_source_name',
    type => DS_TYPE_COUNTER || DS_TYPE_GAUGE,
    min  => value || undef,
    max  => value || undef
  }, ...]

Value-List

A value-list is one structure which features an array of values and fields to identify the values, i. e. time and host, plugin name and plugin-instance as well as a type and type-instance. Since the ``type'' is not included in the value-list but is passed as an extra argument, the general layout looks like this:

  {
    values => [123, 0.5],
    time   => time (),
    host   => $hostname_g,
    plugin => 'myplugin',
    plugin_instance => '',
    type_instance   => ''
  }

Notification

A notification is one structure defining the severity, time and message of the status message as well as an identification of a data instance:

  {
    severity => NOTIF_FAILURE || NOTIF_WARNING || NOTIF_OKAY,
    time     => time (),
    message  => 'status message',
    host     => $hostname_g,
    plugin   => 'myplugin',
    type     => 'mytype',
    plugin_instance => '',
    type_instance   => ''
  }

METHODS

The following functions provide the C-interface to Perl-modules. They are exported by the ``:plugin'' export tag (see the section ``EXPORTS'' below).

plugin_register (type, name, data): Registers a callback-function or data-set.; type can be one of:
plugin_unregister (type, plugin): Removes a callback or data-set from collectd's internal list of functions / datasets.
plugin_dispatch_values (type, value-list): Submits a value-list of type type to the daemon. If the data-set type is found (and the number of values matches the number of data-sources) then the type, data-set and value-list is passed to all write-callbacks that are registered with the daemon.
plugin_flush ([timeout => timeout,] [plugins => ...]): Flush one or more plugins. timeout is passed on to the registered flush-callbacks. If omitted, -1 is used. If the plugins argument has been specified, only named plugins will be flushed. The argument's value may either be a string or a reference to an array of strings.
plugin_flush_one (timeout, plugin): This is identical to using ``plugin_flush (timeout => timeout, plugins => plugin''.
plugin_flush_all (timeout): This is identical to using ``plugin_flush (timeout => timeout)''.
plugin_dispatch_notification (notification): Submits a notification to the daemon which will then pass it to all notification-callbacks that are registered.
plugin_log (log-level, message): Submits a message of level log-level to collectd's logging mechanism. The message is passed to all log-callbacks that are registered with collectd.
ERROR, WARNING, NOTICE, INFO, DEBUG (message): Wrappers around plugin_log, using LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO and LOG_DEBUG respectively as log-level.

GLOBAL VARIABLES

$hostname_g: As the name suggests this variable keeps the hostname of the system collectd is running on. The value might be influenced by the Hostname or FQDNLookup configuration options (see collectd.conf(5) for details).
$interval_g: This variable keeps the interval in seconds in which the read functions are queried (see the Interval configuration option).

Any changes to these variables will be globally visible in collectd.

EXPORTS

By default no symbols are exported. However, the following export tags are available (:all will export all of them):

:plugin

plugin_register ()
plugin_unregister ()
plugin_dispatch_values ()
plugin_flush ()
plugin_flush_one ()
plugin_flush_all ()
plugin_dispatch_notification ()
plugin_log ()
:types

TYPE_INIT
TYPE_READ
TYPE_WRITE
TYPE_FLUSH
TYPE_SHUTDOWN
TYPE_LOG
:ds_types

DS_TYPE_COUNTER
DS_TYPE_GAUGE
:log

ERROR ()
WARNING ()
NOTICE ()
INFO ()
DEBUG ()
LOG_ERR
LOG_WARNING
LOG_NOTICE
LOG_INFO
LOG_DEBUG
:notif

NOTIF_FAILURE
NOTIF_WARNING
NOTIF_OKAY
:globals

$hostname_g
$interval_g

EXAMPLES

Any Perl plugin will start similar to:

  package Collectd::Plugins::FooBar;

  use strict;
  use warnings;

  use Collectd qw( :all );

A very simple read function will look like:

  sub foobar_read
  {
    my $vl = { plugin => 'foobar' };
    $vl->{'values'} = [ rand(42) ];
    plugin_dispatch_values ('gauge', $vl);
    return 1;
  }

A very simple write function will look like:

  sub foobar_write
  {
    my ($type, $ds, $vl) = @_;
    for (my $i = 0; $i < scalar (@$ds); ++$i) {
      print "$vl->{'plugin'} ($vl->{'type'}): $vl->{'values'}->[$i]\n";
    }
    return 1;
  }

To register those functions with collectd:

  plugin_register (TYPE_READ, "foobar", "foobar_read");
  plugin_register (TYPE_WRITE, "foobar", "foobar_write");

See the section ``DATA TYPES'' above for a complete documentation of the data types used by the read and write functions.

NOTES

: Please feel free to send in new plugins to collectd's mailinglist at <collectd at verplant.org> for review and, possibly, inclusion in the main distribution. In the latter case, we will take care of keeping the plugin up to date and adapting it to new versions of collectd.; Before submitting your plugin, please take a look at http://collectd.org/dev-info.shtml.

CAVEATS

: collectd is heavily multi-threaded. Each collectd thread accessing the perl plugin will be mapped to a Perl interpreter thread (see threads(3perl)). Any such thread will be created and destroyed transparently and on-the-fly.; Hence, any plugin has to be thread-safe if it provides several entry points from collectd (i. e. if it registers more than one callback or if a registered callback may be called more than once in parallel). Please note that no data is shared between threads by default. You have to use the threads::shared module to do so.
: Each function name registered with collectd has to be available before the first thread has been created (i. e. basically at compile time). This basically means that hacks (yes, I really consider this to be a hack) like *foo = \&bar; plugin_register (TYPE_READ, "plugin", "foo"); most likely will not work. This is due to the fact that the symbol table is not shared across different threads.
: Each plugin is usually only loaded once and kept in memory for performance reasons. Therefore, END blocks are only executed once when collectd shuts down. You should not rely on END blocks anyway - use shutdown functions instead.

KNOWN BUGS

: Currently, it is not possible to flush a single Perl plugin only. You can either flush all Perl plugins or none at all and you have to use perl as plugin name when doing so.

AUTHOR

The perl plugin has been written by Sebastian Harl <sh at tokkee.org>.

This manpage has been written by Florian Forster <octo at verplant.org> and Sebastian Harl <sh at tokkee.org>.

Manpage collectd-perl(5)

Manpage `collectd-perl(5)`