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       collectd-perl - Documentation of collectd's "perl plugin"


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

           <Plugin FooBar>
             Foo "Bar"


       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.


       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. All Perl-
           based plugins provided with the collectd distributions reside in
           the "Collectd::Plugins" namespace.

       <Plugin Name> block
           This block may be used to pass on configuration settings to a Perl
           plugin. The configuration is converted into a config-item data type
           which is passed to the registered configuration callback. See below
           for details about the config-item data type and how to register

           The name identifies the callback. It is used literally and
           independent of the BaseName setting.

       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

       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 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):

       configuration functions
           This type of functions is called during configuration if an
           appropriate Plugin block has been encountered. It is called once
           for each Plugin block which matches the name of the callback as
           provided with the plugin_register method - see below.

       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

       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

       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.


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

           A config-item is one structure which keeps the information provided
           in the configuration file. The array of children keeps one entry
           for each configuration option. Each such entry is another config-
           item structure, which may nest further if nested blocks are used.

               key      => key,
               values   => [ val1, val2, ... ],
               children => [ { ... }, { ... }, ... ]

           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',
               min  => value || undef,
               max  => value || undef
             }, ...]

           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 (),
               interval => $interval_g,
               host   => $hostname_g,
               plugin => 'myplugin',
               type   => 'myplugin',
               plugin_instance => '',
               type_instance   => ''

           A notification is one structure defining the severity, time and
           message of the status message as well as an identification of a
           data instance. Also, it includes an optional list of user-defined
           meta information represented as (name, value) pairs:

               severity => NOTIF_FAILURE || NOTIF_WARNING || NOTIF_OKAY,
               time     => time (),
               message  => 'status message',
               host     => $hostname_g,
               plugin   => 'myplugin',
               type     => 'mytype',
               plugin_instance => '',
               type_instance   => '',
               meta     => [ { name => <name>, value => <value> }, ... ]

           A match-proc is one structure storing the callbacks of a "match" of
           the filter chain infrastructure. The general layout looks like

               create  => 'my_create',
               destroy => 'my_destroy',
               match   => 'my_match'

           A target-proc is one structure storing the callbacks of a "target"
           of the filter chain infrastructure. The general layout looks like

               create  => 'my_create',
               destroy => 'my_destroy',
               invoke  => 'my_invoke'


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

       plugin_register (type, name, data)
           Registers a callback-function or data-set.

           type can be one of:


           name is the name of the callback-function or the type of the data-
           set, depending on the value of type. (Please note that the type of
           the data-set is the value passed as name here and has nothing to do
           with the type argument which simply tells plugin_register what is
           being registered.)

           The last argument, data, is either a function name or an array-
           reference.  If type is TYPE_DATASET, then the data argument must be
           an array-reference which points to an array of hashes. Each hash
           describes one data-set. For the exact layout see Data-Set above.
           Please note that there is a large number of predefined data-sets
           available in the types.db file which are automatically registered
           with collectd - see types.db(5) for a description of the format of
           this file.

           Note: Using plugin_register to register a data-set is deprecated.
           Add the new type to a custom types.db(5) file instead. This
           functionality might be removed in a future version of collectd.

           If the type argument is any of the other types (TYPE_INIT,
           TYPE_READ, ...) then data is expected to be a function name. If the
           name is not prefixed with the plugin's package name collectd will
           add it automatically.  The interface slightly differs from the C
           interface (which expects a function pointer instead) because Perl
           does not support to share references to subroutines between

           These functions are called in the various stages of the daemon (see
           the section "WRITING YOUR OWN PLUGINS" above) and are passed the
           following arguments:

               The only argument passed is config-item. See above for the
               layout of this data type.

               No arguments are passed.

               The arguments passed are type, data-set, and value-list. type
               is a string. For the layout of data-set and value-list see

               The arguments passed are timeout and identifier. timeout
               indicates that only data older than timeout seconds is to be
               flushed. identifier specifies which values are to be flushed.

               The arguments are log-level and message. The log level is small
               for important messages and high for less important messages.
               The least important level is LOG_DEBUG, the most important
               level is LOG_ERR. In between there are (from least to most
               important): LOG_INFO, LOG_NOTICE, and LOG_WARNING. message is
               simply a string without a newline at the end.

               The only argument passed is notification. See above for the
               layout of this data type.

       plugin_unregister (type, plugin)
           Removes a callback or data-set from collectd's internal list of
           functions / datasets.

       plugin_dispatch_values (value-list)
           Submits a value-list to the daemon. If the data-set identified by
           value-list->{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.

           Note: Prior to version 4.4 of collectd, the data-set type used to
           be passed as the first argument to plugin_register. This syntax is
           still supported for backwards compatibility but has been deprecated
           and will be removed in some future version of collectd.

       plugin_write ([plugins => ...][, datasets => ...], valuelists => ...)
           Calls the write function of the given plugins with the provided
           data sets and value lists. In contrast to plugin_dispatch_values,
           it does not update collectd's internal cache and bypasses the
           filter mechanism (see collectd.conf(5) for details). If the plugins
           argument has been omitted, the values will be dispatched to all
           registered write plugins. If the datasets argument has been
           omitted, the required data sets are looked up according to the
           "type" member in the appropriate value list. The value of all three
           arguments may either be a single scalar or a reference to an array.
           If the datasets argument has been specified, the number of data
           sets has to equal the number of specified value lists.

       plugin_flush ([timeout => timeout][, plugins => ...][, identifiers =>
           Flush one or more plugins. timeout and the specified identifiers
           are passed on to the registered flush-callbacks. If omitted, the
           timeout defaults to "-1". The identifier defaults to the undefined
           value. If the plugins argument has been specified, only named
           plugins will be flushed. The value of the plugins and identifiers
           arguments may either be a string or a reference to an array of

       plugin_flush_one (timeout, plugin)
           This is identical to using "plugin_flush (timeout => timeout,
           plugins => plugin".

           Note: Starting with version 4.5 of collectd, plugin_flush_one has
           been deprecated and will be removed in some future version of
           collectd. Use plugin_flush instead.

       plugin_flush_all (timeout)
           This is identical to using "plugin_flush (timeout => timeout)".

           Note: Starting with version 4.5 of collectd, plugin_flush_all has
           been deprecated and will be removed in some future version of
           collectd. Use plugin_flush instead.

       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.

           Wrappers around plugin_log, using LOG_ERR, LOG_WARNING, LOG_NOTICE,
           LOG_INFO and LOG_DEBUG respectively as log-level.

       The following function provides the filter chain C-interface to Perl-
       modules.  It is exported by the ":filter_chain" export tag (see the
       section "EXPORTS" below).

       fc_register (type, name, proc)
           Registers filter chain callbacks with collectd.

           type may be any of:


           name is the name of the match or target. By this name, the
           callbacks are identified in the configuration file when specifying
           a Match or Target block (see collectd.conf(5) for details).

           proc is a hash reference. The hash includes up to three callbacks:
           an optional constructor (create) and destructor (destroy) and a
           mandatory match or invoke callback. match is called whenever
           processing an appropriate match, while invoke is called whenever
           processing an appropriate target (see the section "FILTER
           CONFIGURATION" in collectd.conf(5) for details). Just like any
           other callbacks, filter chain callbacks are identified by the
           function name rather than a function pointer because Perl does not
           support to share references to subroutines between threads. The
           following arguments are passed to the callbacks:

               The arguments passed are config-item and user-data. See above
               for the layout of the config-item data-type. user-data is a
               reference to a scalar value that may be used to store any
               information specific to this particular instance. The daemon
               does not care about this information at all. It's for the
               plugin's use only.

               The only argument passed is user-data which is a reference to
               the user data initialized in the create callback. This callback
               may be used to cleanup instance-specific information and

           match, invoke
               The arguments passed are data-set, value-list, meta and user-
               data.  See above for the layout of the data-set and value-list
               data-types. meta is a pointer to an array of meta information,
               just like the meta member of the notification data-type (see
               above). user-data is a reference to the user data initialized
               in the create callback.


           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).

           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.


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

           plugin_register ()
           plugin_unregister ()
           plugin_dispatch_values ()
           plugin_flush ()
           plugin_flush_one ()
           plugin_flush_all ()
           plugin_dispatch_notification ()
           plugin_log ()
           ERROR ()
           WARNING ()
           NOTICE ()
           INFO ()
           DEBUG ()


       Any Perl plugin will start similar to:

         package Collectd::Plugins::FooBar;

         use strict;
         use warnings;

         use Collectd qw( :all );

       A very simple read function might 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 might 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;

       A very simple match callback might look like:

         sub foobar_match
           my ($ds, $vl, $meta, $user_data) = @_;
           if (matches($ds, $vl)) {
             return FC_MATCH_MATCHES;
           } else {
             return FC_MATCH_NO_MATCH;

       To register those functions with collectd:

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

         fc_register (FC_MATCH, "foobar", "foobar_match");

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


       o   Please feel free to send in new plugins to collectd's mailing list
           at <collectd at> 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

           Before submitting your plugin, please take a look at


       o   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.

       o   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.

       o   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.

       o   The perl plugin exports the internal API of collectd which is
           considered unstable and subject to change at any time. We try hard
           to not break backwards compatibility in the Perl API during the
           life cycle of one major release.  However, this cannot be
           guaranteed at all times. Watch out for warnings dispatched by the
           perl plugin after upgrades.


       o   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.


       collectd(1), collectd.conf(5), collectd-exec(5), types.db(5), perl(1),
       threads(3perl), threads::shared(3perl), perldebug(1)


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

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