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COLLECTD-PERL(5)		   collectd		      COLLECTD-PERL(5)

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

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

	   <Plugin FooBar>
	     Foo "Bar"
	   </Plugin>
	 </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.

       When loading the "perl plugin", the Globals option should be enabled.
       Else, the perl plugin will fail to load any Perl modules implemented in
       C, which includes, amongst many others, the threads module used by the
       plugin itself. See the documentation of the Globals option in
       collectd.conf(5) for details.

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. 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
	   callbacks.

	   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
	   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):

       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
	   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:

       Config-Item
	   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 => [ { ... }, { ... }, ... ]
	     }

       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 || DS_TYPE_DERIVE || DS_TYPE_ABSOLUTE,
	       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 (),
	       interval => $interval_g,
	       host   => $hostname_g,
	       plugin => 'myplugin',
	       type   => '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. 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> }, ... ]
	     }

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

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

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

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

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:

	   TYPE_CONFIG
	   TYPE_INIT
	   TYPE_READ
	   TYPE_WRITE
	   TYPE_FLUSH
	   TYPE_LOG
	   TYPE_NOTIF
	   TYPE_SHUTDOWN
	   TYPE_DATASET

	   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
	   threads.

	   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:

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

	   TYPE_INIT
	   TYPE_READ
	   TYPE_SHUTDOWN
	       No arguments are passed.

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

	   TYPE_FLUSH
	       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.

	   TYPE_LOG
	       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.

	   TYPE_NOTIF
	       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
	   strings.

       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.

       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.

       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:

	   FC_MATCH
	   FC_TARGET

	   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:

	   create
	       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.

	   destroy
	       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
	       settings.

	   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.

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_CONFIG
	   TYPE_INIT
	   TYPE_READ
	   TYPE_WRITE
	   TYPE_FLUSH
	   TYPE_SHUTDOWN
	   TYPE_LOG
	   TYPE_DATASET
       :ds_types
	   DS_TYPE_COUNTER
	   DS_TYPE_GAUGE
	   DS_TYPE_DERIVE
	   DS_TYPE_ABSOLUTE
       :log
	   ERROR ()
	   WARNING ()
	   NOTICE ()
	   INFO ()
	   DEBUG ()
	   LOG_ERR
	   LOG_WARNING
	   LOG_NOTICE
	   LOG_INFO
	   LOG_DEBUG
       :filter_chain
	   fc_register
	   FC_MATCH_NO_MATCH
	   FC_MATCH_MATCHES
	   FC_TARGET_CONTINUE
	   FC_TARGET_STOP
	   FC_TARGET_RETURN
       :fc_types
	   FC_MATCH
	   FC_TARGET
       :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 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.

NOTES
       ·   Please feel free to send in new plugins to collectd's mailing list
	   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.

       ·   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.

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.

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

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>.

4.10.4				  2011-10-14		      COLLECTD-PERL(5)
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