Provided by: collectd_4.3.0-1_i386 bug

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 these 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.

       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:

           TYPE_INIT
           TYPE_READ
           TYPE_WRITE
           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.

           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_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_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 (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_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_dispatch_notification ()
           plugin_log ()
       :types
           TYPE_INIT
           TYPE_READ
           TYPE_WRITE
           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.

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>.