Provided by: collectd-core_5.4.0-3ubuntu2.2_amd64 
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 => plugin_get_interval (),
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.
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_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.
plugin_get_interval ()
Returns the interval of the current plugin as a floating point number in seconds. This
value depends on the interval configured within the "LoadPlugin perl" block or the
global interval (see collectd.conf(5) for details).
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).
Note: This variable should no longer be used in favor of "plugin_get_interval()" (see
above). This function takes any plugin-specific interval settings into account (see
the "Interval" option of "LoadPlugin" in collectd.conf(5) for details).
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', type => 'gauge' };
$vl->{'values'} = [ rand(42) ];
plugin_dispatch_values ($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>.