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COLLECTD-PYTHON(5)		   collectd		    COLLECTD-PYTHON(5)

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

SYNOPSIS
	 LoadPlugin python
	 # ...
	 <Plugin python>
	   ModulePath "/path/to/your/python/modules"
	   LogTraces true
	   Interactive false
	   Import "spam"

	   <Module spam>
	     spam "wonderful" "lovely"
	   </Module>
	 </Plugin>

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

       The minimum required Python version is 2.6.

CONFIGURATION
       LoadPlugin Plugin
	   Loads the Python plugin Plugin.

       Encoding	Name
	   The default encoding	for Unicode objects you	pass to	collectd. If
	   you omit this option	it will	default	to ascii on Python 2. On
	   Python 3 it will always be utf-8, as	this function was removed, so
	   this	will be	silently ignored.  These defaults are hardcoded	in
	   Python and will ignore everything else, including your locale.

       ModulePath Name
	   Prepends Name to sys.path. You won't	be able	to import any scripts
	   you wrote unless they are located in	one of the directories in this
	   list. Please	note that it only has effect on	plugins	loaded after
	   this	option.	You can	use multiple ModulePath	lines to add more than
	   one directory.

       LogTraces bool
	   If a	Python script throws an	exception it will be logged by
	   collectd with the name of the exception and the message. If you set
	   this	option to true it will also log	the full stacktrace just like
	   the default output of an interactive	Python interpreter. This
	   should probably be set to false most	of the time but	is very	useful
	   for development and debugging of new	modules.

       Interactive bool
	   This	option will cause the module to	launch an interactive Python
	   interpreter that reads from and writes to the terminal. Note	that
	   collectd will terminate right after starting	up if you try to run
	   it as a daemon while	this option is enabled so make sure to start
	   collectd with the -f	option.

	   The collectd	module is not imported into the	interpreter's globals.
	   You have to do it manually. Be sure to read the help	text of	the
	   module, it can be used as a reference guide during coding.

	   This	interactive session will behave	slightly differently from a
	   daemonized collectd script as well as from a	normal Python
	   interpreter:

	   o   1. collectd will	try to import the readline module to give you
	       a decent	way of entering	your commands. The daemonized collectd
	       won't do	that.

	   o   2. Python will be handling SIGINT. Pressing Ctrl+C will usually
	       cause collectd to shut down. This would be problematic in an
	       interactive session, therefore Python will be handling it in
	       interactive sessions. This allows you to	use Ctrl+C to
	       interrupt Python	code without killing collectd. This also means
	       you can catch KeyboardInterrupt exceptions which	does not work
	       during normal operation.

	       To quit collectd	send EOF (press	Ctrl+D at the beginning	of a
	       new line).

	   o   3. collectd handles SIGCHLD. This means that Python won't be
	       able to determine the return code of spawned processes with
	       system(), popen() and subprocess. This will result in Python
	       not using external programs like	less to	display	help texts.
	       You can override	this behavior with the PAGER environment
	       variable, e.g. export PAGER=less	before starting	collectd.
	       Depending on your version of Python this	might or might not
	       result in an OSError exception which can	be ignored.

	       If you really need to spawn new processes from Python you can
	       register	an init	callback and reset the action for SIGCHLD to
	       the default behavior. Please note that this will	break the exec
	       plugin. Do not even load	the exec plugin	if you intend to do
	       this!

	       There is	an example script located in
	       contrib/python/getsigchld.py  to	do this. If you	import this
	       from collectd.conf SIGCHLD will be handled normally and
	       spawning	processes from Python will work	as intended.

       <Module Name> block
	   This	block may be used to pass on configuration settings to a
	   Python module.  The configuration is	converted into an instance of
	   the Config class which is passed to the registered configuration
	   callback. See below for details about the Config class and how to
	   register callbacks.

	   The name identifies the callback.

STRINGS
       There are a lot of places where strings are sent	from collectd to
       Python and from Python to collectd. How exactly this works depends on
       whether byte or unicode strings or Python2 or Python3 are used.

       Python2 has str,	which is just bytes, and unicode. Python3 has str,
       which is	a unicode object, and bytes.

       When passing strings from Python	to collectd all	of these object	are
       supported in all	places,	however	str should be used if possible.	These
       strings must not	contain	a NUL byte. Ignoring this will result in a
       TypeError exception.  If	a byte string was used it will be used as is
       by collectd. If a unicode object	was used it will be encoded using the
       default encoding	(see above). If	this is	not possible Python will raise
       a UnicodeEncodeError exception.

       When passing strings from collectd to Python the	behavior depends on
       the Python version used.	Python2	will always receive a str object.
       Python3 will usually receive a str object as well, however the original
       string will be decoded to unicode using the default encoding. If	this
       fails because the string	is not a valid sequence	for this encoding a
       bytes object will be returned instead.

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
	   These are called during configuration if an appropriate Module
	   block has been encountered. It is called once for each Module block
	   which matches the name of the callback as provided with the
	   register_config method - see	below.

	   Python thread support has not been initialized at this point	so do
	   not use any threading functions here!

       init functions
	   These are 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, ...). This is
	   the earliest	point where you	may use	threads.

       read functions
	   These are 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 this function throws any kind of exception the	plugin
	   will	be skipped for an increasing amount of time until it returns
	   normally again.

       write functions
	   These are used to write the dispatched values. It is	called once
	   for every value that	was dispatched by any plugin.

       flush functions
	   These are 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
	   These are used to pass messages of plugins or the daemon itself to
	   the user.

       notification function
	   These are 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
	   These are 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 throw an	exception in case of
       errors. The exception will be passed on to the user using collectd's
       logging mechanism. If a log callback throws an exception	it will	be
       printed to standard error instead.

       See the documentation of	the various register_ methods in the section
       "FUNCTIONS" 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 module, copy	it to a	place where Python can find it (i. e.
       a directory listed in sys.path) just as any other Python	plugin and add
       an appropriate Import option to the configuration file. After
       restarting collectd you're done.

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

   Signed
       The Signed class	is just	a long.	It has all its methods and behaves
       exactly like any	other long object. It is used to indicate if an
       integer was or should be	stored as a signed or unsigned integer object.

	class Signed(long)

       This is a long by another name. Use it in meta data dicts to choose the
       way it is stored	in the meta data.

   Unsigned
       The Unsigned class is just a long. It has all its methods and behaves
       exactly like any	other long object. It is used to indicate if an
       integer was or should be	stored as a signed or unsigned integer object.

	class Unsigned(long)

       This is a long by another name. Use it in meta data dicts to choose the
       way it is stored	in the meta data.

   Config
       The Config class	is an object which keeps the information provided in
       the configuration file. The sequence of children	keeps one entry	for
       each configuration option. Each such entry is another Config instance,
       which may nest further if nested	blocks are used.

	class Config(object)

       This represents a piece of collectd's config file. It is	passed to
       scripts with config callbacks (see register_config) and is of little
       use if created somewhere	else.

       It has no methods beyond	the bare minimum and only exists for its data
       members.

       Data descriptors	defined	here:

       parent
	   This	represents the parent of this node. On the root	node of	the
	   config tree it will be None.

       key This	is the keyword of this item, i.e. the first word of any	given
	   line	in the config file. It will always be a	string.

       values
	   This	is a tuple (which might	be empty) of all value,	i.e. words
	   following the keyword in any	given line in the config file.

	   Every item in this tuple will be either a string, a float or	a
	   boolean, depending on the contents of the configuration file.

       children
	   This	is a tuple of child nodes. For most nodes this will be empty.
	   If this node	represents a block instead of a	single line of the
	   config file it will contain all nodes in this block.

   PluginData
       This should not be used directly	but it is the base class for both
       Values and Notification.	It is used to identify the source of a value
       or notification.

	class PluginData(object)

       This is an internal class that is the base for Values and Notification.
       It is pretty useless by itself and was therefore	not exported to	the
       collectd	module.

       Data descriptors	defined	here:

       host
	   The hostname	of the host this value was read	from. For dispatching
	   this	can be set to an empty string which means the local hostname
	   as defined in collectd.conf.

       plugin
	   The name of the plugin that read the	data. Setting this member to
	   an empty string will	insert "python"	upon dispatching.

       plugin_instance
	   Plugin instance string. May be empty.

       time
	   This	is the Unix timestamp of the time this value was read. For
	   dispatching values this can be set to zero which means "now". This
	   means the time the value is actually	dispatched, not	the time it
	   was set to 0.

       type
	   The type of this value. This	type has to be defined in your
	   types.db.  Attempting to set	it to any other	value will raise a
	   TypeError exception.	 Assigning a type is mandatory,	calling
	   dispatch without doing so will raise	a RuntimeError exception.

       type_instance
	   Type	instance string. May be	empty.

   Values
       A Value is an object which features a sequence of values. It is based
       on the PluginData type and uses its members to identify the values.

	class Values(PluginData)

       A Values	object used for	dispatching values to collectd and receiving
       values from write callbacks.

       Method resolution order:

       Values
       PluginData
       object

       Methods defined here:

       dispatch([type][, values][, plugin_instance][, type_instance][,
       plugin][, host][, time][, interval]) -> None.
	   Dispatch this instance to the collectd process. The object has
	   members for each of the possible arguments for this method. For a
	   detailed explanation	of these parameters see	the member of the same
	   same.

	   If you do not submit	a parameter the	value saved in its member will
	   be submitted. If you	do provide a parameter it will be used
	   instead, without altering the member.

       write([destination][, type][, values][, plugin_instance][,
       type_instance][,	plugin][, host][, time][, interval]) ->	None.
	   Write this instance to a single plugin or all plugins if
	   "destination" is omitted. This will bypass the main collectd
	   process and all filtering and caching. Other	than that it works
	   similar to "dispatch". In most cases	"dispatch" should be used
	   instead of "write".

       Data descriptors	defined	here:

       interval
	   The interval	is the timespan	in seconds between two submits for the
	   same	data source. This value	has to be a positive integer, so you
	   can't submit	more than one value per	second.	If this	member is set
	   to a	non-positive value, the	default	value as specified in the
	   config file will be used (default: 10).

	   If you submit values	more often than	the specified interval,	the
	   average will	be used. If you	submit less values, your graphs	will
	   have	gaps.

       values
	   These are the actual	values that get	dispatched to collectd.	It has
	   to be a sequence (a tuple or	list) of numbers. The size of the
	   sequence and	the type of its	content	depend on the type member your
	   types.db file. For more information on this read the	types.db(5)
	   manual page.

	   If the sequence does	not have the correct size upon dispatch	a
	   RuntimeError	exception will be raised. If the content of the
	   sequence is not a number, a TypeError exception will	be raised.

       meta
	   These are the meta data for this Value object.  It has to be	a
	   dictionary of numbers, strings or bools. All	keys must be strings.
	   int and <long> objects will be dispatched as	signed integers	unless
	   they	are between 2**63 and 2**64-1, which will result in a unsigned
	   integer.  You can force one of these	storage	classes	by using the
	   classes collectd.Signed and collectd.Unsigned. A meta object
	   received by a write callback	will always contain Signed or Unsigned
	   objects.

   Notification
       A notification is an object defining the	severity and message of	the
       status message as well as an identification of a	data instance by means
       of the members of PluginData on which it	is based.

       class Notification(PluginData) The Notification class is	a wrapper
       around the collectd notification.  It can be used to notify other
       plugins about bad stuff happening. It works similar to Values but has a
       severity	and a message instead of interval and time.  Notifications can
       be dispatched at	any time and can be received with
       register_notification.

       Method resolution order:

       Notification
       PluginData
       object

       Methods defined here:

       dispatch([type][, values][, plugin_instance][, type_instance][,
       plugin][, host][, time][, interval]) -> None.  Dispatch a value list.
	   Dispatch this instance to the collectd process. The object has
	   members for each of the possible arguments for this method. For a
	   detailed explanation	of these parameters see	the member of the same
	   same.

	   If you do not submit	a parameter the	value saved in its member will
	   be submitted. If you	do provide a parameter it will be used
	   instead, without altering the member.

       Data descriptors	defined	here:

       message
	   Some	kind of	description of what's going on and why this
	   Notification	was generated.

       severity
	   The severity	of this	notification. Assign or	compare	to
	   NOTIF_FAILURE, NOTIF_WARNING	or NOTIF_OKAY.

FUNCTIONS
       The following functions provide the C-interface to Python-modules.

       register_*(callback[, data][, name]) -> identifier
	   There are eight different register functions	to get callback	for
	   eight different events. With	one exception all of them are called
	   as shown above.

	   o   callback	is a callable object that will be called every time
	       the event is triggered.

	   o   data is an optional object that will be passed back to the
	       callback	function every time it is called. If you omit this
	       parameter no object is passed back to your callback, not	even
	       None.

	   o   name is an optional identifier for this callback. The default
	       name is python.module. module is	taken from the __module__
	       attribute of your callback function. Every callback needs a
	       unique identifier, so if	you want to register the same callback
	       multiple	times in the same module you need to specify a name
	       here. Otherwise it's safe to ignore this	parameter.

	   o   identifier is the full identifier assigned to this callback.

	   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:

	   register_config
	       The only	argument passed	is a Config object. See	above for the
	       layout of this data type.  Note that you	cannot receive the
	       whole config files this way, only Module	blocks inside the
	       Python configuration block. Additionally	you will only receive
	       blocks where your callback identifier matches python.blockname.

	   register_init
	       The callback will be called without arguments.

	   register_read(callback[, interval][,	data][,	name]) -> identifier
	       This function takes an additional parameter: interval. It
	       specifies the time between calls	to the callback	function.

	       The callback will be called without arguments.

	   register_shutdown
	       The callback will be called without arguments.

	   register_write
	       The callback function will be called with one argument passed,
	       which will be a Values object. For the layout of	Values see
	       above.  If this callback	function throws	an exception the next
	       call will be delayed by an increasing interval.

	   register_flush
	       Like register_config is important for this callback because it
	       determines what flush requests the plugin will receive.

	       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.

	   register_log
	       The arguments are severity and message. The severity is an
	       integer and 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.

	       If this callback	throws an exception it will not	be logged. It
	       will just be printed to sys.stderr which	usually	means silently
	       ignored.

	   register_notification
	       The only	argument passed	is a Notification object. See above
	       for the layout of this data type.

       unregister_*(identifier)	-> None
	   Removes a callback or data-set from collectd's internal list	of
	   callback functions. Every register_*	function has an	unregister_*
	   function.  identifier is either the string that was returned	by the
	   register function or	a callback function. The identifier will be
	   constructed in the same way as for the register functions.

       get_dataset(name) -> definition
	   Returns the definition of a dataset specified by name. definition
	   is a	list of	tuples,	each representing one data source. Each	tuple
	   has 4 values:

	   name
	       A string, the name of the data source.

	   type
	       A string	that is	equal to either	of the variables
	       DS_TYPE_COUNTER,	DS_TYPE_GAUGE, DS_TYPE_DERIVE or
	       DS_TYPE_ABSOLUTE.

	   min A float or None,	the minimum value.

	   max A float or None,	the maximum value.

       flush(plugin[, timeout][, identifier]) -	None
	   Flush one or	all 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	None. If the
	   plugin argument has been specified, only named plugin will be
	   flushed.

       error, warning, notice, info, debug(message)
	   Log a message with the specified severity.

EXAMPLES
       Any Python module will start similar to:

	 import	collectd

       A very simple read function might look like:

	 import	random

	 def read(data=None):
	   vl =	collectd.Values(type='gauge')
	   vl.plugin='python.spam'
	   vl.dispatch(values=[random.random() * 100])

       A very simple write function might look like:

	 def write(vl, data=None):
	   for i in vl.values:
	     print "%s (%s): %f" % (vl.plugin, vl.type,	i)

       To register those functions with	collectd:

	 collectd.register_read(read)
	 collectd.register_write(write)

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

CAVEATS
       o   collectd is heavily multi-threaded. Each collectd thread accessing
	   the Python plugin will be mapped to a Python	interpreter thread.
	   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).

       o   The Python thread module is initialized just	before calling the
	   init	callbacks.  This means you must	not use	Python's threading
	   module prior	to this	point. This includes all config	and possibly
	   other callback as well.

       o   The python 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 Python API during the
	   life	cycle of one major release.  However, this cannot be
	   guaranteed at all times. Watch out for warnings dispatched by the
	   python plugin after upgrades.

KNOWN BUGS
       o   Not all aspects of the collectd API are accessible from Python.
	   This	includes but is	not limited to filters and data	sets.

SEE ALSO
       collectd(1), collectd.conf(5), collectd-perl(5),	collectd-exec(5),
       types.db(5), python(1),

AUTHOR
       The "python plugin" has been written by Sven Trenkel
       <collectd at semidefinite.de>.

       This manpage has	been written by	Sven Trenkel
       <collectd at semidefinite.de>.  It is based on the collectd-perl(5)
       manual page by Florian Forster <octo at collectd.org> and Sebastian
       Harl <sh	at tokkee.org>.

5.7.1				  2017-01-23		    COLLECTD-PYTHON(5)

NAME | SYNOPSIS | DESCRIPTION | CONFIGURATION | STRINGS | WRITING YOUR OWN PLUGINS | CLASSES | FUNCTIONS | EXAMPLES | CAVEATS | KNOWN BUGS | SEE ALSO | AUTHOR

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