Provided by: collectd-core_4.10.1-2_i386 bug

NAME

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

SYNOPSIS

         <LoadPlugin python>
           Globals true
         </LoadPlugin>
         # ...
         <Plugin python>
           ModulePath "/path/to/your/python/modules"
           LogTraces true
           Interactive true
           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.

       At least python version 2.3 is required.

CONFIGURATION

       LoadPlugin Plugin
           Loads the Python plugin Plugin. Unlike most other LoadPlugin lines,
           this one should be a block containing the line "Globals true". This
           will cause collectd to export the name of all objects in the python
           interpreter for all plugins to see. If you don't do this or your
           platform does not support it, the embedded interpreter will start
           anyway but you won't be able to load certain python modules, e.g.
           "time".

       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 and utf-8
           on Python 3.  This is hardcoded in Python and will ignore
           everything else, including your locale.

       ModulePath Name
           Appends 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 to 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. collectd will block SIGINT. Pressing Ctrl+C will usually
               cause collectd to shut down. This would be problematic in an
               interactive session, therefore this signal will be blocked. You
               can still use it to interrupt syscalls like sleep and pause but
               it won't generate a KeyboardInterrupt exception either.

               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 send from collectd to
       python and from python to collectd. How exactly this works depends on
       wheather 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.

       Wenn 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
           This type of functions is 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
           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,
           ...). This is the earliest point where you may use threads.

       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 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
           This type of function is used to write the dispatched values. It is
           called once for every value that was dispatched by any plugin.

       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 throw an exception in case
       of any 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 or 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 then 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 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 time in the same module you need to specify a name
               here. Otherwise it's save to ignore this parameter 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 can not 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 arguments 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.

       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:

         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.

NOTES

       o   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

       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   This plugin is not compatible with python3. Trying to compile it
           with python3 will fail because of the ways string, unicode and
           bytearray behavior was changed.

       o   Not all aspects of the collectd API are accessible from python.
           This includes but is not limited to meta-data, 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 verplant.org> and Sebastian
       Harl <sh at tokkee.org>.