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>.