# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
+=encoding UTF-8
+
=head1 NAME
collectd-python - Documentation of collectd's C<python plugin>
=head1 SYNOPSIS
- <LoadPlugin python>
- Globals true
- </LoadPlugin>
+ LoadPlugin python
# ...
<Plugin python>
ModulePath "/path/to/your/python/modules"
Python-script every time you want to read a value with the C<exec plugin> (see
L<collectd-exec(5)>) and provides a lot more functionality, too.
-At least python I<version 2.3> is required.
+The minimum required Python version is I<2.3>.
=head1 CONFIGURATION
=item B<LoadPlugin> I<Plugin>
-Loads the Python plugin I<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".
+Loads the Python plugin I<Plugin>.
=item B<Encoding> I<Name>
The default encoding for Unicode objects you pass to collectd. If you omit this
-option it will default to B<ascii> on I<Python 2> and B<utf-8> on I<Python 3>.
-This is hardcoded in Python and will ignore everything else, including your
-locale.
+option it will default to B<ascii> on I<Python 2>. On I<Python 3> it will
+always be B<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.
=item B<ModulePath> I<Name>
-Appends I<Name> to B<sys.path>. You won't be able to import any scripts you
+Prepends I<Name> to B<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 B<ModulePath> lines to add more than one directory.
=item B<LogTraces> I<bool>
-If a python script throws an exception it will be logged by collectd with the
+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
+Python interpreter. This should probably be set to false most of the time but
is very useful for development and debugging of new modules.
=item B<Interactive> I<bool>
-This option will cause the module to launch an interactive python interpreter
+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 B<-f> option.
+enabled so make sure to start collectd with the B<-f> option.
The B<collectd> module is I<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:
+collectd script as well as from a normal Python interpreter:
=over 4
-=item
+=item *
B<1.> collectd will try to import the B<readline> module to give you a decent
way of entering your commands. The daemonized collectd won't do that.
-=item
+=item *
-B<2.> collectd will block I<SIGINT>. Pressing I<Ctrl+C> will usually cause
+B<2.> Python will be handling I<SIGINT>. Pressing I<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 I<KeyboardInterrupt>
-exception either.
+therefore Python will be handling it in interactive sessions. This allows you
+to use I<Ctrl+C> to interrupt Python code without killing collectd. This also
+means you can catch I<KeyboardInterrupt> exceptions which does not work during
+normal operation.
To quit collectd send I<EOF> (press I<Ctrl+D> at the beginning of a new line).
-=item
+=item *
-B<3.> collectd handles I<SIGCHLD>. This means that python won't be able to
+B<3.> collectd handles I<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
+subprocess. This will result in Python not using external programs like less
to display help texts. You can override this behavior with the B<PAGER>
environment variable, e.g. I<export PAGER=less> before starting collectd.
-Depending on your version of python this might or might not result in an
+Depending on your version of Python this might or might not result in an
B<OSError> exception which can be ignored.
-If you really need to spawn new processes from python you can register an init
+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 I<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 B<contrib/python/getsigchld.py> to do
this. If you import this from I<collectd.conf> SIGCHLD will be handled
-normally and spawning processes from python will work as intended.
+normally and spawning processes from Python will work as intended.
=back
=head1 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.
+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 I<str>, which is just bytes, and I<unicode>. Python3 has I<str>,
which is a unicode object, and I<bytes>.
-When passing strings from python to collectd all of these object are supported
+When passing strings from Python to collectd all of these object are supported
in all places, however I<str> should be used if possible. These strings must
not contain a NUL byte. Ignoring this will result in a I<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 I<UnicodeEncodeError> exception.
+this is not possible Python will raise a I<UnicodeEncodeError> exception.
-Wenn passing strings from collectd to python the behavior depends on the
-python version used. Python2 will always receive a I<str> object. Python3 will
+When passing strings from collectd to Python the behavior depends on the
+Python version used. Python2 will always receive a I<str> object. Python3 will
usually receive a I<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 I<bytes> object will be
=item configuration functions
-This type of functions is called during configuration if an appropriate
+These are called during configuration if an appropriate
B<Module> block has been encountered. It is called once for each B<Module>
block which matches the name of the callback as provided with the
B<register_config> method - see below.
=item init functions
-This type of functions is called once after loading the module and before any
+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.E<nbsp>g. open sockets, ...). This is the
earliest point where you may use threads.
=item read functions
-This type of function is used to collect the actual data. It is called once
+These are used to collect the actual data. It is called once
per interval (see the B<Interval> configuration option of collectd). Usually
it will call B<plugin_dispatch_values> to dispatch the values to collectd
which will pass them on to all registered B<write functions>. If this function
=item write functions
-This type of function is used to write the dispatched values. It is called
+These are used to write the dispatched values. It is called
once for every value that was dispatched by any plugin.
=item flush functions
-This type of function is used to flush internal caches of plugins. It is
+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.
=item log functions
-This type of function is used to pass messages of plugins or the daemon itself
+These are used to pass messages of plugins or the daemon itself
to the user.
=item notification function
-This type of function is used to act upon notifications. In general, a
+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
=item shutdown functions
-This type of function is called once before the daemon shuts down. It should
+These are called once before the daemon shuts down. It should
be used to clean up the plugin (e.g. close sockets, ...).
=back
-Any function (except log functions) may set throw an exception in case of any
+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.
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,
+Every item in this tuple will be either a string, a float or a boolean,
depending on the contents of the configuration file.
=item children
=head2 Values
-A Value is an object which features a sequence of values. It is based on then
+A Value is an object which features a sequence of values. It is based on the
I<PluginData> type and uses its members to identify the values.
class Values(PluginData)
=item message
-Some kind of description what's going on and why this Notification was
+Some kind of description of what's going on and why this Notification was
generated.
=item severity
=over 4
-=item
+=item *
I<callback> is a callable object that will be called every time the event is
triggered.
-=item
+=item *
I<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.
-=item
+=item *
I<name> is an optional identifier for this callback. The default name is
B<python>.I<module>. I<module> is taken from the B<__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 I<identifier>
-is the full identifier assigned to this callback.
+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.
+
+=item *
+
+I<identifier> is the full identifier assigned to this callback.
=back
The only argument passed is a I<Config> object. See above for the layout of this
data type.
-Note that you can not receive the whole config files this way, only B<Module>
+Note that you cannot receive the whole config files this way, only B<Module>
blocks inside the Python configuration block. Additionally you will only
receive blocks where your callback identifier matches B<python.>I<blockname>.
The callback will be called without arguments.
-=item register_read(callback[, interval][, data][, name]) -> identifier
+=item register_read(callback[, interval][, data][, name]) -> I<identifier>
This function takes an additional parameter: I<interval>. It specifies the
time between calls to the callback function.
=item register_write
-The callback function will be called with one arguments passed, which will be a
+The callback function will be called with one argument passed, which will be a
I<Values> object. For the layout of I<Values> see above.
If this callback function throws an exception the next call will be delayed by
an increasing interval.
or a callback function. The identifier will be constructed in the same way as
for the register functions.
-=item B<flush>(I<plugin[, I<timeout>][, I<identifier>]) -> None
+=item B<get_dataset>(I<name>) -> I<definition>
+
+Returns the definition of a dataset specified by I<name>. I<definition> is a list
+of tuples, each representing one data source. Each tuple has 4 values:
+
+=over 4
+
+=item name
+
+A string, the name of the data source.
+
+=item type
+
+A string that is equal to either of the variables B<DS_TYPE_COUNTER>,
+B<DS_TYPE_GAUGE>, B<DS_TYPE_DERIVE> or B<DS_TYPE_ABSOLUTE>.
+
+=item min
+
+A float or None, the minimum value.
+
+=item max
+
+A float or None, the maximum value.
+
+=back
+
+=item B<flush>(I<plugin[, timeout][, identifier]) -> None
Flush one or all plugins. I<timeout> and the specified I<identifiers> are
passed on to the registered flush-callbacks. If omitted, the timeout defaults
A very simple read function might look like:
+ import random
+
def read(data=None):
vl = collectd.Values(type='gauge')
vl.plugin='python.spam'
To register those functions with collectd:
- collectd.register_read(read);
- collectd.register_write(write);
+ collectd.register_read(read)
+ collectd.register_write(write)
See the section L<"CLASSES"> above for a complete documentation of the data
types used by the read, write and match functions.
-=head1 NOTES
-
-=over 4
-
-=item
-
-Please feel free to send in new plugins to collectd's mailinglist at
-E<lt>collectdE<nbsp>atE<nbsp>verplant.orgE<gt> 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
-L<http://collectd.org/dev-info.shtml>.
-
-=back
-
=head1 CAVEATS
=over 4
-=item
+=item *
-collectd is heavily multi-threaded. Each collectd thread accessing the python
+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.
from collectd (i.E<nbsp>e. if it registers more than one callback or if a
registered callback may be called more than once in parallel).
-=item
+=item *
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.
-=item
+=item *
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
=over 4
-=item
+=item *
-Not all aspects of the collectd API are accessible from python. This includes
+Not all aspects of the collectd API are accessible from Python. This includes
but is not limited to filters and data sets.
=back
This manpage has been written by Sven Trenkel
E<lt>collectdE<nbsp>atE<nbsp>semidefinite.deE<gt>.
It is based on the L<collectd-perl(5)> manual page by
-Florian Forster E<lt>octoE<nbsp>atE<nbsp>verplant.orgE<gt> and
+Florian Forster E<lt>octoE<nbsp>atE<nbsp>collectd.orgE<gt> and
Sebastian Harl E<lt>shE<nbsp>atE<nbsp>tokkee.orgE<gt>.
=cut