+# Permission is hereby granted, free of charge, to any person obtaining a
+# copy of this software and associated documentation files (the "Software"),
+# to deal in the Software without restriction, including without limitation
+# the rights to use, copy, modify, merge, publish, distribute, sublicense,
+# and/or sell copies of the Software, and to permit persons to whom the
+# Software is furnished to do so, subject to the following conditions:
+#
+# 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"
LogTraces true
- Interactive true
+ Interactive false
Import "spam"
<Module spam>
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 embeded
-interpreter will start anywa 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>
=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
collectd to shut down. This would be problematic in an interactive session,
To quit collectd send I<EOF> (press I<Ctrl+D> at the beginning of a new line).
+=item *
+
+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
+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
+B<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 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.
+
=back
=item E<lt>B<Module> I<Name>E<gt> block
=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.
The following complex types are used to pass values between the Python plugin
and collectd:
+=head2 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.
+
+=head2 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.
+
=head2 Config
-The Config class is an object which keeps the informations provided in the
+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.
Data descriptors defined here:
=over 4
-
+
=item parent
This represents the parent of this node. On the root node
of the config tree it will be None.
-
+
=item 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.
-
+
=item 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,
+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
This is a tuple of child nodes. For most nodes this will be empty. If this node
=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)
=over 4
=item B<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.
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.
exception will be raised. If the content of the sequence is not a number, a
I<TypeError> exception will be raised.
+=item 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. I<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
+B<collectd.Signed> and B<collectd.Unsigned>. A meta object received by a write
+callback will always contain B<Signed> or B<Unsigned> objects.
+
=back
=head2 Notification
=over 4
=item B<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.
=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>.
=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<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
=over 4
-=item
+=item *
-Please feel free to send in new plugins to collectd's mailinglist at
+Please feel free to send in new plugins to collectd's mailing list 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.
=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
-
-This plugin is not compatible with python3. Trying to compile it with python3
-will fail because of the ways string, unicode and bytearray bahavior was
-changed.
-
-=item
+=item *
-Not all aspects of the collectd API are accessible from python. This includes
-but is not limited to meta-data, filters and data sets.
+Not all aspects of the collectd API are accessible from Python. This includes
+but is not limited to filters and data sets.
=back
projects / collectd.git / blobdiff