babeltrace2-intro(7) — Linux manual page


BABELTRACE2-INTRO(7)         Babeltrace 2 manual        BABELTRACE2-INTRO(7)

NAME         top

       babeltrace2-intro - Introduction to Babeltrace 2

DESCRIPTION         top

       This manual page is an introduction to the Babeltrace 2 project.

       The “WHAT IS BABELTRACE 2?” section describes the parts of the
       project and shows the major changes from Babeltrace 1 to Babeltrace 2
       while the “BABELTRACE 2 CONCEPTS” section defines the core concepts
       of Babeltrace 2.

       The “TRACE PROCESSING GRAPH REPRESENTATION” section shows how some
       concepts are visually represented in other Babeltrace 2 manual pages.

WHAT IS BABELTRACE 2?         top

       Babeltrace 2 is an open-source software project of which the purpose
       is to process or convert traces (see

       The Babeltrace 2 project includes the following parts:

       Babeltrace 2 library (libbabeltrace2)
           A shared library with a C API.

           With libbabeltrace2, you can programmatically create plugins and
           component classes, build and run trace processing graphs, and
           more (see the “BABELTRACE 2 CONCEPTS” section for more details
           about those concepts).

           All the other Babeltrace 2 parts rely on this library.

       babeltrace2 command-line program
           A command-line interface which uses libbabeltrace2 to load
           plugins, create a trace processing graph, create components,
           connect their ports correctly, and run the graph.

           You can also use babeltrace2 to list the available plugins or to
           query an object from a component class.

           See babeltrace2(1).

       Babeltrace 2 Python bindings
           A Python 3 package (bt2) which offers a Pythonic interface of

           You can perform the same operations which are available in
           libbabeltrace2 with the Python bindings, but more conveniently
           and with less code. However, the Python bindings are less
           performant than libbabeltrace2.

       Babeltrace 2 project’s plugins
           The Babeltrace 2 plugins shipped with the project.

           Those plugins are not special in that they only rely on
           libbabeltrace2 and you don’t need them to use libbabeltrace2,
           babeltrace2(1), or the Python bindings. However, the project’s
           plugins provide many widely used trace format encoders/decoders
           as well as common trace processing graph utilities.

           The Babeltrace 2 project’s plugins are:

               Common Trace Format (see <>) (CTF)
               input/output, including the LTTng live source.

               See babeltrace2-plugin-ctf(7).

               Graph utilities specific to LTTng (see <>)

               See babeltrace2-plugin-lttng-utils(7).

               Plain text input/output.

               See babeltrace2-plugin-text(7).

               Common graph utilities (muxer, trimmer, counter, dummy sink).

               See babeltrace2-plugin-utils(7).

   Changes since Babeltrace 1
       This manual page is an introduction to Babeltrace 2, a rewrite of
       Babeltrace 1 with a focus on extensibility, flexibility, and

       Babeltrace 1 exists since 2010.

       You can install both projects on the same file system as there are no
       file name conflicts.

       The major improvements brought by Babeltrace 2 are:


           ·   Full plugin support: any user can distribute a Babeltrace 2
               plugin and, as long as libbabeltrace2 finds it, any
               application linked to libbabeltrace2 can load it and use it.

               Plugins are not just trace format encoders and decoders: they
               package source, filter, and sink component classes so that
               you can connect specialized, reusable components together in
               a trace processing graph to create a customized trace
               conversion or analysis device.

               This modular strategy is much like how the FFmpeg (see
               <>), GStreamer (see
               <>), and DirectShow (see
               <>) projects approach
               media stream processing.

           ·   All the parts of the Babeltrace 2 project run on the major
               operating systems, including Windows and macOS.

           ·   Some component classes, such as sink.text.pretty (similar to
               the text output format of babeltrace(1)) and
               sink.text.details, can write color codes to the standard
               output when it’s connected to a color-enabled terminal.

               The Babeltrace 2 log, printed to the standard output, can
               also be colorized.

       Command-line interface

           ·   Whereas you can convert traces from one format to another
               with Babeltrace 1’s CLI tool, babeltrace(1), you can also
               execute a custom trace manipulation task with babeltrace2(1)
               thanks to the babeltrace2-run(1) command.

           ·   The babeltrace2-convert(1) command features an automatic
               source component discovery algorithm to find the best suited
               components to create for a given non-option argument (file or
               directory path, or custom string like an LTTng live (see
               <>) URL).

               For example:

                   $ babeltrace2 /path/to/ctf/trace

                   $ babeltrace2 net://localhost/host/myhost/my-session

       CTF (see <>) input/output

           ·   The source.ctf.fs component class, which is more or less the
               equivalent of Babeltrace 1’s ctf input format, has features
               not found in Babeltrace 1:

               ·   The component handles many trace quirks which are the
                   results of known tracer bugs and corner cases (LTTng-UST,
                   LTTng-modules, and barectf (see
                   <>)), making it
                   possible to decode malformed packets.

               ·   The component merges CTF traces sharing the same UUID
                   into a single, logical trace.

                   This feature supports LTTng 2.11’s tracing session
                   rotation trace chunks.

           ·   With a sink.ctf.fs component, you can create CTF traces on
               the file system.

               With babeltrace2(1), you can use the --output-format=ctf and
               --output options to create an implicit sink.ctf.fs component.

               For example:

                   $ babeltrace2 /path/to/input/trace \
                                 --output-format=ctf --output=trace-dir

       LTTng live (see <>) input

           ·   The babeltrace(1) command exits successfully when it cannot
               find an LTTng live (--input-format=lttng-live option) tracing

               The session-not-found-action initialization parameter
               controls what a source.ctf.lttng-live message iterator does
               when it cannot find the remote tracing session.

               If the action is end, the message iterator does like
               babeltrace(1) and simply ends successfully.

               If the action is continue (the default), the message iterator
               never ends: it keeps on trying until the tracing session
               exists, indeed subscribing to the session.


           ·   libbabeltrace2 shares nothing with libbabeltrace.

               The Babeltrace 2 library C API has features such as:

               ·   A single header file.

               ·   Function precondition and postcondition checking.

               ·   Object-oriented model with shared and unique objects.

               ·   Strict C typing and const correctness.

               ·   User-extensible classes.

               ·   Rich, thread-safe error reporting.

               ·   Per-component and per-subsystem logging levels.

               ·   Trace intermediate representation (IR) objects to make
                   the API trace-format-agnostic.

               ·   A versioned protocol for message interchange between
                   components to enable forward and backward compatibility.

           ·   You can build the library in developer mode to enable an
               extensive set of function precondition and postcondition

               The developer mode can help detect programming errors early
               when you develop a Babeltrace 2 plugin or an application
               using libbabeltrace2.

               See the project’s README for build-time requirements and
               detailed build instructions.


       This section defines the main concepts of the Babeltrace 2 project.

       These concepts translate into types and functions in libbabeltrace2
       and its Python bindings, but also as command-line actions and options
       in the babeltrace2 program. The other Babeltrace 2 manual pages
       assume that you are familiar with the following definitions.

       Some Babeltrace 2 concepts are interdependent: it is normal to jump
       from one definition to another to understand the big picture.

       Component class
           A reusable class which you can instantiate as one or more
           components within a trace processing graph.

           There are three types of component classes used to create the
           three types of components: source, filter, and sink.

           A component class implements methods, one of which is an
           initialization method, or constructor, to create a component. You
           pass initialization parameters to this method to customize the
           created component. For example, the initialization method of the
           source.ctf.fs component class accepts a mandatory inputs
           parameter which is an array of file system path(s) to the CTF
           trace(s). It also accepts an optional clock-class-offset-ns
           parameter which is an offset, in nanoseconds, to add to all the
           clock classes (descriptors of stream clocks) found in the
           traces’s metadata.

           A component class can have a description and a help text.

           A node within a trace processing graph.

           There are three types of components:

           Source component
               An input component which produces messages.

               Examples: CTF files input, log file input, LTTng live input,
               random event generator.

           Filter component
               An intermediate component which can transform the messages it
               consumes, augment them, sort them, discard them, or create
               new ones.

               Examples: filter which removes messages based on an
               expression, filter which adds debugging information to
               selected events, message muxer, trace trimmer.

           Sink component
               An output component which consumes messages and usually
               writes them to one or more formatted files.

               Examples: log file output, CTF files output, pretty-printed
               plain text output.

           Components are connected together within a trace processing graph
           through their ports. Source components have output ports, sink
           components have input ports, and filter components have both.

           A component is the instance of a component class. The terms
           component and component class instance are equivalent.

           Within a trace processing graph, each component has a unique
           name. This is not the name of its component class, but an
           instance name. If human is a component class name, than Nancy and
           John could be component names.

           Once a graph is configured (the first time it runs), you cannot
           add components to it for the remaining graph’s lifetime.

           A connection point, on a component, from which are sent or where
           are received messages when the trace processing graph runs.

           An output port is from where messages are sent. An input port is
           where messages are received. Source components have output ports,
           sink components have input ports, and filter components have

           You can only connect an output port to a single input port.

           All ports do not need to be connected.

           A filter or sink component receiving messages from its input
           ports is said to consume messages.

           The link between an output port and input port is a connection.

           Once a graph is configured (the first time it runs), you cannot
           connect ports for the remaining graph’s lifetime.

           The link between an output port and an input port through which
           messages flow when a trace processing graph runs.

       Message iterator
           An iterator on an input port of which the returned elements are

           A component or another message iterator can create many message
           iterators on a single input port, before or while the trace
           processing graph runs.

           The element of a message iterator.

           Messages flow from output ports to input ports.

           A source component message iterator produces messages, while a
           sink component consumes them. A filter component message iterator
           can both consume and produce messages.

           The main types of messages are:

               A trace event record within a packet or within a stream.

           Packet beginning
               The beginning of a packet within a stream.

               A packet is a conceptual container of events.

           Packet end
               The end of a packet within a stream.

           Stream beginning
               The beginning of a stream.

               A stream is a conceptual container of packets and/or events.

               Usually, a given source component’s output port sends packet
               and event messages which belong to a single stream, but it’s
               not required.

           Stream end
               The end of a stream.

           Discarded events
               A count of discarded events within a given time interval for
               a given stream.

           Discarded packets
               A count of discarded packets within a given time interval for
               a given stream.

       Trace processing graph
           A filter graph (see <>)
           where nodes are components and messages flow from output ports to
           input ports.

           You can build a trace processing graph with libbabeltrace2, with
           the Babeltrace 2 Python bindings, or with the babeltrace2-run(1)
           and babeltrace2-convert(1) CLI commands.

           When a trace processing graph runs, the sink components consume
           messages from their input ports, making all the graph’s message
           iterators work one message at a time to perform the trace
           conversion or analysis duty.

           A container, or package, of component classes as a shared library
           or Python module.

           Each component class within a plugin has a type (source, filter,
           or sink) and a name. The type and name pair is unique within a
           given plugin.

           libbabeltrace2 can load a plugin (.so, .dll, or .py file) at run
           time: the result is a plugin object in which you can find a
           specific component class and instantiate it within a trace
           processing graph as a component.

           The babeltrace2 program uses the
           COMP-CLS-TYPE.PLUGIN-NAME.COMP-CLS-NAME format to identify a
           specific component class within a specific plugin.  COMP-CLS-TYPE
           is either source (or src), filter (or flt), or sink.

           You can list the available Babeltrace 2 plugins with the
           babeltrace2-list-plugins(1) command.

           An operation with which you can get a named object from a
           component class, possibly with custom query parameters.

           The plain text metadata stream of a CTF trace and the available
           LTTng live sessions of a given LTTng relay daemon are examples of
           query objects.

           You can use libbabeltrace2, the Babeltrace 2 Python bindings, or
           the babeltrace2-query(1) CLI command to query a component class’s


       In the Babeltrace 2 manual pages, a component is represented with a
       box. The box has the component class type, plugin name, and component
       class name at the top. Just below, between square brackets, is its
       component name within the trace processing graph. Each port is
       represented with an @ symbol on the border(s) of the component box
       with its name inside the box. Output ports are on the box’s right
       border while input ports are on the box’s left border.

       For example, here’s a source component box:

           | src.ctf.fs |
           |  [my-src]  |
           |            |
           |    stream0 @
           |    stream1 @
           |    stream2 @

       This one is an instance of the source.ctf.fs component class named
       my-src. It has three output ports named stream0, stream1, and

       A trace processing graph is represented with multiple component boxes
       connected together. The connections are arrows from output ports to
       input ports.

       For example, here’s a simple conversion graph:

           +------------+    +-----------------+    +------------------+
           | src.ctf.fs |    | flt.utils.muxer |    | sink.text.pretty |
           |    [ctf]   |    |     [muxer]     |    |      [text]      |
           |            |    |                 |    |                  |
           |    stream0 @--->@ in0         out @--->@ in               |
           |    stream1 @--->@ in1             |    +------------------+
           |    stream2 @--->@ in2             |
           +------------+    @ in3             |

       Note that input port in3 of component muxer is not connected in this

       Sometimes, we symbolically represent other resources which are
       consumed from or produced by components. In this case, arrows are
       used, but they do not go to or from port symbols (@), except for
       messages. For example, in the graph above, the ctf source component
       consumes a CTF trace and the text sink component prints plain text to
       the terminal, so here’s a more complete diagram:

           CTF trace
             |   +------------+    +-----------------+    +------------------+
             |   | src.ctf.fs |    | flt.utils.muxer |    | sink.text.pretty |
             '-->|    [ctf]   |    |     [muxer]     |    |      [text]      |
                 |            |    |                 |    |                  |
                 |    stream0 @--->@ in0         out @--->@ in               |
                 |    stream1 @--->@ in1             |    +-----+------------+
                 |    stream2 @--->@ in2             |          |
                 +------------+    @ in3             |          '--> Terminal

       Here’s another example of a more complex graph which splits a
       specific stream using some criteria:

           +------------+    +-----------------+    +------------------+
           | src.ctf.fs |    | flt.utils.muxer |    | sink.text.pretty |
           |  [ctf-in]  |    |     [muxer]     |    |      [text]      |
           |            |    |                 |    |                  |
           |    stream0 @--->@ in0         out @--->@ in               |
           |    stream1 @--->@ in1             |    +------------------+
           |    stream2 @-.  @ in2             |
           +------------+ |  +-----------------+      +-------------+
                          |                           | sink.ctf.fs |
                          |                           |  [ctf-out0] |
                          |  +-------------------+    |             |
                          |  | flt.some.splitter | .->@ in          |
                          |  |     [splitter]    | |  +-------------+
                          |  |                   | |
                          '->@ in              A @-'  +-------------+
                             |                 B @-.  | sink.ctf.fs |
                             +-------------------+ |  |  [ctf-out1] |
                                                   |  |             |
                                                   '->@ in          |

BUGS         top

       If you encounter any issue or usability problem, please report it on
       the Babeltrace bug tracker (see

RESOURCES         top

       The Babeltrace project shares some communication channels with the
       LTTng project (see <>).

       ·   Babeltrace website (see <>)

       ·   Mailing list (see <>) for support and

       ·   IRC channel (see <irc://>): #lttng on

       ·   Bug tracker (see <>)

       ·   Git repository (see <>)

       ·   GitHub project (see <>)

       ·   Continuous integration (see

       ·   Code review (see <>)

AUTHORS         top

       The Babeltrace 2 project is the result of hard work by many regular
       developers and occasional contributors.

       The current project maintainer is Jérémie Galarneau

COPYRIGHT         top

       This manual page is part of the Babeltrace 2 project.

       Babeltrace is distributed under the MIT license (see

SEE ALSO         top


COLOPHON         top

       This page is part of the babeltrace (trace read and write libraries
       and a trace converter) project.  Information about the project can be
       found at ⟨⟩.  If you have a bug
       report for this manual page, send it to
       This page was obtained from the project's upstream Git repository
       ⟨git://⟩ on 2020-07-14.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-06-08.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to

Babeltrace 2.1.0-rc1          14 September 2019         BABELTRACE2-INTRO(7)

Pages that refer to this page: babeltrace2(1)babeltrace2-convert(1)babeltrace2-help(1)babeltrace2-list-plugins(1)babeltrace2-log(1)babeltrace2-query(1)babeltrace2-run(1)babeltrace2-filter.lttng-utils.debug-info(7)babeltrace2-filter.utils.muxer(7)babeltrace2-filter.utils.trimmer(7)babeltrace2-plugin-ctf(7)babeltrace2-plugin-lttng-utils(7)babeltrace2-plugin-text(7)babeltrace2-plugin-utils(7)