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.

       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

           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
               <>) traces.

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

               Plain text input/output.

               See babeltrace2-plugin-text(7).

               Common graph utilities (muxer, trimmer, counter, dummy

               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

               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 session.

               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

           •   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

       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

       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

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

           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 both.

           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

           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 messages.

           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

               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

           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

           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 object.


       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 stream2.

       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 example.

       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 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-15.)  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-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)