1 Overview
Welcome to the BitBake User Manual. This manual provides information on the BitBake tool. The information attempts to be as independent as possible regarding systems that use BitBake, such as OpenEmbedded and the Yocto Project. In some cases, scenarios or examples within the context of a build system are used in the manual to help with understanding. For these cases, the manual clearly states the context.
1.1 Introduction
Fundamentally, BitBake is a generic task execution engine that allows shell and Python tasks to be run efficiently and in parallel while working within complex inter-task dependency constraints. One of BitBake’s main users, OpenEmbedded, takes this core and builds embedded Linux software stacks using a task-oriented approach.
Conceptually, BitBake is similar to GNU Make in some regards but has significant differences:
BitBake executes tasks according to the provided metadata that builds up the tasks. Metadata is stored in recipe (
.bb) and related recipe “append” (.bbappend) files, configuration (.conf) and underlying include (.inc) files, and in class (.bbclass) files. The metadata provides BitBake with instructions on what tasks to run and the dependencies between those tasks.BitBake includes a fetcher library for obtaining source code from various places such as local files, source control systems, or websites.
The instructions for each unit to be built (e.g. a piece of software) are known as “recipe” files and contain all the information about the unit (dependencies, source file locations, checksums, description and so on).
BitBake includes a client/server abstraction and can be used from a command line or used as a service over XML-RPC and has several different user interfaces.
1.2 History and Goals
BitBake was originally a part of the OpenEmbedded project. It was inspired by the Portage package management system used by the Gentoo Linux distribution. On December 7, 2004, OpenEmbedded project team member Chris Larson split the project into two distinct pieces:
BitBake, a generic task executor
OpenEmbedded, a metadata set utilized by BitBake
Today, BitBake is the primary basis of the OpenEmbedded project, which is being used to build and maintain Linux distributions such as the Poky Reference Distribution, developed under the umbrella of the Yocto Project.
Prior to BitBake, no other build tool adequately met the needs of an aspiring embedded Linux distribution. All of the build systems used by traditional desktop Linux distributions lacked important functionality, and none of the ad hoc Buildroot-based systems, prevalent in the embedded space, were scalable or maintainable.
Some important original goals for BitBake were:
Handle cross-compilation.
Handle inter-package dependencies (build time on target architecture, build time on native architecture, and runtime).
Support running any number of tasks within a given package, including, but not limited to, fetching upstream sources, unpacking them, patching them, configuring them, and so forth.
Be Linux distribution agnostic for both build and target systems.
Be architecture agnostic.
Support multiple build and target operating systems (e.g. Cygwin, the BSDs, and so forth).
Be self-contained, rather than tightly integrated into the build machine’s root filesystem.
Handle conditional metadata on the target architecture, operating system, distribution, and machine.
Be easy to use the tools to supply local metadata and packages against which to operate.
Be easy to use BitBake to collaborate between multiple projects for their builds.
Provide an inheritance mechanism to share common metadata between many packages.
Over time it became apparent that some further requirements were necessary:
Handle variants of a base recipe (e.g. native, sdk, and multilib).
Split metadata into layers and allow layers to enhance or override other layers.
Allow representation of a given set of input variables to a task as a checksum. Based on that checksum, allow acceleration of builds with prebuilt components.
BitBake satisfies all the original requirements and many more with extensions being made to the basic functionality to reflect the additional requirements. Flexibility and power have always been the priorities. BitBake is highly extensible and supports embedded Python code and execution of any arbitrary tasks.
1.3 Concepts
BitBake is a program written in the Python language. At the highest level, BitBake interprets metadata, decides what tasks are required to run, and executes those tasks. Similar to GNU Make, BitBake controls how software is built. GNU Make achieves its control through “makefiles”, while BitBake uses “recipes”.
BitBake extends the capabilities of a simple tool like GNU Make by allowing for the definition of much more complex tasks, such as assembling entire embedded Linux distributions.
The remainder of this section introduces several concepts that should be understood in order to better leverage the power of BitBake.
1.3.1 Recipes
BitBake Recipes, which are denoted by the file extension .bb, are
the most basic metadata files. These recipe files provide BitBake with
the following:
Descriptive information about the package (author, homepage, license, and so on)
The version of the recipe
Existing dependencies (both build and runtime dependencies)
Where the source code resides and how to fetch it
Whether the source code requires any patches, where to find them, and how to apply them
How to configure and compile the source code
How to assemble the generated artifacts into one or more installable packages
Where on the target machine to install the package or packages created
Within the context of BitBake, or any project utilizing BitBake as its
build system, files with the .bb extension are referred to as
recipes.
Note
The term “package” is also commonly used to describe recipes. However, since the same word is used to describe packaged output from a project, it is best to maintain a single descriptive term - “recipes”. Put another way, a single “recipe” file is quite capable of generating a number of related but separately installable “packages”. In fact, that ability is fairly common.
1.3.2 Configuration Files
Configuration files, which are denoted by the .conf extension,
define various configuration variables that govern the project’s build
process. These files fall into several areas that define machine
configuration, distribution configuration, possible compiler tuning,
general common configuration, and user configuration. The main
configuration file is the sample bitbake.conf file, which is located
within the BitBake source tree conf directory.
1.3.3 Classes
Class files, which are denoted by the .bbclass extension, contain
information that is useful to share between metadata files. The BitBake
source tree currently comes with one class metadata file called
base.bbclass. You can find this file in the classes directory.
The base.bbclass class files is special since it is always included
automatically for all recipes and classes. This class contains
definitions for standard basic tasks such as fetching, unpacking,
configuring (empty by default), compiling (runs any Makefile present),
installing (empty by default) and packaging (empty by default). These
tasks are often overridden or extended by other classes added during the
project development process.
1.3.4 Layers
Layers allow you to isolate different types of customizations from each other. While you might find it tempting to keep everything in one layer when working on a single project, the more modular your metadata, the easier it is to cope with future changes.
To illustrate how you can use layers to keep things modular, consider
customizations you might make to support a specific target machine.
These types of customizations typically reside in a special layer,
rather than a general layer, called a Board Support Package (BSP) layer.
Furthermore, the machine customizations should be isolated from recipes
and metadata that support a new GUI environment, for example. This
situation gives you a couple of layers: one for the machine
configurations and one for the GUI environment. It is important to
understand, however, that the BSP layer can still make machine-specific
additions to recipes within the GUI environment layer without polluting
the GUI layer itself with those machine-specific changes. You can
accomplish this through a recipe that is a BitBake append
(.bbappend) file.
1.3.5 Append Files
Append files, which are files that have the .bbappend file
extension, extend or override information in an existing recipe file.
BitBake expects every append file to have a corresponding recipe file.
Furthermore, the append file and corresponding recipe file must use the
same root filename. The filenames can differ only in the file type
suffix used (e.g. formfactor_0.0.bb and
formfactor_0.0.bbappend).
Information in append files extends or overrides the information in the underlying, similarly-named recipe files.
When you name an append file, you can use the “%” wildcard character
to allow for matching recipe names. For example, suppose you have an
append file named as follows:
busybox_1.21.%.bbappend
That append file
would match any busybox_1.21.x.bb version of the recipe. So,
the append file would match the following recipe names:
busybox_1.21.1.bb
busybox_1.21.2.bb
busybox_1.21.3.bb
Note
The use of the “ % “ character is limited in that it only works directly in front of the .bbappend portion of the append file’s name. You cannot use the wildcard character in any other location of the name.
If the busybox recipe was updated to busybox_1.3.0.bb, the
append name would not match. However, if you named the append file
busybox_1.%.bbappend, then you would have a match.
In the most general case, you could name the append file something as
simple as busybox_%.bbappend to be entirely version independent.
1.4 Obtaining BitBake
You can obtain BitBake several different ways:
Cloning BitBake: Using Git to clone the BitBake source code repository is the recommended method for obtaining BitBake. Cloning the repository makes it easy to get bug fixes and have access to stable branches and the master branch. Once you have cloned BitBake, you should use the latest stable branch for development since the master branch is for BitBake development and might contain less stable changes.
You usually need a version of BitBake that matches the metadata you are using. The metadata is generally backwards compatible but not forward compatible.
Here is an example that clones the BitBake repository:
$ git clone git://git.openembedded.org/bitbake
This command clones the BitBake Git repository into a directory called
bitbake. Alternatively, you can designate a directory after thegit clonecommand if you want to call the new directory something other thanbitbake. Here is an example that names the directorybbdev:$ git clone git://git.openembedded.org/bitbake bbdev
Installation using your Distribution Package Management System: This method is not recommended because the BitBake version that is provided by your distribution, in most cases, is several releases behind a snapshot of the BitBake repository.
Taking a snapshot of BitBake: Downloading a snapshot of BitBake from the source code repository gives you access to a known branch or release of BitBake.
Note
Cloning the Git repository, as described earlier, is the preferred method for getting BitBake. Cloning the repository makes it easier to update as patches are added to the stable branches.
The following example downloads a snapshot of BitBake version 1.17.0:
$ wget https://git.openembedded.org/bitbake/snapshot/bitbake-1.17.0.tar.gz $ tar zxpvf bitbake-1.17.0.tar.gz
After extraction of the tarball using the tar utility, you have a directory entitled
bitbake-1.17.0.Using the BitBake that Comes With Your Build Checkout: A final possibility for getting a copy of BitBake is that it already comes with your checkout of a larger BitBake-based build system, such as Poky. Rather than manually checking out individual layers and gluing them together yourself, you can check out an entire build system. The checkout will already include a version of BitBake that has been thoroughly tested for compatibility with the other components. For information on how to check out a particular BitBake-based build system, consult that build system’s supporting documentation.
1.5 The BitBake Command
The bitbake command is the primary interface to the BitBake tool.
This section presents the BitBake command syntax and provides several
execution examples.
1.5.1 Usage and syntax
Following is the usage and syntax for BitBake:
$ bitbake -h
Usage: bitbake [options] [recipename/target recipe:do_task ...]
Executes the specified task (default is 'build') for a given set of target recipes (.bb files).
It is assumed there is a conf/bblayers.conf available in cwd or in BBPATH which
will provide the layer, BBFILES and other configuration information.
Options:
--version show program's version number and exit
-h, --help show this help message and exit
-b BUILDFILE, --buildfile=BUILDFILE
Execute tasks from a specific .bb recipe directly.
WARNING: Does not handle any dependencies from other
recipes.
-k, --continue Continue as much as possible after an error. While the
target that failed and anything depending on it cannot
be built, as much as possible will be built before
stopping.
-f, --force Force the specified targets/task to run (invalidating
any existing stamp file).
-c CMD, --cmd=CMD Specify the task to execute. The exact options
available depend on the metadata. Some examples might
be 'compile' or 'populate_sysroot' or 'listtasks' may
give a list of the tasks available.
-C INVALIDATE_STAMP, --clear-stamp=INVALIDATE_STAMP
Invalidate the stamp for the specified task such as
'compile' and then run the default task for the
specified target(s).
-r PREFILE, --read=PREFILE
Read the specified file before bitbake.conf.
-R POSTFILE, --postread=POSTFILE
Read the specified file after bitbake.conf.
-v, --verbose Enable tracing of shell tasks (with 'set -x'). Also
print bb.note(...) messages to stdout (in addition to
writing them to ${T}/log.do_<task>).
-D, --debug Increase the debug level. You can specify this more
than once. -D sets the debug level to 1, where only
bb.debug(1, ...) messages are printed to stdout; -DD
sets the debug level to 2, where both bb.debug(1, ...)
and bb.debug(2, ...) messages are printed; etc.
Without -D, no debug messages are printed. Note that
-D only affects output to stdout. All debug messages
are written to ${T}/log.do_taskname, regardless of the
debug level.
-q, --quiet Output less log message data to the terminal. You can
specify this more than once.
-n, --dry-run Don't execute, just go through the motions.
-S SIGNATURE_HANDLER, --dump-signatures=SIGNATURE_HANDLER
Dump out the signature construction information, with
no task execution. The SIGNATURE_HANDLER parameter is
passed to the handler. Two common values are none and
printdiff but the handler may define more/less. none
means only dump the signature, printdiff means compare
the dumped signature with the cached one.
-p, --parse-only Quit after parsing the BB recipes.
-s, --show-versions Show current and preferred versions of all recipes.
-e, --environment Show the global or per-recipe environment complete
with information about where variables were
set/changed.
-g, --graphviz Save dependency tree information for the specified
targets in the dot syntax.
-I EXTRA_ASSUME_PROVIDED, --ignore-deps=EXTRA_ASSUME_PROVIDED
Assume these dependencies don't exist and are already
provided (equivalent to ASSUME_PROVIDED). Useful to
make dependency graphs more appealing
-l DEBUG_DOMAINS, --log-domains=DEBUG_DOMAINS
Show debug logging for the specified logging domains
-P, --profile Profile the command and save reports.
-u UI, --ui=UI The user interface to use (knotty, ncurses, taskexp or
teamcity - default knotty).
--token=XMLRPCTOKEN Specify the connection token to be used when
connecting to a remote server.
--revisions-changed Set the exit code depending on whether upstream
floating revisions have changed or not.
--server-only Run bitbake without a UI, only starting a server
(cooker) process.
-B BIND, --bind=BIND The name/address for the bitbake xmlrpc server to bind
to.
-T SERVER_TIMEOUT, --idle-timeout=SERVER_TIMEOUT
Set timeout to unload bitbake server due to
inactivity, set to -1 means no unload, default:
Environment variable BB_SERVER_TIMEOUT.
--no-setscene Do not run any setscene tasks. sstate will be ignored
and everything needed, built.
--skip-setscene Skip setscene tasks if they would be executed. Tasks
previously restored from sstate will be kept, unlike
--no-setscene
--setscene-only Only run setscene tasks, don't run any real tasks.
--remote-server=REMOTE_SERVER
Connect to the specified server.
-m, --kill-server Terminate any running bitbake server.
--observe-only Connect to a server as an observing-only client.
--status-only Check the status of the remote bitbake server.
-w WRITEEVENTLOG, --write-log=WRITEEVENTLOG
Writes the event log of the build to a bitbake event
json file. Use '' (empty string) to assign the name
automatically.
--runall=RUNALL Run the specified task for any recipe in the taskgraph
of the specified target (even if it wouldn't otherwise
have run).
--runonly=RUNONLY Run only the specified task within the taskgraph of
the specified targets (and any task dependencies those
tasks may have).
1.5.2 Examples
This section presents some examples showing how to use BitBake.
1.5.2.1 Executing a Task Against a Single Recipe
Executing tasks for a single recipe file is relatively simple. You specify the file in question, and BitBake parses it and executes the specified task. If you do not specify a task, BitBake executes the default task, which is “build”. BitBake obeys inter-task dependencies when doing so.
The following command runs the build task, which is the default task, on
the foo_1.0.bb recipe file:
$ bitbake -b foo_1.0.bb
The following command runs the clean task on the foo.bb recipe file:
$ bitbake -b foo.bb -c clean
Note
The “-b” option explicitly does not handle recipe dependencies. Other than for debugging purposes, it is instead recommended that you use the syntax presented in the next section.
1.5.2.2 Executing Tasks Against a Set of Recipe Files
There are a number of additional complexities introduced when one wants
to manage multiple .bb files. Clearly there needs to be a way to
tell BitBake what files are available and, of those, which you want to
execute. There also needs to be a way for each recipe to express its
dependencies, both for build-time and runtime. There must be a way for
you to express recipe preferences when multiple recipes provide the same
functionality, or when there are multiple versions of a recipe.
The bitbake command, when not using “–buildfile” or “-b” only
accepts a “PROVIDES”. You cannot provide anything else. By default, a
recipe file generally “PROVIDES” its “packagename” as shown in the
following example:
$ bitbake foo
This next example “PROVIDES” the
package name and also uses the “-c” option to tell BitBake to just
execute the do_clean task:
$ bitbake -c clean foo
1.5.2.3 Executing a List of Task and Recipe Combinations
The BitBake command line supports specifying different tasks for
individual targets when you specify multiple targets. For example,
suppose you had two targets (or recipes) myfirstrecipe and
mysecondrecipe and you needed BitBake to run taskA for the first
recipe and taskB for the second recipe:
$ bitbake myfirstrecipe:do_taskA mysecondrecipe:do_taskB
1.5.2.4 Generating Dependency Graphs
BitBake is able to generate dependency graphs using the dot syntax.
You can convert these graphs into images using the dot tool from
Graphviz.
When you generate a dependency graph, BitBake writes two files to the current working directory:
task-depends.dot: Shows dependencies between tasks. These dependencies match BitBake’s internal task execution list.pn-buildlist: Shows a simple list of targets that are to be built.
To stop depending on common depends, use the -I depend option and
BitBake omits them from the graph. Leaving this information out can
produce more readable graphs. This way, you can remove from the graph
DEPENDS from inherited classes such as base.bbclass.
Here are two examples that create dependency graphs. The second example omits depends common in OpenEmbedded from the graph:
$ bitbake -g foo
$ bitbake -g -I virtual/kernel -I eglibc foo
1.5.2.5 Executing a Multiple Configuration Build
BitBake is able to build multiple images or packages using a single command where the different targets require different configurations (multiple configuration builds). Each target, in this scenario, is referred to as a “multiconfig”.
To accomplish a multiple configuration build, you must define each
target’s configuration separately using a parallel configuration file in
the build directory. The location for these multiconfig configuration
files is specific. They must reside in the current build directory in a
sub-directory of conf named multiconfig. Following is an example
for two separate targets:
The reason for this required file hierarchy is because the BBPATH variable is not constructed until the layers are parsed. Consequently, using the configuration file as a pre-configuration file is not possible unless it is located in the current working directory.
Minimally, each configuration file must define the machine and the temporary directory BitBake uses for the build. Suggested practice dictates that you do not overlap the temporary directories used during the builds.
Aside from separate configuration files for each target, you must also
enable BitBake to perform multiple configuration builds. Enabling is
accomplished by setting the
BBMULTICONFIG variable in the
local.conf configuration file. As an example, suppose you had
configuration files for target1 and target2 defined in the build
directory. The following statement in the local.conf file both
enables BitBake to perform multiple configuration builds and specifies
the two extra multiconfigs:
BBMULTICONFIG = "target1 target2"
Once the target configuration files are in place and BitBake has been enabled to perform multiple configuration builds, use the following command form to start the builds:
$ bitbake [mc:multiconfigname:]target [[[mc:multiconfigname:]target] ... ]
Here is an example for two extra multiconfigs: target1 and target2:
$ bitbake mc::target mc:target1:target mc:target2:target
1.5.2.6 Enabling Multiple Configuration Build Dependencies
Sometimes dependencies can exist between targets (multiconfigs) in a multiple configuration build. For example, suppose that in order to build an image for a particular architecture, the root filesystem of another build for a different architecture needs to exist. In other words, the image for the first multiconfig depends on the root filesystem of the second multiconfig. This dependency is essentially that the task in the recipe that builds one multiconfig is dependent on the completion of the task in the recipe that builds another multiconfig.
To enable dependencies in a multiple configuration build, you must declare the dependencies in the recipe using the following statement form:
task_or_package[mcdepends] = "mc:from_multiconfig:to_multiconfig:recipe_name:task_on_which_to_depend"
To better show how to use this statement, consider an example with two
multiconfigs: target1 and target2:
image_task[mcdepends] = "mc:target1:target2:image2:rootfs_task"
In this example, the
from_multiconfig is “target1” and the to_multiconfig is “target2”. The
task on which the image whose recipe contains image_task depends on the
completion of the rootfs_task used to build out image2, which is
associated with the “target2” multiconfig.
Once you set up this dependency, you can build the “target1” multiconfig using a BitBake command as follows:
$ bitbake mc:target1:image1
This command executes all the tasks needed to create image1 for the “target1”
multiconfig. Because of the dependency, BitBake also executes through
the rootfs_task for the “target2” multiconfig build.
Having a recipe depend on the root filesystem of another build might not seem that useful. Consider this change to the statement in the image1 recipe:
image_task[mcdepends] = "mc:target1:target2:image2:image_task"
In this case, BitBake must create image2 for the “target2” build since
the “target1” build depends on it.
Because “target1” and “target2” are enabled for multiple configuration builds and have separate configuration files, BitBake places the artifacts for each build in the respective temporary build directories.