BitBake User Manual

BitBake Team

   Copyright © 2004, 2005, 2006, 2011 Chris Larson, Phil Blundell,
   Richard Purdie

   This work is licensed under the Creative Commons Attribution
   License. To view a copy of this license, visit
   http://creativecommons.org/licenses/by/2.5/ or send a letter to
   Creative Commons, 559 Nathan Abbott Way, Stanford, California
   94305, USA.
     __________________________________________________________

   Table of Contents

   1. Introduction

        Overview
        Background and goals

   2. Metadata

        Description

              Basic variable setting
              Variable expansion
              Setting a default value (?=)
              Setting a weak default value (??=)
              Immediate variable expansion (:=)
              Appending (+=) and prepending (=+)
              Appending (.=) and prepending (=.) without spaces
              Conditional metadata set
              Conditional appending
              Inclusion
              Requiring inclusion
              Python variable expansion
              Defining executable metadata
              Defining Python functions into the global Python
                      namespace

              Variable flags
              Inheritance
              Tasks
              Task Flags
              Events
              Variants

        Variable interaction: Worked Examples

              Override and append ordering
              Key Expansion

        Dependency handling

              Dependencies internal to the .bb file
              Build Dependencies
              Runtime Dependencies
              Recursive Dependencies
              Inter task

        Parsing

              Configuration files
              Classes
              .bb files

   3. File download support

        Overview
        Local file fetcher
        CVS fetcher
        HTTP/FTP fetcher
        SVN fetcher
        GIT fetcher

   4. The BitBake command

        Introduction
        Usage and syntax
        Special variables

              BB_NUMBER_THREADS

        Metadata

   List of Examples

   4.1. Executing a task against a single .bb
   4.2. Executing tasks against a set of .bb files
   4.3. Generating dependency graphs
   4.4. Setting BBFILES
   4.5. Depending on another .bb
   4.6. Using PROVIDES
   4.7. Specifying version preference
   4.8. Using “bbfile collections”

Chapter 1. Introduction

   Table of Contents

   Overview
   Background and goals

Overview

   BitBake is, at its simplest, a tool for executing tasks and
   managing metadata. As such, its similarities to GNU make and
   other build tools are readily apparent. It was inspired by
   Portage, the package management system used by the Gentoo Linux
   distribution. BitBake is the basis of the OpenEmbedded project,
   which is being used to build and maintain a number of embedded
   Linux distributions/projects such as Angstrom and the Yocto
   project.

Background and goals

   Prior to BitBake, no other build tool adequately met the needs
   of an aspiring embedded Linux distribution. All of the
   buildsystems used by traditional desktop Linux distributions
   lacked important functionality, and none of the ad-hoc
   buildroot systems, prevalent in the embedded space, were
   scalable or maintainable.

   Some important original goals for BitBake were:
     * Handle crosscompilation.
     * Handle interpackage 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, et cetera.
     * Must be Linux distribution agnostic (both build and
       target).
     * Must be architecture agnostic
     * Must support multiple build and target operating systems
       (including Cygwin, the BSDs, etc).
     * Must be able to be self contained, rather than tightly
       integrated into the build machine's root filesystem.
     * There must be a way to handle conditional metadata (on
       target architecture, operating system, distribution,
       machine).
     * It must be easy for the person using the tools to supply
       their own local metadata and packages to operate against.
     * Must make it easy to collaborate between multiple projects
       using BitBake for their builds.
     * Should provide an inheritance mechanism to share common
       metadata between many packages.

   Over time it has become apparent that some further requirements
   were necessary:
     * Handle variants of a base recipe (native, sdk, multilib).
     * Able to split metadata into layers and allow layers to
       override each other.
     * 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 additionl requirements. Flexibility and power have
   always been the priorities. It is highly extensible, supporting
   embedded Python code and execution of any arbitrary tasks.

Chapter 2. Metadata

   Table of Contents

   Description

        Basic variable setting
        Variable expansion
        Setting a default value (?=)
        Setting a weak default value (??=)
        Immediate variable expansion (:=)
        Appending (+=) and prepending (=+)
        Appending (.=) and prepending (=.) without spaces
        Conditional metadata set
        Conditional appending
        Inclusion
        Requiring inclusion
        Python variable expansion
        Defining executable metadata
        Defining Python functions into the global Python namespace
        Variable flags
        Inheritance
        Tasks
        Task Flags
        Events
        Variants

   Variable interaction: Worked Examples

        Override and append ordering
        Key Expansion

   Dependency handling

        Dependencies internal to the .bb file
        Build Dependencies
        Runtime Dependencies
        Recursive Dependencies
        Inter task

   Parsing

        Configuration files
        Classes
        .bb files

Description

   BitBake metadata can be classified into 3 major areas:
     * Configuration Files
     * .bb Files
     * Classes

   What follows are a large number of examples of BitBake
   metadata. Any syntax which isn't supported in any of the
   aforementioned areas will be documented as such.

Basic variable setting

VARIABLE = "value"

   In this example, VARIABLE is value.

Variable expansion

   BitBake supports variables referencing one another's contents
   using a syntax which is similar to shell scripting
A = "aval"
B = "pre${A}post"

   This results in A containing aval and B containing preavalpost.

Setting a default value (?=)

A ?= "aval"

   If A is set before the above is called, it will retain its
   previous value. If A is unset prior to the above call, A will
   be set to aval. Note that this assignment is immediate, so if
   there are multiple ?= assignments to a single variable, the
   first of those will be used.

Setting a weak default value (??=)

A ??= "somevalue"
A ??= "someothervalue"

   If A is set before the above, it will retain that value. If A
   is unset prior to the above, A will be set to someothervalue.
   This is a lazy/weak assignment in that the assignment does not
   occur until the end of the parsing process, so that the last,
   rather than the first, ??= assignment to a given variable will
   be used. Any other setting of A using = or ?= will however
   override the value set with ??=

Immediate variable expansion (:=)

   := results in a variable's contents being expanded immediately,
   rather than when the variable is actually used.
T = "123"
A := "${B} ${A} test ${T}"
T = "456"
B = "${T} bval"

C = "cval"
C := "${C}append"

   In that example, A would contain test 123, B would contain 456
   bval, and C would be cvalappend.

Appending (+=) and prepending (=+)

B = "bval"
B += "additionaldata"
C = "cval"
C =+ "test"

   In this example, B is now bval additionaldata and C is test
   cval.

Appending (.=) and prepending (=.) without spaces

B = "bval"
B .= "additionaldata"
C = "cval"
C =. "test"

   In this example, B is now bvaladditionaldata and C is testcval.
   In contrast to the above appending and prepending operators, no
   additional space will be introduced.

Conditional metadata set

   OVERRIDES is a “:” separated variable containing each item you
   want to satisfy conditions. So, if you have a variable which is
   conditional on “arm”, and “arm” is in OVERRIDES, then the “arm”
   specific version of the variable is used rather than the
   non-conditional version. Example:
OVERRIDES = "architecture:os:machine"
TEST = "defaultvalue"
TEST_os = "osspecificvalue"
TEST_condnotinoverrides = "othercondvalue"

   In this example, TEST would be osspecificvalue, due to the
   condition “os” being in OVERRIDES.

Conditional appending

   BitBake also supports appending and prepending to variables
   based on whether something is in OVERRIDES. Example:
DEPENDS = "glibc ncurses"
OVERRIDES = "machine:local"
DEPENDS_append_machine = " libmad"

   In this example, DEPENDS is set to glibc ncurses libmad.

Inclusion

   Next, there is the include directive, which causes BitBake to
   parse whatever file you specify, and insert it at that
   location, which is not unlike make. However, if the path
   specified on the include line is a relative path, BitBake will
   locate the first one it can find within BBPATH.

Requiring inclusion

   In contrast to the include directive, require will raise an
   ParseError if the file to be included cannot be found.
   Otherwise it will behave just like the include directive.

Python variable expansion

DATE = "${@time.strftime('%Y%m%d',time.gmtime())}"

   This would result in the DATE variable containing today's date.

Defining executable metadata

   NOTE: This is only supported in .bb and .bbclass files.
do_mytask () {
    echo "Hello, world!"
}

   This is essentially identical to setting a variable, except
   that this variable happens to be executable shell code.
python do_printdate () {
    import time
    print time.strftime('%Y%m%d', time.gmtime())
}

   This is the similar to the previous, but flags it as Python so
   that BitBake knows it is Python code.

Defining Python functions into the global Python namespace

   NOTE: This is only supported in .bb and .bbclass files.
def get_depends(bb, d):
    if d.getVar('SOMECONDITION', True):
        return "dependencywithcond"
    else:
        return "dependency"

SOMECONDITION = "1"
DEPENDS = "${@get_depends(bb, d)}"

   This would result in DEPENDS containing dependencywithcond.

Variable flags

   Variables can have associated flags which provide a way of
   tagging extra information onto a variable. Several flags are
   used internally by BitBake but they can be used externally too
   if needed. The standard operations mentioned above also work on
   flags.
VARIABLE[SOMEFLAG] = "value"

   In this example, VARIABLE has a flag, SOMEFLAG which is set to
   value.

Inheritance

   NOTE: This is only supported in .bb and .bbclass files.

   The inherit directive is a means of specifying what classes of
   functionality your .bb requires. It is a rudimentary form of
   inheritance. For example, you can easily abstract out the tasks
   involved in building a package that uses autoconf and automake,
   and put that into a bbclass for your packages to make use of. A
   given bbclass is located by searching for
   classes/filename.bbclass in BBPATH, where filename is what you
   inherited.

Tasks

   NOTE: This is only supported in .bb and .bbclass files.

   In BitBake, each step that needs to be run for a given .bb is
   known as a task. There is a command addtask to add new tasks
   (must be a defined Python executable metadata and must start
   with “do_”) and describe intertask dependencies.
python do_printdate () {
    import time
    print time.strftime('%Y%m%d', time.gmtime())
}

addtask printdate before do_build

   This defines the necessary Python function and adds it as a
   task which is now a dependency of do_build, the default task.
   If anyone executes the do_build task, that will result in
   do_printdate being run first.

Task Flags

   Tasks support a number of flags which control various
   functionality of the task. These are as follows:

   'dirs' - directories which should be created before the task
   runs

   'cleandirs' - directories which should created before the task
   runs but should be empty

   'noexec' - marks the tasks as being empty and no execution
   required. These are used as dependency placeholders or used
   when added tasks need to be subsequently disabled.

   'nostamp' - don't generate a stamp file for a task. This means
   the task is always rexecuted.

   'fakeroot' - this task needs to be run in a fakeroot
   environment, obtained by adding the variables in FAKEROOTENV to
   the environment.

   'umask' - the umask to run the task under.

   For the 'deptask', 'rdeptask', 'depends', 'rdepends' and
   'recrdeptask' flags please see the dependencies section.

Events

   NOTE: This is only supported in .bb and .bbclass files.

   BitBake allows installation of event handlers. Events are
   triggered at certain points during operation, such as the
   beginning of operation against a given .bb, the start of a
   given task, task failure, task success, et cetera. The intent
   is to make it easy to do things like email notification on
   build failure.
addhandler myclass_eventhandler
python myclass_eventhandler() {
    from bb.event import getName
    from bb import data

    print("The name of the Event is %s" % getName(e))
    print("The file we run for is %s" % data.getVar('FILE', e.data, True
))
}

   This event handler gets called every time an event is
   triggered. A global variable e is defined. e.data contains an
   instance of bb.data. With the getName(e) method one can get the
   name of the triggered event.

   The above event handler prints the name of the event and the
   content of the FILE variable.

Variants

   Two BitBake features exist to facilitate the creation of
   multiple buildable incarnations from a single recipe file.

   The first is BBCLASSEXTEND. This variable is a space separated
   list of classes used to "extend" the recipe for each variant.
   As an example, setting
BBCLASSEXTEND = "native"

   results in a second incarnation of the current recipe being
   available. This second incarnation will have the "native" class
   inherited.

   The second feature is BBVERSIONS. This variable allows a single
   recipe to build multiple versions of a project from a single
   recipe file, and allows you to specify conditional metadata
   (using the OVERRIDES mechanism) for a single version, or an
   optionally named range of versions:
BBVERSIONS = "1.0 2.0 git"
SRC_URI_git = "git://someurl/somepath.git"
BBVERSIONS = "1.0.[0-6]:1.0.0+ \
              1.0.[7-9]:1.0.7+"
SRC_URI_append_1.0.7+ = "file://some_patch_which_the_new_versions_need.p
atch;patch=1"

   Note that the name of the range will default to the original
   version of the recipe, so given OE, a recipe file of
   foo_1.0.0+.bb will default the name of its versions to 1.0.0+.
   This is useful, as the range name is not only placed into
   overrides; it's also made available for the metadata to use in
   the form of the BPV variable, for use in file:// search paths
   (FILESPATH).

Variable interaction: Worked Examples

   Despite the documentation of the different forms of variable
   definition above, it can be hard to work out what happens when
   variable operators are combined. This section documents some
   common questions people have regarding the way variables
   interact.

Override and append ordering

   There is often confusion about which order overrides and the
   various append operators take effect.
OVERRIDES = "foo"
A_foo_append = "X"

   In this case, X is unconditionally appended to the variable
   A_foo. Since foo is an override, A_foo would then replace A.
OVERRIDES = "foo"
A = "X"
A_append_foo = "Y"

   In this case, only when foo is in OVERRIDES, Y is appended to
   the variable A so the value of A would become XY (NB: no spaces
   are appended).
OVERRIDES = "foo"
A_foo_append = "X"
A_foo_append += "Y"

   This behaves as per the first case above, but the value of A
   would be "X Y" instead of just "X".
A = "1"
A_append = "2"
A_append = "3"
A += "4"
A .= "5"

   Would ultimately result in A taking the value "1 4523" since
   the _append operator executes at the same time as the expansion
   of other overrides.

Key Expansion

   Key expansion happens at the data store finalisation time just
   before overrides are expanded.
A${B} = "X"
B = "2"
A2 = "Y"

   So in this case A2 would take the value of "X".

Dependency handling

   BitBake handles dependencies at the task level since to allow
   for efficient operation with multiple processed executing in
   parallel. A robust method of specifying task dependencies is
   therefore needed.

Dependencies internal to the .bb file

   Where the dependencies are internal to a given .bb file, the
   dependencies are handled by the previously detailed addtask
   directive.

Build Dependencies

   DEPENDS lists build time dependencies. The 'deptask' flag for
   tasks is used to signify the task of each item listed in
   DEPENDS which must have completed before that task can be
   executed.
do_configure[deptask] = "do_populate_staging"

   means the do_populate_staging task of each item in DEPENDS must
   have completed before do_configure can execute.

Runtime Dependencies

   The PACKAGES variable lists runtime packages and each of these
   can have RDEPENDS and RRECOMMENDS runtime dependencies. The
   'rdeptask' flag for tasks is used to signify the task of each
   item runtime dependency which must have completed before that
   task can be executed.
do_package_write[rdeptask] = "do_package"

   means the do_package task of each item in RDEPENDS must have
   completed before do_package_write can execute.

Recursive Dependencies

   These are specified with the 'recrdeptask' flag which is used
   signify the task(s) of dependencies which must have completed
   before that task can be executed. It works by looking though
   the build and runtime dependencies of the current recipe as
   well as any inter-task dependencies the task has, then adding a
   dependency on the listed task. It will then recurse through the
   dependencies of those tasks and so on.

   It may be desireable to recurse not just through the
   dependencies of those tasks but through the build and runtime
   dependencies of dependent tasks too. If that is the case, the
   taskname itself should be referenced in the task list, e.g.
   do_a[recrdeptask] = "do_a do_b".

Inter task

   The 'depends' flag for tasks is a more generic form of which
   allows an interdependency on specific tasks rather than
   specifying the data in DEPENDS.
do_patch[depends] = "quilt-native:do_populate_staging"

   means the do_populate_staging task of the target quilt-native
   must have completed before the do_patch can execute.

   The 'rdepends' flag works in a similar way but takes targets in
   the runtime namespace instead of the build time dependency
   namespace.

Parsing

Configuration files

   The first kind of metadata in BitBake is configuration
   metadata. This metadata is global, and therefore affects all
   packages and tasks which are executed.

   BitBake will first search the current working directory for an
   optional "conf/bblayers.conf" configuration file. This file is
   expected to contain a BBLAYERS variable which is a space
   delimited list of 'layer' directories. For each directory in
   this list, a "conf/layer.conf" file will be searched for and
   parsed with the LAYERDIR variable being set to the directory
   where the layer was found. The idea is these files will setup
   BBPATH and other variables correctly for a given build
   directory automatically for the user.

   BitBake will then expect to find 'conf/bitbake.conf' somewhere
   in the user specified BBPATH. That configuration file generally
   has include directives to pull in any other metadata (generally
   files specific to architecture, machine, local and so on).

   Only variable definitions and include directives are allowed in
   .conf files.

Classes

   BitBake classes are our rudimentary inheritance mechanism. As
   briefly mentioned in the metadata introduction, they're parsed
   when an inherit directive is encountered, and they are located
   in classes/ relative to the directories in BBPATH.

.bb files

   A BitBake (.bb) file is a logical unit of tasks to be executed.
   Normally this is a package to be built. Inter-.bb dependencies
   are obeyed. The files themselves are located via the BBFILES
   variable, which is set to a space separated list of .bb files,
   and does handle wildcards.

Chapter 3. File download support

   Table of Contents

   Overview
   Local file fetcher
   CVS fetcher
   HTTP/FTP fetcher
   SVN fetcher
   GIT fetcher

Overview

   BitBake provides support to download files this procedure is
   called fetching and it handled by the fetch and fetch2 modules.
   At this point the original fetch code is considered to be
   replaced by fetch2 and this manual only related to the fetch2
   codebase.

   The SRC_URI is normally used to tell BitBake which files to
   fetch. The next sections will describe the available fetchers
   and their options. Each fetcher honors a set of variables and
   per URI parameters separated by a “;” consisting of a key and a
   value. The semantics of the variables and parameters are
   defined by the fetcher. BitBake tries to have consistent
   semantics between the different fetchers.

   The overall fetch process is that first, fetches are attempted
   from PREMIRRORS. If those don't work, the original SRC_URI is
   attempted and if that fails, BitBake will fall back to MIRRORS.
   Cross urls are supported, so its possible to mirror a git
   repository on an http server as a tarball for example. Some
   example commonly used mirror definitions are:
PREMIRRORS ?= "\
bzr://.*/.*   http://somemirror.org/sources/ \n \
cvs://.*/.*   http://somemirror.org/sources/ \n \
git://.*/.*   http://somemirror.org/sources/ \n \
hg://.*/.*    http://somemirror.org/sources/ \n \
osc://.*/.*   http://somemirror.org/sources/ \n \
p4://.*/.*    http://somemirror.org/sources/ \n \
svk://.*/.*   http://somemirror.org/sources/ \n \
svn://.*/.*   http://somemirror.org/sources/ \n"

MIRRORS =+ "\
ftp://.*/.*      http://somemirror.org/sources/ \n \
http://.*/.*     http://somemirror.org/sources/ \n \
https://.*/.*    http://somemirror.org/sources/ \n"

   Non-local downloaded output is placed into the directory
   specified by the DL_DIR. For non local archive downloads the
   code can verify sha256 and md5 checksums for the download to
   ensure the file has been downloaded correctly. These may be
   specified either in the form SRC_URI[md5sum] for the md5
   checksum and SRC_URI[sha256sum] for the sha256 checksum or as
   parameters on the SRC_URI such as
   SRC_URI="http://example.com/foobar.tar.bz2;md5sum=4a8e0f237e961
   fd7785d19d07fdb994d". If BB_STRICT_CHECKSUM is set, any
   download without a checksum will trigger an error message. In
   cases where multiple files are listed in SRC_URI, the name
   parameter is used assign names to the urls and these are then
   specified in the checksums in the form SRC_URI[name.sha256sum].

Local file fetcher

   The URN for the local file fetcher is file. The filename can be
   either absolute or relative. If the filename is relative,
   FILESPATH and failing that FILESDIR will be used to find the
   appropriate relative file. The metadata usually extend these
   variables to include variations of the values in OVERRIDES.
   Single files and complete directories can be specified.
SRC_URI= "file://relativefile.patch"
SRC_URI= "file://relativefile.patch;this=ignored"
SRC_URI= "file:///Users/ich/very_important_software"

CVS fetcher

   The URN for the CVS fetcher is cvs. This fetcher honors the
   variables CVSDIR, SRCDATE, FETCHCOMMAND_cvs, UPDATECOMMAND_cvs.
   DL_DIR specifies where a temporary checkout is saved. SRCDATE
   specifies which date to use when doing the fetching (the
   special value of "now" will cause the checkout to be updated on
   every build). FETCHCOMMAND and UPDATECOMMAND specify which
   executables to use for the CVS checkout or update.

   The supported parameters are module, tag, date, method,
   localdir, rsh and scmdata. The module specifies which module to
   check out, the tag describes which CVS TAG should be used for
   the checkout. By default the TAG is empty. A date can be
   specified to override the SRCDATE of the configuration to
   checkout a specific date. The special value of "now" will cause
   the checkout to be updated on every build.method is by default
   pserver. If ext is used the rsh parameter will be evaluated and
   CVS_RSH will be set. Finally, localdir is used to checkout into
   a special directory relative to CVSDIR.
SRC_URI = "cvs://CVSROOT;module=mymodule;tag=some-version;method=ext"
SRC_URI = "cvs://CVSROOT;module=mymodule;date=20060126;localdir=usethat"

HTTP/FTP fetcher

   The URNs for the HTTP/FTP fetcher are http, https and ftp. This
   fetcher honors the variables FETCHCOMMAND_wget. FETCHCOMMAND
   contains the command used for fetching. “${URI}” and “${FILES}”
   will be replaced by the URI and basename of the file to be
   fetched.
SRC_URI = "http://oe.handhelds.org/not_there.aac"
SRC_URI = "ftp://oe.handhelds.org/not_there_as_well.aac"
SRC_URI = "ftp://you@oe.handheld.sorg/home/you/secret.plan"

SVN fetcher

   The URN for the SVN fetcher is svn.

   This fetcher honors the variables FETCHCOMMAND_svn, SVNDIR,
   SRCREV. FETCHCOMMAND contains the subversion command. SRCREV
   specifies which revision to use when doing the fetching.

   The supported parameters are proto, rev and scmdata. proto is
   the Subversion protocol, rev is the Subversion revision. If
   scmdata is set to “keep”, the “.svn” directories will be
   available during compile-time.
SRC_URI = "svn://svn.oe.handhelds.org/svn;module=vip;proto=http;rev=667"
SRC_URI = "svn://svn.oe.handhelds.org/svn/;module=opie;proto=svn+ssh;dat
e=20060126"

GIT fetcher

   The URN for the GIT Fetcher is git.

   The variable GITDIR will be used as the base directory where
   the git tree is cloned to.

   The parameters are tag, protocol and scmdata. tag is a Git tag,
   the default is “master”. protocol is the Git protocol to use
   and defaults to “git” if a hostname is set, otherwise its
   “file”. If scmdata is set to “keep”, the “.git” directory will
   be available during compile-time.
SRC_URI = "git://git.oe.handhelds.org/git/vip.git;tag=version-1"
SRC_URI = "git://git.oe.handhelds.org/git/vip.git;protocol=http"

Chapter 4. The BitBake command

   Table of Contents

   Introduction
   Usage and syntax
   Special variables

        BB_NUMBER_THREADS

   Metadata

Introduction

   bitbake is the primary command in the system. It facilitates
   executing tasks in a single .bb file, or executing a given task
   on a set of multiple .bb files, accounting for
   interdependencies amongst them.

Usage and syntax

$ bitbake --help
usage: bitbake [options] [package ...]

Executes the specified task (default is 'build') for a given set of BitB
ake files.
It expects that BBFILES is defined, which is a space separated list of f
iles to
be executed.  BBFILES does support wildcards.
Default BBFILES are the .bb files in the current directory.

options:
  --version             show program's version number and exit
  -h, --help            show this help message and exit
  -b BUILDFILE, --buildfile=BUILDFILE
                        execute the task against this .bb file, rather t
han a
                        package from BBFILES.
  -k, --continue        continue as much as possible after an error. Whi
le the
                        target that failed, and those that depend on it,
                        cannot be remade, the other dependencies of thes
e
                        targets can be processed all the same.
  -f, --force           force run of specified cmd, regardless of stamp
status
  -i, --interactive     drop into the interactive mode also called the B
itBake
                        shell.
  -c CMD, --cmd=CMD     Specify task to execute. Note that this only exe
cutes
                        the specified task for the providee and the pack
ages
                        it depends on, i.e. 'compile' does not implicitl
y call
                        stage for the dependencies (IOW: use only if you
 know
                        what you are doing). Depending on the base.bbcla
ss a
                        listtasks task is defined and will show availabl
e
                        tasks
  -r FILE, --read=FILE  read the specified file before bitbake.conf
  -v, --verbose         output more chit-chat to the terminal
  -D, --debug           Increase the debug level. You can specify this m
ore
                        than once.
  -n, --dry-run         don't execute, just go through the motions
  -p, --parse-only      quit after parsing the BB files (developers only
)
  -s, --show-versions   show current and preferred versions of all packa
ges
  -e, --environment     show the global or per-package environment (this
 is
                        what used to be bbread)
  -g, --graphviz        emit the dependency trees of the specified packa
ges in
                        the dot syntax
  -I IGNORED_DOT_DEPS, --ignore-deps=IGNORED_DOT_DEPS
                        Stop processing at the given list of dependencie
s when
                        generating dependency graphs. This can help to m
ake
                        the graph more appealing
  -l DEBUG_DOMAINS, --log-domains=DEBUG_DOMAINS
                        Show debug logging for the specified logging dom
ains
  -P, --profile         profile the command and print a report



   Example 4.1. Executing a task against a single .bb

   Executing tasks for a single file is relatively simple. You
   specify the file in question, and BitBake parses it and
   executes the specified task (or “build” by default). It obeys
   intertask dependencies when doing so.

   “clean” task:
$ bitbake -b blah_1.0.bb -c clean

   “build” task:
$ bitbake -b blah_1.0.bb

   Example 4.2. Executing tasks against a set of .bb 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 we want to execute at this time. There also needs
   to be a way for each .bb to express its dependencies, both for
   build time and runtime. There must be a way for the user to
   express their preferences when multiple .bb's provide the same
   functionality, or when there are multiple versions of a .bb.

   The next section, Metadata, outlines how to specify such
   things.

   Note that the bitbake command, when not using --buildfile,
   accepts a PROVIDER, not a filename or anything else. By
   default, a .bb generally PROVIDES its packagename,
   packagename-version, and packagename-version-revision.
$ bitbake blah
$ bitbake blah-1.0
$ bitbake blah-1.0-r0
$ bitbake -c clean blah
$ bitbake virtual/whatever
$ bitbake -c clean virtual/whatever

   Example 4.3. Generating dependency graphs

   BitBake is able to generate dependency graphs using the dot
   syntax. These graphs can be converted to images using the dot
   application from Graphviz. Two files will be written into the
   current working directory, depends.dot containing dependency
   information at the package level and task-depends.dot
   containing a breakdown of the dependencies at the task level.
   To stop depending on common depends, one can use the -I depend
   to omit these from the graph. This can lead to more readable
   graphs. This way, DEPENDS from inherited classes such as
   base.bbclass can be removed from the graph.
$ bitbake -g blah
$ bitbake -g -I virtual/whatever -I bloom blah

Special variables

   Certain variables affect BitBake operation:

BB_NUMBER_THREADS

   The number of threads BitBake should run at once (default: 1).

Metadata

   As you may have seen in the usage information, or in the
   information about .bb files, the BBFILES variable is how the
   BitBake tool locates its files. This variable is a space
   separated list of files that are available, and supports
   wildcards.

   Example 4.4. Setting BBFILES
BBFILES = "/path/to/bbfiles/*.bb"

   With regard to dependencies, it expects the .bb to define a
   DEPENDS variable, which contains a space separated list of
   “package names”, which themselves are the PN variable. The PN
   variable is, in general, set to a component of the .bb filename
   by default.

   Example 4.5. Depending on another .bb

   a.bb:
PN = "package-a"
DEPENDS += "package-b"

   b.bb:
PN = "package-b"

   Example 4.6. Using PROVIDES

   This example shows the usage of the PROVIDES variable, which
   allows a given .bb to specify what functionality it provides.

   package1.bb:
PROVIDES += "virtual/package"

   package2.bb:
DEPENDS += "virtual/package"

   package3.bb:
PROVIDES += "virtual/package"

   As you can see, we have two different .bb's that provide the
   same functionality (virtual/package). Clearly, there needs to
   be a way for the person running BitBake to control which of
   those providers gets used. There is, indeed, such a way.

   The following would go into a .conf file, to select package1:
PREFERRED_PROVIDER_virtual/package = "package1"

   Example 4.7. Specifying version preference

   When there are multiple “versions” of a given package, BitBake
   defaults to selecting the most recent version, unless otherwise
   specified. If the .bb in question has a DEFAULT_PREFERENCE set
   lower than the other .bb's (default is 0), then it will not be
   selected. This allows the person or persons maintaining the
   repository of .bb files to specify their preference for the
   default selected version. In addition, the user can specify
   their preferred version.

   If the first .bb is named a_1.1.bb, then the PN variable will
   be set to “a”, and the PV variable will be set to 1.1.

   If we then have an a_1.2.bb, BitBake will choose 1.2 by
   default. However, if we define the following variable in a
   .conf that BitBake parses, we can change that.
PREFERRED_VERSION_a = "1.1"

   Example 4.8. Using “bbfile collections”

   bbfile collections exist to allow the user to have multiple
   repositories of bbfiles that contain the same exact package.
   For example, one could easily use them to make one's own local
   copy of an upstream repository, but with custom modifications
   that one does not want upstream. Usage:
BBFILES = "/stuff/openembedded/*/*.bb /stuff/openembedded.modified/*/*.b
b"
BBFILE_COLLECTIONS = "upstream local"
BBFILE_PATTERN_upstream = "^/stuff/openembedded/"
BBFILE_PATTERN_local = "^/stuff/openembedded.modified/"
BBFILE_PRIORITY_upstream = "5"
BBFILE_PRIORITY_local = "10"
