poky/bitbake/doc/bitbake-user-manual/bitbake-user-manual-hello.rst - mdmillerii/openbmc - Gitiles

 .. SPDX-License-Identifier: CC-BY-2.5

 ===================
 Hello World Example
 ===================

 BitBake Hello World
 ===================

 The simplest example commonly used to demonstrate any new programming
 language or tool is the "`Hello
 World <http://en.wikipedia.org/wiki/Hello_world_program>`__" example.
 This appendix demonstrates, in tutorial form, Hello World within the
 context of BitBake. The tutorial describes how to create a new project
 and the applicable metadata files necessary to allow BitBake to build
 it.

 Obtaining BitBake
 =================

 See the :ref:`bitbake-user-manual/bitbake-user-manual-intro:obtaining bitbake` section for
 information on how to obtain BitBake. Once you have the source code on
 your machine, the BitBake directory appears as follows::

    $ ls -al
    total 108
    drwxr-xr-x  9 fawkh 10000  4096 feb 24 12:10 .
    drwx------ 36 fawkh 10000  4096 mar  2 17:00 ..
    -rw-r--r--  1 fawkh 10000   365 feb 24 12:10 AUTHORS
    drwxr-xr-x  2 fawkh 10000  4096 feb 24 12:10 bin
    -rw-r--r--  1 fawkh 10000 16501 feb 24 12:10 ChangeLog
    drwxr-xr-x  2 fawkh 10000  4096 feb 24 12:10 classes
    drwxr-xr-x  2 fawkh 10000  4096 feb 24 12:10 conf
    drwxr-xr-x  5 fawkh 10000  4096 feb 24 12:10 contrib
    drwxr-xr-x  6 fawkh 10000  4096 feb 24 12:10 doc
    drwxr-xr-x  8 fawkh 10000  4096 mar  2 16:26 .git
    -rw-r--r--  1 fawkh 10000    31 feb 24 12:10 .gitattributes
    -rw-r--r--  1 fawkh 10000   392 feb 24 12:10 .gitignore
    drwxr-xr-x 13 fawkh 10000  4096 feb 24 12:11 lib
    -rw-r--r--  1 fawkh 10000  1224 feb 24 12:10 LICENSE
    -rw-r--r--  1 fawkh 10000 15394 feb 24 12:10 LICENSE.GPL-2.0-only
    -rw-r--r--  1 fawkh 10000  1286 feb 24 12:10 LICENSE.MIT
    -rw-r--r--  1 fawkh 10000   229 feb 24 12:10 MANIFEST.in
    -rw-r--r--  1 fawkh 10000  2413 feb 24 12:10 README
    -rw-r--r--  1 fawkh 10000    43 feb 24 12:10 toaster-requirements.txt
    -rw-r--r--  1 fawkh 10000  2887 feb 24 12:10 TODO

 At this point, you should have BitBake cloned to a directory that
 matches the previous listing except for dates and user names.

 Setting Up the BitBake Environment
 ==================================

 First, you need to be sure that you can run BitBake. Set your working
 directory to where your local BitBake files are and run the following
 command::

   $ ./bin/bitbake --version
   BitBake Build Tool Core version 2.3.1

 The console output tells you what version
 you are running.

 The recommended method to run BitBake is from a directory of your
 choice. To be able to run BitBake from any directory, you need to add
 the executable binary to your binary to your shell's environment
 ``PATH`` variable. First, look at your current ``PATH`` variable by
 entering the following::

   $ echo $PATH

 Next, add the directory location
 for the BitBake binary to the ``PATH``. Here is an example that adds the
 ``/home/scott-lenovo/bitbake/bin`` directory to the front of the
 ``PATH`` variable::

   $ export PATH=/home/scott-lenovo/bitbake/bin:$PATH

 You should now be able to enter the ``bitbake`` command from the command
 line while working from any directory.

 The Hello World Example
 =======================

 The overall goal of this exercise is to build a complete "Hello World"
 example utilizing task and layer concepts. Because this is how modern
 projects such as OpenEmbedded and the Yocto Project utilize BitBake, the
 example provides an excellent starting point for understanding BitBake.

 To help you understand how to use BitBake to build targets, the example
 starts with nothing but the ``bitbake`` command, which causes BitBake to
 fail and report problems. The example progresses by adding pieces to the
 build to eventually conclude with a working, minimal "Hello World"
 example.

 While every attempt is made to explain what is happening during the
 example, the descriptions cannot cover everything. You can find further
 information throughout this manual. Also, you can actively participate
 in the :oe_lists:`/g/bitbake-devel`
 discussion mailing list about the BitBake build tool.

 .. note::

    This example was inspired by and drew heavily from
    `Mailing List post - The BitBake equivalent of "Hello, World!"
    <https://www.mail-archive.com/yocto@yoctoproject.org/msg09379.html>`_.

 As stated earlier, the goal of this example is to eventually compile
 "Hello World". However, it is unknown what BitBake needs and what you
 have to provide in order to achieve that goal. Recall that BitBake
 utilizes three types of metadata files:
 :ref:`bitbake-user-manual/bitbake-user-manual-intro:configuration files`,
 :ref:`bitbake-user-manual/bitbake-user-manual-intro:classes`, and
 :ref:`bitbake-user-manual/bitbake-user-manual-intro:recipes`.
 But where do they go? How does BitBake find
 them? BitBake's error messaging helps you answer these types of
 questions and helps you better understand exactly what is going on.

 Following is the complete "Hello World" example.

 #.  **Create a Project Directory:** First, set up a directory for the
     "Hello World" project. Here is how you can do so in your home
     directory::

       $ mkdir ~/hello
       $ cd ~/hello

     This is the directory that
     BitBake will use to do all of its work. You can use this directory
     to keep all the metafiles needed by BitBake. Having a project
     directory is a good way to isolate your project.

 #.  **Run BitBake:** At this point, you have nothing but a project
     directory. Run the ``bitbake`` command and see what it does::

        $ bitbake
        ERROR: The BBPATH variable is not set and bitbake did not find a conf/bblayers.conf file in the expected location.
        Maybe you accidentally invoked bitbake from the wrong directory?

     When you run BitBake, it begins looking for metadata files. The
     :term:`BBPATH` variable is what tells BitBake where
     to look for those files. :term:`BBPATH` is not set and you need to set
     it. Without :term:`BBPATH`, BitBake cannot find any configuration files
     (``.conf``) or recipe files (``.bb``) at all. BitBake also cannot
     find the ``bitbake.conf`` file.

 #.  **Setting BBPATH:** For this example, you can set :term:`BBPATH` in
     the same manner that you set ``PATH`` earlier in the appendix. You
     should realize, though, that it is much more flexible to set the
     :term:`BBPATH` variable up in a configuration file for each project.

     From your shell, enter the following commands to set and export the
     :term:`BBPATH` variable::

       $ BBPATH="projectdirectory"
       $ export BBPATH

     Use your actual project directory in the command. BitBake uses that
     directory to find the metadata it needs for your project.

     .. note::

        When specifying your project directory, do not use the tilde
        ("~") character as BitBake does not expand that character as the
        shell would.

 #.  **Run BitBake:** Now that you have :term:`BBPATH` defined, run the
     ``bitbake`` command again::

        $ bitbake
        ERROR: Unable to parse /home/scott-lenovo/bitbake/lib/bb/parse/__init__.py
        Traceback (most recent call last):
        File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 127, in resolve_file(fn='conf/bitbake.conf', d=<bb.data_smart.DataSmart object at 0x7f22919a3df0>):
              if not newfn:
        >            raise IOError(errno.ENOENT, "file %s not found in %s" % (fn, bbpath))
              fn = newfn
        FileNotFoundError: [Errno 2] file conf/bitbake.conf not found in <projectdirectory>


     This sample output shows that BitBake could not find the
     ``conf/bitbake.conf`` file in the project directory. This file is
     the first thing BitBake must find in order to build a target. And,
     since the project directory for this example is empty, you need to
     provide a ``conf/bitbake.conf`` file.

 #.  **Creating conf/bitbake.conf:** The ``conf/bitbake.conf`` includes
     a number of configuration variables BitBake uses for metadata and
     recipe files. For this example, you need to create the file in your
     project directory and define some key BitBake variables. For more
     information on the ``bitbake.conf`` file, see
     https://git.openembedded.org/bitbake/tree/conf/bitbake.conf.

     Use the following commands to create the ``conf`` directory in the
     project directory::

       $ mkdir conf

     From within the ``conf`` directory,
     use some editor to create the ``bitbake.conf`` so that it contains
     the following::

        PN  = "${@bb.parse.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}"

        TMPDIR  = "${TOPDIR}/tmp"
        CACHE   = "${TMPDIR}/cache"
        STAMP   = "${TMPDIR}/${PN}/stamps"
        T       = "${TMPDIR}/${PN}/work"
        B       = "${TMPDIR}/${PN}"

     .. note::

        Without a value for PN , the variables STAMP , T , and B , prevent more
        than one recipe from working. You can fix this by either setting PN to
        have a value similar to what OpenEmbedded and BitBake use in the default
        bitbake.conf file (see previous example). Or, by manually updating each
        recipe to set PN . You will also need to include PN as part of the STAMP
        , T , and B variable definitions in the local.conf file.

     The ``TMPDIR`` variable establishes a directory that BitBake uses
     for build output and intermediate files other than the cached
     information used by the
     :ref:`bitbake-user-manual/bitbake-user-manual-execution:setscene`
     process. Here, the ``TMPDIR`` directory is set to ``hello/tmp``.

     .. tip::

        You can always safely delete the tmp directory in order to rebuild a
        BitBake target. The build process creates the directory for you when you
        run BitBake.

     For information about each of the other variables defined in this
     example, check :term:`PN`, :term:`TOPDIR`, :term:`CACHE`, :term:`STAMP`,
     :term:`T` or :term:`B` to take you to the definitions in the
     glossary.

 #.  **Run BitBake:** After making sure that the ``conf/bitbake.conf`` file
     exists, you can run the ``bitbake`` command again::

        $ bitbake
        ERROR: Unable to parse /home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py
        Traceback (most recent call last):
        File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py", line 67, in inherit(files=['base'], fn='configuration INHERITs', lineno=0, d=<bb.data_smart.DataSmart object at 0x7fab6815edf0>):
              if not os.path.exists(file):
        >            raise ParseError("Could not inherit file %s" % (file), fn, lineno)

        bb.parse.ParseError: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass


     In the sample output,
     BitBake could not find the ``classes/base.bbclass`` file. You need
     to create that file next.

 #.  **Creating classes/base.bbclass:** BitBake uses class files to
     provide common code and functionality. The minimally required class
     for BitBake is the ``classes/base.bbclass`` file. The ``base`` class
     is implicitly inherited by every recipe. BitBake looks for the class
     in the ``classes`` directory of the project (i.e ``hello/classes``
     in this example).

     Create the ``classes`` directory as follows::

       $ cd $HOME/hello
       $ mkdir classes

     Move to the ``classes`` directory and then create the
     ``base.bbclass`` file by inserting this single line::

       addtask build

     The minimal task that BitBake runs is the ``do_build`` task. This is
     all the example needs in order to build the project. Of course, the
     ``base.bbclass`` can have much more depending on which build
     environments BitBake is supporting.

 #.  **Run BitBake:** After making sure that the ``classes/base.bbclass``
     file exists, you can run the ``bitbake`` command again::

        $ bitbake
        Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information.

     BitBake is finally reporting
     no errors. However, you can see that it really does not have
     anything to do. You need to create a recipe that gives BitBake
     something to do.

 #.  **Creating a Layer:** While it is not really necessary for such a
     small example, it is good practice to create a layer in which to
     keep your code separate from the general metadata used by BitBake.
     Thus, this example creates and uses a layer called "mylayer".

     .. note::

        You can find additional information on layers in the
        ":ref:`bitbake-user-manual/bitbake-user-manual-intro:Layers`" section.

     Minimally, you need a recipe file and a layer configuration file in
     your layer. The configuration file needs to be in the ``conf``
     directory inside the layer. Use these commands to set up the layer
     and the ``conf`` directory::

        $ cd $HOME
        $ mkdir mylayer
        $ cd mylayer
        $ mkdir conf

     Move to the ``conf`` directory and create a ``layer.conf`` file that has the
     following::

       BBPATH .= ":${LAYERDIR}"
       BBFILES += "${LAYERDIR}/*.bb"
       BBFILE_COLLECTIONS += "mylayer"
       BBFILE_PATTERN_mylayer := "^${LAYERDIR_RE}/"
       LAYERSERIES_CORENAMES = "hello_world_example"
       LAYERSERIES_COMPAT_mylayer = "hello_world_example"

     For information on these variables, click on :term:`BBFILES`,
     :term:`LAYERDIR`, :term:`BBFILE_COLLECTIONS`, :term:`BBFILE_PATTERN_mylayer <BBFILE_PATTERN>`
     or :term:`LAYERSERIES_COMPAT` to go to the definitions in the glossary.

     .. note::

        We are setting both LAYERSERIES_CORENAMES and LAYERSERIES_COMPAT in this particular case, because we
        are using bitbake without OpenEmbedded.
        You should usually just use LAYERSERIES_COMPAT to specify the OE-Core versions for which your layer
        is compatible, and add the meta-openembedded layer to your project.

     You need to create the recipe file next. Inside your layer at the
     top-level, use an editor and create a recipe file named
     ``printhello.bb`` that has the following::

        DESCRIPTION = "Prints Hello World"
        PN = 'printhello'
        PV = '1'

        python do_build() {
           bb.plain("********************");
           bb.plain("*                  *");
           bb.plain("*  Hello, World!   *");
           bb.plain("*                  *");
           bb.plain("********************");
        }

     The recipe file simply provides
     a description of the recipe, the name, version, and the ``do_build``
     task, which prints out "Hello World" to the console. For more
     information on :term:`DESCRIPTION`, :term:`PN` or :term:`PV`
     follow the links to the glossary.

 #. **Run BitBake With a Target:** Now that a BitBake target exists, run
     the command and provide that target::

       $ cd $HOME/hello
       $ bitbake printhello
       ERROR: no recipe files to build, check your BBPATH and BBFILES?

       Summary: There was 1 ERROR message shown, returning a non-zero exit code.

     We have created the layer with the recipe and
     the layer configuration file but it still seems that BitBake cannot
     find the recipe. BitBake needs a ``conf/bblayers.conf`` that lists
     the layers for the project. Without this file, BitBake cannot find
     the recipe.

 #. **Creating conf/bblayers.conf:** BitBake uses the
     ``conf/bblayers.conf`` file to locate layers needed for the project.
     This file must reside in the ``conf`` directory of the project (i.e.
     ``hello/conf`` for this example).

     Set your working directory to the ``hello/conf`` directory and then
     create the ``bblayers.conf`` file so that it contains the following::

        BBLAYERS ?= " \
            /home/<you>/mylayer \
        "

     You need to provide your own information for ``you`` in the file.

 #. **Run BitBake With a Target:** Now that you have supplied the
     ``bblayers.conf`` file, run the ``bitbake`` command and provide the
     target::

        $ bitbake printhello
        Loading cache: 100% |
        Loaded 0 entries from dependency cache.
        Parsing recipes: 100% |##################################################################################|
        Parsing of 1 .bb files complete (0 cached, 1 parsed). 1 targets, 0 skipped, 0 masked, 0 errors.
        NOTE: Resolving any missing task queue dependencies
        Initialising tasks: 100% |###############################################################################|
        NOTE: No setscene tasks
        NOTE: Executing Tasks
        ********************
        *                  *
        *  Hello, World!   *
        *                  *
        ********************
        NOTE: Tasks Summary: Attempted 1 tasks of which 0 didn't need to be rerun and all succeeded.

     .. note::

        After the first execution, re-running bitbake printhello again will not
        result in a BitBake run that prints the same console output. The reason
        for this is that the first time the printhello.bb recipe's do_build task
        executes successfully, BitBake writes a stamp file for the task. Thus,
        the next time you attempt to run the task using that same bitbake
        command, BitBake notices the stamp and therefore determines that the task
        does not need to be re-run. If you delete the tmp directory or run
        bitbake -c clean printhello and then re-run the build, the "Hello,
        World!" message will be printed again.
	.. SPDX-License-Identifier: CC-BY-2.5

	===================
	Hello World Example
	===================

	BitBake Hello World
	===================

	The simplest example commonly used to demonstrate any new programming
	language or tool is the "`Hello
	World <http://en.wikipedia.org/wiki/Hello_world_program>`__" example.
	This appendix demonstrates, in tutorial form, Hello World within the
	context of BitBake. The tutorial describes how to create a new project
	and the applicable metadata files necessary to allow BitBake to build
	it.

	Obtaining BitBake
	=================

	See the :ref:`bitbake-user-manual/bitbake-user-manual-intro:obtaining bitbake` section for
	information on how to obtain BitBake. Once you have the source code on
	your machine, the BitBake directory appears as follows::

	$ ls -al
	total 108
	drwxr-xr-x 9 fawkh 10000 4096 feb 24 12:10 .
	drwx------ 36 fawkh 10000 4096 mar 2 17:00 ..
	-rw-r--r-- 1 fawkh 10000 365 feb 24 12:10 AUTHORS
	drwxr-xr-x 2 fawkh 10000 4096 feb 24 12:10 bin
	-rw-r--r-- 1 fawkh 10000 16501 feb 24 12:10 ChangeLog
	drwxr-xr-x 2 fawkh 10000 4096 feb 24 12:10 classes
	drwxr-xr-x 2 fawkh 10000 4096 feb 24 12:10 conf
	drwxr-xr-x 5 fawkh 10000 4096 feb 24 12:10 contrib
	drwxr-xr-x 6 fawkh 10000 4096 feb 24 12:10 doc
	drwxr-xr-x 8 fawkh 10000 4096 mar 2 16:26 .git
	-rw-r--r-- 1 fawkh 10000 31 feb 24 12:10 .gitattributes
	-rw-r--r-- 1 fawkh 10000 392 feb 24 12:10 .gitignore
	drwxr-xr-x 13 fawkh 10000 4096 feb 24 12:11 lib
	-rw-r--r-- 1 fawkh 10000 1224 feb 24 12:10 LICENSE
	-rw-r--r-- 1 fawkh 10000 15394 feb 24 12:10 LICENSE.GPL-2.0-only
	-rw-r--r-- 1 fawkh 10000 1286 feb 24 12:10 LICENSE.MIT
	-rw-r--r-- 1 fawkh 10000 229 feb 24 12:10 MANIFEST.in
	-rw-r--r-- 1 fawkh 10000 2413 feb 24 12:10 README
	-rw-r--r-- 1 fawkh 10000 43 feb 24 12:10 toaster-requirements.txt
	-rw-r--r-- 1 fawkh 10000 2887 feb 24 12:10 TODO

	At this point, you should have BitBake cloned to a directory that
	matches the previous listing except for dates and user names.

	Setting Up the BitBake Environment
	==================================

	First, you need to be sure that you can run BitBake. Set your working
	directory to where your local BitBake files are and run the following
	command::

	$ ./bin/bitbake --version
	BitBake Build Tool Core version 2.3.1

	The console output tells you what version
	you are running.

	The recommended method to run BitBake is from a directory of your
	choice. To be able to run BitBake from any directory, you need to add
	the executable binary to your binary to your shell's environment
	``PATH`` variable. First, look at your current ``PATH`` variable by
	entering the following::

	$ echo $PATH

	Next, add the directory location
	for the BitBake binary to the ``PATH``. Here is an example that adds the
	``/home/scott-lenovo/bitbake/bin`` directory to the front of the
	``PATH`` variable::

	$ export PATH=/home/scott-lenovo/bitbake/bin:$PATH

	You should now be able to enter the ``bitbake`` command from the command
	line while working from any directory.

	The Hello World Example
	=======================

	The overall goal of this exercise is to build a complete "Hello World"
	example utilizing task and layer concepts. Because this is how modern
	projects such as OpenEmbedded and the Yocto Project utilize BitBake, the
	example provides an excellent starting point for understanding BitBake.

	To help you understand how to use BitBake to build targets, the example
	starts with nothing but the ``bitbake`` command, which causes BitBake to
	fail and report problems. The example progresses by adding pieces to the
	build to eventually conclude with a working, minimal "Hello World"
	example.

	While every attempt is made to explain what is happening during the
	example, the descriptions cannot cover everything. You can find further
	information throughout this manual. Also, you can actively participate
	in the :oe_lists:`/g/bitbake-devel`
	discussion mailing list about the BitBake build tool.

	.. note::

	This example was inspired by and drew heavily from
	`Mailing List post - The BitBake equivalent of "Hello, World!"
	<https://www.mail-archive.com/yocto@yoctoproject.org/msg09379.html>`_.

	As stated earlier, the goal of this example is to eventually compile
	"Hello World". However, it is unknown what BitBake needs and what you
	have to provide in order to achieve that goal. Recall that BitBake
	utilizes three types of metadata files:
	:ref:`bitbake-user-manual/bitbake-user-manual-intro:configuration files`,
	:ref:`bitbake-user-manual/bitbake-user-manual-intro:classes`, and
	:ref:`bitbake-user-manual/bitbake-user-manual-intro:recipes`.
	But where do they go? How does BitBake find
	them? BitBake's error messaging helps you answer these types of
	questions and helps you better understand exactly what is going on.

	Following is the complete "Hello World" example.

	#. Create a Project Directory: First, set up a directory for the
	"Hello World" project. Here is how you can do so in your home
	directory::

	$ mkdir ~/hello
	$ cd ~/hello

	This is the directory that
	BitBake will use to do all of its work. You can use this directory
	to keep all the metafiles needed by BitBake. Having a project
	directory is a good way to isolate your project.

	#. Run BitBake: At this point, you have nothing but a project
	directory. Run the ``bitbake`` command and see what it does::

	$ bitbake
	ERROR: The BBPATH variable is not set and bitbake did not find a conf/bblayers.conf file in the expected location.
	Maybe you accidentally invoked bitbake from the wrong directory?

	When you run BitBake, it begins looking for metadata files. The
	:term:`BBPATH` variable is what tells BitBake where
	to look for those files. :term:`BBPATH` is not set and you need to set
	it. Without :term:`BBPATH`, BitBake cannot find any configuration files
	(``.conf``) or recipe files (``.bb``) at all. BitBake also cannot
	find the ``bitbake.conf`` file.

	#. Setting BBPATH: For this example, you can set :term:`BBPATH` in
	the same manner that you set ``PATH`` earlier in the appendix. You
	should realize, though, that it is much more flexible to set the
	:term:`BBPATH` variable up in a configuration file for each project.

	From your shell, enter the following commands to set and export the
	:term:`BBPATH` variable::

	$ BBPATH="projectdirectory"
	$ export BBPATH

	Use your actual project directory in the command. BitBake uses that
	directory to find the metadata it needs for your project.

	.. note::

	When specifying your project directory, do not use the tilde
	("~") character as BitBake does not expand that character as the
	shell would.

	#. Run BitBake: Now that you have :term:`BBPATH` defined, run the
	``bitbake`` command again::

	$ bitbake
	ERROR: Unable to parse /home/scott-lenovo/bitbake/lib/bb/parse/__init__.py
	Traceback (most recent call last):
	File "/home/scott-lenovo/bitbake/lib/bb/parse/__init__.py", line 127, in resolve_file(fn='conf/bitbake.conf', d=<bb.data_smart.DataSmart object at 0x7f22919a3df0>):
	if not newfn:
	> raise IOError(errno.ENOENT, "file %s not found in %s" % (fn, bbpath))
	fn = newfn
	FileNotFoundError: [Errno 2] file conf/bitbake.conf not found in <projectdirectory>


	This sample output shows that BitBake could not find the
	``conf/bitbake.conf`` file in the project directory. This file is
	the first thing BitBake must find in order to build a target. And,
	since the project directory for this example is empty, you need to
	provide a ``conf/bitbake.conf`` file.

	#. Creating conf/bitbake.conf: The ``conf/bitbake.conf`` includes
	a number of configuration variables BitBake uses for metadata and
	recipe files. For this example, you need to create the file in your
	project directory and define some key BitBake variables. For more
	information on the ``bitbake.conf`` file, see
	https://git.openembedded.org/bitbake/tree/conf/bitbake.conf.

	Use the following commands to create the ``conf`` directory in the
	project directory::

	$ mkdir conf

	From within the ``conf`` directory,
	use some editor to create the ``bitbake.conf`` so that it contains
	the following::

	PN = "${@bb.parse.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}"

	TMPDIR = "${TOPDIR}/tmp"
	CACHE = "${TMPDIR}/cache"
	STAMP = "${TMPDIR}/${PN}/stamps"
	T = "${TMPDIR}/${PN}/work"
	B = "${TMPDIR}/${PN}"

	.. note::

	Without a value for PN , the variables STAMP , T , and B , prevent more
	than one recipe from working. You can fix this by either setting PN to
	have a value similar to what OpenEmbedded and BitBake use in the default
	bitbake.conf file (see previous example). Or, by manually updating each
	recipe to set PN . You will also need to include PN as part of the STAMP
	, T , and B variable definitions in the local.conf file.

	The ``TMPDIR`` variable establishes a directory that BitBake uses
	for build output and intermediate files other than the cached
	information used by the
	:ref:`bitbake-user-manual/bitbake-user-manual-execution:setscene`
	process. Here, the ``TMPDIR`` directory is set to ``hello/tmp``.

	.. tip::

	You can always safely delete the tmp directory in order to rebuild a
	BitBake target. The build process creates the directory for you when you
	run BitBake.

	For information about each of the other variables defined in this
	example, check :term:`PN`, :term:`TOPDIR`, :term:`CACHE`, :term:`STAMP`,
	:term:`T` or :term:`B` to take you to the definitions in the
	glossary.

	#. Run BitBake: After making sure that the ``conf/bitbake.conf`` file
	exists, you can run the ``bitbake`` command again::

	$ bitbake
	ERROR: Unable to parse /home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py
	Traceback (most recent call last):
	File "/home/scott-lenovo/bitbake/lib/bb/parse/parse_py/BBHandler.py", line 67, in inherit(files=['base'], fn='configuration INHERITs', lineno=0, d=<bb.data_smart.DataSmart object at 0x7fab6815edf0>):
	if not os.path.exists(file):
	> raise ParseError("Could not inherit file %s" % (file), fn, lineno)

	bb.parse.ParseError: ParseError in configuration INHERITs: Could not inherit file classes/base.bbclass


	In the sample output,
	BitBake could not find the ``classes/base.bbclass`` file. You need
	to create that file next.

	#. Creating classes/base.bbclass: BitBake uses class files to
	provide common code and functionality. The minimally required class
	for BitBake is the ``classes/base.bbclass`` file. The ``base`` class
	is implicitly inherited by every recipe. BitBake looks for the class
	in the ``classes`` directory of the project (i.e ``hello/classes``
	in this example).

	Create the ``classes`` directory as follows::

	$ cd $HOME/hello
	$ mkdir classes

	Move to the ``classes`` directory and then create the
	``base.bbclass`` file by inserting this single line::

	addtask build

	The minimal task that BitBake runs is the ``do_build`` task. This is
	all the example needs in order to build the project. Of course, the
	``base.bbclass`` can have much more depending on which build
	environments BitBake is supporting.

	#. Run BitBake: After making sure that the ``classes/base.bbclass``
	file exists, you can run the ``bitbake`` command again::

	$ bitbake
	Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information.

	BitBake is finally reporting
	no errors. However, you can see that it really does not have
	anything to do. You need to create a recipe that gives BitBake
	something to do.

	#. Creating a Layer: While it is not really necessary for such a
	small example, it is good practice to create a layer in which to
	keep your code separate from the general metadata used by BitBake.
	Thus, this example creates and uses a layer called "mylayer".

	.. note::

	You can find additional information on layers in the
	":ref:`bitbake-user-manual/bitbake-user-manual-intro:Layers`" section.

	Minimally, you need a recipe file and a layer configuration file in
	your layer. The configuration file needs to be in the ``conf``
	directory inside the layer. Use these commands to set up the layer
	and the ``conf`` directory::

	$ cd $HOME
	$ mkdir mylayer
	$ cd mylayer
	$ mkdir conf

	Move to the ``conf`` directory and create a ``layer.conf`` file that has the
	following::

	BBPATH .= ":${LAYERDIR}"
	BBFILES += "${LAYERDIR}/*.bb"
	BBFILE_COLLECTIONS += "mylayer"
	BBFILE_PATTERN_mylayer := "^${LAYERDIR_RE}/"
	LAYERSERIES_CORENAMES = "hello_world_example"
	LAYERSERIES_COMPAT_mylayer = "hello_world_example"

	For information on these variables, click on :term:`BBFILES`,
	:term:`LAYERDIR`, :term:`BBFILE_COLLECTIONS`, :term:`BBFILE_PATTERN_mylayer <BBFILE_PATTERN>`
	or :term:`LAYERSERIES_COMPAT` to go to the definitions in the glossary.

	.. note::

	We are setting both LAYERSERIES_CORENAMES and LAYERSERIES_COMPAT in this particular case, because we
	are using bitbake without OpenEmbedded.
	You should usually just use LAYERSERIES_COMPAT to specify the OE-Core versions for which your layer
	is compatible, and add the meta-openembedded layer to your project.

	You need to create the recipe file next. Inside your layer at the
	top-level, use an editor and create a recipe file named
	``printhello.bb`` that has the following::

	DESCRIPTION = "Prints Hello World"
	PN = 'printhello'
	PV = '1'

	python do_build() {
	bb.plain("********************");
	bb.plain("* *");
	bb.plain("* Hello, World! *");
	bb.plain("* *");
	bb.plain("********************");
	}

	The recipe file simply provides
	a description of the recipe, the name, version, and the ``do_build``
	task, which prints out "Hello World" to the console. For more
	information on :term:`DESCRIPTION`, :term:`PN` or :term:`PV`
	follow the links to the glossary.

	#. Run BitBake With a Target: Now that a BitBake target exists, run
	the command and provide that target::

	$ cd $HOME/hello
	$ bitbake printhello
	ERROR: no recipe files to build, check your BBPATH and BBFILES?

	Summary: There was 1 ERROR message shown, returning a non-zero exit code.

	We have created the layer with the recipe and
	the layer configuration file but it still seems that BitBake cannot
	find the recipe. BitBake needs a ``conf/bblayers.conf`` that lists
	the layers for the project. Without this file, BitBake cannot find
	the recipe.

	#. Creating conf/bblayers.conf: BitBake uses the
	``conf/bblayers.conf`` file to locate layers needed for the project.
	This file must reside in the ``conf`` directory of the project (i.e.
	``hello/conf`` for this example).

	Set your working directory to the ``hello/conf`` directory and then
	create the ``bblayers.conf`` file so that it contains the following::

	BBLAYERS ?= " \
	/home/<you>/mylayer \
	"

	You need to provide your own information for ``you`` in the file.

	#. Run BitBake With a Target: Now that you have supplied the
	``bblayers.conf`` file, run the ``bitbake`` command and provide the
	target::

	$ bitbake printhello
	Loading cache: 100% \|
	Loaded 0 entries from dependency cache.
	Parsing recipes: 100% \|##################################################################################\|
	Parsing of 1 .bb files complete (0 cached, 1 parsed). 1 targets, 0 skipped, 0 masked, 0 errors.
	NOTE: Resolving any missing task queue dependencies
	Initialising tasks: 100% \|###############################################################################\|
	NOTE: No setscene tasks
	NOTE: Executing Tasks
	********************
	* *
	* Hello, World! *
	* *
	********************
	NOTE: Tasks Summary: Attempted 1 tasks of which 0 didn't need to be rerun and all succeeded.

	.. note::

	After the first execution, re-running bitbake printhello again will not
	result in a BitBake run that prints the same console output. The reason
	for this is that the first time the printhello.bb recipe's do_build task
	executes successfully, BitBake writes a stamp file for the task. Thus,
	the next time you attempt to run the task using that same bitbake
	command, BitBake notices the stamp and therefore determines that the task
	does not need to be re-run. If you delete the tmp directory or run
	bitbake -c clean printhello and then re-run the build, the "Hello,
	World!" message will be printed again.