The simplest example commonly used to demonstrate any new programming language or tool is the Hello World example. This chapter demonstrates, in tutorial form, Hello World within the context of BitBake. This tutorial describes how to create a new Project and the applicable metadata files necessary to allow BitBake to build it.

Please refer to Chapter 1 Section 1.7 for the various methods to obtain BitBake. Once the source code is on your machine the BitBake directory will appear as follows: $ ls -al total 100 drwxrwxr-x. 9 wmat wmat 4096 Jan 31 13:44 . drwxrwxr-x. 3 wmat wmat 4096 Feb 4 10:45 .. -rw-rw-r--. 1 wmat wmat 365 Nov 26 04:55 AUTHORS drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 bin drwxrwxr-x. 4 wmat wmat 4096 Jan 31 13:44 build -rw-rw-r--. 1 wmat wmat 16501 Nov 26 04:55 ChangeLog drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 classes drwxrwxr-x. 2 wmat wmat 4096 Nov 26 04:55 conf drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 contrib -rw-rw-r--. 1 wmat wmat 17987 Nov 26 04:55 COPYING drwxrwxr-x. 3 wmat wmat 4096 Nov 26 04:55 doc -rw-rw-r--. 1 wmat wmat 69 Nov 26 04:55 .gitignore -rw-rw-r--. 1 wmat wmat 849 Nov 26 04:55 HEADER drwxrwxr-x. 5 wmat wmat 4096 Jan 31 13:44 lib -rw-rw-r--. 1 wmat wmat 195 Nov 26 04:55 MANIFEST.in -rwxrwxr-x. 1 wmat wmat 3195 Jan 31 11:57 setup.py -rw-rw-r--. 1 wmat wmat 2887 Nov 26 04:55 TODO At this point you should have BitBake extracted or cloned to a directory and it should match the directory tree above. Please note that you'll see your username wherever "wmat" appears above.

The recommended method to run BitBake is from a directory of your choice. The directory can be within your home directory or in /usr/local, depending on your preference. Let's run BitBake now to make sure it's working. From the BitBake source code directory issue the following command: $ ./bin/bitbake --version BitBake Build Tool Core version 1.19.0, bitbake version 1.19.0 You're now ready to use BitBake. A final step to make development easier is to add the executable binary to your environment PATH. First, have a look at your current PATH variable. If I check mine, I get: $ echo $PATH /home/wmat/bin:/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin: /usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games Now add the directory location for the BitBake binary to the PATH with: $ export PATH={path to the bitbake executable}:$PATH This will add the directory to the beginning of your PATH environment variable. For example, on my machine: $ export PATH=/media/wmat/Backups/dev/bitbake/bin:$PATH $ echo $PATH /media/wmat/Backups/dev/bitbake/bin:/home/wmat/bin: /usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin: /usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games Now, you should be able to simply enter the bitbake command at the command line to run bitbake. For a more permanent solution and assuming you are running the BASH shell, edit ~/.bashrc and add the following to the end of that file: PATH={path to the bitbake executable}:$PATH Note that if you're a Vim user, you will find useful Vim configuration contributions in the contrib/vim directory. Copy the files from that directory to your /home/yourusername/.vim directory. If it doesn't exist, create it, and restart Vim.

The following example leaps directly into how BitBake works. Every attempt is made to explain what is happening, however, further information can be found in the Metadata chapter. The overall goal of this exercise is to create a Hello World example utilizing concepts used to build and construct a complete example application including Tasks and Layers. This is how modern projects such as OpenEmbedded and the Yocto Project utilize BitBake, therefore it provides an excellent starting point for understanding BitBake. It should be noted that this chapter was inspired by and draws heavily from several sources: Mailing List post - The BitBake equivalent of "Hello, World!" Hambedded Linux blog post - From Bitbake Hello World to an Image

One of the best means to understand anything is to walk through the steps to where we want to be by observing first principles. BitBake allows us to do this through the -D or Debug command line parameter. We know we want to eventually compile a HelloWorld example, but we don't know what we need to do that. Remember that BitBake utilizes three types of metadata files: Configuration Files, Classes, and Recipes. But where do they go, how does BitBake find them, etc. etc.? Hopefully we can use BitBake's error messaging to figure this out and better understand exactly what's going on. First, let's begin by setting up a directory for our HelloWorld project. I'll do this in my home directory and change into that directory: $mkdir ~/dev/hello && cd ~/dev/hello Within this new, empty directory, let's run BitBake with Debugging output and see what happens: $bitbake -DDD The BBPATH variable is not set DEBUG: Removed the following variables from the environment: GNOME_DESKTOP_SESSION_ID, LESSOPEN, WINDOWID, GNOME_KEYRING_CONTROL, DISPLAY, SSH_AGENT_PID, LANG, XDG_SESSION_PATH, XAUTHORITY, LANGUAGE, SESSION_MANAGER, SHLVL, MANDATORY_PATH, COMPIZ_CONFIG_PROFILE, TEXTDOMAIN, GPG_AGENT_INFO, SSH_AUTH_SOCK, XDG_RUNTIME_DIR, COMPIZ_BIN_PATH, GDMSESSION, DEFAULTS_PATH, TEXTDOMAINDIR, XDG_SEAT_PATH, XDG_CONFIG_DIRS, XDG_CURRENT_DESKTOP, DBUS_SESSION_BUS_ADDRESS, _, XDG_SESSION_COOKIE, DESKTOP_SESSION, LESSCLOSE, GNOME_KEYRING_PID, UBUNTU_MENUPROXY, OLDPWD, GTK_MODULES, XDG_DATA_DIRS, COLORTERM, LS_COLORS The majority of this output is specific to environment variables that are not directly relevant to BitBake. However, the very first message The BBPATH variable is not set is and needs to be rectified. So how do we set the BBPATH variable? When BitBake is run it begins looking for metadata files. The BBPATH variable is what tells BitBake where to look. It is possible to set BBPATH as an environment variable as you did above for the BitBake exexcutable's PATH. However, it's much more flexible to set the BBPATH variable for each project, as this allows for greater flexibility. Without BBPATH Bitbake will not find any conf/.conf files or recipe files at all. It will also not find bitbake.conf. Note the reference to conf/. It is standard practice to organize the project's directory tree to include a conf/ and a classes/ directory. Add those now to your project directory. $ mkdir conf classes Now let's copy the sample configuration files provided in the BitBake source tree to their appropriate conf and classes directory. Change to the BitBake source tree directory and: cp conf/bitbake.conf ~/dev/hello/conf/ cp classes/base.bbclass ~/dev/hello/classes/ At this point your project directory structure should look like the following: ~/dev/hello$ tree . ├── classes │   └── base.bbclass └── conf └── bitbake.conf But what about BBPATH, we still haven't set it? The first configuration file that BitBake looks for is always bblayers.conf. With this knowledge we know that to resolve our BBPATH error we can add a conf/bblayers.conf file to our project source tree and populate it with the BBPATH variable declaration. From your project source tree: $ vim conf/bblayers.conf Add the following to the empty bblayers.conf file: BBPATH := "${TOPDIR}" Now from the root of our project directory, let's run BitBake again and see what happens: :~/dev/hello$ bitbake -DDD Nothing to do. Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information. DEBUG: Removed the following variables from the environment: GNOME_DESKTOP_SESSION_ID, LESSOPEN, WINDOWID, GNOME_KEYRING_CONTROL, DISPLAY, SSH_AGENT_PID, LANG, XDG_SESSION_PATH, XAUTHORITY, LANGUAGE, SESSION_MANAGER, SHLVL, MANDATORY_PATH, COMPIZ_CONFIG_PROFILE, TEXTDOMAIN, GPG_AGENT_INFO, SSH_AUTH_SOCK, XDG_RUNTIME_DIR, COMPIZ_BIN_PATH, GDMSESSION, DEFAULTS_PATH, TEXTDOMAINDIR, XDG_SEAT_PATH, XDG_CONFIG_DIRS, XDG_CURRENT_DESKTOP, DBUS_SESSION_BUS_ADDRESS, _, XDG_SESSION_COOKIE, DESKTOP_SESSION, LESSCLOSE, GNOME_KEYRING_PID, UBUNTU_MENUPROXY, OLDPWD, GTK_MODULES, XDG_DATA_DIRS, COLORTERM, LS_COLORS DEBUG: Found bblayers.conf (/home/wmat/dev/hello/conf/ bblayers.conf) DEBUG: LOAD /home/wmat/dev/hello/conf/bblayers.conf DEBUG: LOAD /home/wmat/dev/hello/conf/bitbake.conf DEBUG: BB configuration INHERITs:0: inheriting /home/wmat/dev/ hello/classes/base.bbclass DEBUG: BB /home/wmat/dev/hello/classes/base.bbclass: handle (data, include) DEBUG: LOAD /home/wmat/dev/hello/classes/base.bbclass DEBUG: Clearing SRCREV cache due to cache policy of: clear DEBUG: Using cache in '/home/wmat/dev/hello/tmp/cache/ local_file_checksum_cache.dat' DEBUG: Using cache in '/home/wmat/dev/hello/tmp/cache/ bb_codeparser.dat' NOTE: From this point forward, the environment variable removal messages will be ignored and omitted. Let's examine the relevant DEBUG messages: