# Using Poky

This section gives an overview of the components that make up Poky followed by information about running poky builds and dealing with any problems that may arise.

## Poky Overview

The BitBake task executor together with various types of configuration files form the core of Poky. This section overviews the BitBake task executor and the configuration files by describing what they are used for and they they interact.

BitBake handles the parsing and execution of the data files. The data itself is of various types:

- Recipes: Provides details about particular pieces of software

- Class Data: An abstraction of common build information (e.g. how to build a Linux kernel).

- Configuration Data: Defines machine-specific settings, policy decisions, etc. Configuration data acts a the glue to bind everything together.

BitBake knows how to combine multiple data sources together and refers to each data source as a 'layer'.

Following are some brief details on these core components. For more detailed information on these components see the 'Reference: Directory Structure' appendix.

### BitBake

BitBake is the tool at the heart of Poky and is responsible for parsing the metadata, generating a list of tasks from it and then executing them. To see a list of the options BitBake supports look at 'bitbake --help'.

The most common usage for BitBake is `bitbake <packagename>`, where packagename is the name of the package you want to build (referred to as the 'target' in this manual). The target often equates to the first part of a `.bb` filename. So, to run the `matchbox-desktop_1.2.3.bb` file, you might type the following:

         $ bitbake matchbox-desktop

Several different versions of `matchbox-desktop` might exist. BitBake chooses the one selected by the distribution configuration. You can get more details about how BitBake chooses between different versions and providers in the 'Preferences and Providers' section.

BitBake also tries to execute any dependent tasks first. So for example, before building `matchbox-desktop` BitBake would build a cross compiler and glibc if they had not already been built.

### Metadata (Recipes)

The `.bb` files are usually referred to as 'recipes'. In general, a recipe contains information about a single piece of software such as from where to download the source patches (if any are needed), which special configuration options to apply, how to compile the source files, and how to package the compiled output.

The term 'package' can also be used to describe recipes. However, since the same word is used for the packaged output from Poky (i.e. .ipk or .deb files), this document avoids it.

### Classes

Class files (`.bbclass`) contain information that is useful to share between metadata files. An example is the autotools class, which contains common settings for any application that autotools uses. The Reference: Classes appendix provides details about common classes and how to use them.

### Configuration

The configuration files (`.conf`) define various configuration variables that govern what Poky does. These files are split into several areas that define machine configuration options, distribution configuration options, compiler tuning options, general common configuration options and user configuration options (`local.conf`).

## Running a Build

First the Poky build environment needs to be set up using the following command:

         $ source oe-init-build-env [build_dir]

The build_dir is the dir containing all the build's object files. The default build dir is poky-dir/build. A different build_dir can be used for each of the targets. For example, ~/build/x86 for a qemux86 target, and ~/build/arm for a qemuarm target. Please refer to oe-init-build-env for more detailed information.

Once the Poky build environment is set up, a target can be built using:

         $ bitbake <target>

The target is the name of the recipe you want to build. Common targets are the images in `meta/recipes-core/images`, `/meta/recipes-sato/images`, etc. Or, the target can be the name of a recipe for a specific piece of software such as busybox. For more details about the standard images available, see the 'Reference: Images' appendix.

Building an image without GNU Public License Version 3 (GPLv3) components is only supported for minimal and base images. See 'Reference: Images' for more information.

When building an image using GPL components you need to maintain your original settings and not switch back and forth applying different versions of the GNU Public License. If you rebuild using different versions of GPL you can get dependency errors due to some components not being rebuilt.

## Installing and Using the Result

Once an image has been built it often needs to be installed. The images/kernels built by Poky are placed in the `tmp/deploy/images` directory. Running qemux86 and qemuarm images is described in the 'Using Pre-Built Binaries and QEMU' section of the Yocto Project Quick Start. See for the guide. For information about how to install these images, see the documentation for your particular board/machine.

## Debugging Build Failures

The exact method for debugging Poky depends on the nature of the problem and on the system's area from which the bug originates. Standard debugging practices such as comparison against the last known working version with examination of the changes and the re-application of steps to identify the one causing the problem are valid for Poky just as they are for any other system. Even though it is impossible to detail every possible potential failure, here are some general tips to aid in debugging:

### Task Failures

The log file for shell tasks is available in `${WORKDIR}/temp/log.do_taskname.pid`. For example, the "compile" task of busybox 1.01 on the ARM spitz machine might be `tmp/work/armv5te-poky-linux-gnueabi/busybox-1.01/temp/log.do_compile.1234`. To see what BitBake runs to generate that log, look at the corresponding `run.do_taskname.pid` file located in the same directory.

Presently, the output from python tasks is sent directly to the console.

### Running Specific Tasks

Any given package consists of a set of tasks. In most cases the series is: fetch, unpack, patch, configure, compile, install, package, package_write and build. The default task is "build" and any tasks on which it depends build first - hence, the standard BitBake behaviour. Some tasks exist, such as devshell, that are not part of the default build chain. If you wish to run a task that is not part of the default build chain you can use the "-c" option in BitBake as follows:

         $ bitbake matchbox-desktop -c devshell

If you wish to rerun a task use the force option "-f". For example, the following sequence forces recompilation after changing files in the working directory.

         $ bitbake matchbox-desktop
         [make some changes to the source code in the WORKDIR]
         $ bitbake matchbox-desktop -c compile -f
         $ bitbake matchbox-desktop

This sequence first builds `matchbox-desktop` and then recompiles it. The last command reruns all tasks, basically the packaging tasks, after the compile. BitBake recognizes that the "compile" task was rerun and therefore understands that the other tasks also need to be run again.

You can view a list of tasks in a given package by running the "listtasks" task. For example:

         $ bitbake matchbox-desktop -c

The results are in the file `${WORKDIR}/temp/log.do_listtasks`.

### Dependency Graphs

Sometimes it can be hard to see why BitBake wants to build some other packages before a given package you've specified. The `bitbake -g targetname` command creates the `depends.dot` and `task-depends.dot` files in the current directory. These files show the package and task dependencies and are useful for debugging problems. You can use the `bitbake -g -u depexp targetname` command to display the results in a more human-readable form.

### General BitBake Problems

You can see debug output from BitBake by using the "-D" option. The debug output gives more information about what BitBake is doing and the reason behind it. Each "-D" option you use increases the logging level. The most common usage is `-DDD`.

The output from `bitbake -DDD -v targetname` can reveal why BitBake chose a certain version of a package or why BitBake picked a certain provider. This command could also help you in a situation where you think BitBake did something unexpected.

### Building with No Dependencies

If you really want to build a specific `.bb` file, you can use the command form `bitbake -b somepath/somefile.bb`. This command form does not check for dependencies so you should use it only when you know its dependencies already exist. You can also specify fragments of the filename and BitBake checks for a unique match.

### Variables

The "-e" option dumps the resulting environment for either the configuration (no package specified) or for a specific package when specified with the "-b" option.

### Other Tips

When adding new packages it is worth watching for undesireable items making their way into compiler command lines. For example, you do not want references to local system files like `/usr/lib/` or `/usr/include/`.

If you want to remove the psplash boot splashscreen, add "psplash=false" to the kernel command line. Doing so prevents psplash from loading thus allowing you to see the console. It is also possible to switch out of the splashscreen by switching the virtual console (e.g. Fn+Left or Fn+Right on a Zaurus).