Creating a build directory

The first thing we need to do is create a build directory for our project, where the build output will be generated. Sometimes, the build directory may be referred to as the project directory, but build directory is the appropriate Yocto term.

There is no right way to structure the build directories when you have multiple projects, but a good practice is to have one build directory per architecture or machine type. They can all share a common downloads folders, and even a shared state cache (this will be covered later on), so keeping them separate won't affect the build performance, but it will allow you to develop on multiple projects simultaneously.

To create a build directory, we use the oe-init-build-env script provided by Poky. The script needs to be sourced into your current shell, and it will set up your environment to use the OpenEmbedded/Yocto build system, including adding the BitBake utility to your path. You can specify a build directory to use or it will use build by default. We will use qemuarm for this example.

$ cd /opt/yocto/poky
$ source oe-init-build-env qemuarm

The script will change to the specified directory.

$ source oe-init-build-env-memres 12345 qemuarm

$ bitbake -m

Both scripts call the scripts/oe-setup-builddir script inside the poky directory to create the build directory.

On creation, the build directory contains a conf directory with the following three files:

$ cd /opt/yocto/poky/qemuarm
$ rm -Rf tmp sstate-cache

You can specify a different template configuration file to use when you create your build directory using the TEMPLATECONF variable; for example:

$ TEMPLATECONF=meta-custom/config source oe-init-build-env <build- dir>

The TEMPLATECONF variable needs to refer to a directory containing templates for both local.conf and bblayer.conf, but named local.conf.sample and bblayers.conf.sample.

For our purposes, we can use the unmodified default project configuration files.