Knowing the local.conf file

When we initialize a build environment, it creates a file called build/conf/local.conf, which is a powerful tool that can configure almost every aspect of the build process. We can set the machine we are building for, choose the toolchain host architecture to be used for a custom cross-toolchain, optimize options for maximum build time reduction, and so on. The comments inside the build/conf/local.conf file are a very good documentation and reference of possible variables, and their defaults. The minimal set of variables we probably want to change from the default is the following:

BB_NUMBER_THREADS ?= "${@oe.utils.cpu_count()}"
PARALLEL_MAKE ?= "-j ${@oe.utils.cpu_count()}"
MACHINE ??= "qemux86"

Tip

BB_NUMBER_THREADS and PARALLEL_MAKE should be set to twice the host processor's number of cores.

The MACHINE variable is where we determine the target machine we wish to build for. At the time of writing this book, Poky supports the...