intro

A mainstream distro such Debian can give you an instant, ready-to run system, great if you are using off-the-shelf hardware such as Raspberry Pi, or one of the Beagle Boards. Yocto Project, on the other hand, is the build tool you need to create a fully custom distro from scratch (you see, Yocto Project is not a distro, it *creates* distros) 

Debian has traditionally been thought of by many as a desktop operating system but over the past few years significant effort has gone into enabling Debian to run on embedded targets.
We can create an embedded system derived from Debian packages in a few lines of YAML markup using an open-source tool called Debos: Debian OS builder.

Buildroot => for small RFS, for lesser number of architecture. It is basically a set of makefiles that download, configure and compile the software with the correct options.
Uses Kconfig where all the configurations are there.

Yocto ==> for a large or full-fletched RFS, for larger variations of architectures. Here configurations are in a bitbake recipe file.
to create ur own custom linux distribution for the target. Uses "open Embedded" build system. It basically provides an embedded linux distribution. Not applicable for android.

Buildroot vs Yocto: https://www.youtube.com/watch?v=wCVYQWFIvBs&feature=youtu.be 
Both will create bootloader, kernel, rootfs, toolchain images for you.

The Buildroot project is defined as "a simple, efficient, and easy-to-use tool to generate embedded Linux systems through cross-compilation." It shares many of the same objectives as the Yocto project, however it is focused on simplicity and minimalism.


Open Embedded is the build system used by yocto. It has some metadata which describes the recipes.
Poky is the distribution of OpenEmbedded. There are many other distributions such as Angstrom. But, yocto uses Poky.
Bitbake is the python based build tool. It basically reads the metadata.

Metadata are:

Classes(.bbclass) => inheritance mechanism for common functionality. If many recipes want to use a common  
                                    functionality, then that recipe can just inherit that particular .bbclass file.
Configuration (.conf) => drives the overall behaviour 
Recipes(.bb) => build instructions to build a package.
Append files(.bbappend) => has extra metadata where previosly set values can be overrridden.
Package groups => used to group packages for an RFS image. Ex: all QT related packages can be built in a single go        
                                   instead of giving the bitbake for them separately.

Layers:

All the above metadata are grouped/organised into separate layers.
oe…/build/conf/bblayers.conf => explicitly lists the available layers

User level configurations that can be specified for the build system:
oe…/build/conf/local.conf