What Poky Is

Poky is the reference build system provided by the Yocto Project. It is a git repository that aggregates four components:

• BitBake (bitbake/) — the build engine
• OpenEmbedded-Core (meta/) — the minimal, architecture-agnostic metadata layer
• meta-poky — the distribution policy layer (defines the "poky" distro)
• meta-yocto-bsp — reference BSP for example machines (qemuarm, qemux86, etc.)

When you git clone Poky and run a build, you are using all four components together. Poky is a starting point — real products typically evolve into their own layer stack that keeps Poky as an unmodified upstream dependency.

Source Tree Layout

poky/
├── bitbake/                    # BitBake tool source
│   ├── bin/bitbake             # The bitbake executable
│   └── lib/bb/                 # Core BitBake Python modules
│
├── meta/                       # OpenEmbedded-Core (oe-core)
│   ├── conf/
│   │   ├── bitbake.conf        # Master variable defaults (NEVER edit this)
│   │   └── machine/            # Example machine configs (qemuarm, qemux86)
│   ├── classes/                # Core .bbclass files (base, image, kernel, cmake, etc.)
│   ├── recipes-core/           # Core userspace (busybox, init-ifupdown, etc.)
│   ├── recipes-kernel/         # Kernel and module recipes
│   └── recipes-devtools/       # Build tools (gcc, binutils, gdb, etc.)
│
├── meta-poky/                  # Poky distribution policy
│   └── conf/
│       └── distro/
│           └── poky.conf       # Sets DISTRO="poky", DISTRO_FEATURES, tool versions
│
├── meta-yocto-bsp/             # Reference BSPs
│   └── conf/machine/           # Machine conf files for reference boards
│
├── scripts/                    # Helper scripts (runqemu, devtool, recipetool, etc.)
├── oe-init-build-env           # Setup script — source this before building
└── documentation/              # Yocto Project docs source

oe-init-build-env — What It Does

You run this once per shell session before using bitbake:

source oe-init-build-env [build-dir]

Internally it:

1. Sets BUILDDIR to the specified build directory (default: build/)
2. Creates $BUILDDIR/conf/local.conf from a template if absent
3. Creates $BUILDDIR/conf/bblayers.conf from a template if absent
4. Prepends poky/bitbake/bin and poky/scripts to PATH
5. Sets BB_ENV_PASSTHROUGH_ADDITIONS to allow certain env vars into BitBake's sandbox
6. cds you into $BUILDDIR

After sourcing, bitbake is on your PATH and your working directory is the build directory.

poky.conf — The Distribution Policy File

meta-poky/conf/distro/poky.conf defines what the "poky" distribution means. Key variables it sets:

DISTRO      = "poky"
DISTRO_NAME = "Poky (Yocto Project Reference Distro)"
DISTRO_VERSION = "5.0"

# Package format: ipk, rpm, or deb
PACKAGE_CLASSES ?= "package_rpm"

# Distribution-level feature flags
DISTRO_FEATURES = "acl bluetooth ext2 ipv4 ipv6 largefile usbgadget \
                   usbhost wifi nfs zeroconf pci x11 vfat"

# Preferred versions for key toolchain components
PREFERRED_VERSION_linux-yocto ?= "6.6%"
PREFERRED_VERSION_binutils    = "2.42%"
PREFERRED_VERSION_gcc         = "13.%"

Release Branch Mapping

All layers used in a project must be on matching release branches:

Codename	Poky Branch	Support Window
Kirkstone	kirkstone	LTS 2022–2024
Langdale	langdale	Oct 2022–Apr 2023
Mickledore	mickledore	Standard
Nanbield	nanbield	Standard
Scarthgap	scarthgap	LTS 2024–2026
Styhead	styhead	Standard
Walnascar	walnascar	Standard

If meta-openembedded is on scarthgap but Poky is on styhead, recipe parsing will fail or produce unpredictable results.

Starting a Project with Poky

# 1. Clone Poky at a known release
git clone git://git.yoctoproject.org/poky -b scarthgap

# 2. Clone extra layers alongside poky (same branch)
git clone git://git.openembedded.org/meta-openembedded -b scarthgap
git clone git://git.yoctoproject.org/meta-raspberrypi  -b scarthgap

# 3. Initialize the build environment
cd poky
source oe-init-build-env ../build

# 4. Edit conf/bblayers.conf to register layers
# 5. Edit conf/local.conf to set MACHINE, DISTRO, etc.
# 6. Build
bitbake core-image-minimal

For real products, Poky is typically vendored using repo (Google's git management tool) or as git submodules, with a manifest tracking exact commits for all layers — ensuring reproducible builds months later.

Contributors: Vasu Grover

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