Your First BitBake Recipe: Hello World in a meta- Layer

Yocto uses a recipe (.bb) to describe "how source code becomes an installable package". This post walks the full path with a minimal example: build a layer → write a recipe → compile → land in an image.

Assumptions: poky is cloned into ~/poky on branch kirkstone (LTS). Host: Ubuntu 22.04.

1. Structure: start with a layer

cd ~/poky
source oe-init-build-env
bitbake-layers create-layer ../meta-mylayer
bitbake-layers add-layer ../meta-mylayer

The generated meta-mylayer already ships an example recipes-example/example/example_0.1.bb. A real layer looks like this:

meta-mylayer/
├── conf/layer.conf
└── recipes-example/
    ├── example/example_0.1.bb
    └── myhello/
        ├── myhello_0.1.bb
        └── files/
            └── myhello.c

2. A plain C recipe

myhello.c is omitted here (it prints hello from yocto). The recipe:

SUMMARY = "Minimal hello program"
LICENSE = "MIT"
LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=... "

SRC_URI = "file://myhello.c"
S = "${WORKDIR}/sources"
UNPACKDIR = "${S}"   # unpack directory since kirkstone

do_compile() {
    ${CC} ${CFLAGS} -o myhello myhello.c ${LDFLAGS}
}

do_install() {
    install -d ${D}${bindir}
    install -m 0755 myhello ${D}${bindir}
}

inherit pkgconfig

3. Build a single recipe

bitbake myhello

The result is under:

find tmp/work -name myhello -type f
# .../myhello/0.1-r0/image/usr/bin/myhello

4. Put it into an image and run it in QEMU

# Append to the image of the local target machine
echo 'IMAGE_INSTALL:append = " myhello"' >> conf/local.conf
bitbake core-image-minimal
runqemu qemux86-64

Once booted:

root@qemux86-64:~# myhello
hello from yocto

Common pitfalls

• Source changes not picked up: check for stale do_compile caches, use bitbake -c cleansstate myhello when needed.
• md5= checksum: compute the real hash with sha256sum and replace it.
• Debugging variables: bitbake -e myhello | grep ^S=.

Next up: layer priorities and overriding an official recipe with a .bbappend.