Adding Applications to a Yocto Image

Adding packages to the image

Suppose the minimal Linux image does not contain a particular utility.

We can add packages through image configuration.

For example:

IMAGE_INSTALL:append = " nano"

Multiple packages can be added:

IMAGE_INSTALL:append = " \
    nano \
    openssh \
    curl \
"

This is much better than manually installing packages every time after boot.

The desired system configuration becomes part of the build.

Adding a custom application

Suppose we have an embedded C++ application:

my-app/
├── main.cpp
├── CMakeLists.txt
└── ...

We can create a Yocto recipe for it.

Conceptually:

recipes-apps/
└── my-app/
    └── my-app.bb

The recipe tells Yocto how to:

1. Fetch the source
2. Configure the project
3. Compile it
4. Install the executable
5. Package it

The result becomes part of the final image.

Systemd services

Embedded applications often need to start automatically.

For example:

my-application.service

A service could conceptually contain:

[Unit]
Description=My Embedded Application
After=network.target

[Service]
ExecStart=/usr/bin/my-application
Restart=always

[Install]
WantedBy=multi-user.target

The recipe can install this service into the target filesystem and enable it.

Then the application can start automatically when Linux boots.