alpine-rpi4-aports-docker

A Docker image for building Alpine packages for and on a Raspberry Pi 4.

Intended if you have an rpi4 running something other than Alpine, but want to build Alpine packages, such as a kernel.

Using it

1. Build the container:

    docker build -t alpinebuilder:latest --build-arg HOST_UID=$(id -u) .
   

   • Note the HOST_UID must be set to your host user's UID for permissions to work properly. We use the id command to inject it automatically.)

2. Set up a directory on your Docker host for artifacts that you want to keep after you exit:

    mkdir -p ~/alpinebuilder/{home,distfiles}
   

3. If you have an Alpine builder key, make sure it's in ~/alpinebuilder/home/.abuild. If not, we'll make one later.

4. Start the container:

    docker run -it \
        -v ~/alpinebuilder/home:/home/builder \
        -v ~/alpinebuilder/distfiles:/var/cache/distfiles \
        -e USER_NAME='Micah R Ledbetter' \
        -e USER_EMAIL='me@micahrl.com' \
        -e TIMEZONE=US/Central \
        alpinebuilder:latest
   

5. You need to configure an Alpine builder key

   • If you don't have an Alpine builder key, you'll need to generate one in the container, and copy the public key so that abuild knows how to find it:

       abuild-keygen -a -i
       sudo cp ~/.abuild/me@micahrl.com-5fc94d02.rsa.pub /etc/apk/keys
     

     Note that once there is a key present in ~/.abuild, the entrypoint script will automatically copy it when the container starts, so you don't have to do the second command every time the container starts.

   • If you DO have an Alpine builder key, put it in ~/alpinebuilder/home/.abuild, and make sure the absolute path is specified in ~/alpinebuilder/home/.abuild/abuild.conf to refer to /home/builder/.abuild, because that is the build user in the container. e.g. have this line in abuild.conf

       PACKAGER_PRIVKEY="/home/builder/.abuild/me@micahrl.com-5fc94d02.rsa"
     

6. If you haven't checked out aports, you'll need to do that in your homedir in the container: git clone git://git.alpinelinux.org/aports. You may want to use a branch for your work.

7. Now you can build packages. For instance, to build the kernel with the default settings, run this in the container: cd ~/aports/main/linux-rpi; abuild -rKd.

   • I like to log the results, so I added a simple logcmd.sh to the container. You can run it like logcmd.sh LOGNAME abuild -rKd and it will save the full log to a file like ~/logs/20201205-211333-LOGNAME.log, as well as emit all messages to STDOUT.

   • You can use passwordless sudo to install packages if you need to.

Further reading

Some helpful links:

• https://wiki.alpinelinux.org/wiki/Custom_Kernel
• https://wiki.alpinelinux.org/wiki/Creating_an_Alpine_package#Setup_your_system_and_account

Notes and examples

• Building a kernel
• Reusing a Raspbian sdcard for Alpine

Troubleshooting

Why is root's prompt different?

Root uses ash, while the main user in the container uses bash. This will lead to some differences, such as \t being interpreted in bash as a time in HH:MM:SS format, but in ash as a time in just HH:MM format.