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BlokasLabs / patchbox-os-gen

BSD 3-Clause "New" or "Revised" License
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pi-gen

Tool used to create Raspberry Pi OS images. (Previously known as Raspbian).

Dependencies

pi-gen runs on Debian-based operating systems. Currently it is only supported on either Debian Buster or Ubuntu Xenial and is known to have issues building on earlier releases of these systems. On other Linux distributions it may be possible to use the Docker build described below.

To install the required dependencies for pi-gen you should run:

apt-get install coreutils quilt parted qemu-user-static debootstrap zerofree zip \
dosfstools libarchive-tools libcap2-bin grep rsync xz-utils file git curl bc \
qemu-utils kpartx gpg pigz

The file depends contains a list of tools needed. The format of this package is <tool>[:<debian-package>].

Getting started with building your images

Getting started is as simple as cloning this repository on your build machine. You can do so with:

git clone --depth 1 https://github.com/RPI-Distro/pi-gen.git

Using --depth 1 with git clone will create a shallow clone, only containing the latest revision of the repository. Do not do this on your development machine.

Also, be careful to clone the repository to a base path NOT containing spaces. This configuration is not supported by debootstrap and will lead to pi-gen not running.

After cloning the repository, you can move to the next step and start configuring your build.

Config

Upon execution, build.sh will source the file config in the current working directory. This bash shell fragment is intended to set needed environment variables.

The following environment variables are supported:

A simple example for building Raspbian:

IMG_NAME='Raspbian'

The config file can also be specified on the command line as an argument the build.sh or build-docker.sh scripts.

./build.sh -c myconfig

This is parsed after config so can be used to override values set there.

How the build process works

The following process is followed to build images:

It is recommended to examine build.sh for finer details.

Docker Build

Docker can be used to perform the build inside a container. This partially isolates the build from the host system, and allows using the script on non-debian based systems (e.g. Fedora Linux). The isolate is not complete due to the need to use some kernel level services for arm emulation (binfmt) and loop devices (losetup).

To build:

vi config         # Edit your config file. See above.
./build-docker.sh

If everything goes well, your finished image will be in the deploy/ folder. You can then remove the build container with docker rm -v pigen_work

If something breaks along the line, you can edit the corresponding scripts, and continue:

CONTINUE=1 ./build-docker.sh

To examine the container after a failure you can enter a shell within it using:

sudo docker run -it --privileged --volumes-from=pigen_work pi-gen /bin/bash

After successful build, the build container is by default removed. This may be undesired when making incremental changes to a customized build. To prevent the build script from remove the container add

PRESERVE_CONTAINER=1 ./build-docker.sh

There is a possibility that even when running from a docker container, the installation of qemu-user-static will silently fail when building the image because binfmt-support must be enabled on the underlying kernel. An easy fix is to ensure binfmt-support is installed on the host machine before starting the ./build-docker.sh script (or using your own docker build solution).

Passing arguments to Docker

When the docker image is run various required command line arguments are provided. For example the system mounts the /dev directory to the /dev directory within the docker container. If other arguments are required they may be specified in the PIGEN_DOCKER_OPTS environment variable. For example setting PIGEN_DOCKER_OPTS="--add-host foo:192.168.0.23" will add '192.168.0.23 foo' to the /etc/hosts file in the container. The --name and --privileged options are already set by the script and should not be redefined.

Stage Anatomy

Raspbian Stage Overview

The build of Raspbian is divided up into several stages for logical clarity and modularity. This causes some initial complexity, but it simplifies maintenance and allows for more easy customization.

Stage specification

If you wish to build up to a specified stage (such as building up to stage 2 for a lite system), place an empty file named SKIP in each of the ./stage directories you wish not to include.

Then add an empty file named SKIP_IMAGES to ./stage4 and ./stage5 (if building up to stage 2) or to ./stage2 (if building a minimal system).

# Example for building a lite system
echo "IMG_NAME='Raspbian'" > config
touch ./stage3/SKIP ./stage4/SKIP ./stage5/SKIP
touch ./stage4/SKIP_IMAGES ./stage5/SKIP_IMAGES
sudo ./build.sh  # or ./build-docker.sh

If you wish to build further configurations upon (for example) the lite system, you can also delete the contents of ./stage3 and ./stage4 and replace with your own contents in the same format.

Skipping stages to speed up development

If you're working on a specific stage the recommended development process is as follows:

Regarding Qcow2 image building

Get infos about the image in use

If you issue the two commands shown in the example below in a second command shell while a build is running you can find out, which network block device is currently being used and which qcow2 image is bound to it.

Example:

root@build-machine:~/$ lsblk | grep nbd
nbd1      43:32   0    10G  0 disk
├─nbd1p1  43:33   0    10G  0 part
└─nbd1p1 253:0    0    10G  0 part

root@build-machine:~/$ ps xa | grep qemu-nbd
 2392 pts/6    S+     0:00 grep --color=auto qemu-nbd
31294 ?        Ssl    0:12 qemu-nbd --discard=unmap -c /dev/nbd1 image-stage4.qcow2

Here you can see, that the qcow2 image image-stage4.qcow2 is currently connected to /dev/nbd1 with the associated partition map /dev/mapper/nbd1p1. Don't worry that lsblk shows two entries. It is totally fine, because the device map is accessible via /dev/mapper/nbd1p1 and also via /dev/dm-0. This is all part of the device mapper functionality of the kernel. See dmsetup for further information.

Mount a qcow2 image

If you want to examine the content of a a single stage, you can simply mount the qcow2 image found in the WORK_DIR directory with the tool ./imagetool.sh.

See ./imagetool.sh -h for further details on how to use it.

Disconnect an image if something went wrong

It can happen, that your build stops in case of an error. Normally ./build.sh should handle image disconnection appropriately, but in rare cases, especially during a Docker build, this may not work as expected. If that happens, starting a new build will fail and you may have to disconnect the image and/or device yourself.

A typical message indicating that there are some orphaned device mapper entries is this:

Failed to set NBD socket
Disconnect client, due to: Unexpected end-of-file before all bytes were read

If that happens go through the following steps:

  1. First, check if the image is somehow mounted to a directory entry and umount it as you would any other block device, like i.e. a hard disk or USB stick.

  2. Second, to disconnect an image from qemu-nbd, the QEMU Disk Network Block Device Server, issue the following command (be sure to change the device name to the one actually used):

    sudo qemu-nbd -d /dev/nbd1

    Note: if you use Docker build, normally no active qemu-nbd process exists anymore as it will be terminated when the Docker container stops.

  3. To disconnect a device partition map from the network block device, execute:

    sudo kpartx -d /dev/nbd1
or
sudo ./imagetool.sh --cleanup

    Note: The imagetool.sh command will cleanup any /dev/nbdX that is not connected to a running qemu-nbd daemon. Be careful if you use network block devices for other tasks utilizing NBDs on your build machine as well.

Now you should be able to start a new build without running into troubles again. Most of the time, especially when using Docker build, you will only need no. 3 to get everything up and running again.

Troubleshooting

64 Bit Systems

Please note there is currently an issue when compiling with a 64 Bit OS. See https://github.com/RPi-Distro/pi-gen/issues/271

A 64 bit image can be generated from the arm64 branch in this repository. Just replace the command from this section by the one below, and follow the rest of the documentation:

git clone --depth 1 --branch arm64 https://github.com/RPI-Distro/pi-gen.git

If you want to generate a 64 bits image from a Raspberry Pi running a 32 bits version, you need to add arm_64bit=1 to your config.txt file and reboot your machine. This will restart your machine with a 64 bits kernel. This will only work from a Raspberry Pi with a 64-bit capable processor (i.e. Raspberry Pi Zero 2, Raspberry Pi 3 or Raspberry Pi 4).

binfmt_misc

Linux is able execute binaries from other architectures, meaning that it should be possible to make use of pi-gen on an x86_64 system, even though it will be running ARM binaries. This requires support from the binfmt_misc kernel module.

You may see one of the following errors:

update-binfmts: warning: Couldn't load the binfmt_misc module.
W: Failure trying to run: chroot "/pi-gen/work/test/stage0/rootfs" /bin/true
and/or
chroot: failed to run command '/bin/true': Exec format error

To resolve this, ensure that the following files are available (install them if necessary):

/lib/modules/$(uname -r)/kernel/fs/binfmt_misc.ko
/usr/bin/qemu-arm-static

You may also need to load the module by hand - run modprobe binfmt_misc.

If you are using WSL to build you may have to enable the service sudo update-binfmts --enable