osbuild

A build system for operating system images, working towards an image build pipeline that's more comprehensible, reproducible, and extendable.

Pipelines

The build process for an image is described by a pipeline. Each stage in a pipeline is a program that, given some configuration, modifies a file system tree. Finally, an assembler takes a filesystem tree, and assembles it into an image. Pipelines are defined as JSON files like this one:

{
  "name": "Example Image",
  "stages": [
    {
      "name": "org.osbuild.dnf",
      "options": {
        "releasever": "30",
        "repos": {
          "fedora": {
            "name": "Fedora",
            "metalink": "https://mirrors.fedoraproject.org/metalink?repo=fedora-$releasever&arch=$basearch",
            "gpgkey": "file:///etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-$releasever-$basearch"
          }
        },
        "packages": [ "@Core", "grub2-pc", "httpd" ]
        }
    },
    {
      "name": "org.osbuild.systemd",
      "options": {
        "enabled_services": [ "httpd" ]
      }
    },
    {
      "name": "org.osbuild.grub2",
      "options": {
        "root_fs_uuid": "76a22bf4-f153-4541-b6c7-0332c0dfaeac"
      }
    }
  ],
  "assembler": {
    "name": "org.osbuild.qcow2",
    "options": {
      "filename": "example.qcow2",
      "root_fs_uuid": "76a22bf4-f153-4541-b6c7-0332c0dfaeac",
      "size": 3221225472
    }
  }
}

osbuild runs each of the stages in turn, isolating them from the host and from each other, with the exception that they all operate on the same filesystem-tree. The assembler is similarly isolated, and given the same tree, in read-only mode and assembles it into an image without altering its contents.

The filesystem tree produced by the final stage of a pipeline, is named and optionally saved to be reused as the base for future pipelines.

Each stage is passed the (appended) options object as JSON over stdin.

The above pipeline has no base and produces a qcow2 image.

Running

usage: python3 -m osbuild [-h] [--build-pipeline PIPELINE] [--store DIRECTORY]
                   [-l DIRECTORY] -o DIRECTORY
                   PIPELINE

Build operating system images

positional arguments:
  PIPELINE              json file containing the pipeline that should be built

optional arguments:
  -h, --help            show this help message and exit
  --build-pipeline PIPELINE
                        json file containing the pipeline to create a build
                        environment
  --store DIRECTORY     the directory where intermediary os trees are stored
  -l DIRECTORY, --libdir DIRECTORY
                        the directory containing stages, assemblers, and the
                        osbuild library

required named arguments:
  -o DIRECTORY, --output DIRECTORY
                        provide the empty DIRECTORY as output argument to the
                        last stage

Running example

You can build basic qcow2 image of Fedora 30 by running a following command:

sudo python3 -m osbuild -o output --libdir . samples/base-qcow2.json

• Root rights are required because osbuild heavily relies on creating systemd containers and bind mounting.

  It shouldn't interfere with host OS but please be careful! It's still under development!

• --libdir argument is required because osbuild expects itself to be installed in directories under /usr. Using this argument you can change the expected path.

• You don't need to use any kind of virtual environment, modern version of Python 3 is enough. osbuild uses only standard library and linux commands.