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osbuilder - Clear Containers guest O/S building scripts


The Clear Containers hypervisor creates a virtual machine (VM) in which to run the workload. To do this, the hypervisor requires a root filesystem (rootfs) image and a guest kernel image in order to create the guest environment in which the container runs.

This repository contains scripts to create a custom root filesystem image ("rootfs") and guest kernel image. These custom resources may be used for testing and developing new features.


The scripts in this repository are called by running make(1) specifying particular targets. The scripts use a work directory for storing all files. By default this will be created automatically as ./workdir however this can be changed by setting the WORKDIR environment variable. See Environment Variables.

Building a guest image

A guest image is a rootfs that has been converted into a disk image.

Build a rootfs

The rootfs target will generate a directory called workdir/rootfs, overwriting duplicate files:

$ sudo -E  make rootfs

(optional) Customise the rootfs

It is possible to customise the rootfs; simply modify the files below workdir/rootfs as desired.

Create a rootfs image

The image target will create a disk image called container.img from the workload/rootfs directory. This image file is compatible with the official Clear Containers images provided with a Clear Containers installation.


The image target will not create or populate the workdir/rootfs directory so it is necessary to build a rootfs first.

Use the IMG_SIZE environment variable to change the size of the image if desired. See Environment Variables.

$ sudo -E make image

Default packages

By default, the rootfs image is based on Clear Linux for Intel* Architecture, but the workdir/rootfs directory can be populated with any other source.

Packages are installed inside the generated image. You can install extra packages using the environment variable EXTRA_PKGS. See Environment Variables.

Clear Linux based packages security limitations

Although the Clear Linux rootfs is constructed from rpm packages, Clear Linux itself is not an rpm-based Linux distribution (the software installed on a Clear Linux system is not managed using rpm).

The rpm packages used to generate the rootfs are not signed, so there is no way to ensure that downloaded packages are trustworthy.

If you are willing to use Clear Linux based images, official Clear Containers rootfs images can be obtained from

Build guest kernel

Clear Containers uses the Linux* kernel.

To build a kernel compatible with Clear Containers using the make kernel target. This will clone the Clear Container Kernel in the workdir/linux directory (which will be created if necessary). On success two new kernel images will be created:

  • workdir/vmlinuz.container (compressed kernel image)
  • workdir/vmlinux.container (uncompressed kernel image)
$ # Pull and setup latest kernel for Clear Containers
$ sudo -E make kernel-src
$ sudo -E make kernel

Using the newly generated custom rootfs and kernel images

Clear Containers 3.x

This section covers using the new resources with cc-runtime.

Installing the custom roots image

  1. Install the image file
    $ sudo make install-image

Installing the new kernel

  1. Install the kernel image (run make help for more information)

    $ sudo make install-kernel
  2. Verify kernel is configured

    $ cc-runtime cc-env


In order to work the osbuilder scripts require the following programs:

  • bc
  • dnf or yum
  • gcc
  • gdisk
  • git
  • make
  • parted
  • qemu-img

To check if these tools are available locally, run:

$ make check-deps

Using osbuilder scripts with Docker*

If you do not want to install all the dependencies on your system to run the osbuilder scripts, you can instead run them under Docker. To run the osbuilder scripts inside a Docker container the following requirements must be met:

  1. Docker 1.12+ installed

  2. runc is configured as the default runtime

    To check if runc is the default runtime:

    $ docker info | grep 'Default Runtime: runc'


    This requirement is specifically for docker build which does not work with a hypervisor-based runtime currently (see issue #8 for more information.

  3. Export USE_DOCKER variable

    $ export USE_DOCKER=true
  4. Use osbuilder makefile targets as described in Build guest image


    $ export USE_DOCKER=true
    $ # Download Clear Containers guest base rootfs
    $ sudo -E make rootfs
    $ # Build an image with the conent generated by 'make rootfs'
    $ sudo -E make image


Using osbuilder with ubuntu 14.06 fails because of an old version of rpm. However, it is still possible to run the scripts using docker.

Environment Variables

Run make help to see a list of supported environment variables that can be used to change the tools behaviour.