osbuilder

• Introduction
• Terms
• Usage
  • Rootfs creation
    • Rootfs with systemd as init
    • Rootfs with the agent as init
  • Image creation
    • Image with systemd as init
    • Image with the agent as init
  • Initrd creation

Introduction

The Kata Containers runtime creates a virtual machine (VM) to isolate a set of container workloads. The VM requires a guest kernel and a guest operating system ("guest OS") to boot and create containers inside the guest environment.

This repository contains tools to create a guest OS disk image.

Terms

This section describes the terms used for all documentation in this repository.

• rootfs

  The root filesystem or "rootfs" is a slight misnomer as it is not a true filesystem. It is a tree of files contained in a particular directory, which represents the root disk layout. A rootfs can be turned into either an image or an initrd.

  See the rootfs creation section.

• "Guest OS" (or "Guest Image")

  A "virtual disk" or "disk image" built from a rootfs. It contains a filesystem that is used by the VM, in conjunction with a guest kernel, to create an environment to host the container. Neither the guest OS nor the guest kernel need to be the same as the host operating system.

  See the image creation section.

• initrd (or "initramfs")

  A compressed cpio(1) archive, created from a rootfs which is loaded into memory and used as part of the Linux startup process. During startup, the kernel unpacks it into a special instance of a tmpfs that becomes the initial root filesystem.

  See the initrd creation section.

• "Base OS"

  A particular version of a Linux distribution used to create a rootfs from.

Usage

The top-level Makefile contains an example of how to use the available components.

By default, components will run on the host system. However, some components offer the ability to run from within Docker (for ease of setup) by setting the USE_DOCKER=true variable.

For more detailed information, consult the documentation for a particular component.

Rootfs creation

This section shows how to build a basic rootfs using the default distribution. For further details, see the rootfs builder documentation.

Rootfs with systemd as init

$ sudo -E PATH=$PATH make USE_DOCKER=true rootfs

Rootfs with the agent as init

$ sudo -E PATH=$PATH make USE_DOCKER=true AGENT_INIT=yes rootfs

Image creation

This section shows how to create an image from the already-created rootfs. For further details, see the image builder documentation.

Image with systemd as init

$ sudo -E PATH=$PATH make USE_DOCKER=true image-only

Image with the agent as init

$ sudo -E PATH=$PATH make USE_DOCKER=true AGENT_INIT=yes image-only

Initrd creation

To create an initrd from the already-created rootfs with the agent acting as the init daemon:

$ sudo -E PATH=$PATH make AGENT_INIT=yes initrd-only

For further details, see the initrd builder documentation.