Booting Overview

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Revision as of 16:32, 10 September 2018 by Lars.kurth (talk | contribs) (Direct Kernel Boot)

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This document describes the different mechanisms and config file options that are available for Xen.

The following diagram shows the first steps of the Linux boot and startup sequence to provide a baseline to allow explaining the differences

HVM Guest Boot Process

From a user's perspective the HVM Boot and install process is identical to the process on a native PC or server.

However, behind the scenes

  • The hvmloader is copied into guest memory by Xen (under the control of the Toolstack). The hvmloader sets up all necessary information for the Device Emulator which emulates a HW environment that appears exactly like a physical machine. 
  • The correct firmware is automatically loaded as a binary blob (usually located in /usr/lib64/xen/boot) and copied into guest memory based on config settings, but can be overridden via the firmware config file option. See the various firmware options in the man page.

Direct Kernel Boot

When installing a new guest OS it is often useful to boot directly from a kernel and initrd stored in the host OS' file system, allowing command line arguments to be passed directly to the installer. This capability is usually available for PV, PVH and HVM guests. In this case, the

Works for all guest types

Non standard way of installing/booting

Need to be a host admins to configure�(need access to Dom0).

Useful for netboot, see wiki.xenproject.org/wiki/Xenpvnetboot

PVGrub

PyGrub

PV Guest Install Basic Workflow