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339 lines
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ReStructuredText
339 lines
11 KiB
ReStructuredText
.. role:: since
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===============================
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libxl hypervisor driver for Xen
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===============================
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.. contents::
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The libvirt libxl driver provides the ability to manage virtual machines on any
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Xen release from 4.6.0 onwards.
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Project Links
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-------------
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- The `Xen <https://www.xenproject.org>`__ hypervisor on Linux and Solaris
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hosts
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Deployment pre-requisites
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-------------------------
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The libvirt libxl driver uses Xen's libxl API, also known as libxenlight, to
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implement libvirt's hypervisor driver functionality. libxl provides a
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consolidated interface for managing a Xen host and its virtual machines, unlike
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old versions of Xen where applications often had to communicate with xend,
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xenstored, and the hypervisor itself via hypercalls. With libxl the only
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pre-requisit is a properly installed Xen host with the libxl toolstack running
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in a service domain (often Domain-0).
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Connections to libxl driver
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---------------------------
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The libvirt libxl driver is a single-instance privileged driver, with a driver
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name of 'xen'. Some example connection URIs for the libxl driver are:
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::
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xen:///system (local access, direct)
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xen+unix:///system (local access, via daemon)
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xen://example.com/system (remote access, TLS/x509)
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xen+tcp://example.com/system (remote access, SASl/Kerberos)
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xen+ssh://root@example.com/system (remote access, SSH tunnelled)
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Location of configuration files
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-------------------------------
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The libxl driver comes with sane default values. However, during its
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initialization it reads a configuration file which offers system administrator
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to override some of that default. The file is located under
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``/etc/libvirt/libxl.conf``
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Import and export of libvirt domain XML configs
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-----------------------------------------------
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The libxl driver currently supports three native config formats. The first,
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known as ``xen-xm``, is the original Xen virtual machine config format used by
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the legacy xm/xend toolstack. The second, known as ``xen-sxpr``, is also one of
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the original formats that was used by xend's legacy HTTP RPC service (
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:since:`removed in 5.6.0` )
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The third format is ``xen-xl``, which is the virtual machine config format
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supported by modern Xen. The ``xen-xl`` format is described in the xl.cfg(5) man
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page.
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Converting from XM config files to domain XML
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The ``virsh domxml-from-native`` provides a way to convert an existing set of
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xl, xm, or sxpr config files to libvirt Domain XML, which can then be used by
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libvirt.
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::
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$ virsh -c xen:///system domxml-from-native xen-xm rhel5.cfg
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<domain type='xen'>
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<name>rhel5pv</name>
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<uuid>8f07fe28-753f-2729-d76d-bdbd892f949a</uuid>
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<memory>2560000</memory>
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<currentMemory>307200</currentMemory>
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<vcpu>4</vcpu>
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<bootloader>/usr/bin/pygrub</bootloader>
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<os>
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<type arch='x86_64' machine='xenpv'>linux</type>
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</os>
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<clock offset='utc'/>
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<on_poweroff>destroy</on_poweroff>
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<on_reboot>restart</on_reboot>
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<on_crash>restart</on_crash>
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<devices>
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<disk type='file' device='disk'>
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<driver name='tap' type='aio'/>
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<source file='/var/lib/xen/images/rhel5pv.img'/>
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<target dev='xvda' bus='xen'/>
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</disk>
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<disk type='file' device='disk'>
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<driver name='tap' type='qcow'/>
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<source file='/root/qcow1-xen.img'/>
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<target dev='xvdd' bus='xen'/>
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</disk>
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<interface type='bridge'>
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<mac address='00:16:3e:60:36:ba'/>
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<source bridge='xenbr0'/>
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</interface>
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<console type='pty'>
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<target port='0'/>
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</console>
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<input type='mouse' bus='xen'/>
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<graphics type='vnc' port='-1' autoport='yes' listen='0.0.0.0'/>
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</devices>
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</domain>
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Converting from domain XML to XM config files
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The ``virsh domxml-to-native`` provides a way to convert a guest description
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using libvirt Domain XML into xl, xm, or sxpr config format.
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::
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$ virsh -c xen:///system domxml-to-native xen-xm rhel5pv.xml
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name = "rhel5pv"
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uuid = "8f07fe28-753f-2729-d76d-bdbd892f949a"
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maxmem = 2500
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memory = 300
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vcpus = 4
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bootloader = "/usr/bin/pygrub"
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kernel = "/var/lib/xen/boot_kernel.0YK-cS"
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ramdisk = "/var/lib/xen/boot_ramdisk.vWgrxK"
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extra = "ro root=/dev/VolGroup00/LogVol00 rhgb quiet"
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on_poweroff = "destroy"
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on_reboot = "restart"
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on_crash = "restart"
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sdl = 0
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vnc = 1
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vncunused = 1
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vnclisten = "0.0.0.0"
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disk = [ "tap:aio:/var/lib/xen/images/rhel5pv.img,xvda,w", "tap:qcow:/root/qcow1-xen.img,xvdd,w" ]
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vif = [ "mac=00:16:3e:60:36:ba,bridge=virbr0,script=vif-bridge,vifname=vif5.0" ]
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Pass-through of arbitrary command-line arguments to the qemu device model
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-------------------------------------------------------------------------
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:since:`Since 6.7.0`, the Xen driver supports passing arbitrary command-line
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arguments to the qemu device model used by Xen with the ``<xen:commandline>``
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element under ``domain``. In order to use command-line pass-through, an XML
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namespace request must be issued that pulls in
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``http://libvirt.org/schemas/domain/xen/1.0``. With the namespace in place, it
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is then possible to add ``<xen:arg>``\ sub-elements to ``<xen:commandline>``
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describing each argument passed to the device model when starting the domain.
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The following example illustrates passing arguments to the QEMU device model
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that define a floppy drive, which Xen does not support through its public APIs:
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::
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<domain type="xen" xmlns:xen="http://libvirt.org/schemas/domain/xen/1.0">
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...
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<xen:commandline>
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<xen:arg value='-drive'/>
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<xen:arg value='file=/path/to/image,format=raw,if=none,id=drive-fdc0-0-0'/>
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<xen:arg value='-global'/>
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<xen:arg value='isa-fdc.driveA=drive-fdc0-0-0'/>
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</xen:commandline>
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</domain>
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Example domain XML config
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-------------------------
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Below are some example XML configurations for Xen guest domains. For full
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details of the available options, consult the `domain XML
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format <formatdomain.html>`__ guide.
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Paravirtualized guest bootloader
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Using a bootloader allows a paravirtualized guest to be booted using a kernel
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stored inside its virtual disk image
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::
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<domain type='xen' >
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<name>fc8</name>
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<bootloader>/usr/bin/pygrub</bootloader>
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<os>
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<type>linux</type>
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</os>
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<memory>131072</memory>
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<vcpu>1</vcpu>
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<devices>
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<disk type='file'>
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<source file='/var/lib/xen/images/fc4.img'/>
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<target dev='sda1'/>
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</disk>
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<interface type='bridge'>
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<source bridge='xenbr0'/>
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<mac address='aa:00:00:00:00:11'/>
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<script path='/etc/xen/scripts/vif-bridge'/>
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</interface>
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<console tty='/dev/pts/5'/>
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</devices>
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</domain>
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Paravirtualized guest direct kernel boot
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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For installation of paravirtualized guests it is typical to boot the domain
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using a kernel and initrd stored in the host OS
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::
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<domain type='xen' >
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<name>fc8</name>
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<os>
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<type>linux</type>
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<kernel>/var/lib/xen/install/vmlinuz-fedora8-x86_64</kernel>
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<initrd>/var/lib/xen/install/initrd-vmlinuz-fedora8-x86_64</initrd>
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<cmdline> kickstart=http://example.com/myguest.ks </cmdline>
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</os>
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<memory>131072</memory>
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<vcpu>1</vcpu>
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<devices>
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<disk type='file'>
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<source file='/var/lib/xen/images/fc4.img'/>
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<target dev='sda1'/>
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</disk>
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<interface type='bridge'>
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<source bridge='xenbr0'/>
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<mac address='aa:00:00:00:00:11'/>
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<script path='/etc/xen/scripts/vif-bridge'/>
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</interface>
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<graphics type='vnc' port='-1'/>
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<console tty='/dev/pts/5'/>
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</devices>
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</domain>
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Fullyvirtualized guest BIOS boot
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Fullyvirtualized guests use the emulated BIOS to boot off the primary harddisk,
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CDROM or Network PXE ROM.
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::
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<domain type='xen' id='3'>
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<name>fv0</name>
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<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
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<os>
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<type>hvm</type>
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<loader>/usr/lib/xen/boot/hvmloader</loader>
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<boot dev='hd'/>
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</os>
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<memory>524288</memory>
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<vcpu>1</vcpu>
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<on_poweroff>destroy</on_poweroff>
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<on_reboot>restart</on_reboot>
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<on_crash>restart</on_crash>
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<features>
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<pae/>
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<acpi/>
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<apic/>
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</features>
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<clock sync="localtime"/>
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<devices>
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<emulator>/usr/lib/xen/bin/qemu-dm</emulator>
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<interface type='bridge'>
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<source bridge='xenbr0'/>
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<mac address='00:16:3e:5d:c7:9e'/>
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<script path='vif-bridge'/>
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</interface>
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<disk type='file'>
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<source file='/var/lib/xen/images/fv0'/>
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<target dev='hda'/>
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</disk>
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<disk type='file' device='cdrom'>
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<source file='/var/lib/xen/images/fc5-x86_64-boot.iso'/>
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<target dev='hdc'/>
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<readonly/>
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</disk>
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<disk type='file' device='floppy'>
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<source file='/root/fd.img'/>
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<target dev='fda'/>
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</disk>
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<graphics type='vnc' port='5904'/>
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</devices>
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</domain>
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Fullyvirtualized guest direct kernel boot
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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With Xen 3.2.0 or later it is possible to bypass the BIOS and directly boot a
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Linux kernel and initrd as a fullyvirtualized domain. This allows for complete
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automation of OS installation, for example using the Anaconda kickstart support.
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::
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<domain type='xen' id='3'>
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<name>fv0</name>
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<uuid>4dea22b31d52d8f32516782e98ab3fa0</uuid>
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<os>
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<type>hvm</type>
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<loader>/usr/lib/xen/boot/hvmloader</loader>
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<kernel>/var/lib/xen/install/vmlinuz-fedora8-x86_64</kernel>
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<initrd>/var/lib/xen/install/initrd-vmlinuz-fedora8-x86_64</initrd>
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<cmdline> kickstart=http://example.com/myguest.ks </cmdline>
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</os>
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<memory>524288</memory>
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<vcpu>1</vcpu>
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<on_poweroff>destroy</on_poweroff>
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<on_reboot>restart</on_reboot>
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<on_crash>restart</on_crash>
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<features>
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<pae/>
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<acpi/>
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<apic/>
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</features>
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<clock sync="localtime"/>
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<devices>
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<emulator>/usr/lib/xen/bin/qemu-dm</emulator>
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<interface type='bridge'>
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<source bridge='xenbr0'/>
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<mac address='00:16:3e:5d:c7:9e'/>
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<script path='vif-bridge'/>
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</interface>
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<disk type='file'>
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<source file='/var/lib/xen/images/fv0'/>
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<target dev='hda'/>
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</disk>
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<disk type='file' device='cdrom'>
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<source file='/var/lib/xen/images/fc5-x86_64-boot.iso'/>
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<target dev='hdc'/>
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<readonly/>
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</disk>
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<disk type='file' device='floppy'>
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<source file='/root/fd.img'/>
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<target dev='fda'/>
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</disk>
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<graphics type='vnc' port='5904'/>
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</devices>
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</domain>
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