b417259465
Partial-Bug: #1250515 author: diane fleming Change-Id: I92c9ad25ee5bbd2c9334c4860637faa1b358718b backport: havana
204 lines
10 KiB
XML
204 lines
10 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
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xml:id="kvm">
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<?dbhtml stop-chunking?>
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<title>KVM</title>
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<para>KVM is configured as the default hypervisor for
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Compute.</para>
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<note>
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<para>This document contains several sections about hypervisor
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selection. If you are reading this document linearly, you
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do not want to load the KVM module before you install
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<systemitem class="service">nova-compute</systemitem>.
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The <systemitem class="service">nova-compute</systemitem>
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service depends on qemu-kvm, which installs
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<filename>/lib/udev/rules.d/45-qemu-kvm.rules</filename>,
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which sets the correct permissions on the /dev/kvm device
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node.</para>
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</note>
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<para>To enable KVM explicitly, add the following configuration
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options to the <filename>/etc/nova/nova.conf</filename>
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file:</para>
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<programlisting language="ini">compute_driver=libvirt.LibvirtDriver
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libvirt_type=kvm</programlisting>
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<para>The KVM hypervisor supports the following virtual machine
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image formats:</para>
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<itemizedlist>
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<listitem>
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<para>Raw</para>
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</listitem>
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<listitem>
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<para>QEMU Copy-on-write (qcow2)</para>
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</listitem>
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<listitem>
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<para>QED Qemu Enhanced Disk</para>
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</listitem>
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<listitem>
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<para>VMWare virtual machine disk format (vmdk)</para>
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</listitem>
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</itemizedlist>
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<para>This section describes how to enable KVM on your system. For
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more information, see the following distribution-specific
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documentation:</para>
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<itemizedlist>
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<listitem>
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<para><link
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xlink:href="http://fedoraproject.org/wiki/Getting_started_with_virtualization"
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>Fedora: Getting started with
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virtualization</link> from the Fedora project
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wiki.</para>
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</listitem>
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<listitem>
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<para><link
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xlink:href="https://help.ubuntu.com/community/KVM/Installation"
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>Ubuntu: KVM/Installation</link> from the
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Community Ubuntu documentation.</para>
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</listitem>
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<listitem>
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<para><link
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xlink:href="http://static.debian-handbook.info/browse/stable/sect.virtualization.html#idp11279352"
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>Debian: Virtualization with KVM</link> from the
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Debian handbook.</para>
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</listitem>
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<listitem>
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<para><link
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xlink:href="http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/sect-Virtualization_Host_Configuration_and_Guest_Installation_Guide-Host_Installation-Installing_KVM_packages_on_an_existing_Red_Hat_Enterprise_Linux_system.html"
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>RHEL: Installing virtualization packages on an
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existing Red Hat Enterprise Linux system</link>
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from the <citetitle>Red Hat Enterprise Linux
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Virtualization Host Configuration and Guest
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Installation Guide</citetitle>.</para>
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</listitem>
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<listitem>
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<para><link
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xlink:href="http://doc.opensuse.org/documentation/html/openSUSE/opensuse-kvm/cha.kvm.requires.html#sec.kvm.requires.install"
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>openSUSE: Installing KVM</link> from the openSUSE
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Virtualization with KVM manual.</para>
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</listitem>
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<listitem>
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<para><link
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xlink:href="http://doc.opensuse.org/products/draft/SLES/SLES-kvm_sd_draft/cha.kvm.requires.html#sec.kvm.requires.install"
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>SLES: Installing KVM</link> from the SUSE Linux
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Enterprise Server Virtualization with KVM
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manual.</para>
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</listitem>
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</itemizedlist>
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<xi:include href="../../common/section_kvm_enable.xml"/>
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<section xml:id="libvirt-xml-cpu-model">
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<title>Specify the CPU model of KVM guests</title>
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<para>The Compute service enables you to control the guest CPU
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model that is exposed to KVM virtual machines. Use cases
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include:</para>
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<itemizedlist>
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<listitem>
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<para>To maximize performance of virtual machines by
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exposing new host CPU features to the guest</para>
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</listitem>
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<listitem>
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<para>To ensure a consistent default CPU across all
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machines, removing reliance of variable QEMU
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defaults</para>
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</listitem>
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</itemizedlist>
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<para>In libvirt, the CPU is specified by providing a base CPU
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model name (which is a shorthand for a set of feature
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flags), a set of additional feature flags, and the
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topology (sockets/cores/threads). The libvirt KVM driver
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provides a number of standard CPU model names. These
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models are defined in the
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<filename>/usr/share/libvirt/cpu_map.xml</filename>
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file. Check this file to determine which models are
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supported by your local installation.</para>
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<para>Two Compute configuration options define which type of
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CPU model is exposed to the hypervisor when using KVM:
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<literal>libvirt_cpu_mode</literal> and
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<literal>libvirt_cpu_model</literal>.</para>
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<para>The <literal>libvirt_cpu_mode</literal> option can take
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one of the following values: <literal>none</literal>,
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<literal>host-passthrough</literal>,
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<literal>host-model</literal>, and
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<literal>custom</literal>.</para>
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<simplesect>
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<title>Host model (default for KVM & QEMU)</title>
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<para>If your <filename>nova.conf</filename> file contains
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<literal>libvirt_cpu_mode=host-model</literal>,
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libvirt identifies the CPU model in
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<filename>/usr/share/libvirt/cpu_map.xml</filename>
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file that most closely matches the host, and requests
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additional CPU flags to complete the match. This
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configuration provides the maximum functionality and
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performance and maintains good reliability and
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compatibility if the guest is migrated to another host
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with slightly different host CPUs.</para>
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</simplesect>
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<simplesect>
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<title>Host pass through</title>
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<para>If your <filename>nova.conf</filename> file contains
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<literal>libvirt_cpu_mode=host-passthrough</literal>,
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libvirt tells KVM to pass through the host CPU with no
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modifications. The difference to host-model, instead
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of just matching feature flags, every last detail of
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the host CPU is matched. This gives absolutely best
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performance, and can be important to some apps which
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check low level CPU details, but it comes at a cost
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with respect to migration: the guest can only be
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migrated to an exactly matching host CPU.</para>
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</simplesect>
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<simplesect>
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<title>Custom</title>
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<para>If your <filename>nova.conf</filename> file contains
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<literal>libvirt_cpu_mode=custom</literal>, you
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can explicitly specify one of the supported named
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model using the libvirt_cpu_model configuration
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option. For example, to configure the KVM guests to
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expose Nehalem CPUs, your
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<filename>nova.conf</filename> file should
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contain:</para>
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<programlisting language="ini">libvirt_cpu_mode=custom
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libvirt_cpu_model=Nehalem</programlisting>
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</simplesect>
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<simplesect>
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<title>None (default for all libvirt-driven hypervisors
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other than KVM & QEMU)</title>
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<para>If your <filename>nova.conf</filename> file contains
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<literal>libvirt_cpu_mode=none</literal>, libvirt
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does not specify a CPU model. Instead, the hypervisor
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chooses the default model. This setting is equivalent
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to the Compute service behavior prior to the Folsom
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release.</para>
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</simplesect>
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</section>
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<section xml:id="kvm-performance">
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<title>KVM performance tweaks</title>
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<para>The <link
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xlink:href="http://www.linux-kvm.org/page/VhostNet"
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>VHostNet</link> kernel module improves network
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performance. To load the kernel module, run the following
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command as root:</para>
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<screen><prompt>#</prompt> <userinput>modprobe vhost_net</userinput></screen>
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</section>
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<section xml:id="kvm-troubleshooting">
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<title>Troubleshoot KVM</title>
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<para>Trying to launch a new virtual machine instance fails
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with the <literal>ERROR</literal>state, and the following
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error appears in the
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<filename>/var/log/nova/nova-compute.log</filename>
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file:</para>
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<screen><computeroutput>libvirtError: internal error no supported architecture for os type 'hvm'</computeroutput></screen>
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<para>This message indicates that the KVM kernel modules were
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not loaded.</para>
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<para>If you cannot start VMs after installation without
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rebooting, the permissions might not be correct. This can
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happen if you load the KVM module before you install
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<systemitem class="service">nova-compute</systemitem>.
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To check whether the group is set to kvm, run:</para>
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<screen><prompt>#</prompt> <userinput>ls -l /dev/kvm</userinput></screen>
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<para>If it is not set to kvm, run:</para>
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<screen><prompt>#</prompt> <userinput>sudo udevadm trigger</userinput></screen>
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</section>
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</section>
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