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HTML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /><link rel="stylesheet" type="text/css" href="libvirt.css" /><link rel="SHORTCUT ICON" href="/32favicon.png" /><title>Remote support</title></head><body><div id="container"><div id="intro"><div id="adjustments"></div><div id="pageHeader"></div><div id="content2"><h1 class="style1">Remote support</h1><p>
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<b>NB. Remote support is available only as a <a href="https://www.redhat.com/archives/libvir-list/">series of
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patches posted on libvir-list</a> against <a href="http://libvirt.org/downloads.html">libvirt CVS</a>. It is only
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for experimental use at the moment.</b>
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— Richard Jones, 2007-04-18.
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</p><p>
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Libvirt allows you to access hypervisors running on remote
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machines through authenticated and encrypted connections.
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</p><h3><a name="Remote_basic_usage" id="Remote_basic_usage">Basic usage</a></h3><p>
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On the remote machine, <code>libvirtd</code> should be running.
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See <a href="#Remote_libvirtd_configuration">the section
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on configuring libvirtd</a> for more information.
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</p><p>
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To tell libvirt that you want to access a remote resource,
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you should supply a hostname in the normal URI that is passed
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to <code>virConnectOpen</code> (or <code>virsh -c ...</code>).
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For example, if you normally use <code>qemu:///system</code>
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to access the system-wide QEMU daemon, then to access
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the system-wide QEMU daemon on a remote machine called
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<code>oirase</code> you would use <code>qemu://oirase/system</code>.
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</p><p>
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The <a href="#Remote_URI_reference">section on remote URIs</a>
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describes in more detail these remote URIs.
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</p><p>
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From an API point of view, apart from the change in URI, the
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API should behave the same. For example, ordinary calls
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are routed over the remote connection transparently, and
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values or errors from the remote side are returned to you
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as if they happened locally. Some differences you may notice:
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</p><ul><li> Additional errors can be generated, specifically ones
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relating to failures in the remote transport itself. </li>
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<li> Remote calls are handled synchronously, so they will be
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much slower than, say, direct hypervisor calls. </li>
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</ul><h3><a name="Remote_transports" id="Remote_transports">Transports</a></h3><p>
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Remote libvirt supports a range of transports:
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</p><dl><dt> tls </dt>
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<dd> <a href="http://en.wikipedia.org/wiki/Transport_Layer_Security" title="Transport Layer Security">TLS</a>
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1.0 (SSL 3.1) authenticated and encrypted TCP/IP socket, usually
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listening on a public port number. To use this you will need to
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<a href="#Remote_certificates" title="Generating TLS certificates">generate client and
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server certificates</a>.
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The standard port is 16514.
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</dd>
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<dt> unix </dt>
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<dd> Unix domain socket. Since this is only accessible on the
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local machine, it is not encrypted, and uses Unix permissions or
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SELinux for authentication.
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The standard socket names are
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<code>/var/run/libvirt/libvirt-sock</code> and
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<code>/var/run/libvirt/libvirt-sock-ro</code> (the latter
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for read-only connections).
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</dd>
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<dt> ssh </dt>
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<dd> Transported over an ordinary
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<a href="http://www.openssh.com/" title="OpenSSH homepage">ssh
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(secure shell)</a> connection.
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Requires <a href="http://netcat.sourceforge.net/">Netcat (nc)</a>
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installed on the remote machine, and the remote libvirtd should
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be listening on the unix transport. You should use some sort of
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ssh key management (eg.
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<a href="http://mah.everybody.org/docs/ssh" title="Using ssh-agent with ssh">ssh-agent</a>)
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otherwise programs which use
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this transport will stop to ask for a password. </dd>
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<dt> ext </dt>
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<dd> Any external program which can make a connection to the
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remote machine by means outside the scope of libvirt. </dd>
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<dt> tcp </dt>
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<dd> Unencrypted TCP/IP socket. Not recommended for production
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use, this is normally disabled, but an administrator can enable
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it for testing or use over a trusted network.
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The standard port is 16509.
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</dd>
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</dl><p>
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The default transport, if no other is specified, is <code>tls</code>.
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</p><h3><a name="Remote_URI_reference" id="Remote_URI_reference">Remote URIs</a></h3><p>
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Remote URIs have the general form ("[...]" meaning an optional part):
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</p><p>
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<code>driver</code>[<code>+transport</code>]<code>://</code>[<code>username@</code>]<code>hostname</code>[<code>:port</code>]<code>/</code>[<code>path</code>][<code>?extraparameters</code>]
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</p><p>
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Either the transport or the hostname must be given in order
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to distinguish this from a local URI.
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</p><p>
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Some examples:
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</p><ul><li> <code>xen+ssh://rjones@towada/</code> <br /> — Connect to a
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remote Xen hypervisor on host <code>towada</code> using ssh transport and ssh
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username <code>rjones</code>.
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</li>
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<li> <code>xen://towada/</code> <br /> — Connect to a
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remote Xen hypervisor on host <code>towada</code> using TLS.
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</li>
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<li> <code>xen://towada/?no_verify=1</code> <br /> — Connect to a
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remote Xen hypervisor on host <code>towada</code> using TLS. Do not verify
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the server's certificate.
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</li>
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<li> <code>qemu+unix:///system?socket=/opt/libvirt/run/libvirt/libvirt-sock</code> <br /> —
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Connect to the local qemu instances over a non-standard
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Unix socket (the full path to the Unix socket is
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supplied explicitly in this case).
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</li>
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<li> <code>test+tcp://localhost:5000/default</code> <br /> —
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Connect to a libvirtd daemon offering unencrypted TCP/IP connections
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on localhost port 5000 and use the test driver with default
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settings.
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</li>
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</ul><h4><a name="Remote_URI_parameters" id="Remote_URI_parameters">Extra parameters</a></h4><p>
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Extra parameters can be added to remote URIs as part
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of the query string (the part following <q><code>?</code></q>).
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Remote URIs understand the extra parameters shown below.
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Any others are passed unmodified through to the back end.
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Note that parameter values must be
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<a href="http://xmlsoft.org/html/libxml-uri.html#xmlURIEscapeStr">URI-escaped</a>.
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</p><table><tr><th> Name </th>
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<th> Transports </th>
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<th> Meaning </th>
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</tr><tr><td> <code>name</code> </td>
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<td> <i>any transport</i> </td>
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<td>
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The name passed to the remote virConnectOpen function. The
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name is normally formed by removing transport, hostname, port
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number, username and extra parameters from the remote URI, but in certain
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very complex cases it may be better to supply the name explicitly.
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</td>
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</tr><tr><td colspan="2"></td>
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<td> Example: <code>name=qemu:///system</code> </td>
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</tr><tr><td> <code>command</code> </td>
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<td> ssh, ext </td>
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<td>
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The external command. For ext transport this is required.
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For ssh the default is <code>ssh</code>.
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The PATH is searched for the command.
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</td>
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</tr><tr><td colspan="2"></td>
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<td> Example: <code>command=/opt/openssh/bin/ssh</code> </td>
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</tr><tr><td> <code>socket</code> </td>
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<td> unix, ssh </td>
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<td>
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The path to the Unix domain socket, which overrides the
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compiled-in default. For ssh transport, this is passed to
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the remote netcat command (see next).
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</td>
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</tr><tr><td colspan="2"></td>
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<td> Example: <code>socket=/opt/libvirt/run/libvirt/libvirt-sock</code> </td>
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</tr><tr><td> <code>netcat</code> </td>
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<td> ssh </td>
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<td>
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The name of the netcat command on the remote machine.
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The default is <code>nc</code>. For ssh transport, libvirt
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constructs an ssh command which looks like:
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<pre>
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<i>command</i> -p <i>port</i> [-l <i>username</i>] <i>hostname</i> <i>netcat</i> -U <i>socket</i>
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</pre>
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where <i>port</i>, <i>username</i>, <i>hostname</i> can be
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specified as part of the remote URI, and <i>command</i>, <i>netcat</i>
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and <i>socket</i> come from extra parameters (or
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sensible defaults).
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</td>
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</tr><tr><td colspan="2"></td>
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<td> Example: <code>netcat=/opt/netcat/bin/nc</code> </td>
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</tr><tr><td> <code>no_verify</code> </td>
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<td> tls </td>
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<td>
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If set to a non-zero value, this disables client checks of the
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server's certificate. Note that to disable server checks of
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the client's certificate or IP address you must
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<a href="#Remote_libvirtd_configuration">change the libvirtd
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configuration</a>.
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</td>
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</tr><tr><td colspan="2"></td>
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<td> Example: <code>no_verify=1</code> </td>
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</tr></table><h3><a name="Remote_certificates" id="Remote_certificates">Generating TLS certificates</a></h3><p>
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<i>This section to follow.</i>
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</p><h3><a name="Remote_libvirtd_configuration" id="Remote_libvirtd_configuration">libvirtd configuration</a></h3><p>
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<i>This section to follow.</i>
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</p><h3><a name="Remote_IPv6" id="Remote_IPv6">IPv6 support</a></h3><p>
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IPv6 has received some limited testing and should work. Problems with
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libvirt and IPv6 should be reported as <a href="bugs.html">bugs</a>.
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</p><h3><a name="Remote_limitations" id="Remote_limitations">Limitations</a></h3><ul><li> Remote storage: To be fully useful, particularly for
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creating new domains, it should be possible to enumerate
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and provision storage on the remote machine. This is currently
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in the design phase. </li>
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<li> Migration: We expect libvirt will support migration,
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and obviously remote support is what makes migration worthwhile.
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This is also in the design phase. Issues <a href="https://www.redhat.com/mailman/listinfo/libvir-list" title="libvir-list mailing list">to discuss</a> include
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which path the migration data should follow (eg. client to
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client direct, or client to server to client) and security.
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</li>
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<li> Fine-grained authentication: libvirt in general,
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but in particular the remote case should support more
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fine-grained authentication for operations, rather than
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just read-write/read-only as at present.
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</li>
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</ul><p>
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Please come and discuss these issues and more on <a href="https://www.redhat.com/mailman/listinfo/libvir-list" title="libvir-list mailing list">the mailing list</a>.
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</p><h3><a name="Remote_implementation_notes" id="Remote_implementation_notes">Implementation notes</a></h3><p>
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The current implementation uses <a href="http://en.wikipedia.org/wiki/External_Data_Representation" title="External Data Representation">XDR</a>-encoded packets with a
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simple remote procedure call implementation which also supports
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asynchronous messaging and asynchronous and out-of-order replies,
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although these latter features are not used at the moment.
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</p><p>
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The implementation should be considered <b>strictly internal</b> to
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libvirt and <b>subject to change at any time without notice</b>. If
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you wish to talk to libvirtd, link to libvirt. If there is a problem
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that means you think you need to use the protocol directly, please
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first discuss this on <a href="https://www.redhat.com/mailman/listinfo/libvir-list" title="libvir-list mailing list">the mailing list</a>.
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</p><p>
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The messaging protocol is described in
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<code>qemud/remote_protocol.x</code>.
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</p><p>
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Authentication and encryption (for TLS) is done using <a href="http://www.gnu.org/software/gnutls/" title="GnuTLS project page">GnuTLS</a> and the RPC protocol is unaware of this layer.
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</p><p>
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Protocol messages are sent using a simple 32 bit length word (encoded
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XDR int) followed by the message header (XDR
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<code>remote_message_header</code>) followed by the message body. The
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length count includes the length word itself, and is measured in
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bytes. Maximum message size is <code>REMOTE_MESSAGE_MAX</code> and to
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avoid denial of services attacks on the XDR decoders strings are
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individually limited to <code>REMOTE_STRING_MAX</code> bytes. In the
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TLS case, messages may be split over TLS records, but a TLS record
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cannot contain parts of more than one message. In the common RPC case
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a single <code>REMOTE_CALL</code> message is sent from client to
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server, and the server then replies synchronously with a single
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<code>REMOTE_REPLY</code> message, but other forms of messaging are
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also possible.
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</p><p>
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The protocol contains support for multiple program types and protocol
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versioning, modelled after SunRPC.
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</p></div></div><div class="linkList2"><div class="llinks2"><h3 class="links2"><span>main menu</span></h3><ul><li><a href="index.html">Home</a></li><li><a href="news.html">Releases</a></li><li><a href="intro.html">Introduction</a></li><li><a href="architecture.html">libvirt architecture</a></li><li><a href="downloads.html">Downloads</a></li><li><a href="format.html">XML Format</a></li><li><a href="python.html">Binding for Python</a></li><li><a href="errors.html">Handling of errors</a></li><li><a href="FAQ.html">FAQ</a></li><li><a href="bugs.html">Reporting bugs and getting help</a></li><li><a href="remote.html">Remote support</a></li><li><a href="html/index.html">API Menu</a></li><li><a href="examples/index.html">C code examples</a></li><li><a href="ChangeLog.html">Recent Changes</a></li></ul></div><div class="llinks2"><h3 class="links2"><span>related links</span></h3><ul><li><a href="https://www.redhat.com/archives/libvir-list/">Mail archive</a></li><li><a href="https://bugzilla.redhat.com/bugzilla/buglist.cgi?product=Fedora+Core&component=libvirt&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&bug_status=MODIFIED&short_desc_type=allwordssubstr&short_desc=&long_desc_type=allwordssubstr">Open bugs</a></li><li><a href="http://virt-manager.et.redhat.com/">virt-manager</a></li><li><a href="http://search.cpan.org/~danberr/Sys-Virt-0.1.0/">Perl bindings</a></li><li><a href="http://www.cl.cam.ac.uk/Research/SRG/netos/xen/index.html">Xen project</a></li><li><form action="search.php" enctype="application/x-www-form-urlencoded" method="get"><input name="query" type="text" size="12" value="Search..." /><input name="submit" type="submit" value="Go" /></form></li><li><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-90x34.gif" alt="Made with Libxml2 Logo" /></a></li></ul><p class="credits">Graphics and design by <a href="mail:dfong@redhat.com">Diana Fong</a></p></div></div><div id="bottom"><p class="p1"></p></div></div></body></html>
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