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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>Connection URIs</title></head><body><div id="container"><div id="intro"><div id="adjustments"></div><div id="pageHeader"></div><div id="content2"><h1 class="style1">Connection URIs</h1><p>
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Since libvirt supports many different kinds of virtualization
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(often referred to as "drivers" or "hypervisors"), we need a
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way to be able to specify which driver a connection refers to.
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Additionally we may want to refer to a driver on a remote
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machine over the network.
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</p><p>
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To this end, libvirt uses URIs as used on the Web and as defined in <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>. This page
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documents libvirt URIs.
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</p><ul><li><a href="#URI_libvirt">Specifying URIs to libvirt</a></li>
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<li><a href="#URI_virsh">Specifying URIs to virsh, virt-manager and virt-install</a></li>
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<li><a href="#URI_xen">xen:/// URI</a></li>
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<li><a href="#URI_qemu">qemu:///... QEMU and KVM URIs</a></li>
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<li><a href="#URI_remote">Remote URIs</a></li>
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<li><a href="#URI_test">test:///... Test URIs</a></li>
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<li><a href="#URI_legacy">Other & legacy URI formats</a></li>
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</ul><h3><a name="URI_libvirt" id="URI_libvirt">Specifying URIs to libvirt</a></h3><p>
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The URI is passed as the <code>name</code> parameter to <a href="html/libvirt-libvirt.html#virConnectOpen"><code>virConnectOpen</code></a> or <a href="html/libvirt-libvirt.html#virConnectOpenReadOnly"><code>virConnectOpenReadOnly</code></a>. For example:
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</p><pre>
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virConnectPtr conn = virConnectOpenReadOnly (<b>"test:///default"</b>);
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</pre><h3><a name="URI_virsh" id="URI_virsh">Specifying URIs to virsh, virt-manager and virt-install</a></h3><p>
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In virsh use the <code>-c</code> or <code>--connect</code> option:
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</p><pre>
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virsh <b>-c test:///default</b> list
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</pre><p>
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If virsh finds the environment variable
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<code>VIRSH_DEFAULT_CONNECT_URI</code> set, it will try this URI by
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default.
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</p><p>
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When using the interactive virsh shell, you can also use the
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<code>connect</code> <i>URI</i> command to reconnect to another
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hypervisor.
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</p><p>
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In virt-manager use the <code>-c</code> or <code>--connect=</code><i>URI</i> option:
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</p><pre>
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virt-manager <b>-c test:///default</b>
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</pre><p>
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In virt-install use the <code>--connect=</code><i>URI</i> option:
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</p><pre>
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virt-install <b>--connect=test:///default</b> <i>[other options]</i>
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</pre><h3><a name="URI_xen" id="URI_xen">xen:/// URI</a></h3><p><i>This section describes a feature which is new in libvirt >
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0.2.3. For libvirt ≤ 0.2.3 use <a href="#URI_legacy_xen"><code>"xen"</code></a>.</i>
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</p><p>
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To access a Xen hypervisor running on the local machine
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use the URI <code>xen:///</code>.
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</p><h3><a name="URI_qemu" id="URI_qemu">qemu:///... QEMU and KVM URIs</a></h3><p>
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To use QEMU support in libvirt you must be running the
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<code>libvirt_qemud</code> daemon. The purpose of this
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daemon is to manage qemu instances.
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</p><p>
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The <code>libvirt_qemud</code> daemon can be run in two ways. It may
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be started by init scripts when the machine boots and run in "system
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mode" (<code>libvirt_qemud --system</code>), in which case it manages
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qemu instances on behalf of all users of the machine. It may be also
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be started by the local user in what is known as "session mode"
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(<code>libvirt_qemud --session</code>), to manage qemu instances for
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just the current user. If no <code>libvirt_qemud</code> is running at
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all, then the qemu driver starts one running in session mode.
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</p><p>
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So to connect to the daemon, one of two different URIs is used:
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</p><ul><li> <code>qemu:///system</code> connects to a system mode daemon. </li>
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<li> <code>qemu:///session</code> connects to a session mode daemon. </li>
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</ul><p>
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(If you do <code>libvirt_qemud --help</code>, the daemon will print
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out the paths of the Unix domain socket(s) that it listens on in
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the various different modes).
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</p><p>
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KVM URIs are identical. You select between qemu, qemu accelerated and
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KVM guests in the <a href="format.html#KVM1">guest XML as described
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here</a>.
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</p><h3><a name="URI_remote" id="URI_remote">Remote URIs</a></h3><p>
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Remote URIs are formed by taking ordinary local URIs and adding a
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hostname and/or transport name. For example:
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</p><table class="top_table"><tr><th> Local URI </th>
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<th> Remote URI </th>
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<th> Meaning </th>
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</tr><tr><td> <code>xen:///</code> </td>
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<td> <code>xen://oirase/</code> </td>
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<td> Connect to the Xen hypervisor running on host <code>oirase</code>
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using TLS. </td>
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</tr><tr><td> <code>xen:///</code> </td>
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<td> <code>xen+ssh://oirase/</code> </td>
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<td> Connect to the Xen hypervisor running on host <code>oirase</code>
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by going over an <code>ssh</code> connection. </td>
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</tr><tr><td> <code>test:///default</code> </td>
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<td> <code>test+tcp://oirase/default</code> </td>
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<td> Connect to the test driver on host <code>oirase</code>
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using an unsecured TCP connection. </td>
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</tr></table><p>
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Remote URIs in libvirt offer a rich syntax and many features.
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We refer you to <a href="remote.html#Remote_URI_reference">the libvirt
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remote URI reference</a> and <a href="remote.html">full documentation
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for libvirt remote support</a>.
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</p><h3><a name="URI_test" id="URI_test">test:///... Test URIs</a></h3><p>
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The test driver is a dummy hypervisor for test purposes.
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The URIs supported are:
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</p><ul><li> <code>test:///default</code> connects to a default set of
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host definitions built into the driver. </li>
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<li> <code>test:///path/to/host/definitions</code> connects to
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a set of host definitions held in the named file.
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</li></ul><h3><a name="URI_legacy" id="URI_legacy">Other & legacy URI formats</a></h3><h4><a name="URI_NULL" id="URI_NULL">NULL and empty string URIs</a></h4><p>
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Libvirt allows you to pass a <code>NULL</code> pointer to
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<code>virConnectOpen*</code>. Empty string (<code>""</code>) acts in
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the same way. Traditionally this has meant
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<q>connect to the local Xen hypervisor</q>. However in future this
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may change to mean <q>connect to the best available hypervisor</q>.
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</p><p>
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The theory is that if, for example, Xen is unavailable but the
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machine is running an OpenVZ kernel, then we should not try to
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connect to the Xen hypervisor since that is obviously the wrong
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thing to do.
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</p><p>
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In any case applications linked to libvirt can continue to pass
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<code>NULL</code> as a default choice, but should always allow the
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user to override the URI, either by constructing one or by allowing
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the user to type a URI in directly (if that is appropriate). If your
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application wishes to connect specifically to a Xen hypervisor, then
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for future proofing it should choose a full <a href="#URI_xen"><code>xen:///</code> URI</a>.
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</p><h4><a name="URI_file" id="URI_file">File paths (xend-unix-server)</a></h4><p>
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If XenD is running and configured in <code>/etc/xen/xend-config.sxp</code>:
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</p><pre>
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(xend-unix-server yes)
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</pre><p>
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then it listens on a Unix domain socket, usually at
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<code>/var/lib/xend/xend-socket</code>. You may pass a different path
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using a file URI such as:
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</p><pre>
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virsh -c ///var/run/xend/xend-socket
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</pre><h4><a name="URI_http" id="URI_http">Legacy: <code>http://...</code> (xend-http-server)</a></h4><p>
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If XenD is running and configured in <code>/etc/xen/xend-config.sxp</code>:
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</p><pre>
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(xend-http-server yes)
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</pre><p>
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then it listens on TCP port 8000. libvirt allows you to
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try to connect to xend running on remote machines by passing
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<code>http://<i>hostname</i>[:<i>port</i>]/</code>, for example:
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</p><pre>
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virsh -c http://oirase/ list
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</pre><p>
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This method is unencrypted and insecure and is definitely not
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recommended for production use. Instead use <a href="remote.html">libvirt's remote support</a>.
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</p><p>
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Notes:
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</p><ol><li> The HTTP client does not fully support IPv6. </li>
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<li> Many features do not work as expected across HTTP connections, in
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particular, <a href="html/libvirt-libvirt.html#virConnectGetCapabilities">virConnectGetCapabilities</a>.
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The <a href="remote.html">remote support</a> however does work
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correctly. </li>
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<li> XenD's new-style XMLRPC interface is not supported by
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libvirt, only the old-style sexpr interface known in the Xen
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documentation as "unix server" or "http server".</li>
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</ol><h4><a name="URI_legacy_xen" id="URI_legacy_xen">Legacy: <code>"xen"</code></a></h4><p>
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Another legacy URI is to specify name as the string
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<code>"xen"</code>. This will continue to refer to the Xen
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hypervisor. However you should prefer a full <a href="#URI_xen"><code>xen:///</code> URI</a> in all future code.
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</p><h4><a name="URI_http" id="URI_http">Legacy: Xen proxy</a></h4><p>
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Libvirt continues to support connections to a separately running Xen
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proxy daemon. This provides a way to allow non-root users to make a
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safe (read-only) subset of queries to the hypervisor.
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</p><p>
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There is no specific "Xen proxy" URI. However if a Xen URI of any of
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the ordinary or legacy forms is used (eg. <code>NULL</code>,
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<code>""</code>, <code>"xen"</code>, ...) which fails, <i>and</i> the
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user is not root, <i>and</i> the Xen proxy socket can be connected to
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(<code>/tmp/libvirt_proxy_conn</code>), then libvirt will use a proxy
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connection.
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</p><p>
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You should consider using <a href="remote.html">libvirt remote support</a>
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in future.
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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="uri.html">Connection URIs</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://et.redhat.com/~rjones/ocaml-libvirt/">OCaml 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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