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<!DOCTYPE html> <!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]--> <!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]--> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>QEMU Disk Network Block Device Server — QEMU qemu-kvm-6.2.0-53.module+el8.10.0+2055+8eb7870b.4 documentation</title> <link rel="shortcut icon" href="../_static/qemu_32x32.png"/> <link rel="stylesheet" href="../_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="next" title="QEMU persistent reservation helper" href="qemu-pr-helper.html" /> <link rel="prev" title="QEMU Storage Daemon" href="qemu-storage-daemon.html" /> <script src="../_static/js/modernizr.min.js"></script> </head> <body class="wy-body-for-nav"> <div class="wy-grid-for-nav"> <nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search"> <a href="../index.html" class="icon icon-home"> QEMU <img src="../_static/qemu_128x128.png" class="logo" alt="Logo"/> </a> <div class="version"> 6.2.0 </div> <div role="search"> <form id="rtd-search-form" class="wy-form" action="../search.html" method="get"> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> </div> <div class="wy-menu wy-menu-vertical" data-spy="affix" role="navigation" aria-label="main navigation"> <p class="caption"><span class="caption-text">Contents:</span></p> <ul class="current"> <li class="toctree-l1"><a class="reference internal" href="../about/index.html">About QEMU</a></li> <li class="toctree-l1"><a class="reference internal" href="../system/index.html">System Emulation</a></li> <li class="toctree-l1"><a class="reference internal" href="../user/index.html">User Mode Emulation</a></li> <li class="toctree-l1 current"><a class="reference internal" href="index.html">Tools</a><ul class="current"> <li class="toctree-l2"><a class="reference internal" href="qemu-img.html">QEMU disk image utility</a></li> <li class="toctree-l2"><a class="reference internal" href="qemu-storage-daemon.html">QEMU Storage Daemon</a></li> <li class="toctree-l2 current"><a class="current reference internal" href="#">QEMU Disk Network Block Device Server</a><ul> <li class="toctree-l3"><a class="reference internal" href="#synopsis">Synopsis</a></li> <li class="toctree-l3"><a class="reference internal" href="#description">Description</a></li> <li class="toctree-l3"><a class="reference internal" href="#options">Options</a></li> <li class="toctree-l3"><a class="reference internal" href="#examples">Examples</a></li> <li class="toctree-l3"><a class="reference internal" href="#see-also">See also</a></li> </ul> </li> <li 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class="wy-nav-top" aria-label="top navigation"> <i data-toggle="wy-nav-top" class="fa fa-bars"></i> <a href="../index.html">QEMU</a> </nav> <div class="wy-nav-content"> <div class="rst-content"> <div role="navigation" aria-label="breadcrumbs navigation"> <ul class="wy-breadcrumbs"> <li><a href="../index.html">Docs</a> »</li> <li><a href="index.html">Tools</a> »</li> <li>QEMU Disk Network Block Device Server</li> <li class="wy-breadcrumbs-aside"> <a href="https://gitlab.com/qemu-project/qemu/blob/master/docs/tools/qemu-nbd.rst" class="fa fa-gitlab"> Edit on GitLab</a> </li> </ul> <hr/> </div> <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article"> <div itemprop="articleBody"> <div class="section" id="qemu-disk-network-block-device-server"> <h1>QEMU Disk Network Block Device Server<a class="headerlink" href="#qemu-disk-network-block-device-server" title="Permalink to this headline">¶</a></h1> <div class="section" id="synopsis"> <h2>Synopsis<a class="headerlink" href="#synopsis" title="Permalink to this headline">¶</a></h2> <p><strong>qemu-nbd</strong> [<em>OPTION</em>]… <em>filename</em></p> <p><strong>qemu-nbd</strong> -L [<em>OPTION</em>]…</p> <p><strong>qemu-nbd</strong> -d <em>dev</em></p> </div> <div class="section" id="description"> <h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2> <p>Export a QEMU disk image using the NBD protocol.</p> <p>Other uses:</p> <ul class="simple"> <li>Bind a /dev/nbdX block device to a QEMU server (on Linux).</li> <li>As a client to query exports of a remote NBD server.</li> </ul> </div> <div class="section" id="options"> <h2>Options<a class="headerlink" href="#options" title="Permalink to this headline">¶</a></h2> <p><em>filename</em> is a disk image filename, or a set of block driver options if <code class="docutils literal notranslate"><span class="pre">--image-opts</span></code> is specified.</p> <p><em>dev</em> is an NBD device.</p> <dl class="option"> <dt id="cmdoption-qemu-nbd-object"> <code class="descname">--object</code><code class="descclassname"> type,id=ID,...</code><a class="headerlink" href="#cmdoption-qemu-nbd-object" title="Permalink to this definition">¶</a></dt> <dd><p>Define a new instance of the <em>type</em> object class identified by <em>ID</em>. See the <em class="manpage">qemu(1)</em> manual page for full details of the properties supported. The common object types that it makes sense to define are the <code class="docutils literal notranslate"><span class="pre">secret</span></code> object, which is used to supply passwords and/or encryption keys, and the <code class="docutils literal notranslate"><span class="pre">tls-creds</span></code> object, which is used to supply TLS credentials for the <code class="docutils literal notranslate"><span class="pre">qemu-nbd</span></code> server or client.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-p"> <code class="descname">-p</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--port</code><code class="descclassname">=PORT</code><a class="headerlink" href="#cmdoption-qemu-nbd-p" title="Permalink to this definition">¶</a></dt> <dd><p>TCP port to listen on as a server, or connect to as a client (default <code class="docutils literal notranslate"><span class="pre">10809</span></code>).</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-o"> <code class="descname">-o</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--offset</code><code class="descclassname">=OFFSET</code><a class="headerlink" href="#cmdoption-qemu-nbd-o" title="Permalink to this definition">¶</a></dt> <dd><p>The offset into the image.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-b"> <code class="descname">-b</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--bind</code><code class="descclassname">=IFACE</code><a class="headerlink" href="#cmdoption-qemu-nbd-b" title="Permalink to this definition">¶</a></dt> <dd><p>The interface to bind to as a server, or connect to as a client (default <code class="docutils literal notranslate"><span class="pre">0.0.0.0</span></code>).</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-k"> <code class="descname">-k</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--socket</code><code class="descclassname">=PATH</code><a class="headerlink" href="#cmdoption-qemu-nbd-k" title="Permalink to this definition">¶</a></dt> <dd><p>Use a unix socket with path <em>PATH</em>.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-image-opts"> <code class="descname">--image-opts</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-image-opts" title="Permalink to this definition">¶</a></dt> <dd><p>Treat <em>filename</em> as a set of image options, instead of a plain filename. If this flag is specified, the <code class="docutils literal notranslate"><span class="pre">-f</span></code> flag should not be used, instead the <code class="xref std std-option docutils literal notranslate"><span class="pre">format=</span></code> option should be set.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-f"> <code class="descname">-f</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--format</code><code class="descclassname">=FMT</code><a class="headerlink" href="#cmdoption-qemu-nbd-f" title="Permalink to this definition">¶</a></dt> <dd><p>Force the use of the block driver for format <em>FMT</em> instead of auto-detecting.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-r"> <code class="descname">-r</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--read-only</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-r" title="Permalink to this definition">¶</a></dt> <dd><p>Export the disk as read-only.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-a"> <code class="descname">-A</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--allocation-depth</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-a" title="Permalink to this definition">¶</a></dt> <dd><p>Expose allocation depth information via the <code class="docutils literal notranslate"><span class="pre">qemu:allocation-depth</span></code> metadata context accessible through NBD_OPT_SET_META_CONTEXT.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-bitmap"> <code class="descname">-B</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--bitmap</code><code class="descclassname">=NAME</code><a class="headerlink" href="#cmdoption-qemu-nbd-bitmap" title="Permalink to this definition">¶</a></dt> <dd><p>If <em>filename</em> has a qcow2 persistent bitmap <em>NAME</em>, expose that bitmap via the <code class="docutils literal notranslate"><span class="pre">qemu:dirty-bitmap:NAME</span></code> metadata context accessible through NBD_OPT_SET_META_CONTEXT.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-s"> <code class="descname">-s</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--snapshot</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-s" title="Permalink to this definition">¶</a></dt> <dd><p>Use <em>filename</em> as an external snapshot, create a temporary file with <code class="docutils literal notranslate"><span class="pre">backing_file=</span></code><em>filename</em>, redirect the write to the temporary one.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-l"> <code class="descname">-l</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--load-snapshot</code><code class="descclassname">=SNAPSHOT_PARAM</code><a class="headerlink" href="#cmdoption-qemu-nbd-l" title="Permalink to this definition">¶</a></dt> <dd><p>Load an internal snapshot inside <em>filename</em> and export it as an read-only device, SNAPSHOT_PARAM format is <code class="docutils literal notranslate"><span class="pre">snapshot.id=[ID],snapshot.name=[NAME]</span></code> or <code class="docutils literal notranslate"><span class="pre">[ID_OR_NAME]</span></code></p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-cache"> <code class="descname">--cache</code><code class="descclassname">=CACHE</code><a class="headerlink" href="#cmdoption-qemu-nbd-cache" title="Permalink to this definition">¶</a></dt> <dd><p>The cache mode to be used with the file. Valid values are: <code class="docutils literal notranslate"><span class="pre">none</span></code>, <code class="docutils literal notranslate"><span class="pre">writeback</span></code> (the default), <code class="docutils literal notranslate"><span class="pre">writethrough</span></code>, <code class="docutils literal notranslate"><span class="pre">directsync</span></code> and <code class="docutils literal notranslate"><span class="pre">unsafe</span></code>. See the documentation of the emulator’s <code class="docutils literal notranslate"><span class="pre">-drive</span> <span class="pre">cache=...</span></code> option for more info.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-n"> <code class="descname">-n</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--nocache</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-n" title="Permalink to this definition">¶</a></dt> <dd><p>Equivalent to <code class="xref std std-option docutils literal notranslate"><span class="pre">--cache=none</span></code>.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-aio"> <code class="descname">--aio</code><code class="descclassname">=AIO</code><a class="headerlink" href="#cmdoption-qemu-nbd-aio" title="Permalink to this definition">¶</a></dt> <dd><p>Set the asynchronous I/O mode between <code class="docutils literal notranslate"><span class="pre">threads</span></code> (the default), <code class="docutils literal notranslate"><span class="pre">native</span></code> (Linux only), and <code class="docutils literal notranslate"><span class="pre">io_uring</span></code> (Linux 5.1+).</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-discard"> <code class="descname">--discard</code><code class="descclassname">=DISCARD</code><a class="headerlink" href="#cmdoption-qemu-nbd-discard" title="Permalink to this definition">¶</a></dt> <dd><p>Control whether <code class="docutils literal notranslate"><span class="pre">discard</span></code> (also known as <code class="docutils literal notranslate"><span class="pre">trim</span></code> or <code class="docutils literal notranslate"><span class="pre">unmap</span></code>) requests are ignored or passed to the filesystem. <em>DISCARD</em> is one of <code class="docutils literal notranslate"><span class="pre">ignore</span></code> (or <code class="docutils literal notranslate"><span class="pre">off</span></code>), <code class="docutils literal notranslate"><span class="pre">unmap</span></code> (or <code class="docutils literal notranslate"><span class="pre">on</span></code>). The default is <code class="docutils literal notranslate"><span class="pre">ignore</span></code>.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-detect-zeroes"> <code class="descname">--detect-zeroes</code><code class="descclassname">=DETECT_ZEROES</code><a class="headerlink" href="#cmdoption-qemu-nbd-detect-zeroes" title="Permalink to this definition">¶</a></dt> <dd><p>Control the automatic conversion of plain zero writes by the OS to driver-specific optimized zero write commands. <em>DETECT_ZEROES</em> is one of <code class="docutils literal notranslate"><span class="pre">off</span></code>, <code class="docutils literal notranslate"><span class="pre">on</span></code>, or <code class="docutils literal notranslate"><span class="pre">unmap</span></code>. <code class="docutils literal notranslate"><span class="pre">unmap</span></code> converts a zero write to an unmap operation and can only be used if <em>DISCARD</em> is set to <code class="docutils literal notranslate"><span class="pre">unmap</span></code>. The default is <code class="docutils literal notranslate"><span class="pre">off</span></code>.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-c"> <code class="descname">-c</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--connect</code><code class="descclassname">=DEV</code><a class="headerlink" href="#cmdoption-qemu-nbd-c" title="Permalink to this definition">¶</a></dt> <dd><p>Connect <em>filename</em> to NBD device <em>DEV</em> (Linux only).</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-d"> <code class="descname">-d</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--disconnect</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-d" title="Permalink to this definition">¶</a></dt> <dd><p>Disconnect the device <em>DEV</em> (Linux only).</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-e"> <code class="descname">-e</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--shared</code><code class="descclassname">=NUM</code><a class="headerlink" href="#cmdoption-qemu-nbd-e" title="Permalink to this definition">¶</a></dt> <dd><p>Allow up to <em>NUM</em> clients to share the device (default <code class="docutils literal notranslate"><span class="pre">1</span></code>), 0 for unlimited. Safe for readers, but for now, consistency is not guaranteed between multiple writers.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-t"> <code class="descname">-t</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--persistent</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-t" title="Permalink to this definition">¶</a></dt> <dd><p>Don’t exit on the last connection.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-x"> <code class="descname">-x</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--export-name</code><code class="descclassname">=NAME</code><a class="headerlink" href="#cmdoption-qemu-nbd-x" title="Permalink to this definition">¶</a></dt> <dd><p>Set the NBD volume export name (default of a zero-length string).</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-description"> <code class="descname">-D</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--description</code><code class="descclassname">=DESCRIPTION</code><a class="headerlink" href="#cmdoption-qemu-nbd-description" title="Permalink to this definition">¶</a></dt> <dd><p>Set the NBD volume export description, as a human-readable string.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-list"> <code class="descname">-L</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--list</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-list" title="Permalink to this definition">¶</a></dt> <dd><p>Connect as a client and list all details about the exports exposed by a remote NBD server. This enables list mode, and is incompatible with options that change behavior related to a specific export (such as <a class="reference internal" href="#cmdoption-qemu-nbd-x"><code class="xref std std-option docutils literal notranslate"><span class="pre">--export-name</span></code></a>, <a class="reference internal" href="#cmdoption-qemu-nbd-o"><code class="xref std std-option docutils literal notranslate"><span class="pre">--offset</span></code></a>, …).</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-tls-creds"> <code class="descname">--tls-creds</code><code class="descclassname">=ID</code><a class="headerlink" href="#cmdoption-qemu-nbd-tls-creds" title="Permalink to this definition">¶</a></dt> <dd><p>Enable mandatory TLS encryption for the server by setting the ID of the TLS credentials object previously created with the –object option; or provide the credentials needed for connecting as a client in list mode.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-fork"> <code class="descname">--fork</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-fork" title="Permalink to this definition">¶</a></dt> <dd><p>Fork off the server process and exit the parent once the server is running.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-pid-file"> <code class="descname">--pid-file</code><code class="descclassname">=PATH</code><a class="headerlink" href="#cmdoption-qemu-nbd-pid-file" title="Permalink to this definition">¶</a></dt> <dd><p>Store the server’s process ID in the given file.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-tls-authz"> <code class="descname">--tls-authz</code><code class="descclassname">=ID</code><a class="headerlink" href="#cmdoption-qemu-nbd-tls-authz" title="Permalink to this definition">¶</a></dt> <dd><p>Specify the ID of a qauthz object previously created with the <a class="reference internal" href="#cmdoption-qemu-nbd-object"><code class="xref std std-option docutils literal notranslate"><span class="pre">--object</span></code></a> option. This will be used to authorize connecting users against their x509 distinguished name.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-v"> <code class="descname">-v</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--verbose</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-v" title="Permalink to this definition">¶</a></dt> <dd><p>Display extra debugging information.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-h"> <code class="descname">-h</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--help</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-h" title="Permalink to this definition">¶</a></dt> <dd><p>Display this help and exit.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-version"> <code class="descname">-V</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--version</code><code class="descclassname"></code><a class="headerlink" href="#cmdoption-qemu-nbd-version" title="Permalink to this definition">¶</a></dt> <dd><p>Display version information and exit.</p> </dd></dl> <dl class="option"> <dt id="cmdoption-qemu-nbd-trace"> <code class="descname">-T</code><code class="descclassname"></code><code class="descclassname">, </code><code class="descname">--trace</code><code class="descclassname"> [[enable=]PATTERN][,events=FILE][,file=FILE]</code><a class="headerlink" href="#cmdoption-qemu-nbd-trace" title="Permalink to this definition">¶</a></dt> <dd><p>Specify tracing options.</p> <p><code class="docutils literal notranslate"><span class="pre">[enable=]PATTERN</span></code></p> <blockquote> <div><p>Immediately enable events matching <em>PATTERN</em> (either event name or a globbing pattern). This option is only available if QEMU has been compiled with the <code class="docutils literal notranslate"><span class="pre">simple</span></code>, <code class="docutils literal notranslate"><span class="pre">log</span></code> or <code class="docutils literal notranslate"><span class="pre">ftrace</span></code> tracing backend. To specify multiple events or patterns, specify the <code class="xref std std-option docutils literal notranslate"><span class="pre">-trace</span></code> option multiple times.</p> <p>Use <code class="xref std std-option docutils literal notranslate"><span class="pre">-trace</span> <span class="pre">help</span></code> to print a list of names of trace points.</p> </div></blockquote> <p><code class="docutils literal notranslate"><span class="pre">events=FILE</span></code></p> <blockquote> <div>Immediately enable events listed in <em>FILE</em>. The file must contain one event name (as listed in the <code class="docutils literal notranslate"><span class="pre">trace-events-all</span></code> file) per line; globbing patterns are accepted too. This option is only available if QEMU has been compiled with the <code class="docutils literal notranslate"><span class="pre">simple</span></code>, <code class="docutils literal notranslate"><span class="pre">log</span></code> or <code class="docutils literal notranslate"><span class="pre">ftrace</span></code> tracing backend.</div></blockquote> <p><code class="docutils literal notranslate"><span class="pre">file=FILE</span></code></p> <blockquote> <div>Log output traces to <em>FILE</em>. This option is only available if QEMU has been compiled with the <code class="docutils literal notranslate"><span class="pre">simple</span></code> tracing backend.</div></blockquote> </dd></dl> </div> <div class="section" id="examples"> <h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2> <p>Start a server listening on port 10809 that exposes only the guest-visible contents of a qcow2 file, with no TLS encryption, and with the default export name (an empty string). The command is one-shot, and will block until the first successful client disconnects:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">qemu</span><span class="o">-</span><span class="n">nbd</span> <span class="o">-</span><span class="n">f</span> <span class="n">qcow2</span> <span class="n">file</span><span class="o">.</span><span class="n">qcow2</span> </pre></div> </div> <p>Start a long-running server listening with encryption on port 10810, and whitelist clients with a specific X.509 certificate to connect to a 1 megabyte subset of a raw file, using the export name ‘subset’:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">qemu</span><span class="o">-</span><span class="n">nbd</span> \ <span class="o">--</span><span class="nb">object</span> <span class="n">tls</span><span class="o">-</span><span class="n">creds</span><span class="o">-</span><span class="n">x509</span><span class="p">,</span><span class="nb">id</span><span class="o">=</span><span class="n">tls0</span><span class="p">,</span><span class="n">endpoint</span><span class="o">=</span><span class="n">server</span><span class="p">,</span><span class="nb">dir</span><span class="o">=/</span><span class="n">path</span><span class="o">/</span><span class="n">to</span><span class="o">/</span><span class="n">qemutls</span> \ <span class="o">--</span><span class="nb">object</span> <span class="s1">'authz-simple,id=auth0,identity=CN=laptop.example.com,,</span><span class="se">\</span> <span class="s1"> O=Example Org,,L=London,,ST=London,,C=GB'</span> \ <span class="o">--</span><span class="n">tls</span><span class="o">-</span><span class="n">creds</span> <span class="n">tls0</span> <span class="o">--</span><span class="n">tls</span><span class="o">-</span><span class="n">authz</span> <span class="n">auth0</span> \ <span class="o">-</span><span class="n">t</span> <span class="o">-</span><span class="n">x</span> <span class="n">subset</span> <span class="o">-</span><span class="n">p</span> <span class="mi">10810</span> \ <span class="o">--</span><span class="n">image</span><span class="o">-</span><span class="n">opts</span> <span class="n">driver</span><span class="o">=</span><span class="n">raw</span><span class="p">,</span><span class="n">offset</span><span class="o">=</span><span class="mi">1</span><span class="n">M</span><span class="p">,</span><span class="n">size</span><span class="o">=</span><span class="mi">1</span><span class="n">M</span><span class="p">,</span><span class="n">file</span><span class="o">.</span><span class="n">driver</span><span class="o">=</span><span class="n">file</span><span class="p">,</span><span class="n">file</span><span class="o">.</span><span class="n">filename</span><span class="o">=</span><span class="n">file</span><span class="o">.</span><span class="n">raw</span> </pre></div> </div> <p>Serve a read-only copy of a guest image over a Unix socket with as many as 5 simultaneous readers, with a persistent process forked as a daemon:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">qemu</span><span class="o">-</span><span class="n">nbd</span> <span class="o">--</span><span class="n">fork</span> <span class="o">--</span><span class="n">persistent</span> <span class="o">--</span><span class="n">shared</span><span class="o">=</span><span class="mi">5</span> <span class="o">--</span><span class="n">socket</span><span class="o">=/</span><span class="n">path</span><span class="o">/</span><span class="n">to</span><span class="o">/</span><span class="n">sock</span> \ <span class="o">--</span><span class="n">read</span><span class="o">-</span><span class="n">only</span> <span class="o">--</span><span class="nb">format</span><span class="o">=</span><span class="n">qcow2</span> <span class="n">file</span><span class="o">.</span><span class="n">qcow2</span> </pre></div> </div> <p>Expose the guest-visible contents of a qcow2 file via a block device /dev/nbd0 (and possibly creating /dev/nbd0p1 and friends for partitions found within), then disconnect the device when done. Access to bind <code class="docutils literal notranslate"><span class="pre">qemu-nbd</span></code> to a /dev/nbd device generally requires root privileges, and may also require the execution of <code class="docutils literal notranslate"><span class="pre">modprobe</span> <span class="pre">nbd</span></code> to enable the kernel NBD client module. <em>CAUTION</em>: Do not use this method to mount filesystems from an untrusted guest image - a malicious guest may have prepared the image to attempt to trigger kernel bugs in partition probing or file system mounting.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">qemu</span><span class="o">-</span><span class="n">nbd</span> <span class="o">-</span><span class="n">c</span> <span class="o">/</span><span class="n">dev</span><span class="o">/</span><span class="n">nbd0</span> <span class="o">-</span><span class="n">f</span> <span class="n">qcow2</span> <span class="n">file</span><span class="o">.</span><span class="n">qcow2</span> <span class="n">qemu</span><span class="o">-</span><span class="n">nbd</span> <span class="o">-</span><span class="n">d</span> <span class="o">/</span><span class="n">dev</span><span class="o">/</span><span class="n">nbd0</span> </pre></div> </div> <p>Query a remote server to see details about what export(s) it is serving on port 10809, and authenticating via PSK:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">qemu</span><span class="o">-</span><span class="n">nbd</span> \ <span class="o">--</span><span class="nb">object</span> <span class="n">tls</span><span class="o">-</span><span class="n">creds</span><span class="o">-</span><span class="n">psk</span><span class="p">,</span><span class="nb">id</span><span class="o">=</span><span class="n">tls0</span><span class="p">,</span><span class="nb">dir</span><span class="o">=/</span><span class="n">tmp</span><span class="o">/</span><span class="n">keys</span><span class="p">,</span><span class="n">username</span><span class="o">=</span><span class="n">eblake</span><span class="p">,</span><span class="n">endpoint</span><span class="o">=</span><span class="n">client</span> \ <span class="o">--</span><span class="n">tls</span><span class="o">-</span><span class="n">creds</span> <span class="n">tls0</span> <span class="o">-</span><span class="n">L</span> <span class="o">-</span><span class="n">b</span> <span class="n">remote</span><span class="o">.</span><span class="n">example</span><span class="o">.</span><span class="n">com</span> </pre></div> </div> </div> <div class="section" id="see-also"> <h2>See also<a class="headerlink" href="#see-also" title="Permalink to this headline">¶</a></h2> <p><em class="manpage">qemu(1)</em>, <em class="manpage">qemu-img(1)</em></p> </div> </div> </div> </div> <footer> <div class="rst-footer-buttons" role="navigation" aria-label="footer navigation"> <a href="qemu-pr-helper.html" class="btn btn-neutral float-right" title="QEMU persistent reservation helper" accesskey="n" rel="next">Next <span class="fa fa-arrow-circle-right"></span></a> <a href="qemu-storage-daemon.html" class="btn btn-neutral" title="QEMU Storage Daemon" accesskey="p" rel="prev"><span class="fa fa-arrow-circle-left"></span> Previous</a> </div> <hr/> <div role="contentinfo"> <p> © Copyright 2021, The QEMU Project Developers. </p> </div> Built with <a href="http://sphinx-doc.org/">Sphinx</a> using a <a href="https://github.com/rtfd/sphinx_rtd_theme">theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>. <!-- Empty para to force a blank line after "Built with Sphinx ..." --> <p></p> <p>This documentation is for QEMU version 6.2.0.</p> <p><a href="../about/license.html">QEMU and this manual are released under the GNU General Public License, version 2.</a></p> </footer> </div> </div> </section> </div> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT:'../', VERSION:'qemu-kvm-6.2.0-53.module+el8.10.0+2055+8eb7870b.4', LANGUAGE:'None', COLLAPSE_INDEX:false, FILE_SUFFIX:'.html', HAS_SOURCE: false, SOURCELINK_SUFFIX: '.txt' }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/js/theme.js"></script> <script type="text/javascript"> jQuery(function () { SphinxRtdTheme.Navigation.enable(true); }); </script> </body> </html>