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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>systemd.device</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><style>
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</style><a href="index.html">Index </a>·
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<a href="systemd.directives.html">Directives </a>·
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<a href="../python-systemd/index.html">Python </a>·
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<a href="../libudev/index.html">libudev </a>·
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 217</span><hr><div class="refentry"><a name="systemd.device"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>systemd.device — Device unit configuration</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><p><code class="filename"><em class="replaceable"><code>device</code></em>.device</code></p></div><div class="refsect1"><a name="idm214169484112"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p>A unit configuration file whose name ends in
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"<code class="literal">.device</code>" encodes information about
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a device unit as exposed in the
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sysfs/<a href="udev.html"><span class="citerefentry"><span class="refentrytitle">udev</span>(7)</span></a>
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device tree.</p><p>This unit type has no specific options. See
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<a href="systemd.unit.html"><span class="citerefentry"><span class="refentrytitle">systemd.unit</span>(5)</span></a>
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for the common options of all unit configuration
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files. The common configuration items are configured
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in the generic "<code class="literal">[Unit]</code>" and
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"<code class="literal">[Install]</code>" sections. A separate
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"<code class="literal">[Device]</code>" section does not exist,
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since no device-specific options may be
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configured.</p><p>systemd will dynamically create device units for
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all kernel devices that are marked with the "systemd"
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udev tag (by default all block and network devices,
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and a few others). This may be used to define
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dependencies between devices and other units. To tag a
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udev device, use "<code class="literal">TAG+="systemd"</code>" in
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the udev rules file, see
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<a href="udev.html"><span class="citerefentry"><span class="refentrytitle">udev</span>(7)</span></a>
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for details.</p><p>Device units are named after the
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<code class="filename">/sys</code> and
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<code class="filename">/dev</code> paths they control. Example:
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the device <code class="filename">/dev/sda5</code> is exposed
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in systemd as <code class="filename">dev-sda5.device</code>. For
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details about the escaping logic used to convert a
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file system path to a unit name see
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<a href="systemd.unit.html"><span class="citerefentry"><span class="refentrytitle">systemd.unit</span>(5)</span></a>.</p></div><div class="refsect1"><a name="idm214169471024"></a><h2 id="The udev Database">The udev Database<a class="headerlink" title="Permalink to this headline" href="#The%20udev%20Database">¶</a></h2><p>The settings of device units may either be
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configured via unit files, or directly from the udev
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database (which is recommended). The following udev device
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properties are understood by systemd:</p><div class="variablelist"><dl class="variablelist"><dt id="SYSTEMD_WANTS="><span class="term"><code class="varname">SYSTEMD_WANTS=</code>, </span><span class="term"><code class="varname">SYSTEMD_USER_WANTS=</code></span><a class="headerlink" title="Permalink to this term" href="#SYSTEMD_WANTS=">¶</a></dt><dd><p>Adds dependencies of
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type <code class="varname">Wants</code> from the
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device unit to all listed units. The
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first form is used by the system
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systemd instance, the second by user
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systemd instances. Those settings may
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be used to activate arbitrary units
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when a specific device becomes
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available.</p><p>Note that this and the
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other tags are not taken into account
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unless the device is tagged with the
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"<code class="literal">systemd</code>" string in
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the udev database, because otherwise
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the device is not exposed as a systemd
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unit (see above).</p><p>Note that systemd will only act
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on <code class="varname">Wants</code>
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dependencies when a device first
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becomes active. It will not act on
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them if they are added to devices that
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are already active. Use
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<code class="varname">SYSTEMD_READY=</code> (see
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below) to influence on which udev
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event to trigger the dependencies.
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</p></dd><dt id="SYSTEMD_ALIAS="><span class="term"><code class="varname">SYSTEMD_ALIAS=</code></span><a class="headerlink" title="Permalink to this term" href="#SYSTEMD_ALIAS=">¶</a></dt><dd><p>Adds an additional
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alias name to the device unit. This
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must be an absolute path that is
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automatically transformed into a unit
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name. (See above.)</p></dd><dt id="SYSTEMD_READY="><span class="term"><code class="varname">SYSTEMD_READY=</code></span><a class="headerlink" title="Permalink to this term" href="#SYSTEMD_READY=">¶</a></dt><dd><p>If set to 0, systemd
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will consider this device unplugged
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even if it shows up in the udev
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tree. If this property is unset or set
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to 1, the device will be considered
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plugged if it is visible in the
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udev tree. This property has no
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influence on the behavior when a
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device disappears from the udev
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tree.</p><p>This option is useful to support
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devices that initially show up in an
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uninitialized state in the tree, and
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for which a "<code class="literal">changed</code>"
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event is generated the moment they are
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fully set up. Note that
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<code class="varname">SYSTEMD_WANTS=</code> (see
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above) is not acted on as long as
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<code class="varname">SYSTEMD_READY=0</code> is
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set for a device.</p></dd><dt id="ID_MODEL_FROM_DATABASE="><span class="term"><code class="varname">ID_MODEL_FROM_DATABASE=</code>, </span><span class="term"><code class="varname">ID_MODEL=</code></span><a class="headerlink" title="Permalink to this term" href="#ID_MODEL_FROM_DATABASE=">¶</a></dt><dd><p>If set, this property is
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used as description string for the
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device unit.</p></dd></dl></div></div><div class="refsect1"><a name="idm214173405536"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
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<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
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<a href="systemctl.html"><span class="citerefentry"><span class="refentrytitle">systemctl</span>(1)</span></a>,
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<a href="systemd.unit.html"><span class="citerefentry"><span class="refentrytitle">systemd.unit</span>(5)</span></a>,
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<a href="udev.html"><span class="citerefentry"><span class="refentrytitle">udev</span>(7)</span></a>,
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<a href="systemd.directives.html"><span class="citerefentry"><span class="refentrytitle">systemd.directives</span>(7)</span></a>
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</p></div></div></body></html>
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