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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 219</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="idm140133170137984"></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 a device unit
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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 files. The common
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configuration items are configured in the generic
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"<code class="literal">[Unit]</code>" and "<code class="literal">[Install]</code>"
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sections. A separate "<code class="literal">[Device]</code>" section does not
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exist, since no device-specific options may be configured.</p><p>systemd will dynamically create device units for all kernel
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devices that are marked with the "systemd" udev tag (by default
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all block and network devices, and a few others). This may be used
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to define dependencies between devices and other units. To tag a
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udev device, use "<code class="literal">TAG+="systemd"</code>" in the udev
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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 <code class="filename">/sys</code>
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and <code class="filename">/dev</code> paths they control. Example: the
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device <code class="filename">/dev/sda5</code> is exposed in
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systemd as <code class="filename">dev-sda5.device</code>. For details about
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the escaping logic used to convert a file system path to a unit
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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="idm140133166577520"></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 configured via
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unit files, or directly from the udev database (which is
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recommended). The following udev device properties are understood
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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 type
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<code class="varname">Wants</code> from the device unit to all listed
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units. The first form is used by the system systemd instance,
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the second by user systemd instances. Those settings may be
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used to activate arbitrary units when a specific device
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becomes available.</p><p>Note that this and the other tags are not taken into
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account unless the device is tagged with the
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"<code class="literal">systemd</code>" string in the udev database,
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because otherwise the device is not exposed as a systemd unit
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(see above).</p><p>Note that systemd will only act on
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<code class="varname">Wants</code> dependencies when a device first
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becomes active. It will not act on them if they are added to
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devices that are already active. Use
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<code class="varname">SYSTEMD_READY=</code> (see below) to influence on
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which udev 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 alias name to the device
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unit. This must be an absolute path that is automatically
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transformed into a unit 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 will consider this device
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unplugged even if it shows up in the udev tree. If this
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property is unset or set to 1, the device will be considered
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plugged if it is visible in the udev tree. This property has
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no influence on the behavior when a device disappears from the
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udev tree.</p><p>This option is useful to support devices that initially
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show up in an uninitialized state in the tree, and for which a
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"<code class="literal">changed</code>" event is generated the moment they
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are fully set up. Note that <code class="varname">SYSTEMD_WANTS=</code>
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(see above) is not acted on as long as
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<code class="varname">SYSTEMD_READY=0</code> is set for a
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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 used as description
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string for the device unit.</p></dd></dl></div></div><div class="refsect1"><a name="idm140133170279296"></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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