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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>·
<a href="systemd.directives.html">Directives </a>·
<a href="../python-systemd/index.html">Python </a>·
<a href="../libudev/index.html">libudev </a>·
<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 215</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="idm214189737152"></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
"<code class="literal">.device</code>" encodes information about
a device unit as exposed in the
sysfs/<a href="udev.html"><span class="citerefentry"><span class="refentrytitle">udev</span>(7)</span></a>
device tree.</p><p>This unit type has no specific options. See
<a href="systemd.unit.html"><span class="citerefentry"><span class="refentrytitle">systemd.unit</span>(5)</span></a>
for the common options of all unit configuration
files. The common configuration items are configured
in the generic "<code class="literal">[Unit]</code>" and
"<code class="literal">[Install]</code>" sections. A separate
"<code class="literal">[Device]</code>" section does not exist,
since no device-specific options may be
configured.</p><p>systemd will dynamically create device units for
all kernel devices that are marked with the "systemd"
udev tag (by default all block and network devices,
and a few others). This may be used to define
dependencies between devices and other units. To tag a
udev device, use "<code class="literal">TAG+="systemd"</code>" in
the udev rules file, see
<a href="udev.html"><span class="citerefentry"><span class="refentrytitle">udev</span>(7)</span></a>
for details.</p><p>Device units are named after the
<code class="filename">/sys</code> and
<code class="filename">/dev</code> paths they control. Example:
the device <code class="filename">/dev/sda5</code> is exposed
in systemd as <code class="filename">dev-sda5.device</code>. For
details about the escaping logic used to convert a
file system path to a unit name see
<a href="systemd.unit.html"><span class="citerefentry"><span class="refentrytitle">systemd.unit</span>(5)</span></a>.</p></div><div class="refsect1"><a name="idm214187635920"></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 unit files, or directly from the udev
database (which is recommended). The following udev device
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
type <code class="varname">Wants</code> from the
device unit to all listed units. The
first form is used by the system
systemd instance, the second by user
systemd instances. Those settings may
be used to activate arbitrary units
when a specific device becomes
available.</p><p>Note that this and the
other tags are not taken into account
unless the device is tagged with the
"<code class="literal">systemd</code>" string in
the udev database, because otherwise
the device is not exposed as a systemd
unit (see above).</p><p>Note that systemd will only act
on <code class="varname">Wants</code>
dependencies when a device first
becomes active. It will not act on
them if they are added to devices that
are already active. Use
<code class="varname">SYSTEMD_READY=</code> (see
below) to influence on which udev
event to trigger the dependencies.
</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 unit. This
must be an absolute path that is
automatically 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 unplugged
even if it shows up in the udev
tree. If this property is unset or set
to 1, the device will be considered
plugged if it is visible in the
udev tree. This property has no
influence on the behavior when a
device disappears from the udev
tree.</p><p>This option is useful to support
devices that initially show up in an
uninitialized state in the tree, and
for which a "<code class="literal">changed</code>"
event is generated the moment they are
fully set up. Note that
<code class="varname">SYSTEMD_WANTS=</code> (see
above) is not acted on as long as
<code class="varname">SYSTEMD_READY=0</code> is
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
used as description string for the
device unit.</p></dd></dl></div></div><div class="refsect1"><a name="idm214189381632"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
<a href="systemctl.html"><span class="citerefentry"><span class="refentrytitle">systemctl</span>(8)</span></a>,
<a href="systemd.unit.html"><span class="citerefentry"><span class="refentrytitle">systemd.unit</span>(5)</span></a>,
<a href="udev.html"><span class="citerefentry"><span class="refentrytitle">udev</span>(7)</span></a>,
<a href="systemd.directives.html"><span class="citerefentry"><span class="refentrytitle">systemd.directives</span>(7)</span></a>
</p></div></div></body></html>
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