man/systemd.device.xml

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<refentry id="systemd.device">
        <refentryinfo>
                <title>systemd.device</title>
                <productname>systemd</productname>

                <authorgroup>
                        <author>
                                <contrib>Developer</contrib>
                                <firstname>Lennart</firstname>
                                <surname>Poettering</surname>
                                <email>lennart@poettering.net</email>
                        </author>
                </authorgroup>
        </refentryinfo>

        <refmeta>
                <refentrytitle>systemd.device</refentrytitle>
                <manvolnum>5</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd.device</refname>
                <refpurpose>Device unit configuration</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <para><filename>systemd.device</filename></para>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para>A unit configuration file whose name ends in
                <filename>.device</filename> encodes information about
                a device unit as exposed in the
                sysfs/<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                device tree.</para>

                <para>This unit type has no specific options. See
                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                for the common options of all unit configuration
                files. The common configuration items are configured
                in the generic <literal>[Unit]</literal> and
                <literal>[Install]</literal> sections. A separate
                <literal>[Device]</literal> section does not exist,
                since no device-specific options may be
                configured.</para>

                <para>systemd will automatically create dynamic 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.</para>

                <para>Device units are named after the
                <filename>/sys</filename> and
                <filename>/dev</filename> paths they control. Example:
                the device <filename>/dev/sda5</filename> is exposed
                in systemd as <filename>dev-sda5.device</filename>. For
                details about the escaping logic used to convert a
                file system path to a unit name see
                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

        </refsect1>

        <refsect1>
                <title>The udev Database</title>

                <para>The settings of device units may either be
                configured via unit files, or directly from the udev
                database (which is recommended). The following udev
                properties are understood by systemd:</para>

                <variablelist>
                        <varlistentry>
                                <term><varname>SYSTEMD_WANTS=</varname></term>
                                <listitem><para>Adds dependencies of
                                type <varname>Wants</varname> from
                                this unit to all listed units. This
                                may be used to activate arbitrary
                                units, when a specific device becomes
                                available. Note that this and the
                                other tags are not taken into account
                                unless the device is tagged with the
                                "<literal>systemd</literal>" string in
                                the udev database, because otherwise
                                the device is not exposed as systemd
                                unit.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>SYSTEMD_ALIAS=</varname></term>
                                <listitem><para>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.)</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>SYSTEMD_READY=</varname></term>
                                <listitem><para>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 the moment it shows up in the
                                udev tree. This property has no
                                influence on the behaviour when a
                                device disappears from the udev
                                tree. This option is useful to support
                                devices that initially show up in an
                                uninitialized state in the tree, and for
                                which a changed event is generated the
                                moment they are fully set
                                up.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>ID_MODEL_FROM_DATABASE=</varname></term>
                                <term><varname>ID_MODEL=</varname></term>

                                <listitem><para>If set, this property is
                                used as description string for the
                                device unit.</para></listitem>
                        </varlistentry>

                </variablelist>


        </refsect1>

        <refsect1>
                  <title>See Also</title>
                  <para>
                          <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                  </para>
        </refsect1>

</refentry>