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| Copyright 2010 Lennart Poettering |
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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><replaceable>device</replaceable>.device</filename></para> |
| </refsynopsisdiv> |
| |
| <refsect1> |
| <title>Description</title> |
| |
| <para>A unit configuration file whose name ends in |
| <literal>.device</literal> 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 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 <literal>TAG+="systemd"</literal> in |
| the udev rules file, see |
| <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| for details.</para> |
| |
| <para>Device units are named after the |
| <filename>/sys</filename> and |
| <filename>/dev</filename> paths they control. Example: |
| the device <filename noindex='true'>/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 device |
| properties are understood by systemd:</para> |
| |
| <variablelist class='udev-directives'> |
| <varlistentry> |
| <term><varname>SYSTEMD_WANTS=</varname></term> |
| <term><varname>SYSTEMD_USER_WANTS=</varname></term> |
| <listitem><para>Adds dependencies of |
| type <varname>Wants</varname> 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.</para> |
| |
| <para>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 a systemd |
| unit (see above).</para> |
| |
| <para>Note that systemd will only act |
| on <varname>Wants</varname> |
| dependencies when a device first |
| becomes active. It will not act on |
| them if they are added to devices that |
| are already active. Use |
| <varname>SYSTEMD_READY=</varname> (see |
| below) to influence on which udev |
| event to trigger the dependencies. |
| </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 if it is visible in the |
| udev tree. This property has no |
| influence on the behavior when a |
| device disappears from the udev |
| tree.</para> |
| |
| <para>This option is useful to support |
| devices that initially show up in an |
| uninitialized state in the tree, and |
| for which a <literal>changed</literal> |
| event is generated the moment they are |
| fully set up. Note that |
| <varname>SYSTEMD_WANTS=</varname> (see |
| above) is not acted on as long as |
| <varname>SYSTEMD_READY=0</varname> is |
| set for a device.</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>, |
| <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| </para> |
| </refsect1> |
| |
| </refentry> |