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For all units ensure there's an "Automatic Dependencies" section in the man page, and explain which dependencies are automatically added in all cases, and which ones are added on top if DefaultDependencies=yes is set. This is also done for systemd.exec(5), systemd.resource-control(5) and systemd.unit(5) as these pages describe common behaviour of various unit types.
183 lines
7.3 KiB
XML
183 lines
7.3 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="systemd.device">
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<refentryinfo>
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<title>systemd.device</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd.device</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.device</refname>
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<refpurpose>Device unit configuration</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename><replaceable>device</replaceable>.device</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>A unit configuration file whose name ends in
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<literal>.device</literal> encodes information about a device unit
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as exposed in the
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sysfs/<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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device tree.</para>
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<para>This unit type has no specific options. See
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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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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<literal>[Unit]</literal> and <literal>[Install]</literal>
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sections. A separate <literal>[Device]</literal> section does not
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exist, since no device-specific options may be configured.</para>
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<para>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 <literal>TAG+="systemd"</literal> in the udev
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rules file, see
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<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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for details.</para>
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<para>Device units are named after the <filename>/sys</filename>
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and <filename>/dev</filename> paths they control. Example: the
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device <filename noindex='true'>/dev/sda5</filename> is exposed in
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systemd as <filename>dev-sda5.device</filename>. 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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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
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</refsect1>
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<refsect1>
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<title>Automatic Dependencies</title>
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<para>Many unit types automatically acquire dependencies on device
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units of devices they require. For example,
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<filename>.socket</filename> unit acquire dependencies on the
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device units of the network interface specified in
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<varname>BindToDevice=</varname>. Similar, swap and mount units
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acquire dependencies on the units encapsulating their backing
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block devices.</para>
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</refsect1>
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<refsect1>
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<title>The udev Database</title>
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<para>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:</para>
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<variablelist class='udev-directives'>
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<varlistentry>
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<term><varname>SYSTEMD_WANTS=</varname></term>
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<term><varname>SYSTEMD_USER_WANTS=</varname></term>
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<listitem><para>Adds dependencies of type
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<varname>Wants</varname> 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.</para>
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<para>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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<literal>systemd</literal> 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).</para>
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<para>Note that systemd will only act on
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<varname>Wants</varname> 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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<varname>SYSTEMD_READY=</varname> (see below) to influence on
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which udev event to trigger the dependencies.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYSTEMD_ALIAS=</varname></term>
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<listitem><para>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.)</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYSTEMD_READY=</varname></term>
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<listitem><para>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.</para>
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<para>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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<literal>changed</literal> event is generated the moment they
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are fully set up. Note that <varname>SYSTEMD_WANTS=</varname>
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(see above) is not acted on as long as
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<varname>SYSTEMD_READY=0</varname> is set for a
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device.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ID_MODEL_FROM_DATABASE=</varname></term>
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<term><varname>ID_MODEL=</varname></term>
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<listitem><para>If set, this property is used as description
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string for the device unit.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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