mirror of
https://github.com/systemd/systemd.git
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6d44591141
This reverts commit 0ffddc6e2c. That
causes a rather severe disruption of D-Bus and other services when e. g.
restarting local-fs.target (as spotted by the "storage" test regression).
Fixes #6834
189 lines
7.4 KiB
XML
189 lines
7.4 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>Implicit 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>Default Dependencies</title>
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<para>There are no default dependencies for device units.</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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