man/systemd.device.xml

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  11   Copyright 2010 Lennart Poettering
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  26
  27 <refentry id="systemd.device">
  28   <refentryinfo>
  29     <title>systemd.device</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>systemd.device</refentrytitle>
  44     <manvolnum>5</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>systemd.device</refname>
  49     <refpurpose>Device unit configuration</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv>
  53     <para><filename><replaceable>device</replaceable>.device</filename></para>
  54   </refsynopsisdiv>
  55
  56   <refsect1>
  57     <title>Description</title>
  58
  59     <para>A unit configuration file whose name ends in
  60     <literal>.device</literal> encodes information about a device unit
  61     as exposed in the
  62     sysfs/<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  63     device tree.</para>
  64
  65     <para>This unit type has no specific options. See
  66     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  67     for the common options of all unit configuration files. The common
  68     configuration items are configured in the generic
  69     <literal>[Unit]</literal> and <literal>[Install]</literal>
  70     sections. A separate <literal>[Device]</literal> section does not
  71     exist, since no device-specific options may be configured.</para>
  72
  73     <para>systemd will dynamically create device units for all kernel
  74     devices that are marked with the "systemd" udev tag (by default
  75     all block and network devices, and a few others). This may be used
  76     to define dependencies between devices and other units. To tag a
  77     udev device, use <literal>TAG+="systemd"</literal> in the udev
  78     rules file, see
  79     <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  80     for details.</para>
  81
  82     <para>Device units are named after the <filename>/sys</filename>
  83     and <filename>/dev</filename> paths they control. Example: the
  84     device <filename noindex='true'>/dev/sda5</filename> is exposed in
  85     systemd as <filename>dev-sda5.device</filename>. For details about
  86     the escaping logic used to convert a file system path to a unit
  87     name see
  88     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
  89
  90   </refsect1>
  91
  92   <refsect1>
  93     <title>The udev Database</title>
  94
  95     <para>The settings of device units may either be configured via
  96     unit files, or directly from the udev database (which is
  97     recommended). The following udev device properties are understood
  98     by systemd:</para>
  99
 100     <variablelist class='udev-directives'>
 101       <varlistentry>
 102         <term><varname>SYSTEMD_WANTS=</varname></term>
 103         <term><varname>SYSTEMD_USER_WANTS=</varname></term>
 104         <listitem><para>Adds dependencies of type
 105         <varname>Wants</varname> from the device unit to all listed
 106         units. The first form is used by the system systemd instance,
 107         the second by user systemd instances. Those settings may be
 108         used to activate arbitrary units when a specific device
 109         becomes available.</para>
 110
 111         <para>Note that this and the other tags are not taken into
 112         account unless the device is tagged with the
 113         <literal>systemd</literal> string in the udev database,
 114         because otherwise the device is not exposed as a systemd unit
 115         (see above).</para>
 116
 117         <para>Note that systemd will only act on
 118         <varname>Wants</varname> dependencies when a device first
 119         becomes active. It will not act on them if they are added to
 120         devices that are already active. Use
 121         <varname>SYSTEMD_READY=</varname> (see below) to influence on
 122         which udev event to trigger the dependencies.
 123         </para></listitem>
 124       </varlistentry>
 125
 126       <varlistentry>
 127         <term><varname>SYSTEMD_ALIAS=</varname></term>
 128         <listitem><para>Adds an additional alias name to the device
 129         unit. This must be an absolute path that is automatically
 130         transformed into a unit name. (See above.)</para></listitem>
 131       </varlistentry>
 132
 133       <varlistentry>
 134         <term><varname>SYSTEMD_READY=</varname></term>
 135         <listitem><para>If set to 0, systemd will consider this device
 136         unplugged even if it shows up in the udev tree. If this
 137         property is unset or set to 1, the device will be considered
 138         plugged if it is visible in the udev tree. This property has
 139         no influence on the behavior when a device disappears from the
 140         udev tree.</para>
 141
 142         <para>This option is useful to support devices that initially
 143         show up in an uninitialized state in the tree, and for which a
 144         <literal>changed</literal> event is generated the moment they
 145         are fully set up. Note that <varname>SYSTEMD_WANTS=</varname>
 146         (see above) is not acted on as long as
 147         <varname>SYSTEMD_READY=0</varname> is set for a
 148         device.</para></listitem>
 149       </varlistentry>
 150
 151       <varlistentry>
 152         <term><varname>ID_MODEL_FROM_DATABASE=</varname></term>
 153         <term><varname>ID_MODEL=</varname></term>
 154
 155         <listitem><para>If set, this property is used as description
 156         string for the device unit.</para></listitem>
 157       </varlistentry>
 158
 159     </variablelist>
 160
 161   </refsect1>
 162
 163   <refsect1>
 164       <title>See Also</title>
 165       <para>
 166         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 167         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 168         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 169         <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 170         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 171       </para>
 172   </refsect1>
 173
 174 </refentry>