mirror of
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794 lines
34 KiB
XML
794 lines
34 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<?xml-stylesheet type="text/xsl" href="http://docbook.sourceforge.net/release/xsl/current/xhtml/docbook.xsl"?>
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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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<refentry id="udev">
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<refentryinfo>
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<title>udev</title>
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<productname>udev</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Greg</firstname>
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<surname>Kroah-Hartmann</surname>
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<email>greg@kroah.com</email>
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</author>
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<author>
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<contrib>Developer</contrib>
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<firstname>Kay</firstname>
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<surname>Sievers</surname>
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<email>kay@vrfy.org</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>udev</refentrytitle>
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<manvolnum>7</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>udev</refname>
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<refpurpose>Dynamic device management</refpurpose>
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</refnamediv>
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<refsect1><title>Description</title>
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<para>udev supplies the system software with device events, manages permissions
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of device nodes, may create additional symlinks in the <filename>/dev</filename>
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directory and may rename network interfaces. The kernel usually just assigns unpredictable
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device names based on the order of discovery. Meaningful symlinks or network device
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names provide a way to reliably identify devices based on their properties or
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current configuration.</para>
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<para>The udev daemon, <citerefentry><refentrytitle>udevd</refentrytitle>
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<manvolnum>8</manvolnum></citerefentry>, receives device uevents directly from
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the kernel whenever a device is added or removed from the system, or it changes its
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state. When udev receives a device event, it matches its configured set of rules
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against various device attributes to identify the device. Rules that match may
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provide additional device information to be stored in the udev database or
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to be used to create meaningful symlink names.</para>
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<para>All device information udev processes is stored in the udev database and
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sent out to possible event subscribers. Access to all stored data and the event
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sources is provided by the library libudev.</para>
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</refsect1>
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<refsect1><title>Rules Files</title>
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<para>The udev rules are read from the files located in the system rules
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directory <filename>/lib/udev/rules.d</filename> (additionally
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<filename>/usr/lib/udev/rules.d</filename> when built with --enable-split-usr),
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the volatile runtime directory <filename>/run/udev/rules.d</filename>
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and the local administration directory <filename>/etc/udev/rules.d</filename>.
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All rules files are collectively sorted and processed in lexical order,
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regardless of the directories in which they live. However, files with
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identical filenames replace each other. Files in <filename>/etc</filename>
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have the highest priority, files in <filename>/run</filename> take precedence
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over files with the same name in <filename>/lib</filename> (or
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<filename>/usr/lib</filename>). This can be
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used to override a system-supplied rules file with a local file if needed;
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a symlink in <filename>/etc</filename> with the same name as a rules file in
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<filename>/lib</filename>, pointing to <filename>/dev/null</filename>,
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disables the rules file entirely. Rule files must have the extension
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<filename>.rules</filename>; other extensions are ignored.</para>
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<para>Every line in the rules file contains at least one key-value pair.
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Except for empty lines or lines beginning with <literal>#</literal>, which are ignored.
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There are two kinds of keys: match and assignment.
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If all match keys match against their values, the rule gets applied and the
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assignment keys get the specified values assigned.</para>
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<para>A matching rule may rename a network interface, add symlinks
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pointing to the device node, or run a specified program as part of
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the event handling.</para>
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<para>A rule consists of a comma-separated list of one or more key-value pairs.
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Each key has a distinct operation, depending on the used operator. Valid
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operators are:</para>
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<variablelist>
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<varlistentry>
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<term><literal>==</literal></term>
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<listitem>
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<para>Compare for equality.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>!=</literal></term>
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<listitem>
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<para>Compare for inequality.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>=</literal></term>
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<listitem>
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<para>Assign a value to a key. Keys that represent a list are reset
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and only this single value is assigned.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>+=</literal></term>
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<listitem>
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<para>Add the value to a key that holds a list of entries.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>-=</literal></term>
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<listitem>
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<para>Remove the value from a key that holds a list of entries.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>:=</literal></term>
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<listitem>
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<para>Assign a value to a key finally; disallow any later changes.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>The following key names can be used to match against device properties.
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Some of the keys also match against properties of the parent devices in sysfs,
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not only the device that has generated the event. If multiple keys that match
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a parent device are specified in a single rule, all these keys must match at
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one and the same parent device.</para>
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<variablelist class='udev-directives'>
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<varlistentry>
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<term><varname>ACTION</varname></term>
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<listitem>
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<para>Match the name of the event action.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>DEVPATH</varname></term>
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<listitem>
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<para>Match the devpath of the event device.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>KERNEL</varname></term>
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<listitem>
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<para>Match the name of the event device.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>NAME</varname></term>
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<listitem>
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<para>Match the name of a network interface. It can be used once the
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NAME key has been set in one of the preceding rules.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYMLINK</varname></term>
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<listitem>
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<para>Match the name of a symlink targeting the node. It can
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be used once a SYMLINK key has been set in one of the preceding
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rules. There may be multiple symlinks; only one needs to match.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SUBSYSTEM</varname></term>
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<listitem>
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<para>Match the subsystem of the event device.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>DRIVER</varname></term>
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<listitem>
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<para>Match the driver name of the event device. Only set this key for devices
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which are bound to a driver at the time the event is generated.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ATTR{<replaceable>filename</replaceable>}</varname></term>
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<listitem>
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<para>Match sysfs attribute values of the event device. Trailing
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whitespace in the attribute values is ignored unless the specified match
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value itself contains trailing whitespace.
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</para>
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</listitem>
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<term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term>
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<listitem>
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<para>Match a kernel parameter value.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>KERNELS</varname></term>
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<listitem>
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<para>Search the devpath upwards for a matching device name.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SUBSYSTEMS</varname></term>
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<listitem>
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<para>Search the devpath upwards for a matching device subsystem name.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>DRIVERS</varname></term>
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<listitem>
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<para>Search the devpath upwards for a matching device driver name.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ATTRS{<replaceable>filename</replaceable>}</varname></term>
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<listitem>
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<para>Search the devpath upwards for a device with matching sysfs attribute values.
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If multiple <varname>ATTRS</varname> matches are specified, all of them
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must match on the same device. Trailing whitespace in the attribute values is ignored
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unless the specified match value itself contains trailing whitespace.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TAGS</varname></term>
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<listitem>
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<para>Search the devpath upwards for a device with matching tag.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ENV{<replaceable>key</replaceable>}</varname></term>
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<listitem>
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<para>Match against a device property value.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TAG</varname></term>
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<listitem>
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<para>Match against a device tag.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TEST{<replaceable>octal mode mask</replaceable>}</varname></term>
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<listitem>
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<para>Test the existence of a file. An octal mode mask can be specified
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if needed.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>PROGRAM</varname></term>
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<listitem>
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<para>Execute a program to determine whether there
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is a match; the key is true if the program returns
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successfully. The device properties are made available to the
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executed program in the environment. The program's standard output
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is available in the <varname>RESULT</varname> key.</para>
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<para>This can only be used for very short-running foreground tasks. For details,
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see <varname>RUN</varname>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>RESULT</varname></term>
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<listitem>
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<para>Match the returned string of the last <varname>PROGRAM</varname> call.
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This key can be used in the same or in any later rule after a
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<varname>PROGRAM</varname> call.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Most of the fields support shell glob pattern matching and
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alternate patterns. The following special characters are supported:</para>
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<variablelist>
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<varlistentry>
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<term><literal>*</literal></term>
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<listitem>
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<para>Matches zero or more characters.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>?</literal></term>
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<listitem>
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<para>Matches any single character.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>[]</literal></term>
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<listitem>
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<para>Matches any single character specified within the brackets. For
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example, the pattern string <literal>tty[SR]</literal>
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would match either <literal>ttyS</literal> or <literal>ttyR</literal>.
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Ranges are also supported via the <literal>-</literal> character.
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For example, to match on the range of all digits, the pattern
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<literal>[0-9]</literal> could be used. If the first character
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following the <literal>[</literal> is a <literal>!</literal>,
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any characters not enclosed are matched.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>|</literal></term>
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<listitem>
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<para>Separates alternative patterns. For example, the pattern string
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<literal>abc|x*</literal> would match either <literal>abc</literal>
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or <literal>x*</literal>.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>The following keys can get values assigned:</para>
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<variablelist class='udev-directives'>
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<varlistentry>
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<term><varname>NAME</varname></term>
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<listitem>
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<para>The name to use for a network interface. The name of a device node
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cannot be changed by udev, only additional symlinks can be created.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYMLINK</varname></term>
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<listitem>
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<para>The name of a symlink targeting the node. Every matching rule adds
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this value to the list of symlinks to be created.</para>
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<para>The set of characters to name a symlink is limited. Allowed
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characters are <literal>0-9A-Za-z#+-.:=@_/</literal>, valid UTF-8 character
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sequences, and <literal>\x00</literal> hex encoding. All other
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characters are replaced by a <literal>_</literal> character.</para>
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<para>Multiple symlinks may be specified by separating the names by the
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space character. In case multiple devices claim the same name, the link
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always points to the device with the highest link_priority. If the current
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device goes away, the links are re-evaluated and the device with the
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next highest link_priority becomes the owner of the link. If no
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link_priority is specified, the order of the devices (and which one of
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them owns the link) is undefined.</para>
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<para>Symlink names must never conflict with the kernel's default device
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node names, as that would result in unpredictable behavior.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>OWNER</varname>, <varname>GROUP</varname>, <varname>MODE</varname></term>
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<listitem>
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<para>The permissions for the device node. Every specified value overrides
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the compiled-in default value.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SECLABEL{<replaceable>module</replaceable>}</varname></term>
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<listitem>
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<para>Applies the specified Linux Security Module label to the device node.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ATTR{<replaceable>key</replaceable>}</varname></term>
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<listitem>
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<para>The value that should be written to a sysfs attribute of the
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event device.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term>
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<listitem>
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<para>The value that should be written to kernel parameter.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ENV{<replaceable>key</replaceable>}</varname></term>
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<listitem>
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<para>Set a device property value. Property names with a leading <literal>.</literal>
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are neither stored in the database nor exported to events or
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external tools (run by, for example, the <varname>PROGRAM</varname>
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match key).</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TAG</varname></term>
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<listitem>
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<para>Attach a tag to a device. This is used to filter events for users
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of libudev's monitor functionality, or to enumerate a group of tagged
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devices. The implementation can only work efficiently if only a few
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tags are attached to a device. It is only meant to be used in
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contexts with specific device filter requirements, and not as a
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general-purpose flag. Excessive use might result in inefficient event
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handling.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>RUN{<replaceable>type</replaceable>}</varname></term>
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<listitem>
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<para>Add a program to the list of programs to be executed after
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processing all the rules for a specific event, depending on
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<literal>type</literal>:</para>
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<variablelist>
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<varlistentry>
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<term><literal>program</literal></term>
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<listitem>
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<para>Execute an external program specified as the assigned
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value. If no absolute path is given, the program is expected
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to live in <filename>/lib/udev</filename>, otherwise, the
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absolute path must be specified.</para>
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<para>This is the default if no <replaceable>type</replaceable>
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is specified.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>builtin</literal></term>
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<listitem>
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<para>As <varname>program</varname>, but use one of the
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built-in programs rather than an external one.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>The program name and following arguments are separated by spaces.
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Single quotes can be used to specify arguments with spaces.</para>
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<para>This can only be used for very short-running foreground tasks. Running an
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event process for a long period of time may block all further events for
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this or a dependent device.</para>
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<para>Starting daemons or other long-running processes is not appropriate
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for udev; the forked processes, detached or not, will be unconditionally
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killed after the event handling has finished.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>LABEL</varname></term>
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<listitem>
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<para>A named label to which a <varname>GOTO</varname> may jump.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>GOTO</varname></term>
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<listitem>
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<para>Jumps to the next <varname>LABEL</varname> with a matching name.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>IMPORT{<replaceable>type</replaceable>}</varname></term>
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<listitem>
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<para>Import a set of variables as device properties,
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depending on <literal>type</literal>:</para>
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<variablelist>
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<varlistentry>
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<term><literal>program</literal></term>
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<listitem>
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<para>Execute an external program specified as the assigned value and
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import its output, which must be in environment key
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format. Path specification, command/argument separation,
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and quoting work like in <varname>RUN</varname>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
|
|
<term><literal>builtin</literal></term>
|
|
<listitem>
|
|
<para>Similar to <literal>program</literal>, but use one of the
|
|
built-in programs rather than an external one.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>file</literal></term>
|
|
<listitem>
|
|
<para>Import a text file specified as the assigned value, the content
|
|
of which must be in environment key format.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>db</literal></term>
|
|
<listitem>
|
|
<para>Import a single property specified as the assigned value from the
|
|
current device database. This works only if the database is already populated
|
|
by an earlier event.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>cmdline</literal></term>
|
|
<listitem>
|
|
<para>Import a single property from the kernel command line. For simple flags
|
|
the value of the property is set to <literal>1</literal>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>parent</literal></term>
|
|
<listitem>
|
|
<para>Import the stored keys from the parent device by reading
|
|
the database entry of the parent device. The value assigned to
|
|
<option>IMPORT{parent}</option> is used as a filter of key names
|
|
to import (with the same shell glob pattern matching used for
|
|
comparisons).</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>This can only be used for very short-running foreground tasks. For details
|
|
see <option>RUN</option>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>WAIT_FOR</varname></term>
|
|
<listitem>
|
|
<para>Wait for a file to become available or until a timeout of
|
|
10 seconds expires. The path is relative to the sysfs device;
|
|
if no path is specified, this waits for an attribute to appear.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>OPTIONS</varname></term>
|
|
<listitem>
|
|
<para>Rule and device options:</para>
|
|
<variablelist class='udev-directives'>
|
|
<varlistentry>
|
|
<term><option>link_priority=<replaceable>value</replaceable></option></term>
|
|
<listitem>
|
|
<para>Specify the priority of the created symlinks. Devices with higher
|
|
priorities overwrite existing symlinks of other devices. The default is 0.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>string_escape=<replaceable>none|replace</replaceable></option></term>
|
|
<listitem>
|
|
<para>Usually control and other possibly unsafe characters are replaced
|
|
in strings used for device naming. The mode of replacement can be specified
|
|
with this option.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>static_node=</option></term>
|
|
<listitem>
|
|
<para>Apply the permissions specified in this rule to the
|
|
static device node with the specified name. Static device node
|
|
creation can be requested by kernel modules. These nodes might
|
|
not have a corresponding kernel device at the time udevd is started;
|
|
they can trigger automatic kernel module loading.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>watch</option></term>
|
|
<listitem>
|
|
<para>Watch the device node with inotify; when the node is
|
|
closed after being opened for writing, a change uevent is
|
|
synthesized.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><option>nowatch</option></term>
|
|
<listitem>
|
|
<para>Disable the watching of a device node with inotify.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<para>The <varname>NAME</varname>, <varname>SYMLINK</varname>,
|
|
<varname>PROGRAM</varname>, <varname>OWNER</varname>,
|
|
<varname>GROUP</varname>, <varname>MODE</varname>, and
|
|
<varname>RUN</varname> fields support simple string substitutions.
|
|
The <varname>RUN</varname> substitutions are performed after all rules
|
|
have been processed, right before the program is executed, allowing for
|
|
the use of device properties set by earlier matching rules. For all other
|
|
fields, substitutions are performed while the individual rule is being
|
|
processed. The available substitutions are:</para>
|
|
<variablelist class='udev-directives'>
|
|
<varlistentry>
|
|
<term><option>$kernel</option>, <option>%k</option></term>
|
|
<listitem>
|
|
<para>The kernel name for this device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$number</option>, <option>%n</option></term>
|
|
<listitem>
|
|
<para>The kernel number for this device. For example,
|
|
<literal>sda3</literal> has kernel number <literal>3</literal>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$devpath</option>, <option>%p</option></term>
|
|
<listitem>
|
|
<para>The devpath of the device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$id</option>, <option>%b</option></term>
|
|
<listitem>
|
|
<para>The name of the device matched while searching the devpath
|
|
upwards for <option>SUBSYSTEMS</option>, <option>KERNELS</option>,
|
|
<option>DRIVERS</option>, and <option>ATTRS</option>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$driver</option></term>
|
|
<listitem>
|
|
<para>The driver name of the device matched while searching the
|
|
devpath upwards for <option>SUBSYSTEMS</option>,
|
|
<option>KERNELS</option>, <option>DRIVERS</option>, and
|
|
<option>ATTRS</option>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$attr{<replaceable>file</replaceable>}</option>, <option>%s{<replaceable>file</replaceable>}</option></term>
|
|
<listitem>
|
|
<para>The value of a sysfs attribute found at the device where
|
|
all keys of the rule have matched. If the matching device does not
|
|
have such an attribute, and a previous <option>KERNELS</option>,
|
|
<option>SUBSYSTEMS</option>, <option>DRIVERS</option>, or
|
|
<option>ATTRS</option> test selected a parent device, then the
|
|
attribute from that parent device is used.
|
|
</para>
|
|
<para>If the attribute is a symlink, the last element of the
|
|
symlink target is returned as the value.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$env{<replaceable>key</replaceable>}</option>, <option>%E{<replaceable>key</replaceable>}</option></term>
|
|
<listitem>
|
|
<para>A device property value.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$major</option>, <option>%M</option></term>
|
|
<listitem>
|
|
<para>The kernel major number for the device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$minor</option>, <option>%m</option></term>
|
|
<listitem>
|
|
<para>The kernel minor number for the device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$result</option>, <option>%c</option></term>
|
|
<listitem>
|
|
<para>The string returned by the external program requested with
|
|
<varname>PROGRAM</varname>.
|
|
A single part of the string, separated by a space character, may be selected
|
|
by specifying the part number as an attribute: <literal>%c{N}</literal>.
|
|
If the number is followed by the <literal>+</literal> character, this part plus all remaining parts
|
|
of the result string are substituted: <literal>%c{N+}</literal>.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$parent</option>, <option>%P</option></term>
|
|
<listitem>
|
|
<para>The node name of the parent device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$name</option></term>
|
|
<listitem>
|
|
<para>The current name of the device. If not changed by a rule, it is the
|
|
name of the kernel device.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$links</option></term>
|
|
<listitem>
|
|
<para>A space-separated list of the current symlinks. The value is
|
|
only set during a remove event or if an earlier rule assigned a value.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$sys</option>, <option>%S</option></term>
|
|
<listitem>
|
|
<para>The sysfs mount point.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$devnode</option>, <option>%N</option></term>
|
|
<listitem>
|
|
<para>The name of the device node.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>%%</option></term>
|
|
<listitem>
|
|
<para>The <literal>%</literal> character itself.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><option>$$</option></term>
|
|
<listitem>
|
|
<para>The <literal>$</literal> character itself.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect1>
|
|
|
|
<refsect1><title>Hardware Database Files</title>
|
|
<para>The hwdb files are read from the files located in the
|
|
system hwdb directory <filename>/usr/lib/udev/hwdb.d</filename>,
|
|
the volatile runtime directory <filename>/run/udev/hwdb.d</filename>,
|
|
the local administration directory <filename>/etc/udev/hwdb.d</filename>,
|
|
and any other directory in the <envar>UDEV_HWDB_PATH</envar> search path
|
|
variable. All hwdb files are collectively sorted and processed in
|
|
lexical order, regardless of the directories in which they live. However,
|
|
files with identical filenames replace each other. Files in
|
|
<filename>/etc</filename> have the highest priority, then files in
|
|
<filename>/run</filename>, <filename>/usr/lib</filename> and the ones in
|
|
<envar>UDEV_HWDB_PATH</envar> comes last. Files with higher priority
|
|
take precedence over files with the same name and lower priority.
|
|
This order can be used to override a system-supplied hwdb file with a
|
|
local file if needed; a symlink in <filename>/etc</filename> with the
|
|
same name as a hwdb file in <filename>/usr/lib</filename>, pointing to
|
|
<filename>/dev/null</filename>, disables the hwdb file entirely. hwdb
|
|
files must have the extension <filename>.hwdb</filename>; other
|
|
extensions are ignored.</para>
|
|
|
|
<para>The hwdb file contains data records consisting of matches and
|
|
associated key-value pairs. Every record in the hwdb starts with one or
|
|
more match string, specifying a shell glob to compare the database
|
|
lookup string against. Multiple match lines are specified in additional
|
|
consecutive lines. Every match line is compared individually, they are
|
|
combined by OR. Every match line must start at the first character of
|
|
the line.</para>
|
|
|
|
<para>The match lines are followed by one or more key-value pair lines, which
|
|
are recognized by a leading space character. The key name and value are separated
|
|
by <literal>=</literal>. An empty line signifies the end
|
|
of a record. Lines beginning with <literal>#</literal> are ignored.</para>
|
|
|
|
<para>The content of all hwdb files is read by <citerefentry>
|
|
<refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
|
|
</citerefentry> and compiled to a binary database located at
|
|
<filename>/etc/udev/hwdb.bin</filename>, or alternatively
|
|
<filename>/usr/lib/udev/hwdb.bin</filename>, if you want to ship the
|
|
compiled database in an immutable image by using <option>--usr</option>,
|
|
or anywhere on the system by using <option>--output</option>.
|
|
If <envar>UDEV_HWDB_BIN</envar> is set at run-time, and its value
|
|
identifies a file in the file system, then the binary database located
|
|
under this name will be used. During runtime only the binary database is
|
|
used.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para>
|
|
<citerefentry>
|
|
<refentrytitle>udevd</refentrytitle><manvolnum>8</manvolnum>
|
|
</citerefentry>,
|
|
<citerefentry>
|
|
<refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum>
|
|
</citerefentry></para>
|
|
</refsect1>
|
|
</refentry>
|