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diff --git a/man/udev.xml b/man/udev.xml new file mode 100644 index 0000000..332c7ac --- /dev/null +++ b/man/udev.xml @@ -0,0 +1,860 @@ +<?xml version='1.0'?> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<!-- + SPDX-License-Identifier: LGPL-2.1-or-later + Copyright © 2014 Jason St. John +--> + +<refentry id="udev"> + <refentryinfo> + <title>udev</title> + <productname>systemd</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>udev</refentrytitle> + <manvolnum>7</manvolnum> + </refmeta> + + <refnamediv> + <refname>udev</refname> + <refpurpose>Dynamic device management</refpurpose> + </refnamediv> + + <refsect1> + <title>Description</title> + <para>udev supplies the system software with device events, manages permissions + of device nodes and may create additional symlinks in the <filename>/dev/</filename> + directory, or renames network interfaces. The kernel usually just assigns unpredictable + device names based on the order of discovery. Meaningful symlinks or network device + names provide a way to reliably identify devices based on their properties or + current configuration.</para> + + <para>The udev daemon, <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle> + <manvolnum>8</manvolnum></citerefentry>, receives device uevents directly from + the kernel whenever a device is added or removed from the system, or it changes its + state. When udev receives a device event, it matches its configured set of rules + against various device attributes to identify the device. Rules that match may + provide additional device information to be stored in the udev database or + to be used to create meaningful symlink names.</para> + + <para>All device information udev processes is stored in the udev database and + sent out to possible event subscribers. Access to all stored data and the event + sources is provided by the library libudev.</para> + </refsect1> + + <refsect1> + <title>Rules Files</title> + <para>The udev rules are read from the files located in the system rules directories + <filename>/usr/lib/udev/rules.d</filename> and <filename>/usr/local/lib/udev/rules.d</filename>, the + volatile runtime directory <filename>/run/udev/rules.d</filename> and the local administration + directory <filename>/etc/udev/rules.d</filename>. All rules 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, + files in <filename>/run/</filename> take precedence over files with the same name under + <filename>/usr/</filename>. This can be used to override a system-supplied rules file with a local + file if needed; a symlink in <filename>/etc/</filename> with the same name as a rules file in + <filename>/usr/lib/</filename>, pointing to <filename>/dev/null</filename>, disables the rules file + entirely. Rule files must have the extension <filename>.rules</filename>; other extensions are + ignored.</para> + + <para>Every line in the rules file contains at least one key-value pair. + Except for empty lines or lines beginning with <literal>#</literal>, which are ignored. + There are two kinds of keys: match and assignment. + If all match keys match against their values, the rule gets applied and the + assignment keys get the specified values assigned.</para> + + <para>A matching rule may rename a network interface, add symlinks + pointing to the device node, or run a specified program as part of + the event handling.</para> + + <para>A rule consists of a comma-separated list of one or more key-operator-value expressions. + Each expression has a distinct effect, depending on the key and operator used.</para> + + <refsect2> + <title>Operators</title> + <variablelist> + <varlistentry> + <term><literal>==</literal></term> + <listitem> + <para>Compare for equality. (The specified key has the specified value.)</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><literal>!=</literal></term> + <listitem> + <para>Compare for inequality. (The specified key doesn't have the specified value, or the + specified key is not present at all.) + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><literal>=</literal></term> + <listitem> + <para>Assign a value to a key. Keys that represent a list are reset + and only this single value is assigned.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><literal>+=</literal></term> + <listitem> + <para>Add the value to a key that holds a list of entries.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><literal>-=</literal></term> + <listitem> + <para>Remove the value from a key that holds a list of entries.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><literal>:=</literal></term> + <listitem> + <para>Assign a value to a key finally; disallow any later changes.</para> + </listitem> + </varlistentry> + </variablelist> + </refsect2> + + <refsect2> + <title>Values</title> + <para>Values are written as double quoted strings, such as ("string"). + To include a quotation mark (") in the value, precede it by a backslash (\"). + Any other occurrences of a backslash followed by a character are not unescaped. + That is, "\t\n" is treated as four characters: + backslash, lowercase t, backslash, lowercase n.</para> + + <para>The string can be prefixed with a lowercase e (e"string\n") to mark the string as + <ulink url="https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences">C-style escaped</ulink>. + For example, e"string\n" is parsed as 7 characters: 6 lowercase letters and a newline. + This can be useful for writing special characters when a kernel driver requires them.</para> + + <para>Please note that <constant>NUL</constant> is not allowed in either string variant.</para> + </refsect2> + + <refsect2> + <title>Keys</title> + <para>The following key names can be used to match against device properties. + Some of the keys also match against properties of the parent devices in sysfs, + not only the device that has generated the event. If multiple keys that match + a parent device are specified in a single rule, all these keys must match at + one and the same parent device.</para> + <variablelist class='udev-directives'> + <varlistentry> + <term><varname>ACTION</varname></term> + <listitem> + <para>Match the name of the event action.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>DEVPATH</varname></term> + <listitem> + <para>Match the devpath of the event device.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>KERNEL</varname></term> + <listitem> + <para>Match the name of the event device.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>KERNELS</varname></term> + <listitem> + <para>Search the devpath upwards for a matching device name.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>NAME</varname></term> + <listitem> + <para>Match the name of a network interface. It can be used once the + NAME key has been set in one of the preceding rules.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>SYMLINK</varname></term> + <listitem> + <para>Match the name of a symlink targeting the node. It can be used once a SYMLINK key has + been set in one of the preceding rules. There may be multiple symlinks; only one needs to + match. If the operator is <literal>!=</literal>, the token returns true only if there is no + symlink matched.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>SUBSYSTEM</varname></term> + <listitem> + <para>Match the subsystem of the event device.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>SUBSYSTEMS</varname></term> + <listitem> + <para>Search the devpath upwards for a matching device subsystem name.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>DRIVER</varname></term> + <listitem> + <para>Match the driver name of the event device. Only set this key for devices + which are bound to a driver at the time the event is generated.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>DRIVERS</varname></term> + <listitem> + <para>Search the devpath upwards for a matching device driver name.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>ATTR{<replaceable>filename</replaceable>}</varname></term> + <listitem> + <para>Match sysfs attribute value of the event device.</para> + + <para>Trailing whitespace in the attribute values is ignored unless the specified match value + itself contains trailing whitespace.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>ATTRS{<replaceable>filename</replaceable>}</varname></term> + <listitem> + <para>Search the devpath upwards for a device with matching sysfs attribute values. If + multiple <varname>ATTRS</varname> matches are specified, all of them must match on the same + device.</para> + + <para>Trailing whitespace in the attribute values is ignored unless the specified match value + itself contains trailing whitespace.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term> + <listitem> + <para>Match a kernel parameter value.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>ENV{<replaceable>key</replaceable>}</varname></term> + <listitem> + <para>Match against a device property value.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>CONST{<replaceable>key</replaceable>}</varname></term> + <listitem> + <para>Match against a system-wide constant. Supported keys are:</para> + <variablelist> + <varlistentry> + <term><literal>arch</literal></term> + <listitem> + <para>System's architecture. See <option>ConditionArchitecture=</option> in + <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for possible values.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><literal>virt</literal></term> + <listitem> + <para>System's virtualization environment. See + <citerefentry><refentrytitle>systemd-detect-virt</refentrytitle><manvolnum>1</manvolnum></citerefentry> + for possible values.</para> + </listitem> + </varlistentry> + </variablelist> + <para>Unknown keys will never match.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>TAG</varname></term> + <listitem> + <para>Match against one of device tags. It can be used once a TAG key has been set in one of + the preceding rules. There may be multiple tags; only one needs to match. If the operator is + <literal>!=</literal>, the token returns true only if there is no tag matched.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>TAGS</varname></term> + <listitem> + <para>Search the devpath upwards for a device with matching tag. If the operator is + <literal>!=</literal>, the token returns true only if there is no tag matched.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>TEST{<replaceable>octal mode mask</replaceable>}</varname></term> + <listitem> + <para>Test the existence of a file. An octal mode mask can be specified + if needed.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>PROGRAM</varname></term> + <listitem> + <para>Execute a program to determine whether there is a match; the key is true if the program + returns successfully. The device properties are made available to the executed program in the + environment. The program's standard output is available in the <varname>RESULT</varname> + key.</para> + + <para>This can only be used for very short-running foreground tasks. For details, see + <varname>RUN</varname>.</para> + + <para>Note that multiple <varname>PROGRAM</varname> keys may be specified in one rule, and + <literal>=</literal>, <literal>:=</literal>, and <literal>+=</literal> have the same effect as + <literal>==</literal>.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>RESULT</varname></term> + <listitem> + <para>Match the returned string of the last <varname>PROGRAM</varname> call. + This key can be used in the same or in any later rule after a + <varname>PROGRAM</varname> call.</para> + </listitem> + </varlistentry> + </variablelist> + + <para>Most of the fields support shell glob pattern matching and + alternate patterns. The following special characters are supported:</para> + <variablelist> + <varlistentry> + <term><literal>*</literal></term> + <listitem> + <para>Matches zero or more characters.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><literal>?</literal></term> + <listitem> + <para>Matches any single character.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><literal>[]</literal></term> + <listitem> + <para>Matches any single character specified within the brackets. For + example, the pattern string <literal>tty[SR]</literal> + would match either <literal>ttyS</literal> or <literal>ttyR</literal>. + Ranges are also supported via the <literal>-</literal> character. + For example, to match on the range of all digits, the pattern + <literal>[0-9]</literal> could be used. If the first character + following the <literal>[</literal> is a <literal>!</literal>, + any characters not enclosed are matched.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><literal>|</literal></term> + <listitem> + <para>Separates alternative patterns. For example, the pattern string + <literal>abc|x*</literal> would match either <literal>abc</literal> + or <literal>x*</literal>.</para> + </listitem> + </varlistentry> + </variablelist> + + <para>The following keys can get values assigned:</para> + <variablelist class='udev-directives'> + <varlistentry> + <term><varname>NAME</varname></term> + <listitem> + <para>The name to use for a network interface. See + <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for a higher-level mechanism for setting the interface name. + The name of a device node cannot be changed by udev, only additional + symlinks can be created.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>SYMLINK</varname></term> + <listitem> + <para>The name of a symlink targeting the node. Every matching rule adds + this value to the list of symlinks to be created.</para> + <para>The set of characters to name a symlink is limited. Allowed + characters are <literal>0-9A-Za-z#+-.:=@_/</literal>, valid UTF-8 character + sequences, and <literal>\x00</literal> hex encoding. All other + characters are replaced by a <literal>_</literal> character.</para> + <para>Multiple symlinks may be specified by separating the names by the + space character. In case multiple devices claim the same name, the link + always points to the device with the highest link_priority. If the current + device goes away, the links are re-evaluated and the device with the + next highest link_priority becomes the owner of the link. If no + link_priority is specified, the order of the devices (and which one of + them owns the link) is undefined.</para> + <para>Symlink names must never conflict with the kernel's default device + node names, as that would result in unpredictable behavior. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>OWNER</varname>, <varname>GROUP</varname>, <varname>MODE</varname></term> + <listitem> + <para>The permissions for the device node. Every specified value overrides + the compiled-in default value.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>SECLABEL{<replaceable>module</replaceable>}</varname></term> + <listitem> + <para>Applies the specified Linux Security Module label to the device node.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>ATTR{<replaceable>key</replaceable>}</varname></term> + <listitem> + <para>The value that should be written to a sysfs attribute of the + event device.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>SYSCTL{<replaceable>kernel parameter</replaceable>}</varname></term> + <listitem> + <para>The value that should be written to kernel parameter.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>ENV{<replaceable>key</replaceable>}</varname></term> + <listitem> + <para>Set a device property value. Property names with a leading <literal>.</literal> + are neither stored in the database nor exported to events or + external tools (run by, for example, the <varname>PROGRAM</varname> + match key).</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>TAG</varname></term> + <listitem> + <para>Attach a tag to a device. This is used to filter events for users + of libudev's monitor functionality, or to enumerate a group of tagged + devices. The implementation can only work efficiently if only a few + tags are attached to a device. It is only meant to be used in + contexts with specific device filter requirements, and not as a + general-purpose flag. Excessive use might result in inefficient event + handling.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>RUN{<replaceable>type</replaceable>}</varname></term> + <listitem> + <para>Specify a program to be executed after processing of all the rules for the event. With + <literal>+=</literal>, this invocation is added to the list, and with <literal>=</literal> or + <literal>:=</literal>, it replaces any previous contents of the list. Please note that both + <literal>program</literal> and <literal>builtin</literal> types described below share a common + list, so clearing the list with <literal>:=</literal> and <literal>=</literal> affects both + types.</para> + + <para><replaceable>type</replaceable> may be:</para> + <variablelist> + <varlistentry> + <term><literal>program</literal></term> + <listitem> + <para>Execute an external program specified as the assigned + value. If no absolute path is given, the program is expected + to live in <filename>/usr/lib/udev</filename>; otherwise, the + absolute path must be specified.</para> + <para>This is the default if no <replaceable>type</replaceable> + is specified.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><literal>builtin</literal></term> + <listitem> + <para>As <varname>program</varname>, but use one of the + built-in programs rather than an external one.</para> + </listitem> + </varlistentry> + </variablelist> + + <para>The program name and following arguments are separated by spaces. Single quotes can be + used to specify arguments with spaces.</para> + + <para>This can only be used for very short-running foreground tasks. Running an event process for + a long period of time may block all further events for this or a dependent device.</para> + + <para>Note that running programs that access the network or mount/unmount filesystems is not + allowed inside of udev rules, due to the default sandbox that is enforced on + <filename>systemd-udevd.service</filename>.</para> + + <para>Starting daemons or other long-running processes is not allowed; the forked processes, + detached or not, will be unconditionally killed after the event handling has finished. In order + to activate long-running processes from udev rules, provide a service unit and pull it in from a + udev device using the <varname>SYSTEMD_WANTS</varname> device property. See + <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for details.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>LABEL</varname></term> + <listitem> + <para>A named label to which a <varname>GOTO</varname> may jump.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>GOTO</varname></term> + <listitem> + <para>Jumps to the next <varname>LABEL</varname> with a matching name.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>IMPORT{<replaceable>type</replaceable>}</varname></term> + <listitem> + <para>Import a set of variables as device properties, depending on + <replaceable>type</replaceable>:</para> + + <variablelist> + <varlistentry> + <term><literal>program</literal></term> + <listitem> + <para>Execute an external program specified as the assigned + value and, if it returns successfully, + import its output, which must be in environment key + format. Path specification, command/argument separation, + and quoting work like in <varname>RUN</varname>.</para> + </listitem> + </varlistentry> + <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> + + <para>Note that multiple <varname>IMPORT{}</varname> keys may be specified in one rule, and + <literal>=</literal>, <literal>:=</literal>, and <literal>+=</literal> have the same effect as + <literal>==</literal>. The key is true if the import is successful, unless <literal>!=</literal> + is used as the operator which causes the key to be true if the import failed.</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>When <literal>replace</literal>, possibly unsafe characters in strings + assigned to <varname>NAME</varname>, <varname>SYMLINK</varname>, and + <varname>ENV{<replaceable>key</replaceable>}</varname> are replaced. When + <literal>none</literal>, no replacement is performed. When unset, the replacement + is performed for <varname>NAME</varname>, <varname>SYMLINK</varname>, but not for + <varname>ENV{<replaceable>key</replaceable>}</varname>. Defaults to unset.</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. Also, for every + tag specified in this rule, create a symlink + in the directory + <filename>/run/udev/static_node-tags/<replaceable>tag</replaceable></filename> + pointing at the static device node with the specified name. + Static device node creation is performed by systemd-tmpfiles + before systemd-udevd is started. The static nodes might not + have a corresponding kernel device; they are used to trigger + automatic kernel module loading when they are accessed.</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> + <varlistentry> + <term><option>db_persist</option></term> + <listitem> + <para>Set the flag (sticky bit) on the udev database entry of the event device. Device + properties are then kept in the database even when <command>udevadm info + --cleanup-db</command> is called. This option can be useful in certain cases + (e.g. Device Mapper devices) for persisting device state on the transition from + initrd.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><option>log_level=<replaceable>level</replaceable></option></term> + <listitem> + <para>Takes a log level name like <literal>debug</literal> or + <literal>info</literal>, or a special value <literal>reset</literal>. When a log + level name is specified, the maximum log level is changed to that level. When + <literal>reset</literal> is set, then the previously specified log level is + revoked. Defaults to the log level of the main process of + <command>systemd-udevd</command>.</para> + <para>This may be useful when debugging events for certain devices. Note that the + log level is applied when the line including this rule is processed. So, for + debugging, it is recommended that this is specified at earlier place, e.g., the + first line of <filename>00-debug.rules</filename>.</para> + <para>Example for debugging uevent processing for network interfaces: + <programlisting># /etc/udev/rules.d/00-debug-net.rules +SUBSYSTEM=="net", OPTIONS="log_level=debug"</programlisting></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>, <varname>SECLABEL</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 + 3.</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>$links</option></term> + <listitem> + <para>A space-separated list of the current symlinks. The value is + only set during a remove event or if an earlier rule assigned a value.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><option>$root</option>, <option>%r</option></term> + <listitem> + <para>The udev_root 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> + </refsect2> + </refsect1> + + <refsect1> + <title>See Also</title> + <para> + <citerefentry> + <refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum> + </citerefentry>, + <citerefentry> + <refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum> + </citerefentry>, + <citerefentry> + <refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum> + </citerefentry> + </para> + </refsect1> +</refentry> |