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<article>

<section>

<title>udev</title>

<refentry>

<refentryinfo>

<title>udev</title>

<productname>udev</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 provides a dynamic device directory containing only the files for

actually present devices. It creates or removes device node files in the

<filename>/dev</filename> directory, or it renames network interfaces.</para>

<para>Usually udev runs as <citerefentry><refentrytitle>udevd</refentrytitle>

<manvolnum>8</manvolnum></citerefentry> and receives uevents directly from the

kernel if a device is added or removed from the system.</para>

<para>If udev receives a device event, it matches its configured rules

against the available device attributes provided in sysfs to identify the device.

Rules that match may provide additional device information or specify a device

node name and multiple symlink names and instruct udev to run additional programs

as part of the device event handling.</para>

</refsect1>

<refsect1><title>CONFIGURATION</title>

<para>udev configuration files are placed in <filename>/etc/udev/</filename>

and <filename>/lib/udev/</filename>. All empty lines, or lines beginning with

'#' will be ignored.</para>

<refsect2><title>Configuration file</title>

<para>udev expects its main configuration file at <filename>/etc/udev/udev.conf</filename>.

It consists of a set of variables allowing the user to override default udev values.

The following variables can be set:</para>

<variablelist>

<varlistentry>

<term><option>udev_root</option></term>

<listitem>

<para>Specifies where to place the device nodes in the filesystem.

The default value is <filename>/dev</filename>.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>udev_log</option></term>

<listitem>

<para>The logging priority. Valid values are the numerical syslog priorities

or their textual representations: <option>err</option>, <option>info</option>

and <option>debug</option>.</para>

</listitem>

</varlistentry>

</variablelist>

</refsect2>

<refsect2><title>Rules files</title>

<para>The udev rules are read from the files located in the

default rules directory <filename>/lib/udev/rules.d/</filename>,

the custom rules directory <filename>/etc/udev/rules.d/</filename>

and the temporary rules directory <filename>/dev/.udev/rules.d/</filename>.

All rule files are sorted and processed in lexical order, regardless

in which of these directories they live.</para>

<para>Rule files are required to have a unique name, duplicate file names

are ignored. Files in <filename>/etc/udev/rules.d/</filename> have precedence

over files with the same name in <filename>/lib/udev/rules.d/</filename>. This

can be used to ignore a default rules file if needed.</para>

<para>Every line in the rules file contains at least one key value pair.

There are two kind of keys, match and assignment keys.

If all match keys are matching against its value, the rule gets applied and the

assign keys get the specified value assigned.</para>

<para>A matching rule may specify the name of the device node, add a symlink

pointing to the node, or run a specified program as part of the event handling.

If no matching rule is found, the default device node name is used.</para>

<para>A rule consists of a list of one or more key value pairs separated by

a comma. Each key has a distinct operation, depending on the used operator. Valid

operators are:</para>

<variablelist>

<varlistentry>

<term><option>==</option></term>

<listitem>

<para>Compare for equality.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>!=</option></term>

<listitem>

<para>Compare for inequality.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>=</option></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><option>+=</option></term>

<listitem>

<para>Add the value to a key that holds a list of entries.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>:=</option></term>

<listitem>

<para>Assign a value to a key finally; disallow any later changes,

which may be used to prevent changes by any later rules.</para>

</listitem>

</varlistentry>

</variablelist>

<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>

<varlistentry>

<term><option>ACTION</option></term>

<listitem>

<para>Match the name of the event action.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>DEVPATH</option></term>

<listitem>

<para>Match the devpath of the event device.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>KERNEL</option></term>

<listitem>

<para>Match the name of the event device.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>NAME</option></term>

<listitem>

<para>Match the name of the node or network interface. It can

be used once the NAME key has been set in one of the preceding

rules.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>SYMLINK</option></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.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>SUBSYSTEM</option></term>

<listitem>

<para>Match the subsystem of the event device.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>DRIVER</option></term>

<listitem>

<para>Match the driver name of the event device. Only set for devices

which are bound to a driver at the time the event is generated.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>ATTR{<replaceable>filename</replaceable>}</option></term>

<listitem>

<para>Match sysfs attribute values of the event device. Trailing

whitespace in the attribute values is ignored, if the specified match

value does not contain trailing whitespace itself.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>KERNELS</option></term>

<listitem>

<para>Search the devpath upwards for a matching device name.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>SUBSYSTEMS</option></term>

<listitem>

<para>Search the devpath upwards for a matching device subsystem name.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>DRIVERS</option></term>

<listitem>

<para>Search the devpath upwards for a matching device driver name.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>ATTRS{<replaceable>filename</replaceable>}</option></term>

<listitem>

<para>Search the devpath upwards for a device with matching sysfs attribute values.

If multiple <option>ATTRS</option> matches are specified, all of them

must match on the same device. Trailing whitespace in the attribute values is ignored,

if the specified match value does not contain trailing whitespace itself.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>ENV{<replaceable>key</replaceable>}</option></term>

<listitem>

<para>Match against a device property value.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>TEST{<replaceable>octal mode mask</replaceable>}</option></term>

<listitem>

<para>Test the existence of a file. An octal mode mask can be specified

if needed.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>PROGRAM</option></term>

<listitem>

<para>Execute a program. 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 output printed to

stdout, is available in the RESULT key.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>RESULT</option></term>

<listitem>

<para>Match the returned string of the last PROGRAM call. This key can

be used in the same or in any later rule after a PROGRAM call.</para>

</listitem>

</varlistentry>

</variablelist>

<para>Most of the fields support a shell style pattern matching. The following

pattern characters are supported:</para>

<variablelist>

<varlistentry>

<term><option>*</option></term>

<listitem>

<para>Matches zero, or any number of characters.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>?</option></term>

<listitem>

<para>Matches any single character.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>[]</option></term>

<listitem>

<para>Matches any single character specified within the brackets. For

example, the pattern string 'tty[SR]' would match either 'ttyS' or 'ttyR'.

Ranges are also supported within this match with the '-' character.

For example, to match on the range of all digits, the pattern [0-9] would

be used. If the first character following the '[' is a '!', any characters

not enclosed are matched.</para>

</listitem>

</varlistentry>

</variablelist>

<para>The following keys can get values assigned:</para>

<variablelist>

<varlistentry>

<term><option>NAME</option></term>

<listitem>

<para>The name of the node to be created, or the name the network interface

should be renamed to.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>SYMLINK</option></term>

<listitem>

<para>The name of a symlink targeting the node. Every matching rule will add

this value to the list of symlinks to be created along with the device node.

Multiple symlinks may be specified by separating the names by the space

character.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>OWNER, GROUP, MODE</option></term>

<listitem>

<para>The permissions for the device node. Every specified value overwrites

the compiled-in default value.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>ATTR{<replaceable>key</replaceable>}</option></term>

<listitem>

<para>The value that should be written to a sysfs attribute of the

event device.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>ENV{<replaceable>key</replaceable>}</option></term>

<listitem>

<para>Set a device property value. Property names with a leading '.'

are not stored in the database or exported to external tool or events.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>RUN</option></term>

<listitem>

<para>Add a program to the list of programs to be executed for a specific

device. This can only be used for very short running tasks. Running an

event process for a long period of time may block all further events for

this or a dependent device. Long running tasks need to be immediately

detached from the event process itself. If the option

<option>RUN{<replaceable>fail_event_on_error</replaceable>}</option> is

specified, and the executed program returns non-zero, the event will be

marked as failed for a possible later handling.</para>

<para>If no path is given, the program must be in

<filename>/lib/udev</filename>, otherwise the full path must be

specified.</para>

<para>If the specified string starts with

<option>socket:<replaceable>path</replaceable></option>, all current event

values will be passed to the specified socket, as a message in the same

format the kernel sends an uevent. If the first character of the specified path

is an @ character, an abstract namespace socket is used, instead of an existing

socket file.</para>

<para>Program name and arguments are separated with spaces. To

include spaces in an argument, use single quotes. Please note

that this does not run through a shell.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>LABEL</option></term>

<listitem>

<para>Named label where a GOTO can jump to.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>GOTO</option></term>

<listitem>

<para>Jumps to the next LABEL with a matching name</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>IMPORT{<replaceable>type</replaceable>}</option></term>

<listitem>

<para>Import a set of variables as device properties,

depending on <replaceable>type</replaceable>:</para>

<variablelist>

<varlistentry>

<term><option>program</option></term>

<listitem>

<para>Execute an external program specified as the assigned value and

import its output, which must be in environment key

format. Path specification, command/argument separation,

and quoting work like in <option>RUN</option>.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>file</option></term>

<listitem>

<para>Import a text file specified as the assigned value, which must be in

environment key format.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>db</option></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><option>parent</option></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-style pattern matching used for

comparisons).</para>

</listitem>

</varlistentry>

</variablelist>

<para>If no option is given, udev will choose between <option>program</option>

and <option>file</option> based on the executable bit of the file

permissions.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>WAIT_FOR</option></term>

<listitem>

<para>Wait for a file to become available.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>OPTIONS</option></term>

<listitem>

<para>Rule and device options:</para>

<variablelist>

<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>event_timeout=</option></term>

<listitem>

<para>Number of seconds an event will wait for operations to finish, before it

will terminate itself.</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>watch</option></term>

<listitem>

<para>Watch the device node with inotify, when closed after being opened for

writing, a change uevent will be synthesised.</para>

</listitem>

</varlistentry>

</variablelist>

</listitem>

</varlistentry>

</variablelist>

<para>The <option>NAME</option>, <option>SYMLINK</option>, <option>PROGRAM</option>,

<option>OWNER</option>, <option>GROUP</option>, <option>MODE</option> and <option>RUN</option>

fields support simple printf-like string substitutions. The <option>RUN</option>

format chars gets applied after all rules have been processed, right before the program

is executed. It allows the use of device properties set by earlier matching

rules. For all other fields, substitutions are applied while the individual rule is

being processed. The available substitutions are:</para>

<variablelist>

<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, 'sda3' has

kernel number of '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, follow the chain of parent devices and use the value

of the first attribute that matches.

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 PROGRAM.

A single part of the string, separated by a space character may be selected

by specifying the part number as an attribute: <option>%c{N}</option>.

If the number is followed by the '+' char this part plus all remaining parts

of the result string are substituted: <option>%c{N+}</option></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 node. 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>The current list of symlinks, separated by a space character. The value is

only set if an earlier rule assigned a value, or during a remove events.</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>$tempnode</option>, <option>%N</option></term>

<listitem>

<para>The name of a created temporary device node to provide access to

the device from a external program before the real node is created.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>%%</option></term>

<listitem>

<para>The '%' character itself.</para>

</listitem>

</varlistentry>

<varlistentry>

<term><option>$$</option></term>

<listitem>

<para>The '$' character itself.</para>

</listitem>

</varlistentry>

</variablelist>

</refsect2>

</refsect1>

<refsect1><title>AUTHOR</title>

<para>Written by Greg Kroah-Hartman <email>greg@kroah.com</email> and

Kay Sievers <email>kay.sievers@vrfy.org</email>. With much help from

Dan Stekloff and many others.</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>

</section>

</article>