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| <refentry id="udev"> |
| <refentryinfo> |
| <title>udev</title> |
| <productname>systemd</productname> |
| <authorgroup> |
| <author> |
| <contrib>Developer</contrib> |
| <firstname>Greg</firstname> |
| <surname>Kroah-Hartmann</surname> |
| <email>greg@kroah.com</email> |
| </author> |
| <author> |
| <contrib>Developer</contrib> |
| <firstname>Kay</firstname> |
| <surname>Sievers</surname> |
| <email>kay@vrfy.org</email> |
| </author> |
| </authorgroup> |
| </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 directory <filename>/usr/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 in <filename>/lib</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>/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-value pairs. |
| Each key has a distinct operation, depending on the used operator. Valid |
| operators are:</para> |
| <variablelist> |
| <varlistentry> |
| <term><literal>==</literal></term> |
| <listitem> |
| <para>Compare for equality.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><literal>!=</literal></term> |
| <listitem> |
| <para>Compare for inequality.</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>Assign a value to a key finally; disallow any later changes.</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 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>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. |
| </para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>SUBSYSTEM</varname></term> |
| <listitem> |
| <para>Match the subsystem of the event device.</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>ATTR{<replaceable>filename</replaceable>}</varname></term> |
| <listitem> |
| <para>Match sysfs attribute values of the event device. Trailing |
| whitespace in the attribute values is ignored unless the specified match |
| value itself contains trailing whitespace. |
| </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>SUBSYSTEMS</varname></term> |
| <listitem> |
| <para>Search the devpath upwards for a matching device subsystem name.</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>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. Trailing whitespace in the attribute values is ignored |
| unless the specified match value itself contains trailing whitespace.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>TAGS</varname></term> |
| <listitem> |
| <para>Search the devpath upwards for a device with matching tag.</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>TAG</varname></term> |
| <listitem> |
| <para>Match against a device tag.</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 stdout |
| is available in the RESULT key.</para> |
| <para>This can only be used for very short-running foreground tasks. For details |
| see <varname>RUN</varname>.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>RESULT</varname></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 shell glob pattern matching. The following |
| pattern 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 [0-9] could |
| be used. If the first character following the <literal>[</literal> is a |
| <literal>!</literal>, any characters not enclosed are matched.</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. 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>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>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, say, the PROGRAM 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>Add a program to the list of programs to be executed after processing all the |
| rules for a specific event, depending on <literal>type</literal>:</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 |
| /usr/lib/udev, 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>Starting daemons or other long running processes is not appropriate |
| for udev; the forked processes, detached or not, will be unconditionally |
| killed after the event handling has finished.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LABEL</varname></term> |
| <listitem> |
| <para>A named label to which a GOTO may jump.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>GOTO</varname></term> |
| <listitem> |
| <para>Jumps to the next LABEL 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 <literal>type</literal>:</para> |
| <variablelist> |
| <varlistentry> |
| <term><literal>program</literal></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 <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> |
| </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>event_timeout=</option></term> |
| <listitem> |
| <para>Number of seconds an event waits for operations to finish before |
| giving up and terminating 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>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> |
| </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 KERNELS, SUBSYSTEMS, DRIVERS, or |
| ATTRS 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 PROGRAM. |
| 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> |
| </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> |
| and the local administration directory <filename>/etc/udev/hwdb.d</filename>. |
| 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, files in <filename>/run</filename> take precedence |
| over files with the same name in <filename>/lib</filename>. This 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>/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 indivdually, 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>. |
| During runtime only the binary database is used.</para> |
| </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></para> |
| </refsect1> |
| </refentry> |