hwdb(7) - phpMan

HWDB(7) hwdb HWDB(7)

NAME
hwdb - Hardware Database

DESCRIPTION
The hardware database is a key-value store for associating modalias-like keys to
udev-property-like values. It is used primarily by udev to add the relevant properties to
matching devices, but it can also be queried directly.

HARDWARE DATABASE FILES
The hwdb files are read from the files located in the system hwdb directory
/lib/udev/hwdb.d and the local administration directory /etc/udev/hwdb.d. 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
/etc/ have the highest priority and take precedence over files with the same name in
/lib/. This can be used to override a system-supplied hwdb file with a local file if
needed; a symlink in /etc/ with the same name as a hwdb file in /lib/, pointing to
/dev/null, disables that hwdb file entirely. hwdb files must have the extension .hwdb;
other extensions are ignored.

Each hwdb file contains data records consisting of matches and associated key-value pairs.
Every record in the hwdb starts with one or more match strings, specifying a shell glob to
compare the lookup string against. Multiple match lines are specified in consecutive
lines. Every match line is compared individually, and they are combined by OR. Every match
line must start at the first character of the line.

Match patterns consist of literal characters, and shell-style wildcards:

o Asterisk "*" matches any number of characters

o Question mark "?" matches a single character

o Character list "[chars]" matches one of the characters chars listed between "[" and
"]". A range may be specified as with a dash as "[first-last]". The match may be
inverted with a caret "[^...]".

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 "=". An empty line
signifies the end of a record. Lines beginning with "#" are ignored.

In case multiple records match a given lookup string, the key-value pairs from all records
are combined. If a key is specified multiple times, the value from the record with the
highest priority is used (each key can have only a single value). The priority is higher
when the record is in a file that sorts later lexicographically, and in case of records in
the same file, later records have higher priority.

The content of all hwdb files is read by systemd-hwdb(8) and compiled to a binary database
located at /etc/udev/hwdb.bin, or alternatively /lib/udev/hwdb.bin if you want ship the
compiled database in an immutable image. During runtime, only the binary database is used.

EXAMPLES
Example 1. General syntax of hwdb files

# /lib/udev/hwdb.d/example.hwdb
# Comments can be placed before any records. This is a good spot
# to describe what that file is used for, what kind of properties
# it defines, and the ordering convention.

# A record with three matches and one property
mouse:*:name:*Trackball*:*
mouse:*:name:*trackball*:*
mouse:*:name:*TrackBall*:*
ID_INPUT_TRACKBALL=1

# The rule above could be also be written in a form that
# matches Tb, tb, TB, tB:
mouse:*:name:*[tT]rack[bB]all*:*
ID_INPUT_TRACKBALL=1

# A record with a single match and five properties
mouse:usb:v046dp4041:name:Logitech MX Master:*
MOUSE_DPI=1000@166
MOUSE_WHEEL_CLICK_ANGLE=15
MOUSE_WHEEL_CLICK_ANGLE_HORIZONTAL=26
MOUSE_WHEEL_CLICK_COUNT=24
MOUSE_WHEEL_CLICK_COUNT_HORIZONTAL=14

Example 2. Overriding of properties

# /lib/udev/hwdb.d/60-keyboard.hwdb
evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer*:pn*:*
KEYBOARD_KEY_a1=help
KEYBOARD_KEY_a2=setup
KEYBOARD_KEY_a3=battery

# Match vendor name "Acer" and any product name starting with "X123"
evdev:atkbd:dmi:bvn*:bvr*:bd*:svnAcer:pnX123*:*
KEYBOARD_KEY_a2=wlan

# /etc/udev/hwdb.d/70-keyboard.hwdb
# disable wlan key on all at keyboards
evdev:atkbd:*
KEYBOARD_KEY_a2=reserved
PROPERTY_WITH_SPACES=some string

If the hwdb consists of those two files, a keyboard with the lookup string
"evdev:atkbd:dmi:bvnAcer:bdXXXXX:bd08/05/2010:svnAcer:pnX123" will match all three
records, and end up with the following properties:

KEYBOARD_KEY_a1=help
KEYBOARD_KEY_a2=reserved
KEYBOARD_KEY_a3=battery
PROPERTY_WITH_SPACES=some string