hwdb

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 the
hwdb file entirely. hwdb files must have the extension .hwdb; other extensions are
ignored.

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 strings, 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, and they are
combined by OR. Every match line must start at the first character of the line.

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.

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.