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.

       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.


systemd 229                                                            HWDB(7)
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