dev_mkdb(8) - Manual pages

The dev_mkdb utility creates a db(3) hash access method database in file (/var/run/dev.db by default) which contains the names of all of the character and block special files in directory (/dev by default), using the file type and the st_rdev field as the key.

Keys are a structure containing a mode_t followed by a dev_t, with any padding zero'd out. The former is the type of the file (st_mode & S_IFMT), the latter is the st_rdev field.