+.RI "A sample " udev.conf " might look like this:
+.sp
+.nf
+# udev_root - where in the filesystem to place the device nodes
+udev_root="/udev/"
+
+# udev_db - The name and location of the udev database.
+udev_db="/udev/.udev.tdb"
+
+# udev_rules - The name and location of the udev rules file
+udev_rules="/etc/udev/udev.rules"
+
+# udev_permissions - The name and location of the udev permission file
+udev_permissions="/etc/udev/udev.permissions"
+
+# default_mode - set the default mode for all nodes that have no
+# explicit match in the permissions file
+default_mode="0666"
+.fi
+.P
+The rules for udev to use when naming devices may specified at
+.I /etc/udev/udev.rules
+or specified by the
+.I udev_rules
+value in the
+.I /etc/udev/udev.conf
+file.
+.P
+Every line in the rules file define the mapping between device attributes and
+the device file name. It starts with a keyword defining the method used to
+match, followed by one ore more keys to compare and the filename for the
+device. One ore more optional symlinks targeting the node may be specified.
+.br
+If no matching configuration is found, the default kernel device name
+is used.
+.P
+The line format is:
+.sp
+.I method, key,[key,...] name [, symlink]
+.sp
+where valid methods with corresponding keys are:
+.TP
+.B CALLOUT
+calling external program, that returns a string to match. The
+.B BUS
+key is optional, but if specified, the sysfs device bus must be able to be
+determined by a "device" symlink.
+.br
+.RB "keys: " BUS ", " PROGRAM ", " ID