+All
+.B udev
+configuration files consist of a set of lines of text. All empty
+lines or lines beginning with '#' will be ignored.
+.P
+.B udev
+expects its main configuration file at
+.IR /etc/udev/udev.conf .
+The file consists of a set of variables and values allowing the user to
+override default udev values. The following variables can be overridden
+in this file:
+.TP
+.B udev_root
+Indicates where to place the device nodes in the filesystem. The default
+value is
+.IR @udevdir@/ .
+.TP
+.B udev_db
+The name and location of the udev database. The default value is
+.IR @udevdir@/.udevdb .
+.TP
+.B udev_rules
+The name of the udev rules file or directory to look for files with the suffix
+.IR .rules .
+All rule files are read in lexical order. The default value is
+.IR /etc/udev/rules.d/ .
+.TP
+.B udev_log
+The logging priority which can be set to
+.IR "err " , "info "
+or the corresponding numerical
+.BR syslog (3)
+value.
+The default value is
+.IR err .
+.P
+.RI "A sample " udev.conf " file might look like this:
+.sp
+.nf
+# Where in the filesystem to place the device nodes
+udev_root="@udevdir@"
+
+# The name and location of the udev database.
+udev_db="@udevdir@/.udevdb"
+
+# The name and location of the udev rules file(s).
+udev_rules="@configdir@/rules.d"
+
+# The syslog(3) priority: "err", "info", or the numerical value.
+udev_log="err"
+.fi
+.P
+The rules for device naming are read from the files located in the
+.I /etc/udev/rules.d/
+directory, or at the location specified by the
+.I udev_rules
+value in the
+.I /etc/udev/udev.conf
+file.
+.br
+Every line in the rules file defines the mapping between device attributes
+and the device name. One or more keys are specified to match a rule with
+the current device. If all keys are matching, the rule will be applied and
+the name is used to name the device file or the network interface.