.TH UDEV 8 "October 2003" "" "Linux Administrator's Manual" .SH NAME udev \- Linux configurable dynamic device naming support .SH SYNOPSIS .BI udev " hotplug-subsystem" .SH "DESCRIPTION" .B udev creates or removes device node files usually located in the /dev directory. Its goal is to provide a dynamic device directory that contains only the files for devices that are actually present. .P As part of the .B hotplug subsystem, .B udev is executed if a kernel device is added or removed from the system. On device creation, .B udev reads the sysfs directory of the given device to collect device attributes like label, serial number or bus device number. These attributes are treated as a key to determine a unique name for device file creation. .B udev maintains a database for devices present on the system. .br On device removal, .B udev queries the internal database for the name of the device file to be deleted. .SH "CONFIGURATION" All .B udev configuration files consist of a set of lines of text. All empty lines, and lines beginning with a '#' will be ignored. .P .B udev expects its main configuration file at .I /etc/udev/udev.conf. The file consists of a set of variables and values that allow the user to override default udev values. The current set of variables that can be overridden in this file is: .TP .B udev_root This is the where in the filesystem to place the device nodes. The default value for this is .I /udev/ .TP .B udev_db The name and location of the udev database. The default value for this is .I /udev/.udev.tdb .TP .B udev_rules This is the location of the udev rules file. The default value for this is .I /etc/udev/udev.rules .TP .B udev_permissions This is the location of the udev permission file. The default value for this is .I /etc/udev/udev.permissions .TP .B default_mode This is the default mode for all nodes that have no explicit match in the permissions file. The default value for this is .I 0666 .br .P .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 .TP .B LABEL device label or serial number, like USB serial number, SCSI UUID or file system label. Up to 5 different sysfs files can be checked, with all of the values being required in order to match the rule. The .B BUS key is optional, but if specified, the sysfs device bus must be able to be detemined by a "device" symlink. .br .RB "keys: " BUS ", " SYSFS_ .TP .B NUMBER device number on the bus, like PCI bus id .br .RB "keys: " BUS ", " ID .TP .B TOPOLOGY device position on bus, like physical port of USB device .br .RB "keys: " BUS ", " PLACE .TP .B REPLACE string replacement of the kernel device name .br .RB "key: " KERNEL .P The methods are applied in the following order: .BR CALLOUT ", " LABEL ", " NUMBER ", " TOPOLOGY ", " REPLACE "." .P .RB "The " NAME " ," SYMLINK " and " PROGRAM fields support simple printf-like string substitution: .TP .B %n The "kernel number" of the device. for example, 'sda3' has a "kernel number" of '3' .TP .B %k The "kernel name" for the device. .TP .B %M The kernel major number for the device. .TP .B %m The kernel minor number for the device. .TP .B %b The bus id for the device. .TP .B %c The CALLOUT program returned string. (This does not work within the PROGRAM field for the obvious reason.) .TP .B %D Use the devfs style disk name for this device. For partitions, this will result in 'part%n' If this is not a partition, it will result in 'disc'. .P .RI "A sample " udev.rules " might look like this:" .sp .nf # if /sbin/scsi_id returns "OEM 0815" device will be called disk1 CALLOUT, BUS="scsi", PROGRAM="/sbin/scsi_id", ID="OEM 0815", NAME="disk1" # USB printer to be called lp_color LABEL, BUS="usb", SYSFS_serial="W09090207101241330", NAME="lp_color" # SCSI disk with a specific vendor and model number is to be called boot LABEL, BUS="scsi", SYSFS_vendor="IBM", SYSFS_model="ST336", NAME="boot%n" # sound card with PCI bus id 00:0b.0 to be called dsp NUMBER, BUS="pci", ID="00:0b.0", NAME="dsp" # USB mouse at third port of the second hub to be called mouse1 TOPOLOGY, BUS="usb", PLACE="2.3", NAME="mouse1" # ttyUSB1 should always be called pda with two additional symlinks REPLACE, KERNEL="ttyUSB1", NAME="pda", SYMLINK="palmtop handheld" # multiple USB webcams with symlinks to be called webcam0, webcam1, ... LABEL, BUS="usb", SYSFS_model="XV3", NAME="video%n", SYMLINK="webcam%n" .fi .P Permissions and ownership for the created device files may specified at .I /etc/udev/udev.permissions or specified by the .I udev_permission value in the .I /etc/udev/udev.conf file. .br Every line lists a device name followed by owner, group and permission mode. All values are separated by colons. The name field may contain a pattern to apply the values to a whole class of devices. .br If .B udev was built using klibc or is used before the user database is accessible (e.g. .BR initrd "(4)), only numeric owner and group values may be used." .sp .RI "A sample " udev.permissions " might look like this:" .sp .nf #name:user:group:mode input/*:root:root:644 ttyUSB1:0:8:0660 video*:root:video:0660 dsp1:::0666 .fi .P A number of different fields in the above configuration files support a simple form of shell style pattern matching. It supports the following pattern characters: .TP .B * Matches zero, one, or more characters. .TP .B ? Matches any single character, but does not match zero characters. .TP .B [ ] Matches any single character specified within the brackets. For example, the pattern string "tty[SR]" would match either "ttyS" or "ttyR". Ranges are also supported within this match with the '-' character. For example, to match on the range of all digits, the pattern [0-9] would be used. If the first character following the '[' is a '!' then any character not enclosed is matched. .SH "FILES" .nf /sbin/udev udev program /etc/udev/* udev config files /etc/hotplug.d/default/udev.hotplug hotplug symlink to udev program .fi .LP .SH "SEE ALSO" .BR hotplug (8) .PP The .I http://linux-hotplug.sourceforge.net/ web site. .SH AUTHORS .B udev was developed by Greg Kroah-Hartman with much help from Dan Stekloff , Kay Sievers , and many others.