.TH UDEV 8 "October 2003" "" "Linux Administrator's Manual" .SH NAME udev \- Linux configurable dynamic device naming support .SH SYNOPSIS .BI udev " hotplug-subsystem" .br .B udev .RI "[-q " query_type " -p " sysfs_path "] [-drVh]" .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 may used as keys 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 its database for the name of the device file to be deleted. .SH "OPTIONS" .B udev normally is called by .B hotplug with the subsystem as argument and various environment variables set. .br It may also called with the following options: .TP .B -V Print the version information. .TP .B -r Print the the .B udev_root directory. When used in conjunction with a query for the node name, the .B udev_root will be prepended. .TP .BI -q " query_type" Query the database for specified value of a created device node. Valid types are: .BR name ", " symlink ", " owner " , " group " or " path. .TP .BI -p " sysfs_path" Specify the sysfs path of the device to query. .TP .BI -n " name" Specify the name of the node for the device to query. .TP .B -d Dump the whole database. .TP .B -h Print help text. .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 defines the mapping between device attributes and the device file name. One ore 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 for the device node. One or more optional symlinks targeting the node may be specified. .br If no matching rule is found, the default kernel device name is used. .P The line format is: .sp .I key,[key,...] name [, symlink] .sp where keys are: .TP .B BUS Match the bus type of the device. (The sysfs device bus must be able to be determined by a "device" symlink.) .TP .B KERNEL Match the kernel device name. .TP .B ID Match the device number on the bus, like PCI bus id. .TP .B PLACE Match the topological position on bus, like physical port of USB device .TP .BI SYSFS_ filename Match sysfs device attribute like label, vendor, 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. .TP .B PROGRAM Call external program. This key is valid if the program returns successful. The string returned by the program may additionally matched with the .B RESULT key. .TP .B RESULT Match the returned string of the last .B PROGRAM call. This key may used in any following rule after a .B PROGRAM call. .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 .B PROGRAM returned string. (This does not work within the .B PROGRAM field for the obvious reason.) .TP .B %% The '%' char itself. .P .RI "A sample " udev.rules " might look like this:" .sp .nf # if /sbin/scsi_id returns "OEM 0815" device will be called disk1 BUS="scsi", PROGRAM="/sbin/scsi_id", RESULT="OEM 0815", NAME="disk1" # USB printer to be called lp_color BUS="usb", SYSFS_serial="W09090207101241330", NAME="lp_color" # SCSI disk with a specific vendor and model number is to be called boot BUS="scsi", SYSFS_vendor="IBM", SYSFS_model="ST336", NAME="boot%n" # sound card with PCI bus id 00:0b.0 to be called dsp BUS="pci", ID="00:0b.0", NAME="dsp" # USB mouse at third port of the second hub to be called mouse1 BUS="usb", PLACE="2.3", NAME="mouse1" # ttyUSB1 should always be called pda with two additional symlinks KERNEL="ttyUSB1", NAME="pda", SYMLINK="palmtop handheld" # multiple USB webcams with symlinks to be called webcam0, webcam1, ... 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.