1 .TH UDEV 8 "October 2003" "" "Linux Administrator's Manual"
3 udev \- Linux configurable dynamic device naming support
5 .BI udev " hotplug-subsystem"
8 provides a dynamic device directory containing only the files for actually
9 present devices. It creates or removes device node files usually located in
10 the /dev directory, or it renames network interfaces.
17 is executed if a kernel device is added or removed from the system.
20 reads the sysfs directory of the given device to collect device attributes
21 like label, serial number or bus device number.
22 These attributes may be used as keys to determine a
23 unique name for the device.
25 maintains a database for devices present on the system.
29 queries its database for the name of the device file to be deleted.
33 configuration files consist of a set of lines of text. All empty
34 lines or lines beginning with '#' will be ignored.
37 expects its main configuration file at
38 .IR /etc/udev/udev.conf .
39 The file consists of a set of variables and values allowing the user to
40 override default udev values. The following variables can be overridden
44 Indicates where to place the device nodes in the filesystem. The default
49 The name and location of the udev database. The default value is
50 .IR @udevdir@/.udevdb .
53 The name of the udev rules file or directory to look for files with the suffix
55 All rule files are read in lexical order. The default value is
56 .IR /etc/udev/rules.d/ .
59 The switch to enable/disable logging of udev information
64 The default mode for all nodes where no explicit value is given by a rule.
69 The default owner for all nodes where no explicit value is given by a rule.
74 The default group for all nodes where no explicitly value is given by a rule.
79 .RI "A sample " udev.conf " file might look like this:
82 # udev_root - where to place the device nodes in the filesystem
85 # udev_db - The name and location of the udev database
86 udev_db="/udev/.udevdb"
88 # udev_rules - The name of the udev rules file or directory to look
89 for files with the suffix .rules
90 udev_rules="/etc/udev/rules.d/"
92 # udev_log - set to "yes" if you want logging, else "no"
95 # default_mode - set the default mode for all nodes that have no
96 # permissions specified
99 # default_owner - set the default owner for all nodes that have no
100 # permissions specified
103 # default_group - set the default group for all nodes that have no
104 # permissions specified
108 The rules for device naming are read from the files located in the
109 .I /etc/udev/rules.d/
110 directory, or at the location specified by the
113 .I /etc/udev/udev.conf
116 Every line in the rules file defines the mapping between device attributes
117 and the device name. One or more keys are specified to match a rule with
118 the current device. If all keys are matching, the rule will be applied and
119 the name is used to name the device file or the network interface.
121 If no matching rule is found, the default kernel device name is used.
123 Every rule consists of a list of comma separated fields:
125 .IR "key " ,[ "key " ,...] " name " [, " symlink" ]
130 Match the bus type of the device.
131 (The sysfs device bus must be able to be determined by a "device" symlink.)
134 Match the kernel device name.
137 Match the kernel subsystem name.
140 Match the kernel driver name.
143 Match the device number on the bus, like PCI bus id.
146 Match the topological position on bus, like physical port of USB device
148 .BI SYSFS{ filename }
149 Match sysfs device attribute like label, vendor, USB serial number, SCSI UUID
150 or file system label. Up to 5 different sysfs files can be checked, with
151 all of the values being required to match the rule.
153 Trailing whitespace characters in the sysfs attribute value are ignored, if
154 the key doesn't have any trailing whitespace characters by itself.
157 Call external program. This key is valid if the program returns successful.
158 The environment variables of
160 are also available for the program.
162 The string returned by the program may be additionally matched with the
167 Match the returned string of the last
169 call. This key may be used in any following rule after a
174 The name of the node to be created, or the name, the network interface
175 should be renamed to.
177 If given with the attribute
178 .BR NAME{ all_partitions }
180 will create device nodes for all 15 partitions of a blockdevice.
181 This may be useful for removable media devices.
183 If given with the attribute
184 .BR NAME{ ignore_remove }
186 will ignore any later remove event for this device.
187 This may be useful as a workaround for broken device drivers.
189 Multiple attributes may be separated by comma.
192 The name of a symlink targeting the node. Multiple symlinks may be
193 specified by separating the names by the space character.
195 If both the name and the symlink fields are omitted or its
196 values are empty, the device will be ignored and no node will be created.
198 If only the symlink field is given and the name field is omitted,
199 the rule will not be applied immediately, but the symlink field is added
200 to the symlink list of the rule which will create the node.
201 This makes it possible to specify additional symlinks in a possibly
202 separate rules file, while the device nodes are maintained by the
203 distribution provided rules file.
205 .B OWNER, GROUP, MODE
206 The permissions for the device node. Every specified value overwrites the
207 default value specified in the config file.
209 .RB "The " NAME ", " SYMLINK ", " PROGRAM ", " OWNER " and " GROUP
210 fields support simple printf-like string substitutions:
213 The "kernel number" of the device.
214 For example, 'sda3' has a "kernel number" of '3'.
217 The "kernel name" for the device.
220 The kernel major number for the device.
223 The kernel minor number for the device.
226 The bus id for the device.
229 The string returned by the external program, specified in
231 (This does not work within the
233 field for the obvious reason.)
235 A single part of the string, separated by a space character
236 may be selected by specifying the part number as an attribute:
238 If the number is followed by the + char this part plus
239 all remaining parts of the result string are substituted:
243 The content of a sysfs attribute.
246 If a device node already exists with the name, the smallest positive
247 decimal integer N is substituted such that the resulting name doesn't
248 match an existing device node. Otherwise nothing is substituted. This
249 can be used to create compatibility symlinks and enumerate devices of
250 the same type originating from different kernel subsystems.
253 The '%' character itself.
255 The count of charcters to insert may be limited by specifying
256 the format length value. For example, '%3s{file}' will only insert
257 the first three characters of the sysfs attribute.
259 .RI "A sample " udev.rules " file might look like this:"
262 # if /sbin/scsi_id returns "OEM 0815", the device will be called disk1
263 BUS="scsi", PROGRAM="/sbin/scsi_id", RESULT="OEM 0815", NAME="disk1"
265 # USB printer to be called lp_color
266 BUS="usb", SYSFS{serial}="W09090207101241330", NAME="lp_color"
268 # SCSI disk with a specific vendor and model number will be called boot
269 BUS="scsi", SYSFS{vendor}="IBM", SYSFS{model}="ST336", NAME="boot%n"
271 # sound card with PCI bus id 00:0b.0 to be called dsp
272 BUS="pci", ID="00:0b.0", NAME="dsp"
274 # USB mouse at third port of the second hub to be called mouse1
275 BUS="usb", PLACE="2.3", NAME="mouse1"
277 # ttyUSB1 should always be called pda with two additional symlinks
278 KERNEL="ttyUSB1", NAME="pda", SYMLINK="palmtop handheld"
280 # multiple USB webcams with symlinks to be called webcam0, webcam1, ...
281 BUS="usb", SYSFS{model}="XV3", NAME="video%n", SYMLINK="webcam%n"
283 # grouping of optical drives from multiple kernel subsystems
284 KERNEL="sr*", NAME="%k", SYMLINK="cdrom%e"
285 KERNEL="scd*", NAME="%k", SYMLINK="cdrom%e"
286 KERNEL="pcd*", NAME="%k", SYMLINK="cdrom%e"
287 KERNEL="hd[a-z]", PROGRAM="/bin/cat /proc/ide/%k/media", RESULT="cdrom",
288 NAME="%k", SYMLINK="cdrom%e"
291 A number of different fields in the above configuration files support a simple
292 form of shell style pattern matching. It supports the following pattern characters:
295 Matches zero, one, or more characters.
298 Matches any single character, but does not match zero characters.
301 Matches any single character specified within the brackets. For example, the
302 pattern string "tty[SR]" would match either "ttyS" or "ttyR". Ranges are also
303 supported within this match with the '\-' character. For example, to match on
304 the range of all digits, the pattern [0\-9] would be used. If the first character
305 following the '[' is a '!', any characters not enclosed are matched.
307 After device node creation, removal, or network device renaming,
309 executes the programs located in the directory tree under
311 The name of a program must have the suffix
315 In addition to the hotplug environment variables,
317 is set if udev is configured to use the syslog facility. Executed programs may
318 want to follow that setting.
320 is exported to make the name of the created node, or the name the network
321 device is renamed to, available to the executed program. The programs in every
322 directory are sorted in lexical order, while the directories are searched in
326 /etc/dev.d/$(DEVNAME)/*.dev
327 /etc/dev.d/$(SUBSYSTEM)/*.dev
328 /etc/dev.d/default/*.dev
332 The following variables are read from the environment:
335 .IR add " or " remove
336 signifies the addition or the removal of a device.
339 The sysfs devpath of the device without the mountpoint but a leading slash.
342 The subsystem the device belongs to. Alternatively the subsystem may
343 be passed as the first argument.
346 Overrides the default location of the
351 The default behavior of
353 is to execute programs in the
355 directory after device handling. If set,
360 /sbin/udev udev program
361 /etc/udev/* udev config files
362 /etc/hotplug.d/default/udev.hotplug hotplug symlink to udev program
363 /etc/dev.d/* programs invoked by udev
372 .I http://linux\-hotplug.sourceforge.net/
373 .I http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev.html
377 was developed by Greg Kroah-Hartman <greg@kroah.com> with much help from
378 Dan Stekloff <dsteklof@us.ibm.com>, Kay Sievers <kay.sievers@vrfy.org>, and