1 .TH UDEV 8 "October 2003" "" "Linux Administrator's Manual"
3 udev \- Linux configurable dynamic device naming support
5 .BI udev " hotplug-subsystem"
7 The environment must provide the following variables:
11 signifies the connection or disconnection of a device.
14 The sysfs devpath of the device without the mountpoint but a leading slash.
16 Additional optional environment variables:
19 Overrides the default location of the
24 The default behavior of
26 is to wait until all the sysfs files of the device chain are populated. If set,
28 will continue, regardless of the state of the device representation.
31 The default behavior of
33 is to execute programs in the
35 directory after device handling. If set,
40 provides a dynamic device directory containing only the files for actually
41 present devices. It creates or removes device node files usually located in
42 the /dev directory, or it renames network interfaces.
50 is executed if a kernel device is added or removed from the system.
53 reads the sysfs directory of the given device to collect device attributes
54 like label, serial number or bus device number.
55 These attributes may be used as keys to determine a
56 unique name for the device.
58 maintains a database for devices present on the system.
62 queries its database for the name of the device file to be deleted.
66 configuration files consist of a set of lines of text. All empty
67 lines and lines beginning with a '#' will be ignored.
71 expects its main configuration file at
72 .IR /etc/udev/udev.conf .
73 The file consists of a set of variables and values allowing the user to
74 override default udev values. The following variables can be overridden
78 Indicates where to place the device nodes in the filesystem. The default
83 The name and location of the udev database. The default value is
84 .IR @udevdir@/.udev.tdb .
87 The name of the udev rules file or directory to look for files with the suffix
89 All rule files are read in lexical order. The default value is
90 .IR /etc/udev/rules.d/ .
93 The name of the udev permission file or directory to look for files with the
96 All permission files are read in lexical order. The default value is
97 .IR /etc/udev/permissions.d/ .
100 The switch, if udev logs some information for every device handled.
105 The default mode for all nodes not explicitely matching in the permissions
106 file. The default value is
110 The default owner for all nodes not explicitely matching in the permissions
111 file. The default value is
115 The default group for all nodes not explicitely matching in the permissions
116 file. The default value is
120 .RI "A sample " udev.conf " might look like this:
123 # udev_root - where to place the device nodes in the filesystem
126 # udev_db - The name and location of the udev database
127 udev_db="/udev/.udev.tdb"
129 # udev_rules - The name of the udev rules file or directory to look
130 for files with the suffix .rules
131 udev_rules="/etc/udev/rules.d/"
133 # udev_permissions - The name of the udev permission file or directory
134 to look for files with the suffix .permissions
135 udev_permissions="/etc/udev/udev.permissions"
137 # udev_log - set to "yes" if you want logging, else "no"
140 # default_mode - set the default mode for all nodes not
141 # explicitely matching in the permissions file
144 # default_owner - set the default owner for all nodes not
145 # explicitely matching in the permissions file
148 # default_group - set the default group for all nodes not
149 # explicitely matching in the permissions file
153 The rules for device naming, are read from the files located in the
154 .I /etc/udev/rules.d/
155 directory, or at the location specified by the
158 .I /etc/udev/udev.conf
161 Every line in the rules file defines the mapping between device attributes
162 and the device name. One or more keys are specified to match a rule with
163 the current device. If all keys are matching, the rule will be applied and
164 the name is used to name the device file or the network interface.
166 If no matching rule is found, the default kernel device name is used.
168 Every rule consists of a list of comma separated fields:
170 .IR "key " ,[ "key " ,...] " name " [, " symlink" ]
175 Match the bus type of the device.
176 (The sysfs device bus must be able to be determined by a "device" symlink.)
179 Match the kernel device name.
182 Match the device number on the bus, like PCI bus id.
185 Match the topological position on bus, like physical port of USB device
187 .BI SYSFS{ filename }
188 Match sysfs device attribute like label, vendor, USB serial number, SCSI UUID
189 or file system label. Up to 5 different sysfs files can be checked, with
190 all of the values being required to match the rule.
192 Trailing whitespace characters in the sysfs attribute value are ignored, if
193 the key doesn't have any trailing whitespace characters by itself.
196 Call external program. This key is valid if the program returns successful.
197 The environment variables of
199 are also available for the program.
201 The string returned by the program may be additionally matched with the
206 Match the returned string of the last
208 call. This key may be used in any following rule after a
213 The name of the node to be created, or the name, the network interface
214 should be renamed to.
216 If given with the attribute
217 .BR NAME{ all_partitions }
218 it will create all 15 partitions of a blockdevice.
219 This may be useful for removable media devices.
222 The name of a symlink targeting the node. Multiple symlinks may be
223 specified by separating the names by the space character.
225 If both the name and the symlink fields are omitted or its
226 values empty, the device will be ignored and no node will be created.
228 If only the symlink field is given and the name field is omitted,
229 the rule will not be applied immediatly, but the symlink field is added
230 to the symlink list of the rule which will create the node.
231 This makes it possible to specify additional symlinks in a possibly
232 separate rules file, while the device nodes are maintained by the
233 distribution provided rules file.
235 .B OWNER, GROUP, MODE
236 The permissions for this device. Every specified value overwrites the value
237 given in the permissions file.
239 .RB "The " NAME " ," SYMLINK " and " PROGRAM
240 fields support simple printf-like string substitution:
243 The "kernel number" of the device.
244 For example, 'sda3' has a "kernel number" of '3'.
247 The "kernel name" for the device.
250 The kernel major number for the device.
253 The kernel minor number for the device.
256 The bus id for the device.
259 The string returned from the execution of
261 (This does not work within the
263 field for the obvious reason.)
265 A single part of the string, separated by a space character
266 may be selected by specifying the part number as an attribute:
268 If the number is followed by the + char this part plus
269 all remaining parts of the result string are substituted:
273 The content of a sysfs attribute.
276 If a device node already exists with the name, the smallest positive
277 decimal integer N is substituted such that the resulting name doesn't
278 match an existing device node. Otherwise nothing is substituted. This
279 can be used to create compatibility symlinks and enumerate devices of
280 the same type originating from different kernel subsystems.
283 The '%' character itself.
285 The count of charcters to insert may be limited by specifying
286 the format length value. For example, '%3s{file}' will only insert
287 the first three characters of the sysfs attribute.
289 .RI "A sample " udev.rules " might look like this:"
292 # if /sbin/scsi_id returns "OEM 0815" device will be called disk1
293 BUS="scsi", PROGRAM="/sbin/scsi_id", RESULT="OEM 0815", NAME="disk1"
295 # USB printer to be called lp_color
296 BUS="usb", SYSFS{serial}="W09090207101241330", NAME="lp_color"
298 # SCSI disk with a specific vendor and model number will be called boot
299 BUS="scsi", SYSFS{vendor}="IBM", SYSFS{model}="ST336", NAME="boot%n"
301 # sound card with PCI bus id 00:0b.0 to be called dsp
302 BUS="pci", ID="00:0b.0", NAME="dsp"
304 # USB mouse at third port of the second hub to be called mouse1
305 BUS="usb", PLACE="2.3", NAME="mouse1"
307 # ttyUSB1 should always be called pda with two additional symlinks
308 KERNEL="ttyUSB1", NAME="pda", SYMLINK="palmtop handheld"
310 # multiple USB webcams with symlinks to be called webcam0, webcam1, ...
311 BUS="usb", SYSFS{model}="XV3", NAME="video%n", SYMLINK="webcam%n"
313 # grouping of optical drives from multiple kernel subsystems
314 KERNEL="sr*", NAME="%k", SYMLINK="cdrom%e"
315 KERNEL="scd*", NAME="%k", SYMLINK="cdrom%e"
316 KERNEL="pcd*", NAME="%k", SYMLINK="cdrom%e"
317 KERNEL="hd[a-z]", PROGRAM="/bin/cat /proc/ide/%k/media", RESULT="cdrom",
318 NAME="%k", SYMLINK="cdrom%e"
322 The permissions and ownership of the created device file is read from
323 the files located in the
324 .I /etc/udev/permissions.d/
325 directory, or at the location specified by the
328 .I /etc/udev/udev.conf
331 Every line lists a device name followed by owner, group and permission
332 mode. All values are separated by colons. The name field may contain a
333 pattern to apply the values to a whole class of devices.
335 .RI "A sample " udev.permissions " might look like this:"
338 #name:user:group:mode
339 input/*:root:root:644
341 video*:root:video:0660
347 can be used instead of a specific username. In that case, udev will determine
348 the current local user at the time of device node creation and substitute
349 that username as the owner of the new device node. This is useful, for
350 example, to let hot-plugged devices, such as cameras, be owned by the user at
351 the current console. Note that if no user is currently logged in, or if udev
352 otherwise fails to determine a current user, the
354 value is used in lieu.
356 A number of different fields in the above configuration files support a simple
357 form of shell style pattern matching. It supports the following pattern characters:
360 Matches zero, one, or more characters.
363 Matches any single character, but does not match zero characters.
366 Matches any single character specified within the brackets. For example, the
367 pattern string "tty[SR]" would match either "ttyS" or "ttyR". Ranges are also
368 supported within this match with the '\-' character. For example, to match on
369 the range of all digits, the pattern [0\-9] would be used. If the first character
370 following the '[' is a '!', any character not enclosed is matched.
372 After device node creation, removal, or network device renaming,
374 executes the programs in the directory tree under
376 The name of a program must end with
378 suffix, to be recognized.
380 In addition to the hotplug environment variables,
382 is exported to make the name of the created node, or the name the network
383 device is renamed to, available to the executed program. The programs in every
384 directory are sorted in lexical order, while the directories are searched in
388 /etc/dev.d/$(DEVNAME)/*.dev
389 /etc/dev.d/$(SUBSYSTEM)/*.dev
390 /etc/dev.d/default/*.dev
394 /sbin/udev udev program
395 /etc/udev/* udev config files
396 /etc/hotplug.d/default/udev.hotplug hotplug symlink to udev program
397 /etc/dev.d/* programs invoked by udev
406 .I http://linux\-hotplug.sourceforge.net/
410 was developed by Greg Kroah-Hartman <greg@kroah.com> with much help from
411 Dan Stekloff <dsteklof@us.ibm.com>, Kay Sievers <kay.sievers@vrfy.org>, and