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
63 .RI "A sample " udev.conf " file might look like this:
66 # udev_root - where to place the device nodes in the filesystem
69 # udev_db - The name and location of the udev database
70 udev_db="/udev/.udevdb"
72 # udev_rules - The name of the udev rules file or directory to look
73 for files with the suffix .rules
74 udev_rules="/etc/udev/rules.d/"
76 # udev_log - set to "yes" if you want logging, else "no"
80 The rules for device naming are read from the files located in the
82 directory, or at the location specified by the
85 .I /etc/udev/udev.conf
88 Every line in the rules file defines the mapping between device attributes
89 and the device name. One or more keys are specified to match a rule with
90 the current device. If all keys are matching, the rule will be applied and
91 the name is used to name the device file or the network interface.
93 If no matching rule is found, the default kernel device name is used.
95 Every rule consists of a list of comma separated fields:
97 .IR "key " ,[ "key " ,...] " name " [, " symlink" ]
102 Match the bus type of the device.
103 (The sysfs device bus must be able to be determined by a "device" symlink.)
106 Match the kernel device name.
109 Match the kernel subsystem name.
112 Match the kernel driver name.
115 Match the device number on the bus, like PCI bus id.
118 Match the topological position on bus, like physical port of USB device
120 .BI SYSFS{ filename }
121 Match sysfs device attribute like label, vendor, USB serial number, SCSI UUID
122 or file system label. Up to 5 different sysfs files can be checked, with
123 all of the values being required to match the rule.
125 Trailing whitespace characters in the sysfs attribute value are ignored, if
126 the key doesn't have any trailing whitespace characters by itself.
129 Call external program. This key is valid if the program returns successful.
130 The environment variables of
132 are also available for the program.
134 The string returned by the program may be additionally matched with the
139 Match the returned string of the last
141 call. This key may be used in any following rule after a
146 The name of the node to be created, or the name, the network interface
147 should be renamed to.
149 If given with the attribute
150 .BR NAME{ all_partitions }
152 will create device nodes for all 15 partitions of a blockdevice.
153 This may be useful for removable media devices.
155 If given with the attribute
156 .BR NAME{ ignore_remove }
158 will ignore any later remove event for this device.
159 This may be useful as a workaround for broken device drivers.
161 Multiple attributes may be separated by comma.
164 The name of a symlink targeting the node. Multiple symlinks may be
165 specified by separating the names by the space character.
167 If both the name and the symlink fields are omitted or its
168 values are empty, the device will be ignored and no node will be created.
170 If only the symlink field is given and the name field is omitted,
171 the rule will not be applied immediately, but the symlink field is added
172 to the symlink list of the rule which will create the node.
173 This makes it possible to specify additional symlinks in a possibly
174 separate rules file, while the device nodes are maintained by the
175 distribution provided rules file.
177 .B OWNER, GROUP, MODE
178 The permissions for the device node. Every specified value overwrites the
179 compiled-in default value.
181 .RB "The " NAME ", " SYMLINK ", " PROGRAM ", " OWNER " and " GROUP
182 fields support simple printf-like string substitutions:
185 The "kernel number" of the device.
186 For example, 'sda3' has a "kernel number" of '3'.
189 The "kernel name" for the device.
192 The devpath for the device.
195 The kernel major number for the device.
198 The kernel minor number for the device.
201 The bus id for the device.
204 The string returned by the external program, specified in
206 (This does not work within the
208 field for the obvious reason.)
210 A single part of the string, separated by a space character
211 may be selected by specifying the part number as an attribute:
213 If the number is followed by the + char this part plus
214 all remaining parts of the result string are substituted:
218 The name of a created temporary device node to provide access to the
219 device from a external program.
222 The content of a sysfs attribute.
225 If a device node already exists with the name, the smallest positive
226 decimal integer N is substituted such that the resulting name doesn't
227 match an existing device node. Otherwise nothing is substituted. This
228 can be used to create compatibility symlinks and enumerate devices of
229 the same type originating from different kernel subsystems.
232 The '%' character itself.
234 The count of charcters to insert may be limited by specifying
235 the format length value. For example, '%3s{file}' will only insert
236 the first three characters of the sysfs attribute.
238 .RI "A sample " udev.rules " file might look like this:"
241 # if /sbin/scsi_id returns "OEM 0815", the device will be called disk1
242 BUS="scsi", PROGRAM="/sbin/scsi_id", RESULT="OEM 0815", NAME="disk1"
244 # USB printer to be called lp_color
245 BUS="usb", SYSFS{serial}="W09090207101241330", NAME="lp_color"
247 # SCSI disk with a specific vendor and model number will be called boot
248 BUS="scsi", SYSFS{vendor}="IBM", SYSFS{model}="ST336", NAME="boot%n"
250 # sound card with PCI bus id 00:0b.0 to be called dsp
251 BUS="pci", ID="00:0b.0", NAME="dsp"
253 # USB mouse at third port of the second hub to be called mouse1
254 BUS="usb", PLACE="2.3", NAME="mouse1"
256 # ttyUSB1 should always be called pda with two additional symlinks
257 KERNEL="ttyUSB1", NAME="pda", SYMLINK="palmtop handheld"
259 # multiple USB webcams with symlinks to be called webcam0, webcam1, ...
260 BUS="usb", SYSFS{model}="XV3", NAME="video%n", SYMLINK="webcam%n"
262 # grouping of optical drives from multiple kernel subsystems
263 KERNEL="sr*", NAME="%k", SYMLINK="cdrom%e"
264 KERNEL="scd*", NAME="%k", SYMLINK="cdrom%e"
265 KERNEL="pcd*", NAME="%k", SYMLINK="cdrom%e"
266 KERNEL="hd[a-z]", PROGRAM="/bin/cat /proc/ide/%k/media", RESULT="cdrom",
267 NAME="%k", SYMLINK="cdrom%e"
270 A number of different fields in the above configuration files support a simple
271 form of shell style pattern matching. It supports the following pattern characters:
274 Matches zero, one, or more characters.
277 Matches any single character, but does not match zero characters.
280 Matches any single character specified within the brackets. For example, the
281 pattern string "tty[SR]" would match either "ttyS" or "ttyR". Ranges are also
282 supported within this match with the '\-' character. For example, to match on
283 the range of all digits, the pattern [0\-9] would be used. If the first character
284 following the '[' is a '!', any characters not enclosed are matched.
286 After device node creation, removal, or network device renaming,
288 executes the programs located in the directory tree under
290 The name of a program must have the suffix
294 In addition to the hotplug environment variables,
296 is set if udev is configured to use the syslog facility. Executed programs may
297 want to follow that setting.
299 is exported to make the name of the created node, or the name the network
300 device is renamed to, available to the executed program. The programs in every
301 directory are sorted in lexical order, while the directories are searched in
305 /etc/dev.d/$(DEVNAME)/*.dev
306 /etc/dev.d/$(SUBSYSTEM)/*.dev
307 /etc/dev.d/default/*.dev
311 The following variables are read from the environment:
314 .IR add " or " remove
315 signifies the addition or the removal of a device.
318 The sysfs devpath of the device without the mountpoint but a leading slash.
321 The subsystem the device belongs to. Alternatively the subsystem may
322 be passed as the first argument.
325 Overrides the default location of the
330 The default behavior of
332 is to execute programs in the
334 directory after device handling. If set,
339 /sbin/udev udev program
340 /etc/udev/* udev config files
341 /etc/hotplug.d/default/udev.hotplug hotplug symlink to udev program
342 /etc/dev.d/* programs invoked by udev
351 .I http://linux\-hotplug.sourceforge.net/
352 .I http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev.html
356 was developed by Greg Kroah-Hartman <greg@kroah.com> with much help from
357 Dan Stekloff <dsteklof@us.ibm.com>, Kay Sievers <kay.sievers@vrfy.org>, and