1 .TH UDEV 8 "October 2003" "" "Linux Administrator's Manual"
3 udev \- Linux configurable dynamic device naming support
5 .BI udev " hotplug-subsystem"
8 .RI "[-q " query_type " -p " sysfs_path "] [-drVh]"
11 creates or removes device node files usually located in the /dev directory.
12 Its goal is to provide a dynamic device directory that contains only the files
13 for devices that are actually present.
19 is executed if a kernel device is added or removed from the system.
22 reads the sysfs directory of the given device to collect device attributes
23 like label, serial number or bus device number.
24 These attributes may used as keys to determine a
25 unique name for device file creation.
27 maintains a database for devices present on the system.
31 queries its database for the name of the device file to be deleted.
36 with the subsystem as argument and various environment variables set.
38 It may also called with the following options:
41 Print the version information.
46 directory. When used in conjunction with a query for the node name, the
51 Query the database for specified value of a created device node.
53 .BR name ", " symlink ", " owner " or " group .
56 Specify the sysfs path needed for the query.
59 Dump the whole database.
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 .I /etc/udev/udev.conf.
73 The file consists of a set of variables and values that allow the user to
74 override default udev values. The current set of variables that can be
75 overridden in this file is:
78 This is the where in the filesystem to place the device nodes. The default
83 The name and location of the udev database. The default value for this is
87 This is the location of the udev rules file. The default value for this is
88 .I /etc/udev/udev.rules
91 This is the location of the udev permission file. The default value for this is
92 .I /etc/udev/udev.permissions
95 This is the default mode for all nodes that have no explicit match in the
96 permissions file. The default value for this is
100 .RI "A sample " udev.conf " might look like this:
103 # udev_root - where in the filesystem to place the device nodes
106 # udev_db - The name and location of the udev database.
107 udev_db="/udev/.udev.tdb"
109 # udev_rules - The name and location of the udev rules file
110 udev_rules="/etc/udev/udev.rules"
112 # udev_permissions - The name and location of the udev permission file
113 udev_permissions="/etc/udev/udev.permissions"
115 # default_mode - set the default mode for all nodes that have no
116 # explicit match in the permissions file
120 The rules for udev to use when naming devices may specified at
121 .I /etc/udev/udev.rules
125 .I /etc/udev/udev.conf
128 Every line in the rules file defines the mapping between device attributes
129 and the device file name. One ore more keys are specified to match a rule
130 with the current device. If all keys are matching, the rule will be applied
131 and the name is used for the device node. One or more optional symlinks
132 targeting the node may be specified.
134 If no matching rule is found, the default kernel device name is used.
138 .I key,[key,...] name [, symlink]
143 Match the bus type of the device.
144 (The sysfs device bus must be able to be determined by a "device" symlink.)
147 Match the kernel device name.
150 Match the device number on the bus, like PCI bus id.
153 Match the topological position on bus, like physical port of USB device
156 Match sysfs device attribute like label, vendor, USB serial number, SCSI UUID
157 or file system label. Up to 5 different sysfs files can be checked, with
158 all of the values being required in order to match the rule.
161 Call external program. This key is valid if the program returns successful.
162 The string returned by the program may additionally matched with the
167 Match the returned string of the last
169 call. This key may used in any following rule after a
173 .RB "The " NAME " ," SYMLINK " and " PROGRAM
174 fields support simple printf-like string substitution:
177 The "kernel number" of the device.
178 for example, 'sda3' has a "kernel number" of '3'
181 The "kernel name" for the device.
184 The kernel major number for the device.
187 The kernel minor number for the device.
190 The bus id for the device.
196 (This does not work within the
198 field for the obvious reason.)
201 Use the devfs style disk name for this device.
202 For partitions, this will result in 'part%n'
203 If this is not a partition, it will result in 'disc'.
208 .RI "A sample " udev.rules " might look like this:"
211 # if /sbin/scsi_id returns "OEM 0815" device will be called disk1
212 BUS="scsi", PROGRAM="/sbin/scsi_id", RESULT="OEM 0815", NAME="disk1"
214 # USB printer to be called lp_color
215 BUS="usb", SYSFS_serial="W09090207101241330", NAME="lp_color"
217 # SCSI disk with a specific vendor and model number is to be called boot
218 BUS="scsi", SYSFS_vendor="IBM", SYSFS_model="ST336", NAME="boot%n"
220 # sound card with PCI bus id 00:0b.0 to be called dsp
221 BUS="pci", ID="00:0b.0", NAME="dsp"
223 # USB mouse at third port of the second hub to be called mouse1
224 BUS="usb", PLACE="2.3", NAME="mouse1"
226 # ttyUSB1 should always be called pda with two additional symlinks
227 KERNEL="ttyUSB1", NAME="pda", SYMLINK="palmtop handheld"
229 # multiple USB webcams with symlinks to be called webcam0, webcam1, ...
230 BUS="usb", SYSFS_model="XV3", NAME="video%n", SYMLINK="webcam%n"
233 Permissions and ownership for the created device files may specified at
234 .I /etc/udev/udev.permissions
238 .I /etc/udev/udev.conf
241 Every line lists a device name followed by owner, group and permission
242 mode. All values are separated by colons. The name field may contain a
243 pattern to apply the values to a whole class of devices.
247 was built using klibc or is used before the user database is accessible (e.g.
248 .BR initrd "(4)), only numeric owner and group values may be used."
250 .RI "A sample " udev.permissions " might look like this:"
253 #name:user:group:mode
254 input/*:root:root:644
256 video*:root:video:0660
260 A number of different fields in the above configuration files support a simple
261 form of shell style pattern matching. It supports the following pattern characters:
264 Matches zero, one, or more characters.
267 Matches any single character, but does not match zero characters.
270 Matches any single character specified within the brackets. For example, the
271 pattern string "tty[SR]" would match either "ttyS" or "ttyR". Ranges are also
272 supported within this match with the '-' character. For example, to match on
273 the range of all digits, the pattern [0-9] would be used. If the first character
274 following the '[' is a '!' then any character not enclosed is matched.
277 /sbin/udev udev program
278 /etc/udev/* udev config files
279 /etc/hotplug.d/default/udev.hotplug hotplug symlink to udev program
286 .I http://linux-hotplug.sourceforge.net/
290 was developed by Greg Kroah-Hartman <greg@kroah.com> with much help from
291 Dan Stekloff <dsteklof@us.ibm.com>, Kay Sievers <kay.sievers@vrfy.org>, and