NAME
udev − Linux configurable dynamic device naming support
SYNOPSIS
udev hotplug-subsystem
The environment must provide the following variables:
ACTION |
add or remove signifies the connection or disconnection of a device. |
DEVPATH
The sysfs devpath of the device without the mountpoint but a leading slash.
Additional
optional environment variables:
UDEV_CONFIG_FILE
Overrides the default location of the udev config file.
UDEV_NO_DEVD
The default behavior of udev is to execute programs in the /etc/dev.d/ directory after device handling. If set, udev will skip this step.
DESCRIPTION
udev provides a dynamic device directory containing only the files for actually present devices. It creates or removes device node files usually located in the /dev directory, or it renames network interfaces.
As part of the
hotplug subsystem, udev is executed if a
kernel device is added or removed from the system. On device
creation, udev reads the sysfs directory of the given
device to collect device attributes like label, serial
number or bus device number. These attributes may be used as
keys to determine a unique name for the device. udev
maintains a database for devices present on the system.
On device removal, udev queries its database for the
name of the device file to be deleted.
CONFIGURATION
All udev configuration files consist of a set of lines of text. All empty lines and lines beginning with a ’#’ will be ignored.
udev
expects its main configuration file at
/etc/udev/udev.conf. The file consists of a set of
variables and values allowing the user to override default
udev values. The following variables can be overridden in
this file:
udev_root
Indicates where to place the device nodes in the filesystem. The default value is /dev/.
udev_db
The name and location of the udev database. The default value is /dev/.udev.tdb.
udev_rules
The name of the udev rules file or directory to look for files with the suffix .rules. All rule files are read in lexical order. The default value is /etc/udev/rules.d/.
udev_permissions
The name of the udev permission file or directory to look for files with the suffix .permissions. All permission files are read in lexical order. The default value is /etc/udev/permissions.d/.
udev_log
The switch, if udev logs some information for every device handled. The default value is yes.
default_mode
The default mode for all nodes not explicitely matching in the permissions file. The default value is 0666.
default_owner
The default owner for all nodes not explicitely matching in the permissions file. The default value is root.
default_group
The default group for all nodes not explicitely matching in the permissions file. The default value is root.
A sample udev.conf might look like this:
# udev_root -
where to place the device nodes in the filesystem
udev_root="/udev"
# udev_db - The
name and location of the udev database
udev_db="/udev/.udev.tdb"
# udev_rules -
The name of the udev rules file or directory to look
for files with the suffix .rules
udev_rules="/etc/udev/rules.d/"
#
udev_permissions - The name of the udev permission file or
directory
to look for files with the suffix .permissions
udev_permissions="/etc/udev/udev.permissions"
# udev_log -
set to "yes" if you want logging, else
"no"
udev_log="yes"
# default_mode
- set the default mode for all nodes not
# explicitely matching in the permissions file
default_mode="0666"
# default_owner
- set the default owner for all nodes not
# explicitely matching in the permissions file
default_owner="root"
# default_group
- set the default group for all nodes not
# explicitely matching in the permissions file
default_group="root"
The rules for
device naming, are read from the files located in the
/etc/udev/rules.d/ directory, or at the location
specified by the udev_rules value in the
/etc/udev/udev.conf file.
Every line in the rules file defines the mapping between
device attributes and the device name. One or 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 to name the device file or the network interface.
If no matching rule is found, the default kernel device name
is used.
Every rule consists of a list of comma separated fields:
key ,[key ,...] name [, symlink]
where fields are:
BUS |
Match the bus type of the device. (The sysfs device bus must be able to be determined by a "device" symlink.) | ||
KERNEL |
Match the kernel device name. | ||
ID |
Match the device number on the bus, like PCI bus id. | ||
PLACE |
Match the topological position on bus, like physical port of USB device |
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 to match the rule.
Trailing whitespace characters in the sysfs attribute value
are ignored, if the key doesn’t have any trailing
whitespace characters by itself.
PROGRAM
Call external program. This key
is valid if the program returns successful. The environment
variables of udev are also available for the program.
The string returned by the program may be additionally
matched with the RESULT key.
RESULT |
Match the returned string of the last PROGRAM call. This key may be used in any following rule after a PROGRAM call. | ||
NAME |
The name of the node to be created, or the name, the network interface should be renamed to. |
If given with the attribute NAME{all_partitions} it will create all 15 partitions of a blockdevice. This may be useful for removable media devices.
SYMLINK
The name of a symlink targeting
the node. Multiple symlinks may be specified by separating
the names by the space character.
If both the name and the symlink fields are omitted or its
values empty, the device will be ignored and no node will be
created.
If only the symlink field is given and the name field is
omitted, the rule will not be applied immediatly, but the
symlink field is added to the symlink list of the rule which
will create the node. This makes it possible to specify
additional symlinks in a possibly separate rules file, while
the device nodes are maintained by the distribution provided
rules file.
OWNER, GROUP, MODE
The permissions for this device. Every specified value overwrites the value given in the permissions file.
The NAME ,SYMLINK and PROGRAM fields support simple printf-like string substitution:
%n |
The "kernel number" of the device. For example, ’sda3’ has a "kernel number" of ’3’. | ||
%k |
The "kernel name" for the device. | ||
%M |
The kernel major number for the device. | ||
%m |
The kernel minor number for the device. | ||
%b |
The bus id for the device. | ||
%c |
The string returned from the execution of PROGRAM (This does not work within the PROGRAM field for the obvious reason.) |
A single part of the string, separated by a space character may be selected by specifying the part number as an attribute: %c{N} If the number is followed by the + char this part plus all remaining parts of the result string are substituted: %c{N+}
%s{filename}
The content of a sysfs attribute.
%e |
If a device node already exists with the name, the smallest positive decimal integer N is substituted such that the resulting name doesn’t match an existing device node. Otherwise nothing is substituted. This can be used to create compatibility symlinks and enumerate devices of the same type originating from different kernel subsystems. | ||
%% |
The ’%’ character itself. |
The count of charcters to insert may be limited by specifying the format length value. For example, ’%3s{file}’ will only insert the first three characters of the sysfs attribute.
A sample udev.rules might look like this:
# 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 will 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"
# grouping of
optical drives from multiple kernel subsystems
KERNEL="sr*", NAME="%k",
SYMLINK="cdrom%e"
KERNEL="scd*", NAME="%k",
SYMLINK="cdrom%e"
KERNEL="pcd*", NAME="%k",
SYMLINK="cdrom%e"
KERNEL="hd[a-z]", PROGRAM="/bin/cat
/proc/ide/%k/media", RESULT="cdrom",
NAME="%k", SYMLINK="cdrom%e"
The permissions
and ownership of the created device file is read from the
files located in the /etc/udev/permissions.d/
directory, or at the location specified by the
udev_permission value in the
/etc/udev/udev.conf file.
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.
A sample udev.permissions might look like this:
#name:user:group:mode
input/*:root:root:644
ttyUSB1:0:8:0660
video*:root:video:0660
dsp1:::0666
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:
* |
Matches zero, one, or more characters. | ||
? |
Matches any single character, but does not match zero characters. | ||
[ ] |
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 ’!’, any character not enclosed is matched. |
After device
node creation, removal, or network device renaming,
udev executes the programs in the directory tree
under /etc/dev.d/. The name of a program must end
with .dev suffix, to be recognized.
In addition to the hotplug environment variables,
DEVNAME is exported to make the name of the created
node, or the name the network device is renamed to,
available to the executed program. The programs in every
directory are sorted in lexical order, while the directories
are searched in the following order:
/etc/dev.d/$(DEVNAME)/*.dev
/etc/dev.d/$(SUBSYSTEM)/*.dev
/etc/dev.d/default/*.dev
FILES
/sbin/udev udev
program
/etc/udev/* udev config files
/etc/hotplug.d/default/udev.hotplug hotplug symlink to udev
program
/etc/dev.d/* programs invoked by udev
SEE ALSO
udevinfo(8), udevd(8), hotplug(8)
The http://linux−hotplug.sourceforge.net/ web site.
AUTHORS
udev was developed by Greg Kroah-Hartman <greg [AT] kroah.com> with much help from Dan Stekloff <dsteklof [AT] us.com>, Kay Sievers <kay.sievers [AT] vrfy.org>, and many others.