.SH NAME
udev \- Linux configurable dynamic device naming support
.SH SYNOPSIS
-.BI udev " hotplug-subsystem"
+.BI udev
.SH "DESCRIPTION"
.B udev
-creates or removes device node files usually located in the /dev directory.
-Its goal is to provide a dynamic device directory that contains only the files
-for devices that are actually present.
+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.
+.br
.P
As part of the
.B hotplug
subsystem,
.B udev
is executed if a kernel device is added or removed from the system.
-On device creation,
+A list of rules is used to match against specific device attributes.
+.br
+On device addition,
.B udev
-reads the sysfs directory of the given device to collect device attributes
-like label, serial number or bus device number.
-These attributes are treated as a key
-to determine a unique name for device file creation.
+matches its configured rules against the available device attributes to
+uniquely name the device.
.B udev
-maintains a database for devices present on the system.
+maintains its own database for devices present on the system. This database
+can be queried for the relationship of the kernel device path and the
+name of the device file.
.br
On device removal,
.B udev
-queries the internal database for the name of the device file to be deleted.
+queries its database for the name of the device file to be deleted.
+.br
+After the device node handling, a list of collected programs specific to this
+device is executed.
.SH "CONFIGURATION"
All
.B udev
-configuration files consist of a set of lines of text. All empty
-lines, and lines beginning with a '#' will be ignored.
+configuration files consist of a set of lines of text. All empty
+lines or lines beginning with '#' will be ignored.
.P
-
.B udev
expects its main configuration file at
-.I /etc/udev/udev.conf.
-The file consists of a set of variables and values that allow the user to
-override default udev values. The current set of variables that can be
-overridden in this file is:
+.IR /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:
.TP
.B udev_root
-This is the where in the filesystem to place the device nodes. The default
-value for this is
-.I /udev/
+Indicates where to place the device nodes in the filesystem. The default
+value is
+.IR @udevdir@/ .
.TP
.B udev_db
-The name and location of the udev database. The default value for this is
-.I /udev/.udev.tdb
+The name and location of the udev database. The default value is
+.IR @udevdir@/.udevdb .
.TP
.B udev_rules
-This is the location of the udev rules file. The default value for this is
-.I /etc/udev/udev.rules
-.TP
-.B udev_permissions
-This is the location of the udev permission file. The default value for this is
-.I /etc/udev/udev.permissions
+The name of the udev rules file or directory to look for files with the suffix
+.IR .rules .
+All rule files are read in lexical order. The default value is
+.IR /etc/udev/rules.d/ .
.TP
-.B default_mode
-This is the default mode for all nodes that have no explicit match in the
-permissions file. The default value for this is
-.I 0666
-.br
+.B udev_log
+The logging priority which can be set to
+.IR "err " , "info "
+or the corresponding numerical
+.BR syslog (3)
+value.
+The default value is
+.IR err .
.P
-.RI "A sample " udev.conf " might look like this:
+.RI "A sample " udev.conf " file might look like this:
.sp
.nf
-# udev_root - where in the filesystem to place the device nodes
-udev_root="/udev/"
-
-# udev_db - The name and location of the udev database.
-udev_db="/udev/.udev.tdb"
+# Where in the filesystem to place the device nodes
+udev_root="@udevdir@"
-# udev_rules - The name and location of the udev rules file
-udev_rules="/etc/udev/udev.rules"
+# The name and location of the udev database.
+udev_db="@udevdir@/.udevdb"
-# udev_permissions - The name and location of the udev permission file
-udev_permissions="/etc/udev/udev.permissions"
+# The name and location of the udev rules file(s).
+udev_rules="@configdir@/rules.d"
-# default_mode - set the default mode for all nodes that have no
-# explicit match in the permissions file
-default_mode="0666"
+# The syslog(3) priority: "err", "info", or the numerical value.
+udev_log="err"
.fi
.P
-The rules for udev to use when naming devices may specified at
-.I /etc/udev/udev.rules
-or specified by the
+The rules for device naming are read from the files located in the
+.I /etc/udev/rules.d/
+directory, or at the location specified by the
.I udev_rules
value in the
.I /etc/udev/udev.conf
file.
-.P
-Every line in the rules file define the mapping between device attributes and
-the device file name. It starts with a keyword defining the method used to
-match, followed by one ore more keys to compare and the filename for the
-device. One ore more optional symlinks targeting the node may be specified.
.br
-If no matching configuration is found, the default kernel device name
-is used.
+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.
+.br
+If no matching rule is found, the default kernel device name is used.
.P
-The line format is:
+Every rule consists of a list of comma separated key value fields:
.sp
-.I method, key,[key,...] name [, symlink]
+.IR "key " ,[ "key " ,...]
+.P
+Each key has the following format:
.sp
-where valid methods with corresponding keys are:
+.IR "name op value"
+.P
+There are distinct key operation types, depending on the type of the key, it
+does a comparison or an assignment.
+.P
+Comparison operators are:
.TP
-.B CALLOUT
-calling external program, that returns a string to match
-.br
-.RB "keys: " BUS ", " PROGRAM ", " ID
+.B ==
+Compare for equality.
.TP
-.B LABEL
-device label or serial number, like USB serial number, SCSI UUID or
-file system label
-.br
-.RB "keys: " BUS ", " SYSFS_
+.B !=
+Compare for non-equality.
+.P
+Assignment operators are:
.TP
-.B NUMBER
-device number on the bus, like PCI bus id
-.br
-.RB "keys: " BUS ", " ID
+.B +=
+Add the value to a key that holds a list of entries.
+.TP
+.B :=
+Assign a value to a key finally; disallow any later changes, which
+is useful to prevent changes by any later rules.
+.TP
+.B =
+Asign a value to a key. Keys that represent a list, are reset and only this
+single value is assigned. While this operator still works inplicitely as
+comparison on keys that can't get a value assigned, its usage as an comparison
+operator is deprecated.
+.P
+The following key names can be used to match against device properties:
+.TP
+.B BUS
+Match the bus type of the device.
+(The sysfs device bus must be able to be determined by a "device" symlink.)
+.TP
+.B KERNEL
+Match the kernel device name.
+.TP
+.B SUBSYSTEM
+Match the kernel subsystem name.
+.TP
+.B ACTION
+Match the kernel action name.
.TP
-.B TOPOLOGY
-device position on bus, like physical port of USB device
+.B DRIVER
+Match the kernel driver name.
+.TP
+.B ID
+Match the device number on the bus, like PCI bus id.
+.TP
+.BI SYSFS{ filename }
+Match sysfs device attribute like vendor and product id's, USB serial number
+or the SCSI disk model number. Up to 5 different sysfs files can be checked,
+with all of the values being required to match the rule.
.br
-.RB "keys: " BUS ", " PLACE
+Trailing whitespace characters in the sysfs attribute value are ignored, if
+the key doesn't have any trailing whitespace characters by itself.
.TP
-.B REPLACE
-string replacement of the kernel device name
+.BI ENV{ variable }
+Match an environment variable. Up to 5 different environment variables can be
+checked, with all of the values being required to match the rule.
+.TP
+.B PROGRAM
+Call external program. This key is valid if the program returns successful.
+The environment variables of
+.B udev
+are also available to the program.
.br
-.RB "key: " KERNEL
+The string returned by the program may be additionally matched with the
+.B RESULT
+key in the same or any later rule.
+.TP
+.B RESULT
+Match the returned string of the last
+.B PROGRAM
+call. This key can be used in the same or in any later rule after a
+.B PROGRAM
+call.
.P
-The methods are applied in the following order:
-.BR CALLOUT ", " LABEL ", " NUMBER ", " TOPOLOGY ", " REPLACE "."
+The following keys can get values assigned:
+.TP
+.B NAME
+The name of the node to be created, or the name, the network interface
+should be renamed to. Only one rule can set the a name, all later rules
+with a NAME key will be ignored.
+.TP
+.B SYMLINK
+The name of a symlink targeting the node. Every matching rule can add
+this value to the list of symlinks to be created along with the device node.
+Multiple symlinks may be specified by separating the names by the space
+character.
+.TP
+.B OWNER, GROUP, MODE
+The permissions for the device node. Every specified value overwrites the
+compiled-in default value.
+.TP
+.B RUN
+Add a program to the list of programs to be executed for a specific device.
+.TP
+.B OPTIONS
+.B last_rule
+stops further rules application. No later rules will have any effect.
+.sp
+.B ignore_device
+will ignore this device. No node will be created or program executed.
+.sp
+.B ignore_remove
+will ignore any later remove event for this device.
+This may be useful as a workaround for broken device drivers.
+.sp
+.B all_partitions
+will create device nodes for all available partitions of a blockdevice.
+This may be useful for removable media devices which do not detect a media
+change.
+.sp
+Multiple attributes may be separated by comma.
.P
-.RB "The " NAME " ," SYMLINK " and " PROGRAM
-fields support simple printf-like string substitution:
+.RB "The " NAME ", " SYMLINK ", " PROGRAM ", " OWNER " and " GROUP
+fields support simple printf-like string substitutions:
.TP
.B %n
The "kernel number" of the device.
-for example, 'sda3' has a "kernel number" of '3'
+For example, 'sda3' has a "kernel number" of '3'.
+.TP
+.B %k
+The "kernel name" for the device.
+.TP
+.B %p
+The devpath for the device.
.TP
.B %M
The kernel major number for the device.
The bus id for the device.
.TP
.B %c
-The CALLOUT program returned string.
-(This does not work within the PROGRAM field for the obvious reason.)
+The string returned by the external program, specified in
+.B PROGRAM
+(This does not work within the
+.B PROGRAM
+field for the obvious reason.)
+.br
+A single part of the string, separated by a space character
+may be selected by specifying the part number as an attribute:
+.BI %c{ N }
+If the number is followed by the + char this part plus
+all remaining parts of the result string are substituted:
+.BI %c{ N+ }
+.TP
+.B %N
+The name of a created temporary device node to provide access to the
+device from a external program.
+.TP
+.B %P
+The node name of the parent device.
+.TP
+.BI %s{ filename }
+The content of a sysfs attribute.
+.TP
+.B %r
+The udev_root value.
+.TP
+.B %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.
+.sp
+Note: The use of the enumeration facility is unreliable outside of
+udevstart where the node creation is serialized and predictable.
+The returned numbers rely on the order devices are probed on the
+system. If more than one device requests an enumeration for the same
+name at the same time, it may be possible that both requests receive the
+same name back from the database. The use of enumerations in todays setups
+where device can come and go at any time is not recomended.
.TP
-.B %D
-Use the devfs style disk name for this device.
-For partitions, this will result in 'part%n'
-If this is not a partition, it will result in 'disc'.
+.B %%
+The '%' character itself.
+.P
+The count of characters 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.
.P
-.RI "A sample " udev.rules " might look like this:"
+.RI "A sample " udev.rules " file might look like this:"
.sp
.nf
-# if /sbin/scsi_id returns "OEM 0815" device will be called disk1
-CALLOUT, BUS="scsi", PROGRAM="/sbin/scsi_id", ID="OEM 0815", NAME="disk1"
+# if /sbin/scsi_id returns "OEM 0815", the device will be called disk1
+BUS=="scsi", PROGRAM=="/sbin/scsi_id", RESULT=="OEM 0815", NAME="disk1"
# USB printer to be called lp_color
-LABEL, BUS="usb", SYSFS_serial="W09090207101241330", NAME="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
-NUMBER, BUS="pci", ID="00:0b.0", NAME="dsp"
+BUS=="pci", ID=="00:0b.0", NAME="dsp"
# USB mouse at third port of the second hub to be called mouse1
-TOPOLOGY, BUS="usb", PLACE="2.3", NAME="mouse1"
+BUS=="usb", ID=="2.3", NAME="mouse1"
# ttyUSB1 should always be called pda with two additional symlinks
-REPLACE, KERNEL="ttyUSB1", NAME="pda", SYMLINK="palmtop handheld"
+KERNEL=="ttyUSB1", NAME="pda", SYMLINK="palmtop handheld"
# multiple USB webcams with symlinks to be called webcam0, webcam1, ...
-LABEL, BUS="usb", model="WebCam V3", NAME="video%n", SYMLINK="webcam%n"
-.fi
-.P
-Permissions and ownership for the created device files may specified at
-.I /etc/udev/udev.permissions
-or specified by the
-.I udev_permission
-value in the
-.I /etc/udev/udev.conf
-file.
-.br
-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.
-.br
-If
-.B udev
-was built using klibc or is used before the user database is accessible (e.g.
-.BR initrd "(4)), only numeric owner and group values may be used."
-.sp
-.RI "A sample " udev.permissions " might look like this:"
-.sp
-.nf
-#name:user:group:mode
-input/*:root:root:644
-ttyUSB1:0:8:0660
-video*:root:video:0660
-dsp1:::0666
+BUS=="usb", SYSFS{model}=="XV3", NAME=="video%n", SYMLINK="webcam%n"
.fi
.P
A number of different fields in the above configuration files support a simple
.TP
.B [ ]
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 '!' then any character not enclosed is matched.
+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 characters not enclosed are matched.
+.P
+After device node creation, removal, or network device renaming,
+.B udev
+executes the programs specified by the
+.B RUN
+key.
+.br
+In addition to the kernel provided hotplug environment variables,
+.B UDEV_LOG
+is set and contains the numerical priority value, if udev is configured to use
+.BR syslog (3).
+Executed programs may want to follow that setting.
+.B DEVNAME
+is exported to make the name of the created node, or the name the network
+device is renamed to, available to the executed programs.
+.SH "ENVIRONMENT"
+.P
+The following variables are read from the environment:
+.TP
+.B ACTION
+.IR add " or " remove
+signifies the addition or the removal of a device.
+.TP
+.B DEVPATH
+The sysfs devpath of the device without the mountpoint but a leading slash.
+.TP
+.B SUBSYSTEM
+The subsystem the device belongs to. Alternatively the subsystem may
+be passed as the first argument.
+.TP
+.B UDEV_CONFIG_FILE
+Overrides the default location of the
+.B udev
+config file.
+.TP
+.B UDEV_LOG
+Overrides the log priority specified in the config file.
+.TP
+.B UDEV_RUN
+If set to "0", it disables the execution of programs added by rules.
.SH "FILES"
.nf
/sbin/udev udev program
/etc/udev/* udev config files
-/etc/hotplug.d/default/udev.hotplug hotplug symlink to udev program
.fi
-.LP
.SH "SEE ALSO"
-.BR hotplug (8)
+.BR udevinfo (8),
+.BR udevd (8),
.PP
-The
-.I http://linux-hotplug.sourceforge.net/
-web site.
+.B Web resources:
+.nf
+.I http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev.html
+.I http://linux\-hotplug.sourceforge.net/
+.fi
.SH AUTHORS
.B udev
was developed by Greg Kroah-Hartman <greg@kroah.com> with much help from
~ianmdlvl / elogind.git / blobdiff