udev

UDEV(8)                   Linux Administrator's Manual                   UDEV(8)



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

       The value $local can be used instead of a specific username.  In that
       case, udev will determine the current local user at the time of device
       node creation and substitute that username as the owner of the new device
       node.  This is useful, for example, to let hot-plugged devices, such as
       cameras, be owned by the user at the current console.  Note that if no
       user is currently logged in, or if udev otherwise fails to determine a
       current user, the default_owner value is used in lieu.

       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@kroah.com> with much help
       from Dan Stekloff <dsteklof@us.ibm.com>, Kay Sievers
       <kay.sievers@vrfy.org>, and many others.



                                  October 2003                           UDEV(8)