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jgirata
July 22nd, 2009, 04:59 PM
Hi, I'm trying to work with udev, so I've been reading some articles and tutorials online. They seem to assume that udev will work on Ubuntu, but when I try to execute any of the commands, it says "command not found." Further, I tried to install udev using apt-get (sudo apt-get install udev), but it says udev is already installed.

Am I missing something here?

michy99
July 22nd, 2009, 05:19 PM
Can you give an example of a command which does not work?

jgirata
July 22nd, 2009, 07:58 PM
Any command involving udev...


udev

udevinfo -e

wojox
July 22nd, 2009, 08:01 PM
UDEV(7) udev UDEV(7)



NAME
udev - dynamic device management

DESCRIPTION
udev provides a dynamic device directory containing only the files for actually present devices. It creates or
removes device node files in the /dev directory, or it renames network interfaces.

Usually udev runs as udevd(8) and receives uevents directly from the kernel if a device is added or removed from
the system.

If udev receives a device event, it matches its configured rules against the available device attributes provided
in sysfs to identify the device. Rules that match may provide additional device information or specify a device
node name and multiple symlink names and instruct udev to run additional programs as part of the device event
handling.

CONFIGURATION
udev configuration files are placed in /etc/udev/ and /lib/udev/. All empty lines, or lines beginning with ´#´
will be ignored.

Configuration file
udev expects its main configuration file at /etc/udev/udev.conf. It consists of a set of variables allowing the
user to override default udev values. The following variables can be set:

udev_root
Specifies where to place the device nodes in the filesystem. The default value is /dev.

udev_log
The logging priority. Valid values are the numerical syslog priorities or their textual representations: err,
info and debug.

Rules files
The udev rules are read from the files located in the default rules directory /lib/udev/rules.d/, the custom rules
directory /etc/udev/rules.d/ and the temporary rules directory /dev/.udev/rules.d/. All rule files are sorted and
processed in lexical order, regardless in which of these directories they live.

Rule files are required to have a unique name, duplicate file names are ignored. Files in /etc/udev/rules.d/ have
precedence over files with the same name in /lib/udev/rules.d/. This can be used to ignore a default rules file if
needed.

Every line in the rules file contains at least one key value pair. There are two kind of keys, match and
assignment keys. If all match keys are matching against its value, the rule gets applied and the assign keys get
the specified value assigned.

A matching rule may specify the name of the device node, add a symlink pointing to the node, or run a specified
program as part of the event handling. If no matching rule is found, the default device node name is used.

A rule consists of a list of one or more key value pairs separated by a comma. Each key has a distinct operation,
depending on the used operator. Valid operators are:

==
Compare for equality.

!=
Compare for inequality.

=
Assign a value to a key. Keys that represent a list, are reset and only this single value is assigned.

+=
Add the value to a key that holds a list of entries.

:=
Assign a value to a key finally; disallow any later changes, which may be used to prevent changes by any later
rules.

The following key names can be used to match against device properties. Some of the keys also match against
properties of the parent devices in sysfs, not only the device that has generated the event. If multiple keys that
match a parent device are specified in a single rule, all these keys must match at one and the same parent device.

ACTION
Match the name of the event action.

DEVPATH
Match the devpath of the event device.

KERNEL
Match the name of the event device.

NAME
Match the name of the node or network interface. It can be used once the NAME key has been set in one of the
preceding rules.

SUBSYSTEM
Match the subsystem of the event device.

DRIVER
Match the driver name of the event device. Only set for devices which are bound to a driver at the time the
event is generated.

ATTR{filename}
Match sysfs attribute values of the event device. Trailing whitespace in the attribute values is ignored, if
the specified match value does not contain trailing whitespace itself.

KERNELS
Search the devpath upwards for a matching device name.

SUBSYSTEMS
Search the devpath upwards for a matching device subsystem name.

DRIVERS
Search the devpath upwards for a matching device driver name.

ATTRS{filename}
Search the devpath upwards for a device with matching sysfs attribute values. If multiple ATTRS matches are
specified, all of them must match on the same device. Trailing whitespace in the attribute values is ignored,
if the specified match value does not contain trailing whitespace itself.

ENV{key}
Match against a device property value.

TEST{octal mode mask}
Test the existence of a file. An octal mode mask can be specified if needed.

PROGRAM
Execute a program. The key is true, if the program returns successfully. The device properties are made
available to the executed program in the environment. The program´s output printed to stdout, is available in
the RESULT key.

RESULT
Match the returned string of the last PROGRAM call. This key can be used in the same or in any later rule
after a PROGRAM call.

Most of the fields support a shell style pattern matching. The following pattern characters are supported:

*
Matches zero, or any number of characters.

?
Matches any single character.

[]
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 characters not enclosed are matched.

The following keys can get values assigned:

NAME
The name of the node to be created, or the name the network interface should be renamed to.

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.

OWNER, GROUP, MODE
The permissions for the device node. Every specified value overwrites the compiled-in default value.

ATTR{key}
The value that should be written to a sysfs attribute of the event device.

ENV{key}
Set a device property value.

RUN
Add a program to the list of programs to be executed for a specific device. This can only be used for very
short running tasks. Running an event process for a long period of time may block all further events for this
or a dependent device. Long running tasks need to be immediately detached from the event process itself.

If the specified string starts with socket:path, all current event values will be passed to the specified
socket, as a message in the same format the kernel sends an uevent. If the first character of the specified
path is an @ character, an abstract namespace socket is used, instead of an existing socket file.

LABEL
Named label where a GOTO can jump to.

GOTO
Jumps to the next LABEL with a matching name

IMPORT{type}
Import a set of variables as device properties, depending on type:

program
Execute an external program specified as the assigned value and import its output, which must be in
environment key format.

file
Import a text file specified as the assigned value, which must be in environment key format.

parent
Import the stored keys from the parent device by reading the database entry of the parent device. The
value assigned to IMPORT{parent} is used as a filter of key names to import (with the same shell-style
pattern matching used for comparisons).

If no option is given, udev will choose between program and file based on the executable bit of the file
permissions.

WAIT_FOR
Wait for a file to become available.

OPTIONS
Rule and device options:

last_rule
Stops further rules application. No later rules will have any effect.

ignore_device
Ignore this event completely.

ignore_remove
Do not remove the device node when the device goes away. This may be useful as a workaround for broken
device drivers.

link_priority=value
Specify the priority of the created symlinks. Devices with higher priorities overwrite existing symlinks
of other devices. The default is 0.

all_partitions
Create the device nodes for all available partitions of a block device. This may be useful for removable
media devices where media changes are not detected.

event_timeout=
Number of seconds an event will wait for operations to finish, before it will terminate itself.

string_escape=none|replace
Usually control and other possibly unsafe characters are replaced in strings used for device naming. The
mode of replacement can be specified with this option.

watch
Watch the device node with inotify, when closed after being opened for writing, a change uevent will be
synthesised.

The NAME, SYMLINK, PROGRAM, OWNER, GROUP, MODE and RUN fields support simple printf-like string substitutions. The
RUN format chars gets applied after all rules have been processed, right before the program is executed. It allows
the use of device properties set by earlier matching rules. For all other fields, substitutions are applied while
the individual rule is being processed. The available substitutions are:

$kernel, %k
The kernel name for this device.

$number, %n
The kernel number for this device. For example, ´sda3´ has kernel number of ´3´

$devpath, %p
The devpath of the device.

$id, %b
The name of the device matched while searching the devpath upwards for SUBSYSTEMS, KERNELS, DRIVERS and ATTRS.

$driver
The driver name of the device matched while searching the devpath upwards for SUBSYSTEMS, KERNELS, DRIVERS and
ATTRS.

$attr{file}, %s{file}
The value of a sysfs attribute found at the device, where all keys of the rule have matched. If the matching
device does not have such an attribute, follow the chain of parent devices and use the value of the first
attribute that matches. If the attribute is a symlink, the last element of the symlink target is returned as
the value.

$env{key}, %E{key}
A device property value.

$major, %M
The kernel major number for the device.

$minor, %m
The kernel minor number for the device.

$result, %c
The string returned by the external program requested with PROGRAM. 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+}

$parent, %P
The node name of the parent device.

$name
The current name of the device node. If not changed by a rule, it is the name of the kernel device.

$links
The current list of symlinks, separated by a space character. The value is only set if an earlier rule
assigned a value, or during a remove events.

$root, %r
The udev_root value.

$sys, %S
The sysfs mount point.

$tempnode, %N
The name of a created temporary device node to provide access to the device from a external program before the
real node is created.

%%
The ´%´ character itself.

$$
The ´$´ character itself.

The count of characters to be substituted may be limited by specifying the format length value. For example,
´%3s{file}´ will only insert the first three characters of the sysfs attribute

AUTHOR
Written by Greg Kroah-Hartman greg@kroah.com and Kay Sievers kay.sievers@vrfy.org. With much help from Dan
Stekloff and many others.

SEE ALSO
udevd(8), udevadm(8)



udev August 2005 UDEV(7)

bacil
July 22nd, 2009, 08:01 PM
well there isnt udev as a command but there is udevadm

udevadm

here is list of all comands and man pages involving udev



ata_id (8) - udev callout to read product/serial number from ATA drives
AuDeviceAttributes (3nas) - device attributes structure
cdrom_id (8) - udev callout to determine the capabilities of optical drives and media
create_floppy_devices (8) - udev callout to create all possible floppy devices based on the CMOS type.
edd_id (8) - udev callout to identify BIOS disk drives via EDD
path_id (8) - udev callout to create a device path based unique name for a device to implement the Linux Persistent Device Naming s...
udev (7) - dynamic device management
udevadm (8) - udev management tool
udevd (8) - event managing daemon
usb_id (8) - udev callout to read information from USB devices