udev (Magyar)

Fordítás állapota:
Ez az oldal az angol
udev
című oldal magyar nyelvre lefordított változata. Utolsó fordítás dátuma: 2025.11.29. Amennyiben a lefordítás időpontja óta az angol nyelvű oldalon történtek újabb
módosítások
, akkor Ön segíthet hozzászinkronizálni az angolhoz ezt a magyar nyelvű fordítást.
További oldalak az adott témakörben
udisks (Magyar)
udev
is a userspace system that enables the operating system administrator to register userspace handlers for events. The events received by
udev
's daemon are mainly generated by the (Linux) kernel in response to physical events relating to peripheral devices. As such,
udev
's main purpose is to act upon peripheral detection and hot-plugging, including actions that return control to the kernel, e.g., loading kernel modules or device firmware. Another component of this detection is adjusting the permissions of the device to be accessible to non-root users and groups.
As the successor of
devfsd
and
hotplug
,
udev
also manages device nodes in the
/dev
directory by adding, symlinking and renaming them.
udev
replaces the functionality of both
hotplug
and
hwdetect
.
udev
handles separate events concurrently (in parallel), leading to a potential performance improvement over older systems. At the same time, this can complicate system administration, because, for example, the kernel module loading order is not preserved across boots. If the machine has multiple block devices, this may manifest itself in the form of device nodes changing designations after reboot. For example, if the machine has two hard drives,
/dev/sda
may on next boot become
/dev/sdb
. See below for more info on this.
Telepítés
udev
is part of
systemd
and thus installed by default. See
systemd-udevd.service(8)
for information.
Bevezetés az udev szabályokba
udev
rules written by the administrator go in
/etc/udev/rules.d/
, their file name has to end with
.rules
. The
udev
rules shipped with various packages are found in
/usr/lib/udev/rules.d/
. If there are two files by the same name under
/usr/lib
and
/etc
, the ones in
/etc
take precedence.
To learn about
udev
rules, refer to the
udev(7)
manual. Also see
Writing udev rules
and some practical examples are provided within the guide:
Writing udev rules - Examples
.
udev rule example
Below is an example of a rule that creates a symlink
/dev/video-cam
when a webcamera is connected.
Let say this camera is currently connected and has loaded with the device name
/dev/video2
. The reason for writing this rule is that at the next boot, the device could show up under a different name, like
/dev/video0
.
$ udevadm info --attribute-walk --path=$(udevadm info --query=path --name=/dev/video2)
Udevadm info starts with the device specified by the devpath and then walks up the chain of parent devices.
It prints for every device found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device and the attributes from one single parent device.

looking at device '/devices/pci0000:00/0000:00:04.1/usb3/3-2/3-2:1.0/video4linux/video2':
  KERNEL=="video2"
  SUBSYSTEM=="video4linux"
   ...
looking at parent device '/devices/pci0000:00/0000:00:04.1/usb3/3-2/3-2:1.0':
  KERNELS=="3-2:1.0"
  SUBSYSTEMS=="usb"
  ...
looking at parent device '/devices/pci0000:00/0000:00:04.1/usb3/3-2':
  KERNELS=="3-2"
  SUBSYSTEMS=="usb"
  ATTRS{idVendor}=="05a9"
  ATTRS{manufacturer}=="OmniVision Technologies, Inc."
  ATTRS{removable}=="unknown"
  ATTRS{idProduct}=="4519"
  ATTRS{bDeviceClass}=="00"
  ATTRS{product}=="USB Camera"
  ...
To identify the webcamera, from the
video4linux
device we use
KERNEL=="video2"
and
SUBSYSTEM=="video4linux"
, then walking up two levels above, we match the webcamera using vendor and product ID's from the usb parent
SUBSYSTEMS=="usb"
,
ATTRS{idVendor}=="05a9"
and
ATTRS{idProduct}=="4519"
. Note that this matching is case sensitive, so
"05A9"
can not be used to match the
idVendor
in this example.
We are now able to create a rule match for this device as follows:
/etc/udev/rules.d/83-webcam.rules
KERNEL=="video[0-9]*", SUBSYSTEM=="video4linux", SUBSYSTEMS=="usb", ATTRS{idVendor}=="05a9", ATTRS{idProduct}=="4519", SYMLINK+="video-cam"
Here we create a symlink using
SYMLINK+="video-cam"
but we could easily set user
OWNER="john"
or group using
GROUP="video"
or set the permissions using
MODE="0660"
.
If you intend to write a rule to do something when a device is being removed, be aware that device attributes may not be accessible. In this case, you will have to work with preset device
environment variables
. To monitor those environment variables, execute the following command while unplugging your device:
$ udevadm monitor --property --udev
In this command's output, you will see value pairs such as
ID_VENDOR_ID
and
ID_MODEL_ID
, which match the previously used attributes
idVendor
and
idProduct
. A rule that uses device environment variables instead of device attributes may look like this:
/etc/udev/rules.d/83-webcam-removed.rules
ACTION=="remove", SUBSYSTEM=="usb", ENV{ID_VENDOR_ID}=="05a9", ENV{ID_MODEL_ID}=="4519", RUN+="
/path/to/your/script
"
List the attributes of a device
To get a list of all of the attributes of a device you can use to write rules, run this command:
$ udevadm info --attribute-walk --name=
device_name
Replace
device_name
with the device present in the system, such as
/dev/sda
or
/dev/ttyUSB0
.
If you do not know the device name you can also list all attributes of a specific system path:
$ udevadm info --attribute-walk --path=/sys/class/backlight/acpi_video0
To narrow down the search for a device, figure out the class and run:
$ ls /dev/
class
/by-id
You can use the symlink outright or what it points as the input to
--name
. For example:
$ udevadm info --attribute-walk --name=/dev/input/by-id/usb-foostan_Corne-event-kbd
To get the path of a bare USB device which does not populate any subordinate device you have to use the full USB device path. Start monitor mode and then plug in the USB device to get it:
$ udevadm monitor
...
KERNEL[26652.638931] add      /devices/pci0000:00/0000:00:01.2/0000:02:00.0/0000:03:05.0/0000:05:00.0/usb1/1-3 (usb)
KERNEL[26652.639153] add      /devices/pci0000:00/0000:00:01.2/0000:02:00.0/0000:03:05.0/0000:05:00.0/usb1/1-3/1-3:1.0 (usb)
...
You can just choose the deepest path and
--attribute-walk
will show all parent's attributes anyway:
$ udevadm info --attribute-walk --path=
/devices/pci0000:00/0000:00:01.2/0000:02:00.0/0000:03:05.0/0000:05:00.0/usb1/1-3/1-3:1.0
Testing rules before loading
# udevadm test $(udevadm info --query=path --name=
device_name
) 2>&1
This will not perform all actions in your new rules but it will however process symlink rules on existing devices which might come in handy if you are unable to load them otherwise. You can also directly provide the path to the device you want to test the
udev
rule for:
# udevadm test /sys/class/backlight/acpi_video0/
Új szabályok betöltése
Az
udev
automatikusan érzékeli a szabályfájlok változásait, így a módosítások azonnal életbe lépnek anélkül, hogy az
udev
újraindítására lenne szükség. A szabályok azonban nem futnak le újra a már meglévő eszközökön. A hot-plug eszközöket, például az USB eszközöket valószínűleg újra kell csatlakoztatni ahhoz, hogy az új szabályok érvénybe lépjenek, vagy legalább az ohci-hcd és ehci-hcd kernelmodulfájlok eltávolítására és újratöltésére van szükség a számítógép memóriájában, ezáltal szükség van az összes USB illesztőprogram újratöltésére.
Ha a szabályok nem töltődnek be automatikusan újra:
# udevadm control --reload
Az
udev
manuális úton történő kikényszerítéséhez, azért hogy lefuttassa az Ön szabályait:
# udevadm trigger
udisks
See
udisks
.
Tippek és trükkök
Mounting drives in rules
To mount removable drives, do not call
mount
from
udev
rules. This is ill-advised for two reasons:
systemd by default runs
systemd-udevd.service
with a separate "mount namespace" (see
namespaces(7)
), which means that mounts will not be visible to the rest of the system.
Even if you change the service parameters to fix this (commenting out the
PrivateMounts
and
MountFlags
lines), there is another problem which is that processes started from Udev are killed after a few seconds. In case of FUSE filesystems, such as
NTFS-3G
,
mount
starts a user-space process to handle the filesystem internals; when this is killed you will get
Transport endpoint not connected
errors if you try to access the filesystem.
There are some options that work:
Start a custom systemd service from the Udev rule; the systemd service can invoke a script which can start any number of long-running processes (like FUSE). A concise example which automatically mounts USB disks under
/media
is
udev-media-automount
. A variant of the same idea is explained in
this blog post
.
Use
systemd-mount
instead of
mount
in your Udev rule. This is
recommended by systemd developers
. For example this Udev rule should mount USB disks under
/media
:
ACTION=="add", SUBSYSTEMS=="usb", SUBSYSTEM=="block", ENV{ID_FS_USAGE}=="filesystem", RUN{program}+="/usr/bin/systemd-mount --no-block --automount=yes --collect $devnode /media"
Use a package like
udisks
or
udiskie
. These are very powerful, but difficult to set up. Also, they are meant to be used in single user sessions, since they make some filesystems available under the ownership of the unprivileged user whose session is currently active.
Spawning long-running processes
Programs started by udev will block further events from that device, and any tasks spawned from a udev rule will be killed after event handling is completed. If you need to spawn a long-running process with udev, the intended way is to have a
systemd
unit which handles running the actual command, and a udev rule that merely signals that this unit should run. However, using
systemctl
in a udev rule is discouraged, since it is meant for user interaction and may block, among other things.
The correct way of doing this is to have the rule tag the device as needing a systemd device unit (see
systemd.device(5)
) using
TAG+="systemd"
and adding an device property of either
ENV{SYSTEMD_WANTS}=
for services that would run with
systemctl --system
or
ENV{SYSTEMD_USER_WANTS}=
for services that should run with
systemctl --user
. For example:
SUBSYSTEM=="tty" ACTION=="add" ATTRS{manufacturer}=="Pulse-Eight" ATTRS{product}=="CEC Adapter" TAG+="systemd" ENV{SYSTEMD_WANTS}="inputattach-cec@$devnode.service"
/etc/systemd/system/inputattach-cec@.service
[Unit]
Description=Configure USB serial device at %I

[Service]
Type=simple
ExecStart=/usr/bin/inputattach --pulse8-cec %I
SYSTEMD_WANTS
is equivalent to the
Wants=
directive elsewhere in systemd, meaning the device will not be affected if the service fails, does not exists, or completes successfully at any point.
Annak engedélyezése, hogy a normál felhasználók használhassák az eszközöket
When a
kernel
driver initializes a device, the default state of the device node is to be owned by
root:root
, with permissions
600
.
[1]
This makes devices inaccessible to regular users unless the driver changes the default, or a udev rule in userspace changes the permissions.
The
OWNER
,
GROUP
, and
MODE
udev values can be used to provide access, though one encounters the issue of how to make a device usable to all users without an overly permissive mode. Ubuntu's approach is to create a
plugdev
group that devices are added to, but this practice is not only discouraged by the systemd developers,
[2]
but considered a bug when shipped in udev rules on Arch (
FS#35602
). Another approach historically employed, as described in
Users and groups#Pre-systemd groups
, is to have different groups corresponding to categories of devices.
The modern recommended approach for systemd systems is to use a
MODE
of
660
to let the group use the device, and then attach a
TAG
named
uaccess
[3]
. This special tag makes udev apply a
dynamic user ACL
to the device node, which coordinates with
systemd-logind(8)
to make the device usable to logged-in users. For an example of a udev rule implementing this:
/etc/udev/rules.d/71-device-name.rules
SUBSYSTEMS=="usb", ATTRS{idVendor}=="
vendor_id
", ATTRS{idProduct}=="
product_id
", MODE="0660", TAG+="uaccess"
Megjegyzés
For any rule adding the
uaccess
tag to be effective, the name of the file it is defined in
has to lexically precede
/usr/lib/udev/rules.d/73-seat-late.rules
.
Execute when HDMI cable is plugged in or unplugged
Create the rule
/etc/udev/rules.d/95-hdmi-plug.rules
with the following content:
ACTION=="change", SUBSYSTEM=="drm", ENV{DISPLAY}=":0", ENV{XAUTHORITY}="/home/
username
/.Xauthority", RUN+="
/path/to/script.sh
"
Megjegyzés
If the rule triggers before the X server starts, it may not work as intended. See
#X programs in RUN rules hang when no X server is present
.
Execute on VGA cable plug in
Create the rule
/etc/udev/rules.d/95-monitor-hotplug.rules
with the following content to launch
arandr
on plug in of a VGA monitor cable:
KERNEL=="card0", SUBSYSTEM=="drm", ENV{DISPLAY}=":0", ENV{XAUTHORITY}="/home/
username
/.Xauthority", RUN+="/usr/bin/arandr"
Some display managers store the
.Xauthority
outside the user home directory. You will need to update the
ENV{XAUTHORITY}
accordingly. As an example
GNOME Display Manager
looks as follows:
$ printenv XAUTHORITY
/run/user/1000/gdm/Xauthority
Megjegyzés
If the rule triggers before the X server starts, it may not work as intended. See
#X programs in RUN rules hang when no X server is present
.
Detect new eSATA drives
If your eSATA drive is not detected when you plug it in, there are a few things you can try. You can reboot with the eSATA plugged in. Or you could try:
# echo 0 0 0 | tee /sys/class/scsi_host/host*/scan
Or you could install
scsiadd
AUR
(from the AUR) and try:
# scsiadd -s
Hopefully, your drive is now in
/dev
. If it is not, you could try the above commands while running:
# udevadm monitor
to see if anything is actually happening.
Mark internal SATA ports as eSATA
If you connected an eSATA bay or another eSATA adapter, the system will still recognize this disk as an internal SATA drive.
GNOME
and
KDE
will ask you for your root password all the time. The following rule will mark the specified SATA-Port as an external eSATA-Port. With that, a normal GNOME user can connect their eSATA drives to that port like a USB drive, without any root password and so on.
/etc/udev/rules.d/10-esata.rules
DEVPATH=="/devices/pci0000:00/0000:00:1f.2/host4/*", ENV{UDISKS_SYSTEM}="0"
Megjegyzés
The
DEVPATH
can be found after connection the eSATA drive with the following commands (replace
sdb
accordingly):
$ udevadm info --query=path /dev/sdb
/devices/pci0000:00/0000:00:1f.2/host4/target4:0:0/4:0:0:0/block/sdb
$ find /sys/devices/ -name sdb
/sys/devices/pci0000:00/0000:00:1f.2/host4/target4:0:0/4:0:0:0/block/sdb
Setting static device names
Because
udev
loads all modules asynchronously, they are initialized in a different order. This can result in devices randomly switching names. A
udev
rule can be added to use static device names.
See also
Persistent block device naming
for block devices and
Network configuration#Change interface name
for network devices.
Video device
For setting up the webcam in the first place, refer to
Webcam setup
.
Using multiple webcams will assign video devices as
/dev/video*
randomly on boot. The recommended solution is to create symlinks using a
udev
rule as in the
#udev rule example
:
/etc/udev/rules.d/83-webcam.rules
KERNEL=="video[0-9]*", SUBSYSTEM=="video4linux", SUBSYSTEMS=="usb", ATTRS{idVendor}=="05a9", ATTRS{idProduct}=="4519", SYMLINK+="video-cam1"
KERNEL=="video[0-9]*", SUBSYSTEM=="video4linux", SUBSYSTEMS=="usb", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="08f6", SYMLINK+="video-cam2"
Megjegyzés
Using names other than
/dev/video*
will break preloading of
v4l1compat.so
and perhaps
v4l2convert.so
Printer
If you use multiple printers,
/dev/lp[0-9]
devices will be assigned randomly on boot, which will break e.g.
CUPS
configuration.
You can create the following rule, which will create symlinks under
/dev/lp/by-id
and
/dev/lp/by-path
, similar to
Persistent block device naming
scheme:
/etc/udev/rules.d/60-persistent-printer.rules
ACTION=="remove", GOTO="persistent_printer_end"
# This should not be necessary
#KERNEL!="lp*", GOTO="persistent_printer_end"

SUBSYSTEMS=="usb", IMPORT{builtin}="usb_id"
ENV{ID_TYPE}!="printer", GOTO="persistent_printer_end"

ENV{ID_SERIAL}=="?*", SYMLINK+="lp/by-id/$env{ID_BUS}-$env{ID_SERIAL}"

IMPORT{builtin}="path_id"
ENV{ID_PATH}=="?*", SYMLINK+="lp/by-path/$env{ID_PATH}"

LABEL="persistent_printer_end"
Identifying a disk by its serial
To perform some action on a specific disk device
/dev/sd
X
identified permanently by its unique serial
ID_SERIAL_SHORT
as displayed with
udevadm info /dev/sd
X
, one can use the below rule. It is passing as a parameter the device name found if any to illustrate:
/etc/udev/rules.d/69-disk.rules
ACTION=="add", KERNEL=="sd[a-z]", ENV{ID_SERIAL_SHORT}=="
X5ER1ALX
", RUN+="/path/to/script /dev/%k"
Waking from suspend with USB device
A udev rule can be useful to enable the
wakeup triggers
of a USB device, like a mouse or a keyboard, so that it can be used to wake the system from sleep.
Megjegyzés
By default, the USB host controllers are all enabled for wakeup. The status can be checked using
cat /proc/acpi/wakeup
. The rule below is in this case not necessary but can be used as a template to perform other actions, like disabling the wakeup functionality for example.
First, identify the vendor and product identifiers of the USB device. They will be used to recognize it in the udev rule. For example:
$ lsusb | grep Logitech
Bus 007 Device 002: ID
046d
:
c52b
Logitech, Inc. Unifying Receiver
Then, find where the device is connected to using:
$ grep
c52b
/sys/bus/usb/devices/*/idProduct
/sys/bus/usb/devices/
1-1.1.1.4/
idProduct:c52b
Now create the rule to change the
power/wakeup
attribute of both the device and the USB controller it is connected to whenever it is added:
/etc/udev/rules.d/50-wake-on-device.rules
ACTION=="add", SUBSYSTEM=="usb", DRIVERS=="usb", ATTRS{idVendor}=="
046d
", ATTRS{idProduct}=="
c52b
", ATTR{power/wakeup}="enabled", ATTR{driver/
1-1.1.1.4
/power/wakeup}="enabled"
Triggering events
This article or section is a candidate for merging with
#Testing rules before loading
.
Notes:
similar trick (Discuss in
Talk:Udev (Magyar)
)
It can be useful to trigger various
udev
events. For example, you might want to simulate a USB device disconnect on a remote machine. In such cases, use
udevadm trigger
:
# udevadm trigger --verbose --type=subsystems --action=remove --subsystem-match=usb --attr-match="idVendor=abcd"
This command will trigger a USB remove event on all USB devices with vendor ID
abcd
.
Triggering desktop notifications from a udev rule
To trigger a desktop notification from a
udev
rule, use
systemd-run(1)
as explained in
Desktop notifications#Send notifications to another user
:
Create the file:
/etc/udev/rules.d/99-powersupply_notification.rules
# Rule for when switching to battery
ACTION=="change", SUBSYSTEM=="power_supply", ATTRS{type}=="Mains", ATTRS{online}=="0", RUN+="/usr/bin/systemd-run --machine=
target_user
@.host --user notify-send 'Changing Power States' 'Using battery power'"
# Rule for when switching to AC
ACTION=="change", SUBSYSTEM=="power_supply", ATTRS{type}=="Mains", ATTRS{online}=="1", RUN+="/usr/bin/systemd-run --machine=
target_user
@.host --user notify-send 'Changing Power States' 'Using AC power'"
To launch multiple or long commands, an
executable
script can be given to
systemd-run
:
/usr/local/bin/from_battery.sh
#!/bin/sh

paplay /usr/share/sounds/freedesktop/stereo/power-unplug.oga
notify-send --icon=/usr/share/icons/Adwaita/symbolic/legacy/battery-good-symbolic.svg 'Changing Power States' 'Using battery power' --expire-time=4000
Megjegyzés
If the rule triggers before the X server starts, it may not work as intended. See
#X programs in RUN rules hang when no X server is present
.
Troubleshooting
Blacklisting modules
In rare cases,
udev
can make mistakes and load the wrong modules. To prevent it from doing this, you can
blacklist
modules. Once blacklisted,
udev
will never load that module – not at boot-time and not even later on when a hot-plug event is received (e.g., you plug in your USB flash drive).
Debug output
To get hardware
debug
info, use the
kernel parameter
udev.log-priority=debug
. Alternatively you can set
/etc/udev/udev.conf
udev_log="debug"
This option can also be compiled into your initramfs by adding the configuration file to your
FILES
array:
/etc/mkinitcpio.conf
FILES=(... /etc/udev/udev.conf)
and then
regenerate the initramfs
.
udevd hangs at boot
After migrating to LDAP or updating an LDAP-backed system,
udevd
can hang at boot at the message "Starting UDev Daemon". This is usually caused by
udevd
trying to look up a name from LDAP but failing, because the network is not up yet. The solution is to ensure that all system group names are present locally.
Extract the group names referenced in
udev
rules and the group names actually present on the system:
# grep -Fr GROUP /etc/udev/rules.d/ /usr/lib/udev/rules.d/ | sed 's:.*GROUP="\([-a-z_]\{1,\}\)".*:\1:' | sort -u >udev_groups
# cut -d: -f1 /etc/gshadow /etc/group | sort -u >present_groups
To see the differences, do a side-by-side diff:
# diff -y present_groups udev_groups
...
network							      <
nobody							      <
ntp							      <
optical								optical
power							      |	pcscd
rfkill							      <
root								root
scanner								scanner
smmsp							      <
storage								storage
...
In this case, the
pcscd
group is for some reason not present in the system.
Add the missing groups
. Also, make sure that local resources are looked up before resorting to LDAP.
/etc/nsswitch.conf
should contain the following line:
group: files ldap
Some devices, that should be treated as removable, are not
You need to create a custom
udev
rule for that particular device. To get definitive information of the device you can use either
ID_SERIAL
or
ID_SERIAL_SHORT
(remember to change
/dev/sdb
if needed):
$ udevadm info /dev/sdb | grep ID_SERIAL
Then we set
UDISKS_AUTO="1"
to mark the device for automounting and
UDISKS_SYSTEM="0"
to mark the device as "removable". See
udisks(8)
for details.
/etc/udev/rules.d/99-removable.rules
ENV{ID_SERIAL_SHORT}=="
serial_number
", ENV{UDISKS_AUTO}="1", ENV{UDISKS_SYSTEM}="0"
Remember to reload
udev
rules with
udevadm control --reload
. Next time you plug your device in, it will be treated as an external drive.
Sound problems with some modules not loaded automatically
Some users have traced this problem to old entries in
/etc/modprobe.d/sound.conf
. Try cleaning that file out and trying again.
Megjegyzés
Since
udev>=171
, the OSS emulation modules (
snd_seq_oss
,
snd_pcm_oss
,
snd_mixer_oss
) are not automatically loaded by default.
Optical drives have group ID set to "disk"
If the group ID of your optical drive is set to
disk
and you want to have it set to
optical
, you have to create a custom
udev
rule:
/etc/udev/rules.d
# permissions for SCSI CD devices
SUBSYSTEMS=="scsi", KERNEL=="s[rg][0-9]*", ATTRS{type}=="5", GROUP="optical"
X programs in RUN rules hang when no X server is present
When
xrandr
or another X-based program tries to connect to an X server, it falls back to a TCP connection on failure. However, due to
IPAddressDeny
in the
systemd-udev service configuration
, this hangs. Eventually the program will be killed and event processing will resume.
If the rule is for a drm device and the hang causes event processing to complete once the X server has started, this can cause 3D acceleration to stop working with a
failed to authenticate magic
error.
További olvasnivaló a témában
udev(7)
An Introduction to udev
udev mailing list information
Scripting with udev
Writing udev rules
Device and Module Handling on an LFS System
Running GUI or accessing display variables from udev rules
openSUSE udev documentation