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udevadm

Learn how to use udevadm to inspect device properties, explore sysfs paths, monitor udev events, test udev rules, and debug hardware on Linux systems.

Find the sysfs path for our bluetooth interface

udevadm info -q path -p /sys/class/bluetooth/hci0

Show full dump of hci0 interface

udevadm info -a -p /sys/class/bluetooth/hci0

If you want properties (ENV style) rather than the attribute-walk

udevadm info -p /sys/class/bluetooth/hci0 --query=property

To find the underlying parent device (USB device path), do

udevadm info -a -p /sys/class/bluetooth/hci0 | less

Setting headphones to on/off and following will show up

udevadm monitor
monitor will print the received events for:
UDEV - the event which udev sends out after rule processing
KERNEL - the kernel uevent

KERNEL[114270.712195] remove   /devices/virtual/input/input36/event20 (input)
UDEV  [114270.723087] remove   /devices/virtual/input/input36/event20 (input)
KERNEL[114270.750362] remove   /devices/virtual/input/input36 (input)
UDEV  [114270.750918] remove   /devices/virtual/input/input36 (input)
KERNEL[114271.022271] remove   /devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.3/1-3.3:1.0/bluetooth/hci0/hci0:69 (bluetooth)
UDEV  [114271.024572] remove   /devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.3/1-3.3:1.0/bluetooth/hci0/hci0:69 (bluetooth)
KERNEL[114276.446328] add      /devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.3/1-3.3:1.0/bluetooth/hci0/hci0:71 (bluetooth)
UDEV  [114276.454486] add      /devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.3/1-3.3:1.0/bluetooth/hci0/hci0:71 (bluetooth)
KERNEL[114277.949132] add      /devices/virtual/input/input37 (input)
KERNEL[114277.949530] add      /devices/virtual/input/input37/event20 (input)
UDEV  [114277.951557] add      /devices/virtual/input/input37 (input)
UDEV  [114277.988819] add      /devices/virtual/input/input37/event20 (input)

Simulating udev rule execution for hci0

udevadm test /sys/class/bluetooth/hci0

Identify the PCI controller backing /dev/sda

udevadm info -q property -n /dev/sdb \
    | awk -F= '$1=="ID_PATH"{ sub(/^pci-/,"",$2); sub(/-.*/,"",$2); sub(/^0000:/,"",$2); print $2 }' \
    | xargs -r -n1 lspci -s

Dump info about our harddrive

udevadm info --query=property --name=/dev/sda

See if a drive is luks protected by udevadm

$ udevadm info --query=property --name=/dev/sdb|grep 'ID_FS_TYPE'
ID_FS_TYPE=crypto_LUKS

If rules fail to reload automatically

 udevadm control --reload

To manually force udev to trigger your rules

udevadm trigger

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

Dump serial number for disk drive of sdc

udevadm info --query=property --property=ID_SERIAL,ID_SERIAL_SHORT --name=/dev/sdc

Resource(s)