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This is an old revision of the document!

udevadm

reloading rules

udevadm control --reload-rules

Testing rules

udevadm test /sys/class/tty/ttyACM0

Getting info

udevadm info --attribute-walk --path=/sys/class/tty/ttyACM0

Get Telit modem serial number

udevadm info -q property -n /dev/ttyACM1 | grep ID_SERIAL_SHORT
ID_SERIAL_SHORT=356136070718830

Debug

/etc/udev/udev.conf
udev_log="debug"

Rules

Order

Files should be named xx-descriptive-name.rules, the xx should be chosen first according to the following sequence points:

< 60 most user rules; if you want to prevent an assignment being overriden by default rules, use the := operator.

these cannot access persistent information such as that from vol_id

< 70 rules that run helpers such as vol_id to populate the udev db

< 90 rules that run other programs (often using information in the udev db)

>=90 rules that should run last

Executing commands

Triggering commands should be done using RUN, because it is executed after all systemd actions. 

SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="0", RUN+="/usr/bin/true"
SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="1", RUN+="/usr/bin/true"

RUN vs PROGRAM

PROGRAM is used to return device name, e.g. to return name for symlink. It is called during device setup, so it is not good place to execute external tools. 

ACTION=="add", DRIVERS=="usb", ATTRS{manufacturer}=="Telit", ATTRS{idVendor}=="1bc7", ATTRS{idProduct}=="0021", PROGRAM="/bin/sh -c '/bin/echo -e {\\042imei\\042:\\042%s{serial}\\042} > /etc
/imei.json'"
SUBSYSTEM=="input", KERNEL=="event[0-9]*", ENV{ID_INPUT_TOUCHSCREEN}=="1", ATTRS{name}=="edt-ft53*", SYMLINK+="input/touchscreen", OPTIONS+="link_priority=100"
SUBSYSTEM=="input", KERNEL=="event[0-9]*", ENV{ID_INPUT_TOUCHSCREEN}=="1", ATTRS{name}=="ti-tsc",    SYMLINK+="input/touchscreen", OPTIONS+="link_priority=0"

link_priority: higher has higher priority

Triggering systemd

SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="0", TAG+="systemd", ENV{SYSTEMD_WANTS}="powersaving.service"
SUBSYSTEM=="power_supply", ENV{POWER_SUPPLY_ONLINE}=="1", TAG+="systemd", ENV{SYSTEMD_WANTS}="powersaving.service"
SUBSYSTEM=="printer", TAG+="systemd", ENV{SYSTEMD_WANTS}="printer.target"

Prevent ModemManager

/etc/udev/rules.d/99-nomm.rules
ATTRS{idVendor}=="0451" ATTR{idProduct}=="bef3", ENV{ID_MM_DEVICE_IGNORE}="1"