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I want to know how I can list all udev rules.

I know that in they can be potentially stored as lines (one line = one rule) in *.rules files in these directories

/etc/udev/rules.d
/lib/udev/rules.d
/run/udev/rules.d
/var/run/udev/rules.d

Therefore I though I can find all rules by simple concating all the *.rules files in those directories. This seems not to be working (because some rules are executed which I cannot find anyware as rules in these directories).

At best I thought that there is a command to the udevadm interface which will let me print out all the rules that udev currently has.

To be certain I did a review of man udevadm and especially the part about udevadm info [parameters] does not seem to yield any result.

Given that udev allows for a multitude of files and rules all targeted for the very same device, it is frustrating not to know an efficient/feasible way to compose all the rules for a device.

  • 4
    Unfortunately, if you are using systemd, it's version of udev has a complex "persistent naming scheme" that's hard coded into udevd, so you are right, just parsing the rules.d stuff could leave a lot of mysteries. – goldilocks Feb 1 '15 at 15:46
8

If you use:

udevadm monitor

you get an entry for each action taken by KERNEL and UDEV. Typically add, change, remove. If you include the --property option:

udevadm monitor --property

You will get a listing of what properties are used.


As one can test udev rules with udevadm:

udevadm test $(udevadm info -q path -n <device>)

one could test out something as this:

udevadm test $(udevadm info -q path -n <device>) 2>&1 | \
sed -n 's/.* \(\/[^ ]*\)\.rules:\([0-9]\+\)/\1.rules \2/p' | \
while read -r f n; do printf "%03d:%-50s " $n "$f"; sed -n ${n}p $f; done

but not sure how reliable this is. Anyhow, using e.g. video1 for <device> that could yield something like:

031:/lib/udev/rules.d/50-udev-default.rules            SUBSYSTEM=="video4linux", GROUP="video"
007:/lib/udev/rules.d/60-persistent-v4l.rules          IMPORT{program}="v4l_id $devnode"
009:/lib/udev/rules.d/60-persistent-v4l.rules          SUBSYSTEMS=="usb", IMPORT{builtin}="usb_id"
010:/lib/udev/rules.d/60-persistent-v4l.rules          KERNEL=="video*", ENV{ID_SERIAL}=="?*", SYMLINK+="v4l/by-id/$env{ID_BUS}-$env{ID_SERIAL}-video-index$attr{index}"
016:/lib/udev/rules.d/60-persistent-v4l.rules          IMPORT{builtin}="path_id"
017:/lib/udev/rules.d/60-persistent-v4l.rules          ENV{ID_PATH}=="?*", KERNEL=="video*|vbi*", SYMLINK+="v4l/by-path/$env{ID_PATH}-video-index$attr{index}"
015:/lib/udev/rules.d/73-seat-late.rules               TAG=="uaccess", ENV{MAJOR}!="", RUN{builtin}+="uaccess"
006:/etc/udev/rules.d/83-webcam.rules                  KERNEL=="video[0-9]", SUBSYSTEMS=="usb", ATTRS{idVendor}=="0c45", SYMLINK+="video-webcam1"

But guess looking at the test as a whole is better. Also note the message:

This program is for debugging only, it does not run any program specified by a RUN key. It may show incorrect results, because some values may be different, or not available at a simulation run.


You can also set

udev_log="debug"

in udev.conf and restart udev (reload udev) to get a somewhat more verbose output.

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