udev rule for usb attach/detach not triggering

Question

I'm running RHEL6 and I'm trying to write a udev rule that is triggered upon plugging in and removing usb devices. I created a file called 80-usb.rules in /etc/udev/rules.d/ and I gave it the following contents (so far nothing too specific, just want to test):

ACTION=="add", SUBSYSTEMS=="usb", RUN+="touch /tmp/test"

I saved the file and plugged in a USB drive to test. However, the file /tmp/test was not created.

I figure my udev rule should match my USB drive, since I can run udevadm info on the USB drive and at least one of the parent devices has the attribute SUBSYSTEMS=="usb".

Why might the udev rule not get triggered?

I tried to run udevadm test --action=add /path/to/device and it is clear that the .rules file that I wrote is being processed and that my rules are being matched. Here are a few relevant lines from the output:

parse_file: reading '/etc/udev/rules.d/80-usb.rules' as rules file
udev_rules_apply_to_event: RUN '/bin/touch /tmp/test' /etc/udev/rules.d/80-usb.rules:1
udevadm_test: run: '/bin/touch /tmp/test'

But still, /tmp/test does not exist. I am so confused. Clearly this rule is being matched and the rules are being applied. So why doesn't the command specified by RUN execute?

Answer 1

Your rule must give an absolute path for executable:

ACTION=="add", SUBSYSTEMS=="usb", RUN+="/usr/bin/touch /tmp/test"

Edit:

And if you want to execute a script, you must tell what shell will execute it:

ACTION=="add", SUBSYSTEMS=="usb", RUN+="/bin/sh /path/to/your/script"

Answer 2

You have to ensure the following:

• Paths in the RUN command should be absolute
• The file has to be executable
• The PATH environment is limited within the execution of you command

At first add this script file to /lib/udev/touch.sh

vim /lib/udev/touch.sh

in that file write:

#!/bin/bash
touch /tmp/test

make it executable:

chmod +x /lib/udev/touch.sh

and change your rules file to:

ACTION=="add", SUBSYSTEMS=="usb", RUN+="/lib/udev/touch.sh"

reload your udev rules

udevadm control --reload-rules

This will read your rules in /lib/udev/rules.d/* again. Changes will not apply until now.

Note that udev executes your script with a reduced PATH environment. You have to ensure that any binary that's not within the configured paths has to be accessed with a full path. You could also extend the PATH environment within your script.

Check what path is defined by logging the set output to a log file from your wrapper script:

set >>/tmp/udev-env-test

It might look like this:

PATH='/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'