su command in /usr/bin

user1571823

12/6/22, 11:13 PM

I have an udev rule that runs a command as root. I have two different machines running on ubuntu and the su command in these machines are located in different locations. In one computer is located in /bin/ (ubuntu 20.04.2), while in the other is located in /usr/bin/ (ubuntu 20.10). The rule only works on the machine where su is located in /usr/bin/, even if I modify the path appropriately. How can I install su in /usr/bin/ in ubuntu 20.04.2?

The udev rule is:

ACTION=="add"\ 
, SUBSYSTEM=="bluetooth"\ 
, ATTR{idVendor}=="hci0"\ 
, ATTR{idProduct}=="3585"\ 
, RUN+="/usr/bin/su root -c 'ratbagctl M720\ Triathlon button 7 action set button 3'"

0 + 8

udev

20.04

steeldriver

12/6/22, 11:30 PM

If both systems were installed from scratch, they both should have `/bin` symlinked to `/usr/bin`, and both use `su` from `util-linux` I think. OTOH if either was upgraded (from 18.04 for example) it's possible that it is using the implementation of `su` from the `login` package.

user1571823

12/7/22, 7:41 AM

yes ubuntu 20.04.2 was upgraded from 18.04. I am not sure how/why ubuntu 20.10 has `su` in /usr/bin.

steeldriver

12/7/22, 1:06 PM

This seems like it might be an XY problem - why are you using `su root` at all here, since UDEV rules presumably run as root anyhow (and if they didn't, `su` would need to run interactively, to obtain root's password)

user1571823

12/7/22, 1:36 PM

see the comment from nrayamajhee here https://github.com/libratbag/libratbag/issues/596

steeldriver

12/7/22, 1:58 PM

I suspect that's a "hail mary" solution that the author doesn't really understand why it works - instead of trying to figure out the correct absolute path to `su` with the hope that the `ratbagctl` command is in the root shell's `PATH`, I'd suggest giving an absolute path to `ratbagctl` directly i.e. something like `RUN+=/usr/local/bin/ratbagctl Logitech\ MX\ Anywhere\ 2S dpi set 2400`

user1571823

12/7/22, 8:02 PM

it doesnt work like this `ACTION=="add", SUBSYSTEM=="bluetooth", ATTR{idVendor}=="hci0", ATTR{idProduct}=="3585", RUN+="/usr/bin/ratbagctl M720\ Triathlon button 7 action set button 3"`I remember that last time it took me a while to make the udev rule to work (and the final rule that worked is that I posted above).

user1571823

12/7/22, 8:18 PM

for some reason the udev rule is not being triggered. So at this point the problem is not necessarily the run command (I have replace the run command for another one that writes a time stamp, and it is not working neither)

steeldriver

12/7/22, 8:26 PM

OK so make sure you also give the full path to whatever command writes the timestamp - as noted in `man udev` *If no absolute path is given, the program is expected to live in /lib/udev; otherwise, the absolute path must be specified.*. Apologies for omitting the quotes above, you are correct it should be `RUN+="/path/to/command args"`. Check where `ratbagctl` is actually located with `which ratbagctl` and/or `type -a ratbagctl`.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: su command in /usr/bin

TH: คำสั่ง su ใน /usr/bin

RO: comanda su în /usr/bin

RU: команду su в /usr/bin

VI: lệnh su trong /usr/bin

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