ttyTHSx belonging to different usergroup

Robotics & Edge Computing Jetson & Embedded Systems Jetson Xavier NX
1

Dear forum,

I would like to know why the /dev/ttyTHS0 and /dev/ttyTHS1 on my Jetson Xavier NX / Jetpack-5.1.2 based system have different groups please ?

nvidia@JXNX:~$ ls -l /dev/ttyTHS0
crw--w---- 1 root tty 237, 0 Thg 6   6 10:31 /dev/ttyTHS0

nvidia@JXNX:~$ ls -l /dev/ttyTHS1
crw-rw---- 1 root dialout 237, 1 Thg 6   6 10:31 /dev/ttyTHS1

Thanks,
Khang

3

Hi khang.l4es,

Are you using the devkit or custom board for Xavier NX?

Could you try to disable nvgetty service and reboot the board to check again?

$ sudo systemctl stop nvgetty.service
$ sudo systemctl disable nvgetty.service
4

The driver creates the initial device special file and ownership/permissions. After that, udev can modify this. dialout is the group for a UART without any special ownership. tty is the group when the UART is assigned as a serial console (udev makes the adjustment at the moment serial console takes ownership). What @KevinFFF mentions is how to stop the serial console program. Then it would revert to just dialout and be free to use. Not usually a good idea though to not have serial console on a development system.

5

Hi @KevinFFF,

I am using the custom board with either Orin NX/Nano or Xavier NX on top. For the same Jetpack-5.1.2, both ttyTHS0 / ttyTHS1 belong to the dialout group and I was able to access them without sudoing by just adding the current user into that group. But it is not the same situation with the Xavier NX especially I could not access the ttyTHS0 without sudoing even I already added the current user into the dialout group, and I found out that the ttyTHSx do not belong to the same group.

After searching in the forum, this ttyTHSx belonging to different groups seems normal/by default in following discussion (that I’d expected your confirmation at first) :

https://forums.developer.nvidia.com/t/read-data-from-uart-without-superuser-permissions/173696/19

@linuxdev,

Thanks for your explanation, I also found your useful comments in above discussion as well.

Best Regards,
Khang

6

Please refer to my default configuration on Xavier NX devkit.

nvidia@Jetson:~$ ls -l /dev/ttyTHS*
crw--w---- 1 root tty     237, 0 Jan  1 01:00 /dev/ttyTHS0
crw-rw---- 1 root dialout 237, 1 Mar  3  2025 /dev/ttyTHS1
crw-rw---- 1 root dialout 237, 4 Mar  3  2025 /dev/ttyTHS4

It seems the similar result as the topic you linked.

8

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