Serial Port GID is root (not dialout) on Raspberry Pi CM4

ebab72

5/12/24, 4:31 PM

I am getting "Permission Denied" errors when trying to access /dev/serial0 on the Raspberry Pi CM4. I've tried the common suggestions of adding my user to the dialout and tty groups, but that has not worked. Interestingly, it seems that /dev/serial0 is not in the dialout group. When I run ls -l /dev/serial0 I get:

lrwxrwxrwx 1 root root 5 May 12 11:04 /dev/serial0 -> ttyS0

So you can see that it is part of the root group. Similarly, stat /dev/serial0 yields:

  File: /dev/serial0 -> ttyS0
  Size: 5               Blocks: 0          IO Block: 4096   symbolic link
Device: 5h/5d   Inode: 231         Links: 1
Access: (0777/lrwxrwxrwx)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2023-05-12 11:04:17.809999995 -0500
Modify: 2023-05-12 11:04:11.939999998 -0500
Change: 2023-05-12 11:04:11.939999998 -0500
 Birth: -

Showing the Gid is root, not dialout.

Following the simlink to /dev/ttyS0, I can see that this is part of the tty group:

crw--w---- 1 root tty 4, 64 May 12 11:04 /dev/ttyS0

I tried accessing /dev/ttyS0 directly (instead of /dev/serial0) and I still get the Permission Denied error, even though my user is part of the tty group.

Any suggestions on how to give my user permission on this port?

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guiverc

5/12/24, 11:23 PM

Please provide your OS/release details; is this a Ubuntu Core or Ubuntu Server install? and what release? (*they have some differences!*)

ebab72

5/16/24, 2:47 PM

I'm realizing now I probably shouldn't be in AskUbuntu with Raspberry Pi OS. But I'm on Raspberry Pi OS 5.15.84-v71+.

nobody

5/16/24, 4:01 PM

Maybe this will help https://raspberrypi.stackexchange.com/questions/132147/how-can-i-prevent-raspbian-from-resetting-user-privileges-on-dev-tttys0

guiverc

5/16/24, 10:17 PM

Please refer https://askubuntu.com/help/on-topic, Ubuntu and *official* flavors of Ubuntu (https://ubuntu.com/download/flavours) are on-topic on this site. The on-topic link provides alternate SE sites for non-Ubuntu OSes.

Elon Musk

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

EN: Serial Port GID is root (not dialout) on Raspberry Pi CM4

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