How to symlink a device throught udev and always point to the same device?

Question

I have the following udev rule for a USB thermal printer that works with serial through usb:

SUBSYSTEMS=="usb", ATTRS{idVendor}=="1c8a", ATTRS{idProduct}=="3001", SYMLINK+="ttyS99", MODE="0660", GROUP="lp"

output of ls -la:

lrwxrwxrwx 1 root root 7 ago 21 10:50 /dev/ttyS99 -> ttyACM1

but if I power it off and on again, it symlinks to the wrong device:

output of ls -la after powering off and on again:

lrwxrwxrwx 1 root root 15 ago 22 13:28 /dev/ttyS99 -> bus/usb/001/008

How can I make it always point to ttyACM1 ?

score 2 · Answer 1 · edited Sep 25 '18 at 10:12

2

Found the answer: I added SUBSYSTEM=="tty" at the start:

SUBSYSTEM=="tty", SUBSYSTEMS=="usb", ATTRS{idVendor}=="1c8a", ATTRS{idProduct}=="3001", SYMLINK+="ttyS99", MODE="0660", GROUP="lp"

edited Sep 25 '18 at 10:12

abu_bua

answered Aug 22 '18 at 17:03

Thiago Sayão

score -1 · Answer 2 · edited Sep 25 '18 at 10:10

-1

Change SUBSYSTEMS to SUBSYSTEM in the usb rule in your initial ruleset and then it will work.

edited Sep 25 '18 at 10:10

abu_bua

answered Sep 24 '18 at 08:40

kimusan

This does answer the question. I have now reformulated. – kimusan Sep 25 '18 at 10:06
the case is that the SUBSYSTEM="tty" part is not needed. Problem is that OP had the spelling error in the first place – kimusan Sep 25 '18 at 10:13
The tty is needed since he communicates to usb via serial. – abu_bua Sep 25 '18 at 10:56
that wont be needed until the bind event - the SUBSYSTEM=usb will catch it at the add event. – kimusan Sep 26 '18 at 08:27

2 Answers2