Persistant name in usb device which open several connections || connect USB to specific port [duplicate] - linux

Question

This question already has an answer here:
Change default names for USB virtual serial ports in Linux
(1 answer)
Closed 5 years ago.
I am trying to add a persistent name to a USB device connection to be able to connect to it by writing /dev/multitech instead of /devttyACMx. I have been able to do so with other devices by adding an udev rule, for example:
SUBSYSTEM=="tty", ATTRS{idVendor}=="1bc7", ATTRS{idProduct}=="0021",ATTRS{serial}=="356136967675473", SYMLINK+="multitech"
The problem is that this device open 6 connections, from ttyACM0 to ttyACM5 (if nothing else connected) but to use it you have to use the ttyACM0 (meaning the first connection) but if you write:
$ ls -l /dev/multitech
you may get whatever connection it has open, maybe ttyACM0 or maybe ttyACM3... the thing is that this is useless for me, since it sometimes works and sometimes it does not. Is there anything I can do about this?
Thanks a lot!!

Answer 1

normally each connection the device establishes has its own interface or alternate setting in USB tree structure. in udev rules you can use several other attributes (all you can display using udevadm info --attribute-walk http://www.beyondlogic.org/usbnutshell/usb5.shtml#InterfaceDescriptors )
run an attribute walk with udevadm info --attribute-walk + /sys/class/... or /dev/... path for your device to see the identifiers of the several usb interfaces it has in its usb structure and try to include them in the udev rule, i.e. using the following attributes:
ATTRS{bAlternateSetting}=="..."
ATTRS{bInterfaceClass}=="..."
ATTRS{bInterfaceNumber}=="..."
ATTRS{bInterfaceProtocol}=="..."
ATTRS{bInterfaceSubClass}=="..."
try to assign a specific /dev/ttyACMx for any interface the device has in its usb structure and try to assign the top-level interface in the usb structure to /dev/ttyACM0 ...
http://weininger.net/how-to-write-udev-rules-for-usb-devices.html

Answer 2

Change default names for USB virtual serial ports in Linux
This post was the solution to my troubles, instead of using the /devttyACMx
y changed to used the names in /dev/serial/by-id/
up until now it has worked fine, if it stops doing it I will post it