Linux: Remember path to USB Device

linux

In Linux, Is there a way to remember/change a path to a USB device?

In my case, I need linux to remember that my USB serial adapter will stay on /dev/ttyUSB0, but when I unplug it and plug it back in, it switches to /dev/ttyUSB1.

I'm using a debian-based distro(mint), if that helps. Thanks!

Best Answer

Get to know properties of the device while it is switched in:

udevinfo -a -p $(udevinfo -q path -n /dev/ttyUSB0)

If you have some newer distribution where udevinfo is not available, use this instead:

udevadm info -q all -p $(udevadm info -q path -n /dev/ttyUSB0)
Find some property that can identify the device (uniquely), for instance "serial"
Create a file called /etc/udev/rules.d/10-usb-serial which contains the line:

BUS=="usb", ATTR{serial}=="xxxx", NAME="ttyUSB0"

Note the two equal signs for properties that are tested, and one for that which is assigned to.

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If you run udevadm monitor --properties you should see the various properties you can use to create rules from. The ID_PATH property indicates the port the device was plugged into. Insert the serial to usb device to see what udev sees.

So it should be straightforward to create a udev rule that creates a symlink when the device is plugged in, something like:

SUBSYSTEM=="usb_device", SYSFS{idVendor}=="xxxx", SYSFS{idProduct}=="xxxx", ENV{ID_PATH}=="pci....usb-0:1:0",SYMLINK+="ttyUSBport0"
SUBSYSTEM=="usb_device", SYSFS{idVendor}=="xxxx", SYSFS{idProduct}=="xxxx", ENV{ID_PATH}=="pci....usb-0:1:1",SYMLINK+="ttyUSBport1"

This is done from memory so you'll want to confirm the syntax. Change the idvendor and idproduct to the USB VID and PID, and change the ID_PATH to whatever you found in udevadm monitor.

This should leave the normal /dev/ttyUSB0 device there, but also create a symlink to it depending on which port it was plugged into. If you use the symlink in minicom or whatever you are using, you'll always get the right adapter based on the port you plug it into.

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I believe I am running these on Debian. Try installing wvdial, and edit /etc/wvdial.conf to look like below. Then run wvdial and see what it says.

[Dialer Defaults]
Stupid mode = 1
Dial Command = atdt
Carrier Check = no
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Modem Type = USB Modem
Phone = *99***3#
ISDN = 0
Password = 1
New PPPD = yes
Username = 1
Modem = /dev/ttyACM0
Baud = 460800

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