Linux – How to get address of connected USB modem

I'm with @Renan: it looks like this problem was fixed in newer kernels. (One such thread on LKML.)

The key error is the invalid interface number one. It means the USB driver sees the device, but it's numbering its features (interfaces) in a way the driver doesn't expect, and it can't cope. Googling around, you can find several cases where people are fixing weaknesses in the kernel to cope with these newer devices, and their odd interface numbering behavior.

I'm not 100% certain on this, since I can't find a definitive document that says either that out-of-order interface numbers are wrong, or that it's all been fixed for all USB devices in kernel x.y.z. It appears to be more of a Whac-a-Mole sort of development effort.

Upgrading the kernel on a server is not an easy fix by any means. I would try an intermediate step to check the hypothesis first: put your server's version of Debian in to a VM, make a snapshot, upgrade the kernel there, and see if it will see the USB device after the upgrade. (Obviously you need to be using VM software that will push a USB device into the VM. Most will these days.)

If that doesn't work, you can easily roll back to the snapshot, since this VM should be useful for future testing before you roll something out to the prodouction server.

Try socat - /dev/ttyUSB2,crnl

This tells socat to send a carriage return as well as a line feed.

Clarification - this goes back to the dark days of electric typewriters, where you would have to tell it to roll the carriage back to position 0 on the page - ergo, a carriage return - as well as telling it to move the paper up one line.