Raspberry Pi Console over USB: Configuring an Ethernet Gadget (Shallow Thoughts)

Raspberry Pi Console over USB: Configuring an Ethernet Gadget

When I work with a Raspberry Pi from anywhere other than home, I want to make sure I can do what I need to do without a network.

With a Pi model B, you can use an ethernet cable. But that doesn't work with a Pi Zero, at least not without an adapter. The lowest common denominator is a serial cable, and I always recommend that people working with headless Pis get one of these; but there are a lot of things that are difficult or impossible over a serial cable, like file transfer, X forwarding, and running any sort of browser or other network-aware application on the Pi.

Recently I learned how to configure a Pi Zero as a USB ethernet gadget, which lets you network between the Pi and your laptop using only a USB cable. It requires a bit of setup, but it's definitely worth it. (This apparently only works with Zero and Zero W, not with a Pi 3.)

The Cable

The first step is getting the cable. For a Pi Zero or Zero W, you can use a standard micro-USB cable: you probably have a bunch of them for charging phones (if you're not an Apple person) and other devices.

Set up the Pi

Setting up the Raspberry Pi end requires editing two files in /boot, which you can do either on the Pi itself, or by mounting the first SD card partition on another machine.

In /boot/config.txt add this at the end:

dtoverlay=dwc2

In /boot/cmdline.txt, at the end of the long list of options but on the same line, add a space, followed by: modules-load=dwc2,g_ether

Set a static IP address

This step is optional. In theory you're supposed to use some kind of .local address that Bonjour (the Apple protocol that used to be called zeroconf, and before that was called Rendezvous, and on Linux machines is called Avahi). That doesn't work on my Linux machine. If you don't use Bonjour, finding the Pi over the ethernet link will be much easier if you set it up to use a static IP address. And since there will be nobody else on your USB network besides the Pi and the computer on the other end of the cable, there's no reason not to have a static address: you're not going to collide with anybody else.

You could configure a static IP in /etc/network/interfaces, but that interferes with the way Raspbian handles wi-fi via wpa_supplicant and dhcpcd; so you'd have USB networking but your wi-fi won't work any more.

Instead, configure your address in Raspbian via dhcpcd. Edit /etc/dhcpcd.conf and add this:

interface usb0
static ip_address=192.168.7.2
static routers=192.168.7.1
static domain_name_servers=192.168.7.1

This will tell Raspbian to use address 192.168.7.2 for its USB interface. You'll set up your other computer to use 192.168.7.1.

Now your Pi should be ready to boot with USB networking enabled. Plug in a USB cable (if it's a model A or B) or a micro USB cable (if it's a Zero), plug the other end into your computer, then power up the Pi.

Setting up a Linux machine for USB networking

The final step is to configure your local computer's USB ethernet to use 192.168.7.1.

On Linux, find the name of the USB ethernet interface. This will only show up after you've booted the Pi with the ethernet cable plugged in to both machines.

ip a

The USB interface will probably start eith en and will probably be the last interface shown.

On my Debian machine, the USB network showed up as enp0s26u1u1. So I can configure it thusly (as root, of course):

ip a add 192.168.7.1/24 dev enp0s26u1u1
ip link set dev enp0s26u1u1 up

(You can also use the older ifconfig rather than ip: sudo ifconfig enp0s26u1u1 192.168.7.1 up)

You should now be able to ssh into your Raspberry Pi using the address 192.168.7.2, and you can make an appropriate entry in /etc/hosts, if you wish.

For a less hands-on solution, if you're using Mac or Windows, try Adafruit's USB gadget tutorial. It's possible that might also work for Linux machines running Avahi. If you're using Windows, you might prefer CircuitBasics' ethernet gadget tutorial.

Happy networking!

Update: there's now a Part 2: Routing to the Outside World and Part 3: an Automated Script.

Tags: raspberry pi, linux, networking
[ 14:53 Feb 02, 2018    More linux | permalink to this entry | ]