Can I connect two Linux systems via USB?

Question

I would like to hook up my new Raspberry Pi A+ to an older B model without having to connect the A+ to WiFi. Can I connect them somehow via USB? Can I do it with a hub in between?

Answer 1

I wanted to expand upon Chisight's helpful answer.

I lack a keyboard/monitor that can connect to a Pi, so I followed gbaman's "quick route" instructions linked from the first Gist.

I connected a Pi Zero to a Pi 3 B+ in this way. I could use ping and ssh to access the link-local name raspberrypi.local with no problem, I think this is thanks to avahi-daemon. I also verified this using the command getent hosts -s mdns4_minimal raspberrypi.local which I had learned about from this serverfault question. However, when the Pi Zero was connected to my Arch Linux machine I did not have a working raspberrypi.local and so had to discover the IP of the connected device using arp-scan as described here.

Being able to ssh into the Zero was great, but not the end of the road. At this point the Zero did not have network access, and in fact its presence as a USB network device caused the Pi 3 to lose outgoing wireless access. (This was due to a usb0 link-local entry which appeared in the Pi 3 routing table with higher priority than the wireless gateway) To give access to the Pi Zero, I configured a static IP for both ends of the USB device, and set up NAT on the Pi 3 to forward connections from the Zero. This was according to instructions from BurtyB on Freenode's #raspberrypi:

## Pi Zero add to /etc/dhcpcd.conf

profile fb_usb0
static ip_address=172.19.180.1/24
static routers=172.19.180.254
static domain_name_servers=8.8.8.8 208.67.222.222

interface usb0
fallback fb_usb0

## Pi 3 add to /etc/dhcpcd.conf

profile fb_usb0
static ip_address=172.19.180.254/24

interface usb0
fallback fb_usb0

## Pi 3 setup NAT

sudo sh -c "echo 'net.ipv4.ip_forward=1' >> /etc/sysctl.conf"
sudo sysctl -p /etc/sysctl.conf

sudo iptables -t nat -A POSTROUTING -s 172.19.180.0/24 ! -o usb0 -j MASQUERADE
sudo iptables -A FORWARD -i usb0 ! -o usb0 -j ACCEPT
sudo iptables -A FORWARD -o usb0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
sudo sh -c "iptables-save > /etc/iptables/rules.v4"

# ^ first you need to
# apt-get install iptables-persistent

These instructions could be easily adapted to give the Pi Zero network access via a laptop or other computer. Once I followed them, I was able to run apt-get on the Zero and finish configuring it to my liking. Before BurtyB told me to use NAT, I had gotten sidetracked trying to set up a bridge with brctl, which doesn't work between ethernet and wireless devices - so don't do that...

(Strangely, after I did these things I no longer had an issue with the routing table on the Pi 3. It had been suggested earlier that I configure metric values in /etc/dhcpcd.conf to fix the routing priority table issue but the problem persisted, which was a mystery. This is from the Pi 3

$ ip route
default dev usb0 scope link
default via 192.168.1.1 dev wlan0 src 192.168.1.123 metric 200
169.254.0.0/16 dev usb0 proto kernel scope link src 169.254.38.33 metric 300
192.168.1.0/24 dev wlan0 proto kernel scope link src 192.168.1.123 metric 200

whose dhcpcd.conf still has the metric values:

interface wlan0
metric 200

# from BurtyB at #raspberrypi
profile fb_usb0
static ip_address=172.19.180.254/24

interface usb0
fallback fb_usb0
metric 300

...)

Answer 2

You can't use USB to connect to computers to each other. Use a crossover ethernet cable! Make sure to configure the IPs.

edit: a+ doesn't have ethernet cable. Consider using USB ethernet adapter.

Answer 3

Connect them via UART! You will have them talking in no time.

Here is a link to get you started:http://www.raspberry-projects.com/pi/programming-in-c/uart-serial-port/using-the-uart

just connect tx to the other rx and rx to the other tx.

Answer 4

Yes! The Pi A, A+ and Zero are special, they each support USB OTG and can connect directly to other computers via USB.

These models alone are special and this feature does not exist on any Pi that has more than one USB data connector like the B, B+ 2B, 3B and likely not any bigger Pi in the future.

The basic steps are in this gist https://gist.github.com/gbaman/50b6cca61dd1c3f88f41

Note that the command including BRANCH=next should not be used, it no longer works and isn't even available anymore, you just update your Pi the usual way and you'll get the updates needed.

Answer 5

There are two options:

1.) A special USB Cable with USB-A Plugs on each end. They have a chip inside that tels both sides that this would be an USB Stick or something. So you will need a special software and that software for ARM to use it. So this is the hard way.

2.) Just use a Ethernet Cable and two USB-Ethernet Adapters. This will be supported by the Kernel and you now have a LAN connection between the two. Only issue is that at least one of the USB-Ethernet Adapters has to support Auto-MDI. If they both do not support it then you need a Cross-Over Cable. A cross over Cable is a special LAN cable that has a special pin layout so that two host can be connected with each other. In the normal case you connect a host to a switch. The Auto-MDI feature automatically detects if a normal cable or a cross over cable is needed and can do the cross over part automatically if needed.

Answer 6

As others have pointed out you can't do this via USB (at least without writing your own drivers).

There are 3 simple options (without any additional hardware); serial, SPI or I²C.

You first have to define what you are trying to achieve.

Serial is the time honoured solution; indeed once all UNIX machines did this, before IP was invented. There is a lot of support built into any Linux system to support this.

The other protocols are more suitable to using one device as a slave.

Answer 7

The only thing that comes close is to access one Pi over the Serial Console using a serial USB adapter

These are the same used to programme Arduino 3.3v boards. basically it gives you a Console over USB on Pi, and a Serial on the other.

You asked for USB, but you may just connect the two directly RX to TX and TX to RX. The problem with this is that 2 is the max. There are ways to get more but it get more complicated than needed.