Boot Raspi Zero from networked USB Port

"On-The-Go" OTG-Ports allow USB connector operate in two different modes

• Host mode
• Slave mode (Gadget mode)

USBBoot utility

First start by downloading the USBBoot utility and follow the instructions to compile the program.

(requires apt-get install git, build-essential)

git clone --depth=1 https://github.com/raspberrypi/usbboot

cd usbboot

sudo apt-get install libusb-1.0-0-dev

make

Prepare Raspi boot server:

Download latest Raspbian Stretch image to directory "downloads".

cd ~

mkdir downloads

cd downloads

wget https://downloads.raspberrypi.org/raspbian_lite_latest

Unzip image:

unzip raspbian_lite_latest

Setup loop device (and verify "losetup -a"):

cd ~

losetup -P /dev/loop0 downloads/[20..-..-..]-raspbian-stretch-lite.img

losetup -a

Create two mountpoints for boot and rootfs directories...

mkdir -p /pi/{boot,root}

...and mount the loop devices there:

mount /dev/loop0p1 /pi/boot

mount /dev/loop0p2 /pi/root

Setup NFS Server:

Install nfs-server:

apt install nfs-kernel-server

Make the /pi/root folder a NFS mount point, add this in the NFS config file `/etc/exports`

echo "/pi/root 192.168.100.10(rw,sync,no_subtree_check,no_root_squash)" | tee -a /etc/exports

Save and restart the NFS server.

systemctl start nfs-server.service

exportfs -a

Prepare the Pi Zero for the last parts.

Edit config.txt in the boot directory (/pi/boot) to enable USB OTG mode and add some instructions to add initramfs. This will load extra kernel modules, so the Pi Zero can use the USB cable as an ethernet connection.

Add these 4 lines in config.txt :

# enable OTG

 dtoverlay=dwc2

# set initramfs

 initramfs initrd.img followkernel

Then add and make your cmdline.txt look like this:

otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/nfs nfsroot=10.42.0.1:/pi/root rw ip=10.42.0.14:10.42.0.1::255.255.255.0:pi:usb0:static elevator=deadline modules-load=dwc2,g_ether fsck.repair=yes rootwait g_ether.host_addr=5e:a1:4f:5d:cf:d2

Let’s explain this. We need NFS mount (root=/dev/nfs), we set the network address (nfsroot=10.42.0.1:/pi/root rw) rw is read/write. We need the modules dwc2 ethernet gadget and g_ether and we set a fixed ethernet MAC address to ease, and we set the network addresses.

ip=10.42.0.14:10.42.0.1::255.255.255.0:pi:usb0:static

ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf> 

Remember Ubuntu/Linux will set USB networks on the 10.42.0.1 address range, and we give the pi the fixed address 10.42.0.14. Please read my other posts about setting up an USB connnecting with the pi Zero, if you need more information.

Now we need to make a initramfs to supply some needed kernel modules. This is the best done on another Pi 1 or Pi Zero. We need to add the g_ether module and it dependencies in initramfs.

Make initramfs

First install the needed tools.

sudo apt install initramfs-tools

Add these modules to the modules file:

sudo vi /etc/initramfs-tools/modules

g_ether

 libcomposite

 u_ether

 udc-core

 usb_f_rndis

 usb_f_ecm

Save and create the initramfs .

sudo update-initramfs -c -k `uname -r`

It will be saved (initrd.img-4.9.80+ or newer) in the boot directory. Copy that file to the boot directory on your laptop: /pi/boot/, and name it initrd.img. As long it is the same name as in the config.txt file, it’s OK.

Now where nearly done.

Modify /pi/root/etc/fstab in the Pi root directory, and comment out (or delete) the last two lines. The Pi shouldn’t try to mount SD-card images anymore.

Update: Then we need SSH to start automatically. (Thanks to Charlie for pointing this out. I forgot to document this step at first). An empty ssh file in boot will not do the trick this time, so we need to make it start it by adding this symlink in pi/root:

ln -s /lib/systemd/system/ssh.service /etc/systemd/system/multi-user.target.wants/ssh.service

Connect your Pi

Connect your Pi. Run the utility rpiboot:

 usbboot/rpiboot -d /pi/boot/ 

Make sure you set the connection on shared. And your Pi Zero will boot, a bit slowly.

ssh pi@10.42.0.14

Does your Pi connect to the internet?

apt update && apt upgrade -y

Yes, and actually quite fast!

The Raspberry Pi Zero is really a 5 dollar computer in the end. No SD card, no keyboard, no monitor, no mouse needed. Just a Zero and an (old Phone) USB micro cable.

All your changes will persist. The image in your directory will update. When you decide you need a SD card in the end, just flash the image to a SD card.