Can't achieve process about booting from USB

Question

I'm trying to install RetroPie on an USB stick and I want to boot on it. So I follow this instructions HOW TO CREATE A RETROPIE USB BOOT DRIVE FOR RASPBERRY PI 3

The start of the instructions seems standard (I've seen this on other sites, for booting on USB, not specifically for retroPie), but It doesn't work for me.

I do

sudo apt-get update && sudo apt-get install rpi-update
sudo BRANCH=next rpi-update
echo program_usb_boot_mode=1 | sudo tee -a /boot/config.txt

after this, the file /boot/config.txt ends with the sentence, but when I type sudo reboot (I tried two times), after reboot the Pi is blocked, just after the launch screen. The red led is on, and the green one blinks. I have a Raspberry 3B+, I don't understand what's the problem.

Answer 1

The instructions you used are seriously outdated.

sudo BRANCH=next rpi-update actually installed old firmware that is incompatible with the Pi3B+. The 3B+ also does not need the program_usb_boot_mode=1 changed because that has already been done at the factory.

I think the easiest way to install retropie on a USB stick is to download the Pi2/3 image from the Retropie website and write it directly to the USB stick. On Windows I would use Etcher (https://etcher.io).

Put the USB stick in the Pi and power it up. Be aware that there are some USB devices that are not compatible with the Pi.