How to boot RetroPie (or Raspbian) from a USB drive on the Raspberry Pi 3 B(+)

Boot RetroPie from USB.md

Boot RetroPie from USB on the Raspberry Pi 3 B(+)

You will need a Raspberry Pi 3 B(+) with a microSD card running RetroPie (or Raspbian).

1. Update Raspbian.

   $ sudo apt-get update && sudo apt-get upgrade -y

2. Make sure you are running on the latest Raspberry Pi firmware.

   $ sudo BRANCH=next rpi-update

3. Enable booting from USB. (This feature is experimental and cannot be reversed.)

   $ echo program_usb_boot_mode=1 | sudo tee -a /boot/config.txt
   $ sudo reboot

4. (Optional) Verify that USB booting was enabled successfully.

   $ vcgencmd otp_dump | grep 17:
   17:3020000a

5. Set up the USB drive. This should be blank and unintialized. (No existing partitions.) The drive should be mounted as /dev/sda, but you should verify this before continuing.

     # start the partition manager
   $ sudo parted /dev/sda
     # add a FAT partition table
   (parted) mktable msdos
     # create a FAT32 boot partition
   (parted) mkpart primary fat32 0% 100M
     # create an EXT4 partition for RetroPie
   (parted) mkpart primary ext4 100M 100%
     # double check that you are creating two partitions
   (parted) print
   (parted) quit

6. Format the partitions you just created on the USB drive.

   $ sudo mkfs.vfat -n BOOT -F 32 /dev/sda1
   $ sudo mkfs.ext4 -n /dev/sda2

7. Install rsync.

   $ sudo apt-get update && sudo apt-get install rsync -y

8. Copy the files from the SD card to the USB drive. (This step may take some time.)

     # mount the target Linux partition
   $ sudo mkdir /mnt/target
   $ sudo mount /dev/sda2 /mnt/target
     # mount the target boot partition
   $ sudo mkdir /mnt/target/boot
   $ sudo mount /dev/sda1 /mnt/target/boot
     # synchronize the files between the SD card and USB drive
   $ sudo rsync -ax --progress / /boot/ /mnt/target

9. Mount the virtual filesystem on the USB drive.

   $ sudo mount --bind /dev dev
   $ sudo mount --bind /sys sys
   $ sudo mount --bind /proc proc

10. Reset the SSH keys on the new installation. (They match the old host.)

    $ sudo chroot /mnt/target
    # rm /etc/ssh/ssh_host*
    # dpkg-reconfigure openssh-server
    # exit

11. Unmount the virtual filesystem.

    $ sudo umount dev
    $ sudo umount sys
    $ sudo umount proc

12. Reconfigure the boot files on the USB drive to search for the operating system on the new drive.

    $ sudo sed -i "s,root=/dev/mmcblk0p2,root=/dev/sda2," /mnt/target/boot/cmdline.txt
    $ sudo sed -i "s,/dev/mmcblk0p,/dev/sda," /mnt/target/etc/fstab

13. Unmount the USB drive and power down.

    $ cd ~
    $ sudo umount /mnt/target/boot
    $ sudo umount /mnt/target
    $ sudo poweroff

14. Remove the microSD card and boot from the USB drive.