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Update msd.md for Raspbian 2017-04-10 release
andrum993 Apr 12, 2017
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Update msd.md
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96 changes: 14 additions & 82 deletions hardware/raspberrypi/bootmodes/msd.md
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# How to boot from a USB Mass Storage Device on a Raspberry Pi 3
This tutorial explains how to boot your Raspberry Pi 3 from a USB mass storage device such as a flash drive or USB hard disk. Be warned that this feature is experimental and may not work with all USB mass storage devices.
This tutorial explains how to boot your Raspberry Pi 3 from a USB mass storage device such as a flash drive or USB hard disk. Be warned that this feature is experimental and does not work with all USB mass storage devices. See [this blog post](https://www.raspberrypi.org/blog/pi-3-booting-part-i-usb-mass-storage-boot/) from Gordon Hollingworth for an explanation of why some USB mass storage devices don't work, as well as some background information.

## Program USB Boot Mode
Before a Raspberry Pi will boot from a mass storage device, it needs to be booted from an SD card with a config option to enable USB boot mode. This will set a bit in the OTP (One Time Programmable) memory in the Raspberry Pi SoC that enables network booting. Once this is done, the SD card is no longer required.
Before a Raspberry Pi 3 will boot from a mass storage device, it needs to be booted from an SD card with a config option to enable USB boot mode. This will set a bit in the OTP (One Time Programmable) memory in the Raspberry Pi SoC that will enable booting from a USB mass storage device. Once this bit has been set, the SD card is no longer required. Note that any change you make to the OTP is permanent and cannot be undone.

Install Raspbian Lite (or Raspbian with PIXEL) on the SD card in the normal way [See here](../../../installation/installing-images/README.md).
You can use any SD card running Raspbian or Raspbian Lite to program the OTP bit. If you don't have such an SD card then you can install Raspbian or Raspbian Lite in the normal way - [See here](../../../installation/installing-images/README.md).

First, prepare the `/boot` directory with up to date boot files:
```
$ sudo apt-get update
$ sudo apt-get update && sudo apt-get upgrade
```
The above step is not required if you use the 2017-04-10 release of Raspbian / Raspbian Lite or later.

Then enable USB boot mode with this code:
```
echo program_usb_boot_mode=1 | sudo tee -a /boot/config.txt
Expand All @@ -22,86 +24,16 @@ $ vcgencmd otp_dump | grep 17:
17:3020000a
```

Ensure the output `0x3020000a` is correct.

If you wish, you can remove the `program_usb_boot_mode` line from config.txt, so that if you put the SD card in another Raspberry Pi, it won't program USB boot mode. Make sure there is no blank line at the end of config.txt. You can do this with `sudo nano /boot/config.txt`, for example.
Ensure the output `0x3020000a` is shown. If it is not, then the OTP bit has not been successfully programmed.

## Prepare the USB storage device
Now that your Raspberry Pi is USB boot-enabled, you can prepare a USB storage device to boot from. Start by inserting the USB storage device into the Raspberry Pi. Note that the USB storage device will be completely erased. Rather than downloading the Raspbian image again, we will copy it from the SD card on the Raspberry Pi. The source device (SD card) will be `/dev/mmcblk0` and the destination device (USB disk) should be `/dev/sda`, assuming you have no other USB devices connected.
If you wish, you can remove the `program_usb_boot_mode` line from config.txt, so that if you put the SD card in another Raspberry Pi, it won't program USB boot mode. Make sure there is no blank line at the end of config.txt. You can edit config.txt using the nano editor using the command `sudo nano /boot/config.txt`, for example.

We will start by using Parted to create a 100MB FAT32 partition, followed by a Linux ext4 partition that will take up the rest of the disk.

```
sudo parted /dev/sda

(parted) mktable msdos
Warning: The existing disk label on /dev/sda will be destroyed and all data on this disk will be lost. Do you want to continue?
Yes/No? Yes
(parted) mkpart primary fat32 0% 100M
(parted) mkpart primary ext4 100M 100%
(parted) print
Model: SanDisk Ultra (scsi)
Disk /dev/sda: 30.8GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number Start End Size Type File system Flags
1 1049kB 99.6MB 98.6MB primary fat32 lba
2 99.6MB 30.8GB 30.7GB primary ext4 lba
```
Your `parted print` output should look similar to the one above.
Now power down the Raspberry Pi 3 and remove the SD card.

Type `quit` to exit parted.

Create the boot and root file systems:
```
sudo mkfs.vfat -n BOOT -F 32 /dev/sda1
sudo mkfs.ext4 /dev/sda2
```

Mount the target file system and copy the running Raspbian system to it:
```
sudo mkdir /mnt/target
sudo mount /dev/sda2 /mnt/target/
sudo mkdir /mnt/target/boot
sudo mount /dev/sda1 /mnt/target/boot/
sudo apt-get update; sudo apt-get install rsync
sudo rsync -ax --progress / /boot /mnt/target
```
## Prepare the USB mass storage device
Starting with the 2017-04-10 release of Raspbian you can install a working Rasbian system to a USB mass storage device by copying the operating system image directly onto your USB device, in the same way that you would for an SD card. To perform this step, follow the instructions [here](../../../installation/installing-images/README.md), remembering to select the drive that corresponds to your USB mass storage device.

Regenerate SSH host keys:
```
cd /mnt/target
sudo mount --bind /dev dev
sudo mount --bind /sys sys
sudo mount --bind /proc proc
sudo chroot /mnt/target
rm /etc/ssh/ssh_host*
dpkg-reconfigure openssh-server
exit
sudo umount dev
sudo umount sys
sudo umount proc
```

Edit `/boot/cmdline.txt` so that it uses the USB storage device as the root file system, instead of the SD card.

```
sudo sed -i "s,root=/dev/mmcblk0p2,root=/dev/sda2," /mnt/target/boot/cmdline.txt
```

The same needs to be done for `fstab`:
```
sudo sed -i "s,/dev/mmcblk0p,/dev/sda," /mnt/target/etc/fstab
```

Finally, unmount the target file systems, and power the Raspberry Pi off.
```
cd ~
sudo umount /mnt/target/boot
sudo umount /mnt/target
sudo poweroff
```
Once you have finished imaging your USB mass storage device, remove it from your computer and insert it into your Raspberry Pi 3.

Disconnect the power supply from the Raspberry Pi, remove the SD card, and reconnect the power supply. If all has gone well, the Raspberry Pi should begin to boot after a few seconds.
## Boot your Pi 3 from the USB mass storage device
Go to your Pi 3 and remove any SD card. Then attach the USB mass storage device and power up the Pi 3. After between 5 and 10 seconds the Pi 3 should begin booting and display the rainbow splash on an attached screen.