Raspberry Pi (any model)

How to use a USB disk as the primary disk

There’s a rumor that the Raspberry Pi 3 can boot directly from a USB disk without needing an SD Card at all. We have not tried this, and it apparently only works for the Raspberry Pi 3.

The following works for all Raspberry Pi models: boot from the SD card, but switch over to the USB disk as soon as possible and ignore it from that point. To do that:

  1. Boot your Raspberry Pi from an SD card that has UBOS installed as described in Run UBOS on Raspberry Pi Zero or 1 or Run UBOS on Raspberry Pi 2 or 3.

  2. Connect your external USB disk to your Raspberry Pi and turn it on.

  3. Verify that UBOS has recognized the external disk by executing lsblk. It should show your drive with a name such as /dev/sda. It might be helpful to compare the output of the command with the drive turned off and turned on.

  4. Install UBOS on the USB disk with a command such as ubos-install /dev/sda.


    Make sure you get the device name right, otherwise you might accidentally destroy the data on some other hard drive!


    This will destroy all existing data on your USB disk, so make sure you want to do this.

  5. After the command completes, edit file /boot/cmdline.txt. Look for where it currently says something like /dev/mmcblk0p2 (identifying the root partition on the SD Card) and change it to /dev/sda2 (the root partition on the USB disk). Note: depending how exactly you installed UBOS on the SD card and the USB disk, the device names might be different; this page reflects the default.

  6. Execute systemctl reboot.

  7. Once the system has rebooted, log in as root and check that your root disk is now /dev/sda2 by executing lsblk.

Bonus: edit /etc/fstab to mount the SD Card’s first partition as /boot. That way UBOS updates can update the boot parameters on your SD Card in the future.

How to use the Raspberry Pi’s camera

Using the Raspberry Pi’s official camera while running UBOS is quite simple, as everything you need is pre-installed on UBOS for the Raspberry Pi.

However, you need to make one change in one file, which is to allocate more of the Pi’s limited memory to graphics. We could have pre-configured that, but we figure most people running the Pi do not use a camera, and much rather have access to all of the RAM.

To make this change, become root and open the file with your favorite editor, such as vi:

% sudo su
# vi /boot/config.txt

Add the very end of the file, add the following content:


(In vi, you would hit G to go to the end of the file, then hit A to append, then type the above text. When done, hit Escape to leave editing mode, and ZZ to save and quit the editor.)

Then, shutdown your Pi:

% sudo systemctl poweroff

and physically connect the camera to the Pi with the appropriate cable. Re-apply power, and once the Pi has booted, you can take a picture with:

/opt/vc/bin/raspistill -o mypicture.jpg

or take a video with:

/opt/vc/bin/raspivid -o myvideo.mpg

Invoke those commands without arguments to see their many options.