Raspberry Pi


How to use a USB disk or stick as the primary disk

Some Raspberry Pi’s can boot directly from a USB disk or stick without needing an SD card at all. This appears to include some Raspberry Pi 3’s and the Raspberry Pi 4 (but not the Zero, 1, 2). For this to work, any of them need to have a relatively recent boot loader. For how to upgrade the boot loader on your Raspberry Pi 4, see below.

To install UBOS to boot directly from a USB disk or stick without an SD card, you have two choices:

  • either follow the normal installation instructions (Run UBOS on Raspberry Pi 2 or 3 or :Run UBOS on Raspberry Pi 4) and simply use the USB disk or stick in every place where the instructions refer to the SD card; or

  • boot your Raspberry Pi from a UBOS SD card, then attach the USB disk or stick, and run:

    % sudo ubos-install /dev/sdX

    where /dev/sdX needs to be replaced with the name of your USB disk or stick (e.g. /dev/sdb). Once this command is complete, you can shut down your Raspberry Pi, remove the SD card, and reboot directly from the USB disk or stick.

    This alternative may be preferable because ubos-install gives you more options in terms of disk layout and will use the memory capacity of your entire disk or stick.

    To find the name of the USB disk or stick, execute lsblk before and after you plug it into USB. The difference contains the name of the USB disk or stick.

How to switch boot over to a USB disk or stick as soon as possible

Some of the older Raspberry Pi’s cannot directly boot from a USB disk or stick. However, you can start the boot on an SD card and switch over to the USB disk or stick as soon as possible. This will use the SD card only at the very beginning of the boot process, and not at all during regular operation, bringing many of the benefits of booting from a USB disk or stick to older devices.

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 upgrade your Raspberry Pi 4’s boot loader

Whether such an upgrade is necessary depends on when your Raspberry Pi 4 was manufactured. More recent versions know how to boot from USB disks, while previous ones don’t.

To check for the current version of your Raspberry Pi 4’s bootloader:

% /opt/vc/bin/vcgencmd bootloader_version

For example, it may output:

May 10 2019 19:40:36
version d2402c53cdeb0f072ff05d52987b1b6b6d474691 (release)
timestamp 0

If the date is older than June 15, 2020, we recommend you upgrade. First, install the Raspberry Pi 4 EEPROM update package:

% sudo pacman -S rpi-eeprom

and then run the update:

% sudo rpi-eeprom-update -d -a

Correct output may be like:

BCM2711 detected
Dedicated VL805 EEPROM detected
BOOTFS /boot
BOOTLOADER: update available
CURRENT: Fri May 10 06:40:36 PM UTC 2019 (1557513636)
 LATEST: Fri Jul 31 01:43:39 PM UTC 2020 (1596203019)
 FW DIR: /lib/firmware/raspberrypi/bootloader/critical
VL805: update available
CURRENT: 00013701
 LATEST: 000138a1
BOOTFS /boot
EEPROM updates pending. Please reboot to apply the update.

and reboot:

% sudo systemctl reboot

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 Raspberry Pi’s limited memory to graphics. We could have pre-configured that, but we figure most people running UBOS on a Raspberry 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.)

% sudo systemctl poweroff

and physically connect the camera to the Raspberry Pi with the appropriate cable. Re-apply power, and once the Raspberry 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.