Based on this documentation:

To enable USB host boot mode, the Raspberry Pi needs to be booted from an SD card with a special option to set the USB host boot mode bit in the one-time programmable (OTP) memory. Once this bit has been set, the SD card is no longer required.

IMPORTANT Any change you make to the OTP is permanent and cannot be undone.

I get this is a one time programmable option. The language is kind of weird so I'm having a hard time understanding the consequences.

My question: If I program this bit to be able to boot my RPi2 with an SSD over USB. Does that mean it will never boot from an SD card ever again?

  • Seeing as this only applies to the Pi3 the question is meaningless.
    – Milliways
    Sep 8, 2021 at 10:06
  • @Milliways I think you're mistaken. The title of that section says "Raspberry Pi 2B, 3A+, 3B, CM 3, 3+". Sep 8, 2021 at 10:11
  • If you are referring to the official documentation (which has recently been stuffed) only a very few late Pi2 models which use Pi3 SOC support this, but it also answers your question.
    – Milliways
    Sep 8, 2021 at 10:20
  • no, it does not mean that at all - you can boot from SD - consider that at least the 3B+/3A+ models come with USB boot pre-enabled - so, really, only the newer pi2 and all 3B's (I don't know about the CM's) need to have USB boot specifically enabled y the end user
    – Bravo
    Sep 10, 2021 at 5:01

2 Answers 2


I was thinking this myself. I am setting up a RPi4B/8GB in an Argon One m.2 case with 250 GB SSD and searched for an answer. I found it here https://forums.raspberrypi.com/viewtopic.php?t=234669

The answer is that although the One Time Programmable boot option is changed you cannot revert.

However, as the RPi defaults to booting from SD card first, this is not a problem. Remove the USB bootable device and the Pi will boot from SDCard. More information is available at the Ri forum link above.


That is the theory. I am more a practical person, so I tried :)

And I can confirm: my Pi 4B boots both from SSD over USB and from SD, without a problem!

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