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I was reading this article about booting the Pi from USB

It mentions that

the Raspberry Pi 3 requires the USB boot bit to be set in the OTP (one-time programmmble) memory.

...

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.

  1. Are there any repercussions for doing this, security-wise?
  2. Being aware that not all USB devices will work, If I burned a distro image onto a disc and plugged it into a CD drive and to the Pi via USB, what are the chances of it booting?
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    the new 3B+ and 3A+ come with that bit set already anyway - so, there's no repercussions - also, CD? why? it's read only - plus a CD doesn't have partitions like a disk drive, so an image burnt on a CD won't be useful – Jaromanda X Jan 4 at 8:15
  • Hi. Thanks for answering. I am using older Pis though. – user942937 Jan 4 at 8:16
  • older pi's ... i.e 0, 1 or 2? then you dont' have to worry at all - they can not ever boot from USB without a sd card (you can have an SD card with just bootcode.bin then have the rest on an USB drive – Jaromanda X Jan 4 at 8:17
  • Nope. 2 and 3 without the +. – user942937 Jan 4 at 8:17
  • well the 2 can't boot from USB (except as pointed out above), the 3 can once you set the OTP - there's no harm and no negative consequence – Jaromanda X Jan 4 at 8:18
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There is no harm in setting that OTP bit by booting from SDCard once with

program_usb_boot_mode=1

in /boot/config.txt. It has no security implications as your RPi is instantly insecure if someone has physical access. They can swap SDCard or USB boot device and you can't stop them (without using hot glue).

All four of my 3Bs, my 3B+ and one of my 3A+s boot from USB.

Any valid USB device should boot. I've never tried a CD/DVD drive but it should work as long as you've got a "live CD" version of ARM Linux.

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