I have rpi3b+ a 32 gb scard and a sandisk usb 16 gb . I want to boot only from my usb though I have my scard inserted That's it.. Sorry if my language is pour

Thank u

  • I would think if your SD card does not have a bootcode.bin in the primary FAT partition, then the pi would attempt to boot from the USB instead - what's on the SD card? – Jaromanda X May 7 '19 at 5:21
  • An alternative is Boot flow - however, there are caveats to using that ... I would recommend you read it, then read it again, then only if you're sure that is your only solution, you read it again, and then go through with it – Jaromanda X May 7 '19 at 5:22
  • If the SD card is bootable, the RPi prefers that to the USB drive. – user96931 May 7 '19 at 16:10

Your question is unclear.

If you have a bootable SD Card the Pi will boot from that.

It is possible to have boot code on a SD Card and boot to a root partition on a USB drive. This is usable even on older models which do not support USB boot.

All that is needed is to change /boot/cmdline.txt so root=PARTUUID=… points to the root partition (which needs to have /etc/fstab set to mount this partition as root).

This can be used to use a read-only SD Card, and a read-write partition on a HDD or SSD.

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