Understanding Boot modes

I read about the different possible boot modes from here:


My questions are:

  1. I thought we don’t have grub bootloader, only Cboot in earlier JPs and now UEFI. where this GRUB bootloader came from and what I need it for?
  2. Whats is the difference between kernel/DTB in filesystem vs in partitions?
    from what I understood we have two copies of kernel and DTB (A/B mechanism) each in its own partition and we load one of them. what the “in filesystem” means?
  3. same question regarding recovery kernel and DTB.


The GRUB is more like an experimental feature that was enabled on jetpack5. Not in use right now.

APP partition has the file system. There are dtb and kernel inside the file system. This is the default path the system gets the kernel and dtb. That is why you can replace kernel image in /boot/Image. Because it is a filesystem.

The kernel and dtb could be read from other partitions too.

Recovery kernel and dtb is when the system fails to boot in multiple times, it will load the recovery kernel to boot instead.

Thank you for your answer. So just to clarify:
If my kernel and dtb are inside the rootfs, why I need both backup and another partitions containing the kernel and DTB?

why two copies are not enough? (filesystem and backup)

What do you mean backup ?

sorry… recovery.

what I’m trying to say is that we have 4 different places for kernel+dtb;

  1. rootFS
  2. partitions A slot
  3. partitions B slot
  4. recovery partition

why 1+4 are not enough?

4 are not same device tree and kernel image as 1. They are a fixed kernel and dtb.
Not anything built by you.

Thank you

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