An overview of the files on the /boot/firmware partition (the 1st partition
on the SD card) used by the Ubuntu boot process (roughly in order) is as
follows:
* bootcode.bin - this is the second stage bootloader loaded by all pis with
the exception of the pi4 (where this is replaced by flash
memory)
* config.txt - the first configuration file read by the boot process
* syscfg.txt - the file in which system modified configuration will be
placed, included by config.txt
* usercfg.txt - the file in which user modified configuration should be
placed, included by config.txt
* start*.elf - the third stage bootloader, which handles device-tree
modification and which loads...
* uboot*.bin - various u-boot binaries for different pi platforms; these
are launched as the "kernel" by config.txt
* boot.scr - the boot script executed by uboot*.bin which in turn
loads...
* vmlinuz - the Linux kernel, executed by boot.scr
* initrd.img - the initramfs, executed by boot.scr
* meta-data - meta-data for cloud-init; usually just contains the
instance id
* network-config - network configuration for cloud-init; edit this to set up
wifi access points and other networking settings
* user-data - user-data for cloud-init; edit this to configure initial
users, SSH keys, packages, etc.
