In this tutorial, we create squashfs root filesystem, copy kernel, filesystem and dtb to the SD card. We modify U-boot env variables so that the Linux kernel and the filesystem boots from the SD card.
https://www.nayab.xyz/rpi3b-elinux/embedded-linux-rpi3-100-elinux-on-sdcard.html
#raspberrypi #busybox #squashfs