I am using the kernel after modifying it.
I'm replacing the kernel after using the sdcard, but I want a different method.
I wish I could flash with my kernel(zImage).

I'm using Smart4418 (Ubuntu 16.04.5 LTS 4.4.172-s5p4418).
I will automatically log in to pi after booting, but I want to change my login to root. Please help me.