extlinux

ubuntu@ubuntu:~$ cat /boot/extlinux/extlinux.conf
## /boot/extlinux/extlinux.conf
##
## IMPORTANT WARNING
##
## The configuration of this file is generated automatically.
## Do not edit this file manually, use: u-boot-update

default l0
menu title U-Boot menu
prompt 0
timeout 50


label l0
	menu label Ubuntu 20.04.2 LTS 5.8.0-14-generic
	fdt /boot/hifive-unleashed-a00.dtb
	linux /boot/Image

	append console=ttySIF0,115200 root=/dev/mmcblk0p1 rootfs=ext4 rootwait rw earlycon

label l0r
	menu label Ubuntu 20.04.2 LTS 5.8.0-14-generic (rescue target)
	fdt /boot/hifive-unleashed-a00.dtb
	linux /boot/Image

	append console=ttySIF0,115200 root=/dev/mmcblk0p1 rootfs=ext4 rootwait rw earlycon single