sudo ./refind-install

mkdir /Volumes/ESP
sudo mount -t msdos /dev/disk0s1 /Volumes/ESP
cd /Volumes/ESP/EFI/refind
vim refind.conf

https://wiki.gentoo.org/wiki/Refind FILE /boot/EFI/gentoo/refind_linux.conf

"Default"	"root=/dev/sda2 rootfstype=ext4 ro quiet"
"Console"	"root=/dev/sda2 rootfstype=ext4 ro quiet nox nogui"
"Emergency"	"root=/dev/sda2 rootfstype=ext4 ro 1"

Custom (static) initramfs and microcode loading:

FILE /boot/EFI/gentoo/refind_linux.conf

"Standard boot"       "root=LABEL=root initrd=intel-ucode.img initrd=initramfs-custom.img quiet"
"Single-user mode"    "root=LABEL=root initrd=intel-ucode.img initrd=initramfs-custom.img single"
"Minimal options"     "ro root=LABEL=root initrd=initramfs-custom.img"

1. https://blog.csdn.net/XiaoshaXs/article/details/52016628
2. https://huataihuang.gitbooks.io/cloud-atlas/content/develop/mac/refind.html
3. https://www.rodsbooks.com/refind/installing.html