What filesystems should I use on grub and ESP?

Question

I'm following the Gentoo Handbook to partition the disk.

After partitioning, the result is:
Now I have to choose the filesystems for each. The guide recommends:

root # mkfs.ext2 /dev/sda2
root # mkfs.ext4 /dev/sda4
root # mkswap /dev/sda3
root # swapon /dev/sda3

It doesn't specify a filesystem for sda1. Which one should I use?

Also, in a previous section the guide said:

The ESP must be a FAT variant (sometimes shown as vfat on Linux systems). The official UEFI specification denotes FAT12, 16, or 32 filesystems will be recognized by the UEFI firmware, although FAT32 is recommended for the ESP. Proceed in formatting the ESP as FAT32:

root # mkfs.fat -F 32 /dev/sda2

The ESP is located in the sda2, but the guide also says to use ext2 on sda2.

Which is the correct filesystem?

Answer 1

If you are using UEFI, then the ESP (/dev/sda2) must be a FAT variant, FAT32 is the normal choice. The BIOS boot partition (/dev/sda1) should not be formatted at all, i.e. it should not have a filesystem at all. It is for GRUB, when using a GPT disk in BIOS mode. If you are using UEFI mode, the partition is not needed.