Linux /boot tends to be on ext3 or ext4 on most distributions. Recently it's XFS on the server flavor of Fedora, CentOS, and RHEL. For openSUSE the default is Btrfs, /boot is just a directory.
The bootloader/bootmanager is what determines what fs choices you have for /boot. GRUB2 reads anything, including ZFS, Btrfs, LUKS, even md/mdadm raid5/6 and even if it's degraded, and conventional LVM (not thinp stuff or the md raid support).
The bootloader/bootmanager is what determines what fs choices you have for /boot. GRUB2 reads anything, including ZFS, Btrfs, LUKS, even md/mdadm raid5/6 and even if it's degraded, and conventional LVM (not thinp stuff or the md raid support).