What filesystem should /boot be?

Solution 1:

In theory, almost anything that both the Linux kernel and GRUB (or whatever boot loader you use) can read is suitable for /boot. Most distributions default to ext4fs, but I've used ext2fs, ext3fs, and XFS with no problems under Ubuntu. I don't recall offhand if JFS is supported at installation. If so it should work fine, too. ReiserFS, HFS+, and FAT are not supported for /boot by Ubuntu's installer, but they all work fine if you set them up after the fact. Chances are a few more (NTFS, exFAT, and some others) would work, too, but I've never tried them -- at least, not with GRUB. FAT deserves special mention because, if you're using EFI, the EFI System Partition (ESP) is FAT, and mounting the ESP at /boot can simplify use of certain boot loaders and boot managers, such as ELILO and gummiboot, which require the kernel to reside on the same partition as the boot loader. Ubuntu uses GRUB 2 by default, so this isn't an issue with Ubuntu if you use the default boot loader, but if you want to experiment it might be worth considering. OTOH, using FAT for /boot will slightly complicate OS version updates and re-installations.

One complication to changing the filesystem on /boot (on an already-installed system) is that you may need to completely re-install GRUB. The reason is that its filesystem driver gets built into its binary (stored in the sectors following the MBR, in the BIOS Boot Partition, or in the grubx64.efi file, depending on the boot mode and partition table type). Thus, if you change the filesystem, that binary must be reconstructed, which is done by grub-install. This isn't an issue for fresh Ubuntu installations, since the installer will run grub-install as part of the installation process, so it should work fine as long as the Ubuntu installer itself accepts your choice of filesystem -- which, as I've said, will actually narrow your choices from what GRUB permits.

Solution 2:

Do not use ext2:-

[root ~]# grub2-install /dev/sda3
Installing for i386-pc platform.
grub2-install: warning: File system `ext2' doesn't support embedding.
grub2-install: warning: Embedding is not possible.  GRUB can only be installed in this setup by using blocklists.  However, blocklists are UNRELIABLE and their use is discouraged..
grub2-install: error: will not proceed with blocklists.
[root ~]# 

Solution 3:

I use ext2 (more of a habit), you can use ext3, ext4 too for grub2, it is not that important.

Nowdays on modern Linux distros ext2, ext3 and ext4 are equally supported so it means you can use one of them.

source: https://superuser.com/questions/470688/why-100mb-ext2-boot-partition-recommended-for-linux