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According to the UEFI specification (13.3.1.1 File System Format) an EFI firmware must support FAT12, FAT16 and FAT32 file systems for the EFI system partition (ESP). However, the Arch Wiki states that "any conformant vendor can optionally add support for additional file systems".

Does one know of a vendor supporting additional file systems, like ext2/3/4? Or does one even (successfully) use a journaling file system on an ESP?

In particular I am interested in Lenovo and Dell laptops from 2017 or newer.

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  • Most likely it would at most support NTFS additionally. Unlikely exFAT, hardly any Linux filesystems.
    – Tom Yan
    Commented Dec 16, 2019 at 4:13
  • Reason? How the world works.
    – Tom Yan
    Commented Dec 16, 2019 at 4:14

2 Answers 2

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+50

Any vendor that will support in the UEFI firmware additional file systems like ext2/3/4 will be strictly non-standard and will require a specialized UEFI firmware. This is unlikely to exist (except on Apple computers).

The UEFI Specification Version 2.5, published by UEFI.org, April 2015, says this in section "12.3 File System Format", pp. 536:

EFI encompasses the use of FAT32 for a system partition, and FAT12 or FAT16 for removable media. The FAT32 system partition is identified by an OSType value other than that used to identify previous versions of FAT. This unique partition type distinguishes an EFI defined file system from a normal FAT file system. The file system supported by EFI includes support for long file names.

The definition of the EFI file system will be maintained by specification and will not evolve over time to deal with errata or variant interpretations in OS file system drivers or file system utilities. Future enhancements and compatibility enhancements to FAT will not be automatically included in EFI file systems. The EFI file system is a target that is fixed by the EFI specification, and other specifications explicitly referenced by the EFI specification.

Please note that the above UEFI Specification does not anywhere make reference to any other file-system format than its own.

The above applies to the base UEFI implementation. To extend the UEFI is always possible by loading during the boot a EFI/UEFI file system driver. (I don't know where/if the drivers in this link are actually used.)

For example, to access an NTFS partition you can from the EFI Shell issue commands such as:

load ntfs_x6efi
map -r

However, all drivers and bootloaders are loaded from the EFI partition, which is always identified by its unique partition ID and so must be formatted according to the EFI specifications that are compatible only with FAT32/16/12. Support for other file-system formats can only come after that the UEFI firmware was loaded, after it found its FAT partition, and after it starts executing the configuration files that it finds inside.

As far as I know, Apple is the only computer manufacturer that created a specialized UEFI version, for supporting HFS+. The standard EFI partition is still present in Apple computers, but is usually left empty and is then bypassed in the normal course of events.

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  • You can also use startup.nsh to script the loading of the drivers and then calling upon the boot loader .
    – HackSlash
    Commented Dec 16, 2019 at 17:59
  • +1 since this might indeed be the correct answer. However, I am still hoping someone comes up with a counterexample.
    – dirdi
    Commented Dec 17, 2019 at 13:03
  • @dirdi - There isn’t one; Windows EFI support doesn’t support anything other than FAT32; Since Apple is the other OEM that does not sell Windows machines; They are the only manufacturer that implemented support for HFS+ because Apple developed HFS+ they can support it 100%;
    – Ramhound
    Commented Dec 17, 2019 at 14:05
  • Apple also supports exFAT ESP, but it's because they use EFI and not UEFI which is newer
    – phuclv
    Commented Dec 17, 2019 at 15:57
  • @Ramhound I do not plan to install Windows.
    – dirdi
    Commented Dec 17, 2019 at 16:03
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It is always safest to use an FAT32 partition for UEFI.

You don't know what other computers will be accessing the partition, and FAT32 is the best supported for the purpose.

Windows 10 and several other systems require at least 550MB for the UEFI partition so this eliminates FAT12 from the options and makes FAT16 no longer favorable.

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  • What other computer beside the one containing the drive holding the ESP would ever access it?
    – dirdi
    Commented Dec 17, 2019 at 13:00
  • @dirdi - It doesn’t matter; if you plan on installing Windows you must use FAT32. Dell nor Lenovo UEFI implementation supports ext2/3/4
    – Ramhound
    Commented Dec 17, 2019 at 14:01
  • @Ramhound I do not plan to install Windows.
    – dirdi
    Commented Dec 17, 2019 at 16:00
  • @dirdi - Dell and Lenovo are primary Microsoft OEMs which means their UEFI firmware support will be limited to what Windows supports.
    – Ramhound
    Commented Dec 17, 2019 at 16:08

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