EFI System Partition
Advanced partition selection (CONFIG_PARTITION_ADVANCED) and EFI GUID Partition support (CONFIG_EFI_PARTITION) must be enabled:
-*- Enable the block layer ---> Partition Types ---> [*] Advanced partition selection [*] EFI GUID Partition support
ISO8859-1 codepage must be enabled too, in order to mount the FAT EFI partition:
-*- File Systems ---> DOS/FAT/EXFAT/NT Filesystems ---> <*> VFAT (Windows-95) fs support (437) Default codepage for FAT (iso8859-1) Default iocharset for FAT Native Language support ---> [*] NLS ISO 8859-1 (Latin 1; Western European Languages)
For creation instructions see Handbook.
parted (sys-block/parted) will show it with the boot, esp flags:
parted /dev/sda print
Model: ATA SAMSUNG SSD SM84 (scsi) Disk /dev/sda: 256GB Sector size (logical/physical): 512B/512B Partition Table: gpt Disk Flags: Number Start End Size File system Name Flags 1 1049kB 99.6MB 98.6MB fat32 EFI System Partition boot, esp
gdisk (sys-apps/gptfdisk) will show it with partition code EF00:
gdisk -l /dev/sda
GPT fdisk (gdisk) version 1.0.1 Partition table scan: MBR: protective BSD: not present APM: not present GPT: present Found valid GPT with protective MBR; using GPT. Disk /dev/sda: 500118192 sectors, 238.5 GiB Logical sector size: 512 bytes Disk identifier (GUID): 1B59C2C8-8795-4625-9718-4D636B005AC1 Partition table holds up to 128 entries First usable sector is 34, last usable sector is 500118158 Partitions will be aligned on 2048-sector boundaries Total free space is 2669 sectors (1.3 MiB) Number Start (sector) End (sector) Size Code Name 1 2048 194559 94.0 MiB EF00 EFI System Partition
Its filesystem can be created using the mkfs.fat command:
mkfs.fat -F 32 /dev/sda1
256 MiB should be enough for some primary bootloader payloads such as EFI stub kernels or Windows.
/dev/sda1 /efi vfat noauto,noatime 0 2
There is a standard layout for the ESP. Vendors and distributions are supposed to put their stuff into vendor specific directories.
tree -L 3 /efi
/efi └── EFI ├── Boot │ └── bootx64.efi ├── Gentoo │ └── bzImage-4.9.76-r1.efi └── Microsoft ├── Boot └── Recovery
Here the Microsoft subtree - and also the Boot subtree - was created by an earlier installation of Windows 10 Creators Update. The Boot subtree is the fallback directory. If UEFI can't find any vendor specific directories it will boot from here. In a multiboot environment with properly set up vendor specific subtrees the Boot subtree can be deleted.
UEFI boot items
Computers with UEFI usually provide a boot menu and a configuration tool for creating, sorting or deleting boot items. The content of the ESP is visible to these tools and creating a boot item is like choosing the medium from a given selection, then surfing through the ESP and selecting the item, e.g bzImage-4.9.76-r1-gentoo.efi.
Alternatively, efibootmgr can be used for generating the UEFI boot items.
- Handbook:AMD64/Installation/Disks#What is the EFI System Partition (ESP)?
- UEFI — a firmware standard for boot ROM designed to provide a stable API for interacting with system hardware. On x86 it replaced the legacy BIOS.
- FAT — filesystem originally created for use with MS-DOS (and later pre-NT Microsoft Windows).
- EFI stub — provides instructions on configuring and installing kernels in the EFI System Partition (ESP) of a computer running in EFI mode
- efibootmgr — a tool for managing UEFI boot entries.
- EFI Shell The UEFI Shell is a shell/terminal for the firmware which allows launching uefi applications which include uefi bootloaders.
- REFInd — a boot manager for EFI and UEFI platforms forked from and successor to rEFIt.