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EFI System Partition
The EFI system partition (ESP) is a fat formatted partition containing the boot loaders or kernel images for all installed operating systems.
Kernel
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 EFI partition:
-*- File Systems ---> Native Language support ---> [*] NLS ISO 8859-1 (Latin 1; Western European Languages)
Characteristics
parted (sys-block/parted) will show it with the boot, esp flags:
root #parted /dev/sda printModel: 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
For creation instructions see Handbook
gdisk (sys-apps/gptfdisk) will show it with partition code EF00:
root #gdisk -l /dev/sdaGPT 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
Having the ESP as /dev/sda1 (Number 1) deviates from Gentoo Handbook where Boot/EFI system partition is /dev/sda2.
Size considerations
100 MB should be enough for some kernels, a boot manager and dual-booting Windows 10.
Mount point
An entry in /etc/fstab is not needed for booting but might be useful for manually mounting the ESP.
/etc/fstabConfiguring the ESP mountpoint/dev/sda1 /boot vfat noauto,noatime 0 2
Standard layout
There is a standard layout for the ESP. Vendors and distributions are supposed to put their stuff into vendor specific directories.
user $tree -L 3 /boot /boot
└── EFI
├── Boot
│ └── bootx64.efi
├── Gentoo
│ └── vmlinuz-4.9.76-r1.efi
└── Microsoft
├── Boot
└── Recovery
Here the Microsoft subtree - and also the Boot subtree[1] - 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 vmlinuz-4.9.76-r1-gentoo.efi.
Alternatively, efibootmgr can be used for generating the UEFI boot items.
See also
- Handbook:AMD64/Blocks/Disks#Using_UEFI
- EFI stub kernel — Linux kernel, able to boot without a boot manager
- 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
- Discussion page in Gentoo Handbook — how to use grub2 with ESP
- Property:Efi-system-partition — Gentoo handbook property using /dev/sda1
- Talk:GRUB2_Quick_Start#UEFI.2FGPT