EFI-Boot-process http://itman.in/efi-boot/
# EFI boot processThe boot process when using EFI is different from the boot process of the computer with the BIOS
When using EFI, the following happens:
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EFI bootloader starts. Its task is to select a device for further loading, similar to the user choosing a device when using BIOS .
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After selecting a device, the bootloader finds the system partition on the disk (EFI System partition) and downloads a file from it that is responsible for further loading of the operating system. This file is always located at the same address. For amd64, this is /efi/boot/bootx64.efi
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ESR is determined by the loader by a specific GUID and formatted in the FAT system.
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After transferring control to the OS loader from the ESR system partition, the further process continues as usual and depends on the operating system.
Content [ hide ]
- Description by Redhat
- Booting an OS using UEFI
- Boot Process under UEFI
- Detecting UEFI Firmware Arch
- UEFI Support in Linux Kernel
- UEFI Variables Support
- Linux Bootloaders for UEFI
- Create an UEFI System Partition in Linux
- UEFI Shell
- Hardware Compatibility
- Create UEFI bootable USB from ISO
- Remove UEFI boot support from ISO
GRUB loads itself into the memory in stages:
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UEFI platforms read the partition table and connect an ESP partition (EFI System Partition) - a VFAT partition with a unique GUID (Globally Unique Identifier). ESP contains EFI applications — loaders and utilities. In Red Hat Enterprise Linux 6, this is a section
/boot/efi/, and EFI programs are located at/boot/efi/EFI/redhat/. -
/boot/efi/EFI/redhat/содержит grub.efi — версию загрузчика, скомпилированную специально для EFI. В самом простом случае менеджер загрузки EFI выбирает этот файл в качестве загрузчика и загружает его в память.Если раздел ESP содержит другие программы EFI, менеджер загрузки предложит выбрать программу для выполнения.
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Как только GRUB определит операционную систему или ядро для загрузки, они будут загружены в память и им будет передано управление.
Так как производители оборудования обычно добавляют собственные каталоги в раздел ESP, необходимо создать условия для цепной загрузки. Менеджер загрузки EFI может запустить загрузчики любых операционных систем, если они расположены в ESP.
UEFI firmware does not support booting through the above mentioned method which is the only way supported by BIOS**.** UEFI has support for reading both the partition table as well as understanding filesystems.
The commonly used UEFI firmwares support both MBR and GPT partition table**.** EFI in Apple-Intel Macs are known to support Apple Partition Map also apart from MBR and GPT**.** Most of the UEFI firmwares have support for accessing FAT12 (floppy disks) , FAT16 and FAT32 filesystems in HDD and ISO9660 (and UDF) in CD/DVDs**.** EFI in Apple-Intel Macs can access HFS/HFS+ filesystems also apart from the mentioned ones**.**
UEFI does not launch any boot code in the MBR whether it exists or not**.** Instead it uses a special partition in the partition table called «EFI SYSTEM PARTITION» in which files required to be launched by the firmware are stored**.** Each vendor can store its files under /EFI// folder and can use the firmware or its shell (UEFI shell) to launch the boot program**.** An EFI System Partition is usually formatted as FAT32**.**
Under UEFI, every program whether they are OS loaders or some utilities (like memory testing apps) or recovery tools outside the OS, should be a UEFI Application corresponding to the EFI firmware architecture**.** Most of the UEFI firmware in the market, including recent Apple Macs use x86_64 EFI firmware**.** Only some older macs use i386 EFI firmware while no non-Apple UEFI system is known to use i386 EFI firmware**.**
Note: Some older Intel Server boards are known to operate on Intel EFI 1**.**10 firmware, and require i386 EFI applications.
A x86_64 EFI firmware does not include support for launching 32-bit EFI apps unlike the 64-bit Linux and Windows which include such support**.** Therefore the bootloader must be compiled for that architecture correctly**.**
Since each OS or vendor can maintain its own files within the EFI SYSTEM PARTITION without affecting the other, multi-booting using UEFI is just a matter of launching a different UEFI application corresponding to the particular OS’s bootloader**.** This removes the need for relying on chainloading mechanisms of one bootloader to load another to switch OSes**.**
Windows Vista (SP1+) and 7 pr 8 x86_64 versions support booting natively using UEFI firmware**.** But for this they need GPT partitioning of the disk used for UEFI booting**.Windows x86_64 versions support either UEFI-GPT booting or BIOS-MBR booting.Windows 32-bit versions support only BIOS-MBR booting.** Follow the instructions provided in the forum link given in the references sections as to how to do this**.** Seehttp://support.microsoft.com/default.aspx**?**scid=kb;EN-US;2581408 for more info**.**
This limitation does not exist in Linux Kernel but rather depends on the bootloader used**.For the sake of Windows UEFI booting, the Linux bootloader used should also be installed in UEFI-GPT mode if booting from the same disk.**
- System switched on — Power On Self Test, or POST process**.**
- UEFI firmware is loaded**.**
- Firmware reads its Boot Manager to determine which UEFI application to be launched and from where (ie**.** from which disk and partition).
- Firmware launches the UEFI application from the FAT32 formatted UEFISYS partition as defined in the boot entry in the firmware’s boot manager**.**
- UEFI application may launch another application (in case of UEFI Shell or a boot manager like rEFInd) or the kernel and initramfs (in case of a bootloader like GRUB) depending on how the UEFI application was configured**.**
If you have a non-mac UEFI system, then you have a x86_64 (aka 64-bit) UEFI 2**.x firmware.**
Some of the known x86_64 UEFI 2.x firmwares are Phoenix SecureCore Tiano, AMI Aptio, Insyde H2O**.**
Some of the known systems using these firmwares are Asus EZ Mode BIOS (in Sandy Bridge P67 and H67 motherboards), MSI ClickBIOS, HP EliteBooks, Sony Vaio Z series, many Intel Server and Desktop motherboards
Pre-2008 Macs mostly have i386-efi firmware while >=2008 Macs have mostly x86_64-efi**.** All macs capable of running Mac OS X Snow Leopard 64-bit Kernel have x86_64 EFI 1**.**x firmware.
To find out the arch of the efi firmware in a Mac, boot into Mac OS X and type the following command
ioreg -l -p IODeviceTree | grep firmware-abi
If the command returns EFI32 then it is i386 EFI 1**.x firmware. If it returns EFI64 then it is x86_64 EFI 1.x firmware. Macs do not have UEFI 2.x firmware as Apple’s EFI implementation is not fully compliant with UEFI Specification.**
The required Linux Kernel configuration options for UEFI systems are :
CONFIG_EFI=y CONFIG_EFI_STUB=y CONFIG_RELOCATABLE=y CONFIG_FB_EFI=y CONFIG_FRAMEBUFFER_CONSOLE=y
UEFI Runtime Variables/Services Support — ‘efivars’ kernel module . This option is important as this is required to manipulate UEFI Runtime Variables using tools likeefibootmgr****.
CONFIG_EFI_VARS=m
Note: This option is compiled as module in Arch core/testing kernel**.**
Note: For Linux to access UEFI Runtime Services, the UEFI Firmware processor architecture and the Linux kernel processor architecture must match**.** This is independent of the bootloader used**.**
Note: If the UEFI Firmware arch and Linux Kernel arch are different, then the «noefi» kernel parameter must be used to avoid the kernel panic and boot successfully**.** The «noefi» option instructs the kernel not to access the UEFI Runtime Services**.**
GUID Partition Table GPT config option — mandatory for UEFI support
CONFIG_EFI_PARTITION=y
Note: All of the above options are required to boot Linux via UEFI, and are enabled in Archlinux kernels in official repos**.**
Retrieved fromhttp://git.kernel.org/**?**p=linux/kernel/git/torvalds/linux.git;a=blob_plain;f=Documentation/x86/x86_64/uefi.txt;hb=HEAD.
UEFI defines variables through which an operating system can interact with the firmware**.UEFI Boot Variables are used by the boot-loader and used by the OS only for early system start-up.** UEFI Runtime Variables allow an OS to manage certain settings of the firmware like the UEFI Boot Manager or managing the keys for UEFI Secure Boot Protocol etc**.**
Note: The below steps will not work if the system has been booted in BIOS mode and will not work if the UEFI processor architecture does not match the kernel one, i.e. x86_64 UEFI + x86 32-bit Kernel and vice-versa config will not work**.** This is true only for efivars kernel module and efibootmgr step**.** The other steps (ie. upto setting up /EFI/arch/refind/{refindx64.efi,refind.conf} ) can be done even in BIOS/Legacy boot mode**.**
Access to UEFI Runtime services is provided by «efivars» kernel module which is enabled through the CONFIG_EFI_VAR=m kernel config option**.** This module once loaded exposes the variables under the directory /sys/firmware/efi/vars. One way to check whether the system has booted in UEFI boot mode is to load the «efivars» kernel module and check for the existence of /sys/firmware/efi/vars directory with contents similar to :
Sample output (x86_64-UEFI 2**.**3.1 in x86_64 Kernel): # ls -1 /sys/firmware/efi/vars/ Boot0000-8be4df61-93ca-11d2-aa0d-00e098032b8c/ BootCurrent-8be4df61-93ca-11d2-aa0d-00e098032b8c/ BootOptionSupport-8be4df61-93ca-11d2-aa0d-00e098032b8c/ BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c/ ConIn-8be4df61-93ca-11d2-aa0d-00e098032b8c/ ConInDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/ ConOut-8be4df61-93ca-11d2-aa0d-00e098032b8c/ ConOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/ ErrOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/ Lang-8be4df61-93ca-11d2-aa0d-00e098032b8c/ LangCodes-8be4df61-93ca-11d2-aa0d-00e098032b8c/ MTC-eb704011-1402-11d3-8e77-00a0c969723b/ MemoryTypeInformation-4c19049f-4137-4dd3-9c10-8b97a83ffdfa/ PlatformLang-8be4df61-93ca-11d2-aa0d-00e098032b8c/ PlatformLangCodes-8be4df61-93ca-11d2-aa0d-00e098032b8c/ RTC-378d7b65-8da9-4773-b6e4-a47826a833e1/ del_var new_var
The UEFI Runtime Variables will not be exposed to the OS if you have used «noefi» kernel parameter in the boot-loader menu**.** This parameter instructs the kernel to completely ignore UEFI Runtime Services**.**
There are few tools that can access/modify the UEFI variables, namely
- efibootmgr — Used to create/modify boot entries in the UEFI Boot Manager —efibootmgr or efibootmgr-git
- uefivars — simply dumps the variables — uefivars-git — uses efibootmgr library
- Ubuntu’s Firmware Test Suite — fwts — fwts-git — uefidump command —
fwts uefidump
Warning: Using efibootmgr in Apple Macs will brick the firmware and may need reflash of the motherboard ROM**.** There have been bug reports regarding this in Ubuntu/Launchpad bug tracker**.** Use bless command alone in case of Macs. Experimental «bless» utility for Linux by Fedora developers — mactel-boot .
Note: efibootmgr command will work only if you have booted the system in UEFI mode itself, since it requires access to UEFI Runtime Variables which are available only in UEFI boot mode (with «noefi» kernel parameter NOT being used). Otherwise the message Fatal: Couldn't open either sysfs or procfs directories for accessing EFI variables is shown**.**
Initially the user may be required to manually launch the boot-loader from the firmware itself (using maybe the UEFI Shell) if the UEFI boot-loader was installed when the system is booted in BIOS mode**.** Then efibootmgr should be run to make the UEFI boot-loader entry as the default entry in the UEFI Boot Manager**.**
To use efibootmgr, first load the ‘efivars’ kernel module:
# modprobe efivars
If you get no such device found error for this command, that means you have not booted in UEFI mode or due to some reason the kernel is unable to access UEFI Runtime Variables (noefi**?).**
Verify whether there are files in /sys/firmware/efi/vars/ directory**.** This directory and its contents are created by «efivars» kernel module and it will exist only if you have booted in UEFI mode, without the «noefi» kernel parameter**.**
If /sys/firmware/efi/vars/ directory is empty or does not exist, then efibootmgr command will not work**.** If you are unable to make the ISO/CD/DVD/USB boot in UEFI mode try#Create_UEFI_bootable_USB_from_ISO.
Note: The below commands use gummiboot-efi boot-loader as example**.**
Assume the boot-loader file to be launched is /boot/efi/EFI/gummiboot/gummibootx64.efi./boot/efi/EFI/gummiboot/gummibootx64.efi can be split up as /boot/efi and/EFI/gummiboot/gummibootx64.efi, wherein /boot/efi is the mountpoint of the UEFI System Partition, which is assumed to be /dev/sdXY (here X and Y are just placeholders for the actual values — eg:- in /dev/sda1 , X=a Y=1).
To determine the actual device path for the UEFI System Partition (should be in the form/dev/sdXY), try :
# findmnt /boot/efi TARGET SOURCE FSTYPE OPTIONS /boot/efi /dev/sdXY vfat rw,flush,tz=UTC
Then create the boot entry using efibootmgr as follows :
# efibootmgr -c -g -d /dev/sdX -p Y -w -L "Gummiboot" -l '\EFI\gummiboot\gummibootx64.efi'
In the above command /boot/efi/EFI/gummiboot/gummibootx64.efi translates to /boot/efi and/EFI/gummiboot/gummibootx64.efi which in turn translate to drive /dev/sdX -> partition Y -> file /EFI/gummiboot/gummibootx64.efi.
UEFI uses backward slash as path separator (similar to Windows paths).
The ‘label’ is the name of the menu entry shown in the UEFI boot menu**.** This name is user’s choice and does not affect the booting of the system**.** More info can be obtained from efibootmgr GIT README .
FAT32 filesystem is case-insensitive since it does not use UTF-8 encoding by default**.** In that case the firmware uses capital ‘EFI’ instead of small ‘efi’, therefore using\EFI\gummiboot\gummibootx64.efi or \efi\gummiboot\gummibootx64.efi does not matter (this will change if the filesystem encoding is UTF-8).
See UEFI Bootloaders .
Note: The UEFISYS partition can be of any size supported by FAT32 filesystem**.According to Microsoft Documentation, the minimum partition/volume size for FAT32 is 512 MiB.** Therefore it is recommended for UEFISYS partition to be at least 512 MiB**.Higher partition sizes are fine, especially if you use multiple UEFI bootloaders, or multiple OSes booting via UEFI, so that there is enough space to hold all the related files.If you are using Linux EFISTUB booting, then you need to make sure there is adequate space available for keeping the Kernel and Initramfs files in the UEFISYS partition.**
Two choices:
- Using GNU Parted/GParted: Create a FAT32 partition**.** Set «boot» flag on for that partition**.**
- Using GPT fdisk (aka gdisk): Create a partition with gdisk type code «EF00». Then format that partition as FAT32 using
mkfs.vfat -F32 /dev/<THAT_PARTITION>
Note: Setting «boot» flag in parted in a MBR partition marks that partition as active, while the same «boot» flag in a GPT partition marks that partition as «UEFI System Partition».
Warning: Do not use util-linux fdisk, cfdisk or sfdisk to change the type codes in a GPT disk**.** Similarly do not use gptfdisk gdisk, cgdisk or sgdisk on a MBR disk, it will be automatically converted to GPT (no data loss will occur, but the system will fail to boot).
Two choices:
- Using GNU Parted/GParted: Create FAT32 partition**.** Change the type code of that partition to 0xEF using fdisk, cfdisk or sfdisk**.**
- Using fdisk: Create a partition with partition type 0xEF and format it as FAT32 using
mkfs.vfat -F32 /dev/<THAT_PARTITION>
Note: It is recommended to use always GPT for UEFI boot as some UEFI firmwares do not allow UEFI-MBR boot**.**
The UEFI Shell is a shell/terminal for the firmware which allows launching uefi applications which include uefi bootloaders**.** Apart from that, the shell can also be used to obtain various other information about the system or the firmware like memory map (memmap), modifying boot manager variables (bcfg), running partitioning programs (diskpart), loading uefi drivers, editing text files (edit), hexedit etc**.**
You can download a BSD licensed UEFI Shell from Intel’s Tianocore UDK/EDK2 Sourceforge.net project**.**
Shell 2.0 works only in UEFI 2.3+ systems and is recommended over Shell 1.0 in those systems. Shell 1**.0 should work in all UEFI systems irrespective of the spec.** version the firmware follows**.** More info at ShellPkg and this mail
Few Asus and other AMI Aptio x86_64 UEFI firmware based motherboards (from Sandy Bridge onwards) provide an option called "Launch EFI Shell from filesystem device" . For those motherboards, download the x86_64 UEFI Shell and copy it to your UEFI SYSTEM PARTITION as <UEFI_SYSTEM_PARTITION>/shellx64.efi (mostly /boot/efi/shellx64.efi) .
Systems with Phoenix SecureCore Tiano UEFI firmware are known to have embedded UEFI Shell which can be launched using either F6, F11 or F12 key**.**
Note: If you are unable to launch UEFI Shell from the firmware directly using any of the above mentioned methods, create a FAT32 USB pen drive with Shell.efi copied as (USB)/efi/boot/bootx64.efi . This USB should come up in the firmware boot menu. Launching this option will launch the UEFI Shell for you**.**
UEFI Shell commands usually support -b option which makes output pause after each page**.** map lists recognized filesystems (fs0, ...) and data storage devices (blk0, ...). Run help -b to list available commands**.**
More info at http://software.intel.com/en-us/articles/efi-shells-and-scripting/
BCFG command is used to modify the UEFI NVRAM entries, which allow the user to change the boot entries or driver options**.** This command is described in detail in page 83 (Section 5**.**3) of «UEFI Shell Specification 2.0» pdf document.
Note: Users are recommended to try bcfg only if efibootmgr fails to create working boot entries in their system**.**
Note: UEFI Shell 1**.0 does not support bcfg command.**
To dump a list of current boot entries —
Shell> bcfg boot dump -v
To add a boot menu entry for rEFInd (for example) as 4th (numbering starts from zero) option in the boot menu
Shell> bcfg boot add 3 fs0:\EFI\arch\refind\refindx64.efi "Arch Linux (rEFInd)"
where fs0: is the mapping corresponding to the UEFI System Partition and \EFI\arch\refind\refindx64.efi is the file to be launched**.**
To remove the 4th boot option
Shell> bcfg boot rm 3
To move the boot option #3 to #0 (i**.**e. 1st or the default entry in the UEFI Boot menu)
Shell> bcfg boot mv 3 0
For bcfg help text
Shell> help bcfg -v -b
Shell> bcfg -**?** -v -b
EDIT command provides a basic text editor with an interface similar to nano text editor, but slightly less functional**.** It handles UTF-8 encoding and takes care or LF vs CRLF line endings**.**
To edit, for example rEFInd’s refind.conf in the UEFI System Partition (fs0: in the firmware)
Shell> fs0: FS0:\> cd \EFI\arch\refind FS0:\EFI\arch\refind\> edit refind.conf
Type Ctrl-E for help**.**
Main page HCL/Firmwares/UEFI
Note: The instructions below are specifically for Archiso /official media; Archbootpreparation is identical, with this refind.conf instead of the one mentioned below (which is for Archiso) and without the filesystem label requirement**.**
Note: The USB can use either MBR or GPT partition table**.** The filesystem should be either FAT32 (recommended) or FAT16**.** FAT12 is designed for floppy drives and therefore not recommended for USB drives**.**
First create a MBR partition table in the USB using fdisk**.** Mount the USB partition and create a FAT32 filesystem with LABEL as used in the Archiso configuration**.**
# mkdir -p /mnt/{usb,iso}
# mount -o loop archlinux-2012**.**12.01-dual.iso /mnt/iso
Obtain the label from /mnt/iso/loader/entries/archiso-x86_64.conf; this is used by the archisohook in initramfs to identify the udev path to the installation media**.**
# awk 'BEGIN {FS="="} /archisolabel/ {print $3}' /mnt/iso/loader/entries/archiso-x86_64.conf | xargs mkfs.vfat /dev/sdXY -n
Mount the newly created FAT32 USB partition, and copy the contents of the installation media to the USB media**.**
# mount /dev/sdXY /mnt/usb
# cp -r / mnt / iso / * / mnt / usb
# umount /mnt/{usb,iso}
# sync
If you find the error: «No loader found**.** Configuration files in /loader/entries/*.conf are needed**.**« A possible fix is to use a different uefi bootloader to the included one, gummiboot**.**
Download refind-efi pkg and extract the file /usr/lib/refind/refind_x64.efi from within the package to (USB)/EFI/boot/bootx64.efi (overwrite or rename any existing(USB)/EFI/boot/bootx64.efi file).
Then copy this text to EFI/boot/refind.conf. Take care that the label in the Arch menu section (ARCH_201302 here) matches that of your usb’s**.**
refind.conf
timeout 5
textonly
showtools about,reboot,shutdown,exit
# scan_driver_dirs EFI/tools/drivers_x64
scanfor manual,internal,external,optical
scan_delay 1
dont_scan_dirs EFI/boot
max_tags 0
default_selection "Arch Linux Archiso x86_64 UEFI USB"
menuentry "Arch Linux Archiso x86_64 UEFI USB" {
loader /arch/boot/x86_64/vmlinuz
initrd /arch/boot/x86_64/archiso.img
ostype Linux
graphics off
options "archisobasedir=arch archisolabel=ARCH_201302 add_efi_memmap"
}
menuentry "UEFI x86_64 Shell v2" {
loader /EFI/shellx64_v2.efi
graphics off
}
menuentry "UEFI x86_64 Shell v1" {
loader /EFI/shellx64_v1.efi
graphics off
}
You should now be able to successfully boot, and you can choose which EFI you’d like to load**.**
Warning: In the event that UEFI+isohybrid El Torito/MBR really causes problems, it would be better to just UEFI boot using the USB stick instructions in the previous section
Most of the 32-bit EFI Macs and some 64-bit EFI Macs refuse to boot from a UEFI(X64)+BIOS bootable CD/DVD**.** If one wishes to proceed with the installation using optical media, it might be necessary to remove UEFI support first**.**
Mount the official installation media and obtain the archisolabel as shown in the previous section**.**
Rebuild the ISO using xorriso from libisoburn :
$ xorriso -as mkisofs -iso-level 3 \
-full-iso9660-filenames\
-volid "ARCH_201212" \
-appid "Arch Linux CD" \
-publisher "Arch Linux " \
-preparer "prepared like a BAWSE" \
-eltorito-boot isolinux/isolinux.bin \
-eltorito-catalog isolinux/boot.cat \
-no-emul-boot -boot-load-size 4 -boot-info-table \
-isohybrid-mbr "/mnt/iso/isolinux/isohdpfx.bin" \
-output "~/archiso.iso" "/mnt/iso/"
Burn ~/archiso.iso to optical media and proceed with installation normally**.**
21.02.2013](http://itman.in/efi-boot/)Author Sergey Sharmazanov Categories
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