Unified Extensible Firmware Interface
Related articles
Unified Extensible Firmware Interface (or UEFI for short) is a new type of firmware. It introduces new ways of booting an OS that is distinct from the commonly used "MBR boot code" method followed for BIOS systems. See Arch boot process#Firmware types for their differences. This page explains What is UEFI and UEFI support in Linux kernel. To set up UEFI Boot Loaders, see Boot loaders.
Contents
UEFI versions
- UEFI started as Intel's EFI in versions 1.x.
- Later, a group of companies called the UEFI Forum took over its development, which renamed it as Unified EFI starting with version 2.0.
- Unless specified as EFI 1.x, EFI and UEFI terms are used interchangeably to denote UEFI 2.x firmware.
- As of 15 April 2015, UEFI Specification 2.5 is the most recent version.
- Apple's EFI implementation is neither a EFI 1.x version nor UEFI 2.x version but mixes up both. This kind of firmware does not fall under any one (U)EFI specification and therefore is not a standard UEFI firmware. Unless stated explicitly, these instructions are general and some of them may not work or may be different in Apple Macs.
Boot Process under UEFI
- System switched on - Power On Self Test, or POST process.
- UEFI firmware is loaded. Firmware initializes the hardware required for booting.
- Firmware then reads its Boot Manager data to determine which UEFI application to be launched and from where (i.e. from which disk and partition).
- Firmware then launches the UEFI application as defined in the boot entry in the firmware's boot manager.
- The launched 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 boot loader like GRUB) depending on how the UEFI application was configured.
Multibooting in UEFI
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 boot loader to load another to switch OSes.
Booting Microsoft Windows
Detecting UEFI Firmware bitness
Non Macs
Check whether the dir /sys/firmware/efi
exists, if it exists it means the kernel has booted in EFI mode. In that case the UEFI bitness is same as kernel bitness. (ie. i686 or x86_64)
Apple Macs
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, type the following into the Mac OS X terminal:
ioreg -l -p IODeviceTree | grep firmware-abi
If the command returns EFI32 then it is IA32 (32-bit) EFI firmware. If it returns EFI64 then it is x86_64 EFI firmware. Most of the Macs do not have UEFI 2.x firmware as Apple's EFI implementation is not fully compliant with UEFI 2.x Specification.
Secure Boot
For an overview about Secure Boot in Linux see Rodsbooks' Secure Boot article. This section focuses on how to set up Secure Boot in Arch Linux. For the time being, this section is limited to explain the procedure of booting the archiso with Secure Boot enabled.
Booting the archiso with Secure Boot enabled is possible since the EFI applications PreLoader.efi
and HashTool.efi
have been added to it. A message will show up that says Failed to Start loader... I will now execute HashTool. To use HashTool for enrolling the hash of loader.efi
and vmlinuz.efi
, follow these steps.
- Select
OK
- In the HashTool main menu, select
Enroll Hash
, choose\loader.efi
and confirm withYes
. Again, selectEnroll Hash
andarchiso
to enter the archiso directory, then selectvmlinuz-efi
and confirm withYes
. Then chooseExit
to return to the boot device selection menu. - In the boot device selection menu choose
Arch Linux archiso x86_64 UEFI CD
The archiso boots, and you are presented with a shell prompt, automatically logged in as root. To check if the archiso was booted with Secure Boot, use this command:
$ od -An -t u1 /sys/firmware/efi/efivars/SecureBoot-XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
The characters denoted by XXXX
differ from machine to machine. To help with this, you can use tab completion or list the EFI variables.
If a Secure Boot is enabled, this command returns 1
as the final integer in a list of five, for example:
6 0 0 0 1
For a verbose status, another way is to execute:
# bootctl status
Linux Kernel Config options for UEFI
The required Linux Kernel configuration options for UEFI systems are :
CONFIG_RELOCATABLE=y CONFIG_EFI=y CONFIG_EFI_STUB=y CONFIG_FB_EFI=y CONFIG_FRAMEBUFFER_CONSOLE=y
UEFI Runtime Variables Support (efivarfs filesystem - /sys/firmware/efi/efivars
). This option is important as this is required to manipulate UEFI Runtime Variables using tools like /usr/bin/efibootmgr
. The below config option has been added in kernel 3.10 and above.
CONFIG_EFIVAR_FS=y
UEFI Runtime Variables Support (old efivars sysfs interface - /sys/firmware/efi/vars
). This option should be disabled to prevent any potential issues with both efivarfs and sysfs-efivars enabled.
CONFIG_EFI_VARS=n
GUID Partition Table GPT config option - mandatory for UEFI support
CONFIG_EFI_PARTITION=y
Retrieved from https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/x86/x86_64/uefi.txt .
UEFI Variables
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. You can get the list using
$ efivar -l
UEFI Variables Support in Linux Kernel
Linux kernel exposes EFI variables data to userspace via 2 interfaces:
- OLD sysfs-efivars interface (CONFIG_EFI_VARS) - populated by
efivars
kernel module at/sys/firmware/efi/vars
- 1024 byte maximum per-variable data size limitation, no UEFI Secure Boot variables support (due to the size limitation) and not recommended by kernel upstream anymore. Still supported by kernel upstream but completely disabled in Arch's official kernels.
- NEW efivarfs (EFI VARiable FileSystem) interface (CONFIG_EFIVAR_FS) - mounted using
efivarfs
kernel module at/sys/firmware/efi/efivars
- replacement for the OLD sysfs-efivars interface, has no maximum per-variable size limitation, supports UEFI Secure Boot variables and recommended by kernel upstream. Introduced in kernel 3.8 and NEWefivarfs
module split from OLDefivars
kernel module in kernel 3.10 .
Inconsistency between efivarfs and sysfs-efivars
Enabling both OLD sysfs-efivars and NEW efivarfs can cause data inconsistency issues (see See https://lkml.org/lkml/2013/4/16/473 for more info). Due to this OLD sysfs-efivars is completely disabled in Arch's official kernels (since core/linux-3.11 and core/linux-lts-3.10) and only NEW efivarfs is enabled/supported going forward. All the UEFI Variables related tools and utilities in official repositories support efivarfs as of 01 October 2013.
If you have both interfaces enabled, you need to disable one of them, and disable and re-enable the other interface (to refresh the data, to prevent inconsistencies) before accessing the EFI VAR data using any userspace tool:
To disable sysfs-efivars and refresh efivarfs:
# modprobe -r efivars # umount /sys/firmware/efi/efivars # modprobe -r efivarfs # modprobe efivarfs # mount -t efivarfs efivarfs /sys/firmware/efi/efivars
To disable efivarfs and refresh sysfs-efivars:
# umount /sys/firmware/efi/efivars # modprobe -r efivarfs # modprobe -r efivars # modprobe efivars
Requirements for UEFI variable support
- EFI Runtime Services support should be present in the kernel (
CONFIG_EFI=y
, check if present withzgrep CONFIG_EFI /proc/config.gz
). - Kernel processor bitness/arch and EFI processor bitness/arch should match
- Kernel should be booted in EFI mode (via EFISTUB or any EFI boot loader, not via BIOS/CSM or Apple's "bootcamp" which is also BIOS/CSM)
- EFI Runtime Services in the kernel SHOULD NOT be disabled via kernel cmdline, i.e.
noefi
kernel parameter SHOULD NOT be used -
efivarfs
filesystem should be mounted at/sys/firmware/efi/efivars
, otherwise follow #Mount efivarfs section below. -
efivar
should list (option-l
) the EFI Variables without any error. For sample output see #Sample List of UEFI Variables.
If EFI Variables support does not work even after the above conditions are satisfied, try the below workarounds:
- If any userspace tool is unable to modify efi variables data, check for existence of
/sys/firmware/efi/efivars/dump-*
files. If they exist, delete them, reboot and retry again. - If the above step does not fix the issue, try booting with
efi_no_storage_paranoia
kernel parameter to disable kernel efi variable storage space check that may prevent writing/modification of efi variables.
Mount efivarfs
If efivarfs
is not automatically mounted at /sys/firmware/efi/efivars
by systemd during boot, then you need to manually mount it to expose UEFI Variable support to the userspace tools like efibootmgr
etc.:
# mount -t efivarfs efivarfs /sys/firmware/efi/efivars
It is also a good idea to auto-mount efivarfs
during boot via /etc/fstab
as follows:
/etc/fstab
efivarfs /sys/firmware/efi/efivars efivarfs defaults 0 0
Userspace Tools
There are few tools that can access/modify the UEFI variables, namely
- efivar - Library and Tool to manipulate UEFI Variables (used by efibootmgr) - https://github.com/vathpela/efivar - efivar or efivar-gitAUR
- efibootmgr - Tool to manipulate UEFI Firmware Boot Manager Settings - https://github.com/vathpela/efibootmgr - efibootmgr or efibootmgr-gitAUR
- uefivars - Dumps list of EFI variables with some additional PCI related info (uses efibootmgr code internally) - https://github.com/fpmurphy/Various/tree/master/uefivars-2.0 supports only efivarfs and https://github.com/fpmurphy/Various/tree/master/uefivars-1.0 supports only sysfs-efivars . AUR package uefivars-gitAUR
- efitools - Tools to Create and Setup own UEFI Secure Boot Certificates, Keys and Signed Binaries (requires efivarfs) - efitools-gitAUR
- Ubuntu's Firmware Test Suite - https://wiki.ubuntu.com/FirmwareTestSuite/ - fwtsAUR (along with fwts-efi-runtime-dkmsAUR) or fwts-gitAUR
efibootmgr
Assuming the boot-loader file to be launched is /boot/efi/EFI/refind/refind_x64.efi
, /boot/efi/EFI/refind/refind_x64.efi
can be split up as /boot/efi
and /EFI/refind/refind_x64.efi
, wherein /boot/efi
is the mountpoint of the EFI 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 EFI System Partition (assuming mountpoint /boot/efi
for example) (should be in the form /dev/sdXY
), try :
# findmnt /boot/efi TARGET SOURCE FSTYPE OPTIONS /boot/efi /dev/sdXY vfat rw,flush,tz=UTC
Verify that uefi variables support in kernel is working properly by running:
# efivar -l
If efivar lists the uefi variables without any error, then you can proceed. If not, check whether all the conditions in #Requirements for UEFI Variables support to work properly are met.
Then create the boot entry using efibootmgr as follows:
# efibootmgr -c -d /dev/sdX -p Y -l /EFI/refind/refind_x64.efi -L "rEFInd"
In the above command /boot/efi/EFI/refind/refind_x64.efi
translates to /boot/efi
and /EFI/refind/refind_x64.efi
which in turn translate to drive /dev/sdX
-> partition Y
-> file /EFI/refind/refind_x64.efi
.
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\refind\refindx64.efi
or \efi\refind\refind_x64.efi
does not matter (this will change if the filesystem encoding is UTF-8).
EFI System Partition
The EFI System Partition (also called ESP or EFISYS) is a FAT32 formatted physical partition (in the main partition table of the disk, not LVM or software raid etc.) from where the UEFI firmware launches the UEFI bootloader and application.
It is an OS independent partition that acts as the storage place for the EFI bootloaders and applications to be launched by the EFI firmware. It is mandatory for UEFI boot. It should have the EFI System partition type (see #GPT partitioned disks). It is recommended to keep ESP size at 512 MiB although smaller/larger sizes are fine (see note below). For more information see Wikipedia:EFI System partition.
GPT partitioned disks
-
fdisk/gdisk: Create a partition with partition type EFI System (
EFI System
in fdisk oref00
in gdisk). Then format that partition as FAT32 usingmkfs.fat -F32 /dev/<THAT_PARTITION>
(or)
-
GNU Parted: Create a FAT32 partition and in Parted set/activate the
boot
flag (notlegacy_boot
flag) on that partition
MBR partitioned disks
-
fdisk: Create a partition with partition type EFI System using fdisk. Then format that partition as FAT32 using
mkfs.fat -F32 /dev/<THAT_PARTITION>
ESP on RAID
It is possible to make the ESP part of a RAID1 array, but doing so brings the risk of data corruption, and further considerations need to be taken when creating the ESP. See https://bbs.archlinux.org/viewtopic.php?pid=1398710#p1398710 and https://bbs.archlinux.org/viewtopic.php?pid=1390741#p1390741 for details.
UEFI Shell
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.
Obtaining UEFI Shell
You can download a BSD licensed UEFI Shell from Intel's Tianocore UDK/EDK2 Sourceforge.net project:
- AUR package uefi-shell-svnAUR (recommended) - provides x86_64 Shell in x86_64 system and IA32 Shell in i686 system - compiled directly from latest Tianocore EDK2 SVN source
- There are copies of Shell v1 and Shell v2 in the EFI directory on the Arch install media image.
- Precompiled x86_64 UEFI Shell v2 binary (may not be up-to-date)
- Precompiled x86_64 UEFI Shell v1 binary (not updated anymore upstream)
- Precompiled IA32 UEFI Shell v2 binary (may not be up-to-date)
- Precompiled IA32 UEFI Shell v1 binary (not updated anymore upstream)
Shell v2 works best in UEFI 2.3+ systems and is recommended over Shell v1 in those systems. Shell v1 should work in all UEFI systems irrespective of the spec. version the firmware follows. More info at ShellPkg and this mail
Launching UEFI Shell
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 EFI System Partition as <EFI_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.
Important UEFI Shell Commands
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
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.
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\refind\refind_x64.efi "rEFInd"
where fs0:
is the mapping corresponding to the EFI System Partition and fs0:\EFI\refind\refind_x64.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
or:
Shell> bcfg -? -v -b
edit
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 EFI 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.
UEFI Linux Hardware Compatibility
See Unified Extensible Firmware Interface/Hardware for more information.
UEFI Bootable Media
Create UEFI bootable USB from ISO
Follow USB flash installation media#BIOS and UEFI Bootable USB
Remove UEFI boot support from Optical Media
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.
# mount -o loop input.iso /mnt/iso
- Then rebuild the ISO, excluding the UEFI Optical Media booting support, using
xorriso
from libisoburn. Be sure to set the correct archisolabel, e.g. "ARCH_201411" or similar:
$ xorriso -as mkisofs -iso-level 3 \ -full-iso9660-filenames\ -volid "archisolabel" \ -appid "Arch Linux CD" \ -publisher "Arch Linux <https://www.archlinux.org>" \ -preparer "prepared by $USER" \ -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 output.iso /mnt/iso/
- Burn
output.iso
to optical media and proceed with installation normally.
Testing UEFI in systems without native support
OVMF for Virtual Machines
OVMF is a tianocore project to enable UEFI support for Virtual Machines. OVMF contains a sample UEFI firmware for QEMU.
You can build OVMF (with Secure Boot support) from AUR ovmf-svnAUR and run it as follows:
$ qemu-system-x86_64 -enable-kvm -net none -m 1024 -pflash /usr/share/ovmf/x86_64/bios.bin
DUET for BIOS only systems
DUET is a tianocore project that enables chainloading a full UEFI environment from a BIOS system, in a way similar to BIOS OS booting. This method is being discussed extensively in http://www.insanelymac.com/forum/topic/186440-linux-and-windows-uefi-boot-using-tianocore-duet-firmware/. Pre-build DUET images can be downloaded from one of the repos at https://gitorious.org/tianocore_uefi_duet_builds. Specific instructions for setting up DUET is available at https://gitorious.org/tianocore_uefi_duet_builds/tianocore_uefi_duet_installer/blobs/raw/master/Migle_BootDuet_INSTALL.txt.
You can also try http://sourceforge.net/projects/cloverefiboot/ which provides modified DUET images that may contain some system specific fixes and is more frequently updated compared to the gitorious repos.
Troubleshooting
Windows 7 will not boot in UEFI Mode
If you have installed Windows to a different hard disk with GPT partitioning and still have a MBR partitioned hard disk in your computer, then it is possible that the firmware (UEFI) is starting its CSM support (for booting MBR partitions) and therefore Windows will not boot. To solve this merge your MBR hard disk to GPT partitioning or disable the SATA port where the MBR hard disk is plugged in or unplug the SATA connector from this hard disk.
Mainboards with this kind of problem:
- Gigabyte Z77X-UD3H rev. 1.1 (UEFI version F19e)
- The firmware option for booting "UEFI Only" does not prevent the firmware from starting CSM.
Windows changes boot order
In some motherboards (confirmed in ASRock Z77 Extreme4) Windows 8 changes the boot order in the NVRAM everytime is booted. This can be fixed making the Windows Boot Manager to load another loader instead of booting Windows. Run this command in a Administrator mode console in Windows:
bcdedit /set {bootmgr} path \EFI\boot_app_dir\boot_app.efi
USB media gets struck with black screen
- This issue can occur either due to KMS issue. Try Disabling KMS while booting the USB.
- If the issue is not due to KMS, then it may be due to bug in EFISTUB booting (see [2] and [3] for more information.). Both Official ISO (Archiso) and Archboot iso use EFISTUB (via Gummiboot Boot Manager for menu) for booting the kernel in UEFI mode. In such a case you have to use GRUB as the USB's UEFI bootloader by following the below section.
Using GRUB
- Backup
EFI/boot/loader.efi
toEFI/boot/gummiboot.efi
- Create a GRUB standalone image and copy the generate
grub*.efi
to the USB asEFI/boot/loader.efi
,EFI/boot/bootx64.efi
and/orEFI/boot/bootia32.efi
(useful when running on a 32-bit UEFI)
- Create
EFI/boot/grub.cfg
with the following contents (replaceARCH_YYYYMM
with the required archiso label e.g.ARCH_201507
):
grub.cfg for Official ISO
insmod part_gpt insmod part_msdos insmod fat insmod efi_gop insmod efi_uga insmod video_bochs insmod video_cirrus insmod font if loadfont "${prefix}/fonts/unicode.pf2" ; then insmod gfxterm set gfxmode="1024x768x32;auto" terminal_input console terminal_output gfxterm fi menuentry "Arch Linux archiso x86_64" { set gfxpayload=keep search --no-floppy --set=root --label ARCH_YYYYMM linux /arch/boot/x86_64/vmlinuz archisobasedir=arch archisolabel=ARCH_YYYYMM add_efi_memmap initrd /arch/boot/x86_64/archiso.img } menuentry "UEFI Shell x86_64 v2" { search --no-floppy --set=root --label ARCH_YYYYMM chainloader /EFI/shellx64_v2.efi } menuentry "UEFI Shell x86_64 v1" { search --no-floppy --set=root --label ARCH_YYYYMM chainloader /EFI/shellx64_v1.efi }
grub.cfg for Archboot ISO
insmod part_gpt insmod part_msdos insmod fat insmod efi_gop insmod efi_uga insmod video_bochs insmod video_cirrus insmod font if loadfont "${prefix}/fonts/unicode.pf2" ; then insmod gfxterm set gfxmode="1024x768x32;auto" terminal_input console terminal_output gfxterm fi menuentry "Arch Linux x86_64 Archboot" { set gfxpayload=keep search --no-floppy --set=root --file /boot/vmlinuz_x86_64 linux /boot/vmlinuz_x86_64 cgroup_disable=memory loglevel=7 add_efi_memmap initrd /boot/initramfs_x86_64.img } menuentry "UEFI Shell x86_64 v2" { search --no-floppy --set=root --file /boot/vmlinuz_x86_64 chainloader /EFI/tools/shellx64_v2.efi } menuentry "UEFI Shell x86_64 v1" { search --no-floppy --set=root --file /boot/vmlinuz_x86_64 chainloader /EFI/tools/shellx64_v1.efi }
On some UEFI motherboards like boards with an Intel Z77 chipset, adding entries with efibootmgr
or bcfg
from the EFI Shell will not work because they do not show up on the boot menu list after being added to NVRAM.
This issue is caused because the motherboards can only load Microsoft Windows. To solve this you have to place the .efi
file in the location that Windows uses.
Copy the bootx64.efi
file from the Arch Linux installation medium (FSO:
) to the Microsoft directory your ESP partition on your hard drive (FS1:
). Do this by booting into EFI shell and typing:
FS1: cd EFI mkdir Microsoft cd Microsoft mkdir Boot cp FS0:\EFI\BOOT\bootx64.efi FS1:\EFI\Microsoft\Boot\bootmgfw.efi
After reboot, any entries added to NVRAM should show up in the boot menu.
See also
- Wikipedia:UEFI
- UEFI Forum - contains the official UEFI Specifications - GUID Partition Table is part of UEFI Specification
- UEFI boot: how does that actually work, then? - A blog post by AdamW
- Wikipedia:EFI System partition
- The EFI System Partition and the Default Boot Behavior
- Linux Kernel x86_64 UEFI Documentation
- Intel's page on EFI
- Intel UEFI Community Resource Center
- Matt Fleming - The Linux EFI Boot Stub
- Matt Fleming - Accessing UEFI Variables from Linux
- Rod Smith - Linux on UEFI: A Quick Installation Guide
- UEFI Boot problems on some newer machines (LKML)
- LPC 2012 Plumbing UEFI into Linux
- LPC 2012 UEFI Tutorial : part 1
- LPC 2012 UEFI Tutorial : part 2
- Intel's Tianocore Project for Open-Source UEFI firmware which includes DuetPkg for direct BIOS based booting and OvmfPkg used in QEMU and Oracle VirtualBox
- FGA: The EFI boot process
- Microsoft's Windows and GPT FAQ
- Convert Windows x64 from BIOS-MBR mode to UEFI-GPT mode without Reinstall
- Create a Linux BIOS+UEFI and Windows x64 BIOS+UEFI bootable USB drive
- Rod Smith - A BIOS to UEFI Transformation
- EFI Shells and Scripting - Intel Documentation
- UEFI Shell - Intel Documentation
- UEFI Shell - bcfg command info
- UEFI Shell v2 binary with bcfg modified to work with UEFI pre-2.3 firmware - from Clover efiboot