Difference between revisions of "Unified Extensible Firmware Interface"

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[[ru:Unified Extensible Firmware Interface]]
 
[[ru:Unified Extensible Firmware Interface]]
 
[[zh-CN:Unified Extensible Firmware Interface]]
 
[[zh-CN:Unified Extensible Firmware Interface]]
{{Article summary start}}
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{{Related articles start}}
{{Article summary text|An overview of the Unified Extensible Firmware Interface.}}
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{{Related|Arch boot process}}
{{Article summary heading|Overview}}
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{{Related|Master Boot Record}}
{{Article summary text|{{Boot process overview}}}}
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{{Related|EFI System Partition}}
{{Article summary heading|Related}}
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{{Related|GUID Partition Table}}
{{Article summary wiki|GUID Partition Table}}
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{{Related|Secure Boot}}
{{Article summary wiki|Master Boot Record}}
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{{Related|UEFI/Hardware}}
{{Article summary wiki|Arch Boot Process}}
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{{Related articles end}}
{{Article summary end}}
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{{Warning|While the choice to install in UEFI mode is forward looking, early vendor UEFI implementations may carry more bugs than their BIOS counterparts. It is advised to do a search relating to your particular mainboard model before proceeding.}}
  
'''Unified Extensible Firmware Interface''' (or UEFI for short) is a new type of firmware that was initially designed by Intel (known as EFI then) mainly for its Itanium based systems. It introduces new ways of booting an OS that is distinct from the commonly used "MBR boot code" method followed for BIOS systems. It started as Intel's EFI in versions 1.x and then a group of companies called the UEFI Forum took over its development from which it was called Unified EFI starting with version 2.0 . As of 23 May 2012, UEFI Specification 2.3.1 is the most recent version.
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The [http://www.uefi.org/ Unified Extensible Firmware Interface] (EFI or UEFI for short) is a new model for the interface between operating systems and firmware. It provides a standard environment for booting an operating system and running pre-boot applications.
  
{{Note|Unless specified as EFI 1.x , EFI and UEFI terms are used interchangeably to denote UEFI 2.x firmware. Also unless stated explicitely, these instructions are general and not Mac specific. Some of them may not work or may be different in Macs. 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 UEFI Specification version and therefore it is not a standard UEFI firmware.}}
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It is distinct from the commonly used "[[MBR]] boot code" method followed for [[Wikipedia:BIOS|BIOS]] systems. See [[Arch boot process]] for their differences and the boot process using UEFI. To set up UEFI Boot Loaders, see [[Boot loaders]].
  
== Booting an OS using BIOS ==
+
== 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.
 +
* 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 [[MacBook|Apple Macs]].
  
A BIOS or Basic Input-Output System is the very first program that is executed once the system is switched on. After all the hardware has been initialized and the POST operation has completed, the BIOS executes the first boot code in the first device in the device booting list.  
+
The latest UEFI Specification can be found at http://uefi.org/specifications.
  
If the list starts with a CD/DVD drive, then the El-Torito entry in the CD/DVD is executed. This is how bootable CD/DVD works. If the list starts with a HDD, then BIOS executes the very first 440 bytes MBR boot code. The boot code then chainloads or bootstraps a much larger and complex bootloader which then loads the OS.
+
== UEFI Firmware bitness ==
  
Basically, the BIOS does not know how to read a partition table or filesystem. All it does is initialize the hardware, then load and run the 440-byte boot code.
+
Under UEFI, every program whether it is an OS loader or a utility (e.g. a memory testing app or recovery tool), should be a UEFI Application corresponding to the EFI firmware bitness/architecture.
  
=== Multiboot on BIOS ===
+
The vast majority of UEFI firmwares, including recent Apple Macs, use x86_64 EFI firmware. The only known devices that use IA32 (32-bit) EFI are older (pre 2008) Apple Macs, some Intel Cloverfield ultrabooks and some older Intel Server boards that are known to operate on Intel EFI 1.10 firmware.
  
Since very little can be achieved by a program that fits into the 440-byte boot code area, multi-booting using BIOS requires a multi-boot capable bootloader (multi-boot refers to booting multiple operating systems, not to booting a kernel in the Multiboot format specified by the GRUB developers). So usually a common bootloader like [[GRUB]] or [[Syslinux]] or [[LILO]] would be loaded by the BIOS, and it would load an operating system by either chain-loading or directly loading the kernel.
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An x86_64 EFI firmware does not include support for launching 32-bit EFI apps (unlike x86_64 Linux and Windows versions which include such support). Therefore the UEFI application must be compiled for that specific firmware processor bitness/architecture.
  
== Booting an OS using UEFI ==
+
=== Non Macs ===
  
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.  
+
Check whether the dir {{ic|/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)
  
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.
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{{Note|Intel Atom System-on-Chip systems ship with 32-bit UEFI (as on 2 November 2013). See [[#Booting 64-bit kernel on 32-bit UEFI]] for more info.}}
  
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 SYSTEM PARTITION>/EFI/<VENDOR NAME>/ 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.
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=== Apple Macs ===
  
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.
+
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.
{{Note|Some older Intel Server boards are known to operate on Intel EFI 1.10 firmware, and require i386 EFI applications.}}
+
  
 +
To find out the arch of the efi firmware in a Mac, type the following into the Mac OS X terminal:
  
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.
+
$ ioreg -l -p IODeviceTree | grep firmware-abi
  
=== Multibooting on UEFI ===
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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.
  
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.
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== Linux Kernel Config options for UEFI ==
  
==== Linux Windows x86_64 UEFI-GPT Multiboot ====
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The required Linux Kernel configuration options for UEFI systems are :
  
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. See http://support.microsoft.com/default.aspx?scid=kb;EN-US;2581408 for more info.
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CONFIG_RELOCATABLE=y
 +
CONFIG_EFI=y
 +
CONFIG_EFI_STUB=y
 +
CONFIG_FB_EFI=y
 +
CONFIG_FRAMEBUFFER_CONSOLE=y
  
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.
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UEFI Runtime Variables Support ('''efivarfs''' filesystem - {{ic|/sys/firmware/efi/efivars}}). This option is important as this is required to manipulate UEFI Runtime Variables using tools like {{ic|/usr/bin/efibootmgr}}. The below config option has been added in kernel 3.10 and above.
  
== Boot Process under UEFI ==
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CONFIG_EFIVAR_FS=y
  
# System switched on - Power On Self Test, or POST process.
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UEFI Runtime Variables Support (old '''efivars sysfs''' interface - {{ic|/sys/firmware/efi/vars}}). This option should be disabled to prevent any potential issues with both efivarfs and sysfs-efivars enabled.
# UEFI firmware is loaded.
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# Firmware reads its Boot Manager to determine which UEFI application to be launched and from where (ie. from which disk and partition).
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# Firmware launches the UEFI application from the FAT32 formatted UEFISYS partition as defined in the boot entry in the firmware's boot manager.
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# 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.
+
  
== Detecting UEFI Firmware Arch ==
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CONFIG_EFI_VARS=n
  
If you have a non-mac UEFI system, then you have a x86_64 (aka 64-bit) UEFI 2.x firmware.
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GUID Partition Table [[GPT]] config option - mandatory for UEFI support
  
Some of the known x86_64 UEFI 2.x firmwares are Phoenix SecureCore Tiano, AMI Aptio, Insyde H2O.
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CONFIG_EFI_PARTITION=y
  
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
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{{Note|All of the above options are required to boot Linux via UEFI, and are enabled in Archlinux kernels in official repos.}}
  
 +
Retrieved from https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/x86/x86_64/uefi.txt .
  
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.
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== UEFI Variables ==
  
To find out the arch of the efi firmware in a Mac, boot into Mac OS X and type the following command
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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
  
<pre>
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=== UEFI Variables Support in Linux Kernel ===
ioreg -l -p IODeviceTree | grep firmware-abi
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</pre>
+
  
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.
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Linux kernel exposes EFI variables data to userspace via '''efivarfs''' ('''EFI''' '''VAR'''iable '''F'''ile'''S'''ystem) interface ({{ic|CONFIG_EFIVAR_FS}}) - mounted using {{ic|efivarfs}} kernel module at {{ic|/sys/firmware/efi/efivars}} - it has no maximum per-variable size limitation and supports UEFI Secure Boot variables. Introduced in kernel 3.8.
  
== UEFI Support in Linux Kernel ==
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=== Requirements for UEFI variable support ===
  
=== Linux Kernel config options for UEFI ===
+
# Kernel processor [[#UEFI Firmware bitness|bitness]] and EFI processor bitness should match.
 +
# Kernel should be booted in EFI mode (via [[EFISTUB]] or any [[Boot loaders|EFI boot loader]], not via BIOS/CSM or Apple's "bootcamp" which is also BIOS/CSM).
 +
# EFI Runtime Services support should be present in the kernel ({{ic|1=CONFIG_EFI=y}}, check if present with {{ic|zgrep CONFIG_EFI /proc/config.gz}}).
 +
# EFI Runtime Services in the kernel SHOULD NOT be disabled via kernel cmdline, i.e. {{ic|noefi}} kernel parameter SHOULD NOT be used.
 +
# {{ic|efivarfs}} filesystem should be mounted at {{ic|/sys/firmware/efi/efivars}}, otherwise follow [[#Mount efivarfs]] section below.
 +
# {{ic|efivar}} should list (option {{ic|-l}}) the EFI Variables without any error.
  
The required Linux Kernel configuration options for UEFI systems are :
+
If EFI Variables support does not work even after the above conditions are satisfied, try the below workarounds:
  
CONFIG_EFI=y
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# If any userspace tool is unable to modify efi variables data, check for existence of {{ic|/sys/firmware/efi/efivars/dump-*}} files. If they exist, delete them, reboot and retry again.
CONFIG_EFI_STUB=y
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# If the above step does not fix the issue, try booting with {{ic|efi_no_storage_paranoia}} kernel parameter to disable kernel efi variable storage space check that may prevent writing/modification of efi variables.
CONFIG_RELOCATABLE=y
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CONFIG_FB_EFI=y
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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 like '''efibootmgr'''.
+
{{Note|{{ic|efi_no_storage_paranoia}} should only be used when needed and should not be left as a normal boot option. The effect of this kernel command line parameter turns off a safeguard that was put in place to help avoid the bricking of machines when the NVRAM gets too full.}}
 
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CONFIG_EFI_VARS=y
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{{Note| This option is compiled built-in into the Arch core/testing kernel.}}
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==== Mount efivarfs ====
  
{{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.}}
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{{Warning|1=''efivars'' is mounted writeable by default [https://github.com/systemd/systemd/issues/2402], which may cause permanent damage to the system. [https://bbs.archlinux.org/viewtopic.php?id=207549]{{Dead link|2016|08|21}} As such, consider mounting ''efivars'' read-only ({{ic|-o ro}}) as described below. Note that when it is mounted read-only, tools such as ''efibootmgr'' and bootloaders will not be able to change boot settings, nor will commands like {{ic|systemctl reboot --firmware-setup}} work.}}
  
{{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.}}
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If {{ic|efivarfs}} is not automatically mounted at {{ic|/sys/firmware/efi/efivars}} by [[systemd]] during boot, then you need to manually mount it to expose UEFI variables to [[#Userspace tools]] like {{ic|efibootmgr}}:
  
GUID Partition Table [[GPT]] config option - mandatory for UEFI support
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# mount -t efivarfs efivarfs /sys/firmware/efi/efivars
  
CONFIG_EFI_PARTITION=y
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{{Note|The above command should be run both '''outside''' ('''before''') and '''inside''' the [[chroot]], if any.}}
  
{{Note|All of the above options are required to boot Linux via UEFI, and are enabled in Archlinux kernels in official repos.}}
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To mount {{ic|efivarfs}} read-only during boot, add to {{ic|/etc/fstab}}:
  
Retrieved from http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob_plain;f=Documentation/x86/x86_64/uefi.txt;hb=HEAD .
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{{hc|/etc/fstab|2=
 +
efivarfs    /sys/firmware/efi/efivars    efivarfs    '''ro''',nosuid,nodev,noexec,noatime 0 0
 +
}}
  
== UEFI Variables Support ==
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To remount with write support, run:
  
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.
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# mount -o remount /sys/firmware/efi/efivars -o '''rw''',nosuid,nodev,noexec,noatime
  
{{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 <UEFISYS>/EFI/arch/refind/{refindx64.efi,refind.conf} ) can be done even in BIOS/Legacy boot mode.}}
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=== Userspace tools ===
  
Access to UEFI Runtime services is provided by "efivars" kernel module which is enabled through the {{ic|<nowiki>CONFIG_EFI_VARS=y</nowiki>}} kernel config option. This module exposes the variables under the directory {{ic|/sys/firmware/efi/vars}} (for kernels >=3.8 through {{ic|/sys/firmware/efi/efivars}}). One way to check whether the system has booted in UEFI boot mode is to check for the existence of {{ic|/sys/firmware/efi/vars}} (and in kernels >=3.8 for {{ic|/sys/firmware/efi/efivars}})directory with contents similar to :
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There are few tools that can access/modify the UEFI variables, namely
  
Sample output (x86_64-UEFI 2.3.1 in x86_64 Kernel):
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* {{App|efivar|Library and Tool to manipulate UEFI Variables (used by efibootmgr)|https://github.com/vathpela/efivar|{{Pkg|efivar}}, {{AUR|efivar-git}}}}
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* {{App|efibootmgr|Tool to manipulate UEFI Firmware Boot Manager Settings|https://github.com/vathpela/efibootmgr|{{Pkg|efibootmgr}}, {{AUR|efibootmgr-git}}}}
# ls -1 /sys/firmware/efi/vars/
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* {{App|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|{{AUR|uefivars-git}}}}
Boot0000-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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* {{App|efitools|Tools for manipulating UEFI secure boot platforms|http://git.kernel.org/cgit/linux/kernel/git/jejb/efitools.git|{{Pkg|efitools}}, {{AUR|efitools-git}}}}
BootCurrent-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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* {{App|Ubuntu's Firmware Test Suite|Test suite that performs sanity checks on Intel/AMD PC firmware|https://wiki.ubuntu.com/FirmwareTestSuite/|{{AUR|fwts-git}}}}
BootOptionSupport-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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ConIn-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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ConInDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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ConOut-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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ConOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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ErrOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
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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/
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RTC-378d7b65-8da9-4773-b6e4-a47826a833e1/
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del_var
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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.
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==== efibootmgr ====
  
=== Userspace Tools ===
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{{Note|
 +
* If {{ic|efibootmgr}} completely fails to work in your system, you can reboot into UEFI Shell v2 and use {{ic|bcfg}} command to create a boot entry for the bootloader.
 +
* If you are unable to use {{ic|efibootmgr}}, some UEFI firmwares allow users to directly manage uefi boot entries from within its boot-time interface.  For example, some ASUS firmwares have an "Add New Boot Option" choice which enables you to select a local EFI System Partition and manually enter the EFI stub location. (for example {{ic|\EFI\refind\refind_x64.efi}}).
 +
* The below commands use {{Pkg|refind-efi}} boot-loader as example.
 +
}}
  
There are few tools that can access/modify the UEFI variables, namely
+
Assuming the boot-loader file to be launched is {{ic|/boot/efi/EFI/refind/refind_x64.efi}}, {{ic|/boot/efi/EFI/refind/refind_x64.efi}} can be split up as {{ic|/boot/efi}} and {{ic|/EFI/refind/refind_x64.efi}}, wherein {{ic|/boot/efi}} is the mountpoint of the EFI System Partition, which is assumed to be {{ic|/dev/sdXY}} (here {{ic|X}} and {{ic|Y}} are just placeholders for the actual values - eg:- in {{ic|/dev/sda1}} , {{ic|1=X==a}} {{ic|1=Y==1}}).
  
# efibootmgr - Used to create/modify boot entries in the UEFI Boot Manager - {{Pkg|efibootmgr}} or {{AUR|efibootmgr-git}}
+
To determine the actual device path for the EFI System Partition (assuming mountpoint {{ic|/boot/efi}} for example) (should be in the form {{ic|/dev/sdXY}}), try :
# uefivars - simply dumps the variables - {{AUR|uefivars-git}} - uses efibootmgr library
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# Ubuntu's Firmware Test Suite - fwts - {{AUR|fwts-git}} - uefidump command - {{ic|fwts uefidump}}  
+
  
=== Non-Mac UEFI systems ===
+
{{hc|# findmnt /boot/efi|2=
 +
  TARGET SOURCE  FSTYPE OPTIONS
 +
/boot/efi  /dev/sdXY  vfat        rw,flush,tz=UTC
 +
}}
  
==== efibootmgr ====
+
Verify that uefi variables support in kernel is working properly by running:
  
{{Warning|Using {{ic|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 - {{AUR|mactel-boot}}.}}
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# efivar -l
  
{{Note|{{ic|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 {{ic|Fatal: Couldn't open either sysfs or procfs directories for accessing EFI variables}} is shown.}}
+
If efivar lists the uefi variables without any error, then you can proceed. If not, check whether all the conditions in [[#Requirements for UEFI variable support]] are met.
  
{{Note| If you are unable to use {{ic|efibootmgr}}, some UEFI BIOSes allow users to directly manage uefi boot options from within the BIOS.  For example, some ASUS BIOSes have a "Add New Boot Option" choice which enables you to select a local EFI system partition and manually enter the EFI stub location. (for example '\EFI\refind\refind_x64.efi')}}
+
Then create the boot entry using efibootmgr as follows:
  
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 {{ic|efibootmgr}} should be run to make the UEFI boot-loader entry as the default entry in the UEFI Boot Manager.
+
# efibootmgr --create --disk /dev/sdX --part Y --loader /EFI/refind/refind_x64.efi --label "rEFInd Boot Manager"
  
To use efibootmgr, first load the 'efivars' kernel module (if compiled as a external module):
+
{{Note|1=UEFI uses backward slash {{ic|\}} as path separator (similar to Windows paths), but the official {{Pkg|efibootmgr}} pkg support passing unix-style paths with forward-slash {{ic|/}} as path-separator for the {{ic|-l}}/{{ic|--loader}} option. Efibootmgr internally converts {{ic|/}} to {{ic|\}} before encoding the loader path.}}
  
# modprobe efivars
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In the above command {{ic|/boot/efi/EFI/refind/refind_x64.efi}} translates to {{ic|/boot/efi}} and {{ic|/EFI/refind/refind_x64.efi}} which in turn translate to drive {{ic|/dev/sdX}} -> partition {{ic|Y}} -> file {{ic|/EFI/refind/refind_x64.efi}}.
  
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?).
+
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 [http://linux.dell.com/cgi-bin/cgit.cgi/efibootmgr.git/plain/README efibootmgr GIT README] .
  
Verify whether there are files in ''/sys/firmware/efi/vars/'' (and ''/sys/firmware/efi/efivars/'' for kernel >=3.8) 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.
+
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 {{ic|\EFI\refind\refindx64.efi}} or {{ic|\efi\refind\refind_x64.efi}} does not matter (this will change if the filesystem encoding is UTF-8).
  
If ''/sys/firmware/efi/vars/'' directory is empty or does not exist, then {{ic|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]].
+
== UEFI Shell ==
  
{{Note| The below commands use {{Pkg|gummiboot}} boot-loader as example.}}
+
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.
{{out of date|[[Gummiboot]] has its own installer now, therefore the following instructions should not be used to install [[gummiboot]]. This example should be changed to use something else.}}
+
  
Assume the boot-loader file to be launched is {{ic|/boot/efi/EFI/gummiboot/gummibootx64.efi}}. {{ic|/boot/efi/EFI/gummiboot/gummibootx64.efi}} can be split up as {{ic|/boot/efi}} and {{ic|/EFI/gummiboot/gummibootx64.efi}}, wherein {{ic|/boot/efi}} is the mountpoint of the UEFI System Partition, which is assumed to be {{ic|/dev/sdXY}} (here X and Y are just placeholders for the actual values - eg:- in {{ic|/dev/sda1}} , X=a Y=1).
+
=== Obtaining UEFI Shell ===
  
To determine the actual device path for the UEFI System Partition (should be in the form {{ic|/dev/sdXY}}), try :
+
You can download a BSD licensed UEFI Shell from Intel's Tianocore UDK/EDK2 Sourceforge.net project:
 +
* [[AUR]] package {{AUR|uefi-shell-git}} (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.
 +
* [https://github.com/tianocore/edk2/tree/master/ShellBinPkg Precompiled UEFI Shell v2 binaries] (may not be up-to-date)
 +
* [https://github.com/tianocore/edk2/tree/master/EdkShellBinPkg Precompiled UEFI Shell v1 binaries] (not updated anymore upstream)
 +
* [http://dl.dropbox.com/u/17629062/Shell2.zip Precompiled UEFI Shell v2 binary with bcfg modified to work with UEFI pre-2.3 firmware] - from Clover EFI bootloader
  
# findmnt /boot/efi
+
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 [http://sourceforge.net/apps/mediawiki/tianocore/index.php?title=ShellPkg ShellPkg] and [http://sourceforge.net/mailarchive/message.php?msg_id=28690732 this mail]{{Dead link|2016|08|21}}
TARGET SOURCE  FSTYPE OPTIONS
+
/boot/efi  /dev/sdXY  vfat        rw,flush,tz=UTC
+
  
Then create the boot entry using efibootmgr as follows :
+
=== Launching UEFI Shell ===
  
# efibootmgr -c -g -d /dev/sdX -p Y -w -L "Gummiboot" -l '\EFI\gummiboot\gummibootx64.efi'
+
Few Asus and other AMI Aptio x86_64 UEFI firmware based motherboards (from Sandy Bridge onwards) provide an option called {{ic|"Launch EFI Shell from filesystem device"}} . For those motherboards, download the x86_64 UEFI Shell and copy it to your EFI System Partition as {{ic|<EFI_SYSTEM_PARTITION>/shellx64.efi}} (mostly {{ic|/boot/efi/shellx64.efi}}) .
  
In the above command {{ic|/boot/efi/EFI/gummiboot/gummibootx64.efi}} translates to {{ic|/boot/efi}} and {{ic|/EFI/gummiboot/gummibootx64.efi}} which in turn translate to drive {{ic|/dev/sdX}} -> partition {{ic|Y}} -> file {{ic|/EFI/gummiboot/gummibootx64.efi}}.
+
Systems with Phoenix SecureCore Tiano UEFI firmware are known to have embedded UEFI Shell which can be launched using either {{ic|F6}}, {{ic|F11}} or {{ic|F12}} key.
  
UEFI uses backward slash as path separator (similar to Windows paths).
+
{{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 {{ic|Shell.efi}} copied as {{ic|(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.}}
  
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 [http://linux.dell.com/cgi-bin/gitweb/gitweb.cgi?p=efibootmgr.git;a=blob_plain;f=README;hb=HEAD efibootmgr GIT README] .
+
=== Important UEFI Shell Commands ===
  
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 {{ic|\EFI\gummiboot\gummibootx64.efi}} or {{ic|\efi\gummiboot\gummibootx64.efi}} does not matter (this will change if the filesystem encoding is UTF-8).
+
UEFI Shell commands usually support {{ic|-b}} option which makes output pause after each page. Run {{ic|help -b}} to list available commands.
  
== Linux Bootloaders for UEFI ==
+
More info at http://software.intel.com/en-us/articles/efi-shells-and-scripting/
  
See [[UEFI Bootloaders]].
+
==== bcfg ====
  
== EFI System Partition ==
+
{{ic|bcfg}} modifies the UEFI NVRAM entries which allows 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|UEFI System Partition and EFI System Partition (ESP) are same, the terminologies are used interchangeably in some places.}}
+
{{Note|
 +
* Try {{ic|bcfg}} only if {{ic|efibootmgr}} fails to create working boot entries on your system.
 +
* UEFI Shell v1 official binary does not support {{ic|bcfg}} command. See [[#Obtaining UEFI Shell]] for a modified UEFI Shell v2 binary which may work in UEFI pre-2.3 firmwares.
 +
}}
  
{{Note|1=The EFI System Partition can be of any size supported by FAT32 filesystem. According to Microsoft Documentation, the minimum partition/volume size for FAT32 is 512 MiB. However ESP with size >=100 MiB but formatted as FAT32 are also allowed by many Linux distros and by Microsoft Windows, hence smaller partitions are fine. However >=512 MiB size for ESP is recommended for most conmpatibility. Non-FAT filesystems like ext2/3/4, reiserfs, NTFS, UDF etc. are not supported for ESP.}}
+
To dump a list of current boot entries:
  
{{Note|The ESP should be outside LVM or any other software RAID or RAID like systems. ESP should be accessible by the UEFI firmware, which cannot read LVM and such systems.}}
+
Shell> bcfg boot dump -v
  
{{Note|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.}}
+
To add a boot menu entry for rEFInd (for example) as 4th (numbering starts from zero) option in the boot menu:
  
=== For GPT partitioned disks ===
+
Shell> bcfg boot add 3 fs0:\EFI\refind\refind_x64.efi "rEFInd"
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 {{ic|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".}}
+
where {{ic|fs0:}} is the mapping corresponding to the EFI System Partition and {{ic|fs0:\EFI\refind\refind_x64.efi}} is the file to be launched.
  
{{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).}}
+
To add an entry to boot directly into your system without a bootloader, configure a boot option using your kernel as an [[EFISTUB#UEFI_Shell|EFISTUB]]:
  
=== For MBR partitioned disks ===
+
Shell> bcfg boot add '''N''' fs'''V''':\vmlinuz-linux "Arch Linux"
Two choices:
+
Shell> bcfg boot -opt '''N''' "root='''/dev/sdX#''' initrd=\initramfs-linux.img"
* 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 {{ic|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.}}
+
where {{ic|N}} is the priority, {{ic|V}} is the volume number of your EFI partition, and {{ic|/dev/sdX#}} is your root partition.
  
== UEFI Shell ==
+
To remove the 4th boot option:
  
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.
+
Shell> bcfg boot rm 3
  
=== UEFI Shell download links ===
+
To move the boot option #3 to #0 (i.e. 1st or the default entry in the UEFI Boot menu):
  
You can download a BSD licensed UEFI Shell from Intel's Tianocore UDK/EDK2 Sourceforge.net project.
+
Shell> bcfg boot mv 3 0
  
* [https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/ShellBinPkg/UefiShell/X64/Shell.efi x86_64 UEFI Shell 2.0 (Beta)]
+
For bcfg help text:
* [https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/EdkShellBinPkg/FullShell/X64/Shell_Full.efi x86_64 UEFI Shell 1.0 (Old)]
+
* [https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/ShellBinPkg/UefiShell/Ia32/Shell.efi i386 UEFI Shell 2.0 (Beta)]
+
* [https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/EdkShellBinPkg/FullShell/Ia32/Shell_Full.efi i386 UEFI Shell 1.0 (Old)]
+
  
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 [http://sourceforge.net/apps/mediawiki/tianocore/index.php?title=ShellPkg ShellPkg] and [http://sourceforge.net/mailarchive/message.php?msg_id=28690732 this mail]
+
Shell> help bcfg -v -b
  
=== Launching UEFI Shell ===
+
or:
  
Few Asus and other AMI Aptio x86_64 UEFI firmware based motherboards (from Sandy Bridge onwards) provide an option called {{ic|"Launch EFI Shell from filesystem device"}} . For those motherboards, download the x86_64 UEFI Shell and copy it to your UEFI SYSTEM PARTITION as {{ic|<UEFI_SYSTEM_PARTITION>/shellx64.efi}} (mostly {{ic|/boot/efi/shellx64.efi}}) .
+
Shell> bcfg -? -v -b
  
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.
+
==== map ====
  
{{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.}}
+
{{ic|map}} displays a list of device mappings i.e. the names of available file systems ({{ic|fs0}}) and storage devices ({{ic|blk0}}).
  
=== Important UEFI Shell Commands ===
+
Before running file system commands such as {{ic|cd}} or {{ic|ls}}, you need to change the shell to the appropriate file system by typing its name:
  
UEFI Shell commands usually support {{ic|-b}} option which makes output pause after each page. {{ic|map}} lists recognized filesystems ({{ic|fs0}}, ...) and data storage devices ({{ic|blk0}}, ...). Run {{ic|help -b}} to list available commands.
+
Shell> fs0:
 +
fs0:\> cd EFI/
  
More info at http://software.intel.com/en-us/articles/efi-shells-and-scripting/
+
==== edit ====
  
==== bcfg ====
+
{{ic|edit}} provides a basic text editor with an interface similar to nano, but slightly less functional. It handles UTF-8 encoding and takes care or LF vs CRLF line endings.
  
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.
+
For example, to edit rEFInd's {{ic|refind.conf}} in the EFI System Partition ({{ic|fs0:}} in the firmware),
  
{{Note| Users are recommended to try {{ic|bcfg}} only if {{ic|efibootmgr}} fails to create working boot entries in their system.}}
+
Shell> edit FS0:\EFI\refind\refind.conf
  
{{Note| UEFI Shell 1.0 does not support {{ic|bcfg}} command.}}
+
Type {{ic|Ctrl-E}} for help.
  
To dump a list of current boot entries -
+
== UEFI Linux Hardware Compatibility ==
  
Shell> bcfg boot dump -v
+
See [[Unified Extensible Firmware Interface/Hardware]] for more information.
  
To add a boot menu entry for rEFInd (for example) as 4th (numbering starts from zero) option in the boot menu
+
== UEFI Bootable Media ==
  
Shell> bcfg boot add 3 fs0:\EFI\arch\refind\refindx64.efi "Arch Linux (rEFInd)"
+
=== Create UEFI bootable USB from ISO ===
  
where fs0: is the mapping corresponding to the UEFI System Partition and \EFI\arch\refind\refindx64.efi is the file to be launched.
+
Follow [[USB flash installation media#BIOS and UEFI Bootable USB]]
  
To remove the 4th boot option
+
=== Remove UEFI boot support from Optical Media ===
  
Shell> bcfg boot rm 3
+
{{Note|This section mentions removing UEFI boot support from a '''CD/DVD only''' (Optical Media), not from a USB flash drive.}}
  
To move the boot option #3 to #0 (i.e. 1st or the default entry in the UEFI Boot menu)
+
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.
  
Shell> bcfg boot mv 3 0
+
* Mount the official installation media and obtain the {{ic|archisolabel}} as shown in the previous section.
  
For bcfg help text
+
# mount -o loop ''input.iso'' /mnt/iso
  
Shell> help bcfg -v -b
+
* Then rebuild the ISO, excluding the UEFI Optical Media booting support, using {{ic|xorriso}} from {{pkg|libisoburn}}. Be sure to set the correct archisolabel, e.g. "ARCH_201411" or similar:
 +
{{bc|1=
 +
$ 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/
 +
}}
  
or
+
* Burn {{ic|''output.iso''}} to optical media and proceed with installation normally.
  
Shell> bcfg -? -v -b
+
== Testing UEFI in systems without native support ==
  
==== edit ====
+
=== OVMF for Virtual Machines ===
  
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.
+
[https://tianocore.github.io/ovmf/ OVMF] is a tianocore project to enable UEFI support for Virtual Machines. OVMF contains a sample UEFI firmware for QEMU.
  
To edit, for example rEFInd's refind.conf in the UEFI System Partition (fs0: in the firmware)
+
You can install {{pkg|ovmf}} from the extra repository and run it as follows:
  
  Shell> fs0:
+
  $ qemu-system-x86_64 -enable-kvm -net none -m 1024 -drive file=/usr/share/ovmf/ovmf_x64.bin,format=raw,if=pflash,readonly
FS0:\> cd \EFI\arch\refind
+
FS0:\EFI\arch\refind\> edit refind.conf
+
  
Type {{ic|Ctrl-E}} for help.
+
As shorter alternative, {{Pkg|ovmf}} can be loaded using {{ic|-bios}} parameter
  
== Hardware Compatibility ==
+
$ qemu-system-x86_64 -enable-kvm -m 1G -bios /usr/share/ovmf/ovmf_x64.bin
  
Main page [[HCL/Firmwares/UEFI]]
+
=== DUET for BIOS only systems ===
  
== Create UEFI bootable USB from ISO ==
+
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 {{Dead link|2016|08|21}}. 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 {{Dead link|2016|08|21}}.
  
{{Note|1=The instructions below are specifically for [[Archiso]]/official media; [[Archboot]] preparation is identical, with this [https://bbs.archlinux.org/viewtopic.php?pid=1190788#p1190788 refind.conf] instead of the one mentioned below (which is for Archiso) and without the filesystem label requirement.}}
+
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.
  
{{Note|The USB can use either MBR or GPT partition table (so it is fine to use an already partitioned USB). The filesystem should be either FAT32 (recommended) or FAT16. FAT12 is designed for floppy drives and therefore not recommended for USB drives.}}
+
== Troubleshooting ==
  
First create a partition table and at most one partition in the USB. Mount the ISO image from the [https://www.archlinux.org/download/ Arch Linux download page].
+
=== Windows 7 will not boot in UEFI Mode ===
  
{{bc|1=<nowiki>
+
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.
# mkdir -p /mnt/{usb,iso}
+
# mount -o loop archlinux-2012.12.01-dual.iso /mnt/iso
+
</nowiki>}}
+
  
Then create a FAT32 filesystem in the partition on the USB (unmount before if necessary) with LABEL as used in the Archiso configuration. Obtain the label from {{ic|/mnt/iso/loader/entries/archiso-x86_64.conf}}; this is used by the {{ic|archiso}} hook in initramfs to identify the udev path to the installation media. {{ic|mkfs.vfat}} is part of package {{Pkg|dosfstools}}.
+
Mainboards with this kind of problem:
  
{{bc|1=<nowiki>
+
* Gigabyte Z77X-UD3H rev. 1.1 (UEFI version F19e)
# awk 'BEGIN {FS="="} /archisolabel/ {print $3}' /mnt/iso/loader/entries/archiso-x86_64.conf | xargs mkfs.vfat -F32 /dev/sdXY -n
+
** The firmware option for booting "UEFI Only" does not prevent the firmware from starting CSM.
</nowiki>}}
+
  
Mount the newly created FAT32 USB partition, and copy the contents of the installation media to the USB media.
+
=== Windows changes boot order ===
  
{{bc|1=<nowiki>
+
If you [[dual boot with Windows]] and your motherboard just boots Windows immediately instead of your chosen UEFI application, there are several possible causes and workarounds.
# mount /dev/sdXY /mnt/usb
+
# cp -a /mnt/iso/* /mnt/usb
+
# sync
+
# umount /mnt/{usb,iso}</nowiki>}}
+
  
 +
* Ensure [[Dual boot with Windows#Fast_Start-Up|Fast Startup]] is disabled in your Windows power options
 +
* Ensure [[Secure Boot]] is disabled in your BIOS (if you are not using a signed boot loader)
 +
* Ensure your UEFI boot order does not have Windows Boot Manager set first e.g. using [[#efibootmgr]] and what you see in the configuration tool of the UEFI. Some motherboards override by default any settings set with efibootmgr by Windows if it detects it. This is confirmed in a Packard Bell laptop.
 +
* If your motherboard is booting the default UEFI path ({{ic|\EFI\BOOT\BOOTX64.EFI}}), this file may have been overwritten with the Windows boot loader. Try setting the correct boot path e.g. using [[#efibootmgr]].
 +
* If the previous steps do not work, you can tell the Windows boot loader to run a different UEFI application. From a Windows Administrator command prompt: {{bc|# bcdedit /set {bootmgr} path \EFI\''path''\''to''\''app.efi''}}
 +
* Alternatively, you can set a startup script in Windows that ensures that the boot order is set correctly every time you boot Windows.
 +
*# Open a command prompt with admin privlages. Run {{ic|bcdedit /enum firmware}} and find your desired boot entry.
 +
*# Copy the Identifier, including the brackets, e.g. {{ic|<nowiki>{31d0d5f4-22ad-11e5-b30b-806e6f6e6963}</nowiki>}}
 +
*# Create a batch file with the command {{ic|bcdedit /set {fwbootmgr} DEFAULT ''{copied boot identifier}''}}
 +
*# Open ''gpedit'' and under ''Local Computer Policy > Computer Configuration > Windows Settings > Scripts(Startup/Shutdown)'', choose ''Startup''
 +
*# Under the ''Scripts'' tab, choose the ''Add'' button, and select your batch file
  
=== Fixing errors ===
+
=== USB media gets struck with black screen ===
  
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.
+
This issue can occur due to [[KMS]] issue. Try [[Kernel mode setting#Disabling_modesetting|Disabling KMS]] while booting the USB.
  
Download [https://www.archlinux.org/packages/extra/any/refind-efi/download/ refind-efi pkg] and extract the file {{ic|/usr/lib/refind/refind_x64.efi}} from within the package to {{ic|(USB)/EFI/boot/bootx64.efi}} (overwrite or rename any existing {{ic|(USB)/EFI/boot/bootx64.efi}} file).
+
=== Booting 64-bit kernel on 32-bit UEFI ===
  
Then copy this text to {{ic|EFI/boot/refind.conf}}. Take care that the label in the Arch menu section ({{ic|ARCH_201302}} here) matches that of your usb's.
+
Both Official ISO ([[Archiso]]) and [[Archboot]] iso use EFISTUB (via [[systemd-boot]] 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.
  
{{hc|refind.conf|<nowiki>
+
==== Using GRUB ====
timeout 5
+
{{Tip|The given configuration entries can also be entered inside a [[GRUB#Using_the_command_shell|GRUB command-shell]].}}
textonly
+
  
showtools about,reboot,shutdown,exit
+
* [[USB flash installation media#BIOS_and_UEFI_Bootable_USB|Create an USB Flash Installation]]
# scan_driver_dirs EFI/tools/drivers_x64
+
scanfor manual,internal,external,optical
+
  
scan_delay 1
+
* Backup {{ic|EFI/boot/loader.efi}} to {{ic|EFI/boot/gummiboot.efi}}
dont_scan_dirs EFI/boot
+
  
max_tags 0
+
* [[GRUB#GRUB_standalone|Create a GRUB standalone image]] and copy the generate {{ic|grub*.efi}} to the USB as {{ic|EFI/boot/loader.efi}} and/or {{ic|EFI/boot/bootia32.efi}}
default_selection "Arch Linux Archiso x86_64 UEFI USB"
+
  
menuentry "Arch Linux Archiso x86_64 UEFI USB" {
+
* Create {{ic|EFI/boot/grub.cfg}} with the following contents (replace {{ic|ARCH_YYYYMM}} with the required archiso label e.g. {{ic|ARCH_201507}}):
  loader /arch/boot/x86_64/vmlinuz
+
 
  initrd /arch/boot/x86_64/archiso.img
+
{{hc|grub.cfg for Official ISO|<nowiki>
  ostype Linux
+
insmod part_gpt
  graphics off
+
insmod part_msdos
  options "archisobasedir=arch archisolabel=ARCH_201302 add_efi_memmap"
+
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 x86_64 Shell v2" {
+
menuentry "UEFI Shell x86_64 v2" {
  loader /EFI/shellx64_v2.efi
+
    search --no-floppy --set=root --label ARCH_YYYYMM
  graphics off
+
    chainloader /EFI/shellx64_v2.efi
 
}
 
}
  
menuentry "UEFI x86_64 Shell v1" {
+
menuentry "UEFI Shell x86_64 v1" {
  loader /EFI/shellx64_v1.efi
+
    search --no-floppy --set=root --label ARCH_YYYYMM
  graphics off
+
    chainloader /EFI/shellx64_v1.efi
 
}
 
}
 
</nowiki>}}
 
</nowiki>}}
  
You should now be able to successfully boot, and you can choose which EFI you'd like to load.
+
{{hc|grub.cfg for Archboot ISO|<nowiki>
 +
insmod part_gpt
 +
insmod part_msdos
 +
insmod fat
  
== Remove UEFI boot support from ISO ==
+
insmod efi_gop
 +
insmod efi_uga
 +
insmod video_bochs
 +
insmod video_cirrus
  
{{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}}
+
insmod font
  
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.
+
if loadfont "${prefix}/fonts/unicode.pf2" ; then
 +
    insmod gfxterm
 +
    set gfxmode="1024x768x32;auto"
 +
    terminal_input console
 +
    terminal_output gfxterm
 +
fi
  
Mount the official installation media and obtain the {{ic|archisolabel}} as shown in the previous section.
+
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
 +
}
  
Rebuild the ISO using {{ic|xorriso}} from {{pkg|libisoburn}}:
+
menuentry "UEFI Shell x86_64 v2" {
 +
    search --no-floppy --set=root --file /boot/vmlinuz_x86_64
 +
    chainloader /EFI/tools/shellx64_v2.efi
 +
}
  
{{bc|1=<nowiki>
+
menuentry "UEFI Shell x86_64 v1" {
$ xorriso -as mkisofs -iso-level 3 \
+
     search --no-floppy --set=root --file /boot/vmlinuz_x86_64
    -full-iso9660-filenames\
+
     chainloader /EFI/tools/shellx64_v1.efi
    -volid "ARCH_201212" \
+
}
     -appid "Arch Linux CD" \
+
</nowiki>}}
    -publisher "Arch Linux <https://www.archlinux.org>" \
+
    -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/"</nowiki>}}
+
  
Burn {{ic|~/archiso.iso}} to optical media and proceed with installation normally.
+
=== UEFI boot loader does not show up in firmware menu ===
  
== QEMU with OVMF ==
+
On certain UEFI motherboards like some boards with an Intel Z77 chipset, adding entries with {{ic|efibootmgr}} or {{ic|bcfg}} from the EFI Shell will not work because they do not show up on the boot menu list after being added to NVRAM.
  
OVMF [http://sourceforge.net/apps/mediawiki/tianocore/index.php?title=OVMF] is a project to enable UEFI support for Virtual Machines. OVMF contains a sample UEFI firmware for QEMU and KVM.
+
This issue is caused because the motherboards can only load Microsoft Windows. To solve this you have to place the {{ic|.efi}} file in the location that Windows uses.
  
You can build OVMF from AUR [https://aur.archlinux.org/packages/ovmf-svn/] and use it like this:
+
Copy the {{ic|bootx64.efi}} file from the Arch Linux installation medium ({{ic|FSO:}}) to the Microsoft directory your [[ESP]] partition on your hard drive ({{ic|FS1:}}). Do this by booting into EFI shell and typing:
  
  qemu-system-x86_64 -bios /usr/share/ovmf/bios.bin ...
+
  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 ==
 
== See also ==
  
* Wikipedia's page on [http://en.wikipedia.org/wiki/UEFI UEFI]
+
* [[Wikipedia:UEFI]]
* Wikipedia's page on [http://en.wikipedia.org/wiki/EFI_System_partition UEFI SYSTEM Partition]
+
* [http://www.uefi.org/home/ UEFI Forum] - contains the official [http://uefi.org/specifications UEFI Specifications] - GUID Partition Table is part of UEFI Specification
* [http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob_plain;f=Documentation/x86/x86_64/uefi.txt;hb=HEAD Linux Kernel UEFI Documentation]
+
* [https://www.happyassassin.net/2014/01/25/uefi-boot-how-does-that-actually-work-then/ UEFI boot: how does that actually work, then? - A blog post by AdamW]
* [http://www.uefi.org/home/ UEFI Forum] - contains the official [http://www.uefi.org/specs/ UEFI Specifications] - GUID Partition Table is part of UEFI Specification
+
* [https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/x86/x86_64/uefi.txt Linux Kernel x86_64 UEFI Documentation]
 +
* [http://www.intel.com/technology/efi/ Intel's page on EFI]{{Dead link|2016|07|16}}
 +
* [http://firmware.intel.com/ Intel Architecture Firmware Resource Center]
 +
* [http://firmware.intel.com/blog/linux-efi-boot-stub Matt Fleming - The Linux EFI Boot Stub]
 +
* [http://firmware.intel.com/blog/accessing-uefi-variables-linux Matt Fleming - Accessing UEFI Variables from Linux]
 +
* [http://www.rodsbooks.com/linux-uefi/ Rod Smith - Linux on UEFI: A Quick Installation Guide]
 +
* [https://lkml.org/lkml/2011/6/8/322 UEFI Boot problems on some newer machines (LKML)]
 +
* [http://linuxplumbers.ubicast.tv/videos/plumbing-uefi-into-linux/ LPC 2012 Plumbing UEFI into Linux]
 +
* [http://linuxplumbers.ubicast.tv/videos/uefi-tutorial-part-1/ LPC 2012 UEFI Tutorial : part 1]
 +
* [http://linuxplumbers.ubicast.tv/videos/uefi-tutorial-part-2/ LPC 2012 UEFI Tutorial : part 2]
 
* [http://sourceforge.net/apps/mediawiki/tianocore/index.php?title=Welcome_to_TianoCore 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
 
* [http://sourceforge.net/apps/mediawiki/tianocore/index.php?title=Welcome_to_TianoCore 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
* [http://www.intel.com/technology/efi/ Intel's page on EFI]
+
* [https://jdebp.eu/FGA/efi-boot-process.html FGA: The EFI boot process]
* [http://homepage.ntlworld.com/jonathan.deboynepollard/FGA/efi-boot-process.html FGA: The EFI boot process]
+
* [http://www.microsoft.com/whdc/device/storage/GPT_FAQ.mspx Microsoft's Windows and GPT FAQ]
* [http://www.microsoft.com/whdc/device/storage/GPT_FAQ.mspx Microsoft's Windows and GPT FAQ] - Contains info on Windows UEFI booting also
+
* [https://gitorious.org/tianocore_uefi_duet_builds/pages/Windows_x64_BIOS_to_UEFI Convert Windows x64 from BIOS-MBR mode to UEFI-GPT mode without Reinstall]{{Dead link|2016|08|21}}
* [https://gitorious.org/tianocore_uefi_duet_builds/pages/Windows_x64_BIOS_to_UEFI Convert Windows Vista SP1+ or 7 x86_64 boot from BIOS-MBR mode to UEFI-GPT mode without Reinstall]
+
* [https://gitorious.org/tianocore_uefi_duet_builds/pages/Linux_Windows_BIOS_UEFI_boot_USB Create a Linux BIOS+UEFI and Windows x64 BIOS+UEFI bootable USB drive]{{Dead link|2016|08|21}}
* [https://gitorious.org/tianocore_uefi_duet_builds/pages/Linux_Windows_BIOS_UEFI_boot_USB Create a Linux BIOS+UEFI and Windows x64 BIOS+UEFI bootable USB drive]
+
 
* [http://rodsbooks.com/bios2uefi/ Rod Smith - A BIOS to UEFI Transformation]
 
* [http://rodsbooks.com/bios2uefi/ Rod Smith - A BIOS to UEFI Transformation]
* [https://lkml.org/lkml/2011/6/8/322 UEFI Boot problems on some newer machines (LKML)]
 
 
* [http://software.intel.com/en-us/articles/efi-shells-and-scripting/ EFI Shells and Scripting - Intel Documentation]
 
* [http://software.intel.com/en-us/articles/efi-shells-and-scripting/ EFI Shells and Scripting - Intel Documentation]
 
* [http://software.intel.com/en-us/articles/uefi-shell/ UEFI Shell  - Intel Documentation]
 
* [http://software.intel.com/en-us/articles/uefi-shell/ UEFI Shell  - Intel Documentation]
 
* [http://www.hpuxtips.es/?q=node/293 UEFI Shell - bcfg command info]
 
* [http://www.hpuxtips.es/?q=node/293 UEFI Shell - bcfg command info]
* [http://hackthejoggler.freeforums.org/download/file.php?id=28 Some useful 32-bit UEFI Shell utilities]
 
* [http://linuxplumbers.ubicast.tv/videos/plumbing-uefi-into-linux/ LPC 2012 Plumbing UEFI into Linux]
 
* [http://linuxplumbers.ubicast.tv/videos/uefi-tutorial-part-1/ LPC 2012 UEFI Tutorial : part 1]
 
* [http://linuxplumbers.ubicast.tv/videos/uefi-tutorial-part-2/ LPC 2012 UEFI Tutorial : part 2]
 

Latest revision as of 17:45, 30 August 2016

Warning: While the choice to install in UEFI mode is forward looking, early vendor UEFI implementations may carry more bugs than their BIOS counterparts. It is advised to do a search relating to your particular mainboard model before proceeding.

The Unified Extensible Firmware Interface (EFI or UEFI for short) is a new model for the interface between operating systems and firmware. It provides a standard environment for booting an operating system and running pre-boot applications.

It is distinct from the commonly used "MBR boot code" method followed for BIOS systems. See Arch boot process for their differences and the boot process using UEFI. To set up UEFI Boot Loaders, see Boot loaders.

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.
  • 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.

The latest UEFI Specification can be found at http://uefi.org/specifications.

UEFI Firmware bitness

Under UEFI, every program whether it is an OS loader or a utility (e.g. a memory testing app or recovery tool), should be a UEFI Application corresponding to the EFI firmware bitness/architecture.

The vast majority of UEFI firmwares, including recent Apple Macs, use x86_64 EFI firmware. The only known devices that use IA32 (32-bit) EFI are older (pre 2008) Apple Macs, some Intel Cloverfield ultrabooks and some older Intel Server boards that are known to operate on Intel EFI 1.10 firmware.

An x86_64 EFI firmware does not include support for launching 32-bit EFI apps (unlike x86_64 Linux and Windows versions which include such support). Therefore the UEFI application must be compiled for that specific firmware processor bitness/architecture.

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)

Note: Intel Atom System-on-Chip systems ship with 32-bit UEFI (as on 2 November 2013). See #Booting 64-bit kernel on 32-bit UEFI for more info.

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.

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
Note: All of the above options are required to boot Linux via UEFI, and are enabled in Archlinux kernels in official repos.

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 efivarfs (EFI VARiable FileSystem) interface (CONFIG_EFIVAR_FS) - mounted using efivarfs kernel module at /sys/firmware/efi/efivars - it has no maximum per-variable size limitation and supports UEFI Secure Boot variables. Introduced in kernel 3.8.

Requirements for UEFI variable support

  1. Kernel processor bitness and EFI processor bitness should match.
  2. 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).
  3. EFI Runtime Services support should be present in the kernel (CONFIG_EFI=y, check if present with zgrep CONFIG_EFI /proc/config.gz).
  4. EFI Runtime Services in the kernel SHOULD NOT be disabled via kernel cmdline, i.e. noefi kernel parameter SHOULD NOT be used.
  5. efivarfs filesystem should be mounted at /sys/firmware/efi/efivars, otherwise follow #Mount efivarfs section below.
  6. efivar should list (option -l) the EFI Variables without any error.

If EFI Variables support does not work even after the above conditions are satisfied, try the below workarounds:

  1. 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.
  2. 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.
Note: efi_no_storage_paranoia should only be used when needed and should not be left as a normal boot option. The effect of this kernel command line parameter turns off a safeguard that was put in place to help avoid the bricking of machines when the NVRAM gets too full.

Mount efivarfs

Warning: efivars is mounted writeable by default [1], which may cause permanent damage to the system. [2][dead link 2016-08-21] As such, consider mounting efivars read-only (-o ro) as described below. Note that when it is mounted read-only, tools such as efibootmgr and bootloaders will not be able to change boot settings, nor will commands like systemctl reboot --firmware-setup work.

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 variables to #Userspace tools like efibootmgr:

# mount -t efivarfs efivarfs /sys/firmware/efi/efivars
Note: The above command should be run both outside (before) and inside the chroot, if any.

To mount efivarfs read-only during boot, add to /etc/fstab:

/etc/fstab
efivarfs    /sys/firmware/efi/efivars    efivarfs    ro,nosuid,nodev,noexec,noatime 0 0

To remount with write support, run:

# mount -o remount /sys/firmware/efi/efivars -o rw,nosuid,nodev,noexec,noatime

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, efivar-gitAUR
  • efibootmgr — Tool to manipulate UEFI Firmware Boot Manager Settings
https://github.com/vathpela/efibootmgr || efibootmgr, 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 || uefivars-gitAUR
  • efitools — Tools for manipulating UEFI secure boot platforms
http://git.kernel.org/cgit/linux/kernel/git/jejb/efitools.git || efitools, efitools-gitAUR
  • Ubuntu's Firmware Test Suite — Test suite that performs sanity checks on Intel/AMD PC firmware
https://wiki.ubuntu.com/FirmwareTestSuite/ || fwts-gitAUR

efibootmgr

Note:
  • If efibootmgr completely fails to work in your system, you can reboot into UEFI Shell v2 and use bcfg command to create a boot entry for the bootloader.
  • If you are unable to use efibootmgr, some UEFI firmwares allow users to directly manage uefi boot entries from within its boot-time interface. For example, some ASUS firmwares have an "Add New Boot Option" choice which enables you to select a local EFI System Partition and manually enter the EFI stub location. (for example \EFI\refind\refind_x64.efi).
  • The below commands use refind-efi boot-loader as example.

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 variable support are met.

Then create the boot entry using efibootmgr as follows:

# efibootmgr --create --disk /dev/sdX --part Y --loader /EFI/refind/refind_x64.efi --label "rEFInd Boot Manager"
Note: UEFI uses backward slash \ as path separator (similar to Windows paths), but the official efibootmgr pkg support passing unix-style paths with forward-slash / as path-separator for the -l/--loader option. Efibootmgr internally converts / to \ before encoding the loader path.

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).

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:

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[dead link 2016-08-21]

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.

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.

Important UEFI Shell Commands

UEFI Shell commands usually support -b option which makes output pause after each page. Run help -b to list available commands.

More info at http://software.intel.com/en-us/articles/efi-shells-and-scripting/

bcfg

bcfg modifies the UEFI NVRAM entries which allows 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:
  • Try bcfg only if efibootmgr fails to create working boot entries on your system.
  • UEFI Shell v1 official binary does not support bcfg command. See #Obtaining UEFI Shell for a modified UEFI Shell v2 binary which may work in UEFI pre-2.3 firmwares.

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 add an entry to boot directly into your system without a bootloader, configure a boot option using your kernel as an EFISTUB:

Shell> bcfg boot add N fsV:\vmlinuz-linux "Arch Linux"
Shell> bcfg boot -opt N "root=/dev/sdX# initrd=\initramfs-linux.img"

where N is the priority, V is the volume number of your EFI partition, and /dev/sdX# is your root partition.

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

map

map displays a list of device mappings i.e. the names of available file systems (fs0) and storage devices (blk0).

Before running file system commands such as cd or ls, you need to change the shell to the appropriate file system by typing its name:

Shell> fs0:
fs0:\> cd EFI/

edit

edit provides a basic text editor with an interface similar to nano, but slightly less functional. It handles UTF-8 encoding and takes care or LF vs CRLF line endings.

For example, to edit rEFInd's refind.conf in the EFI System Partition (fs0: in the firmware),

Shell> edit FS0:\EFI\refind\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

Note: This section mentions removing UEFI boot support from a CD/DVD only (Optical Media), not from a USB flash drive.

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 install ovmf from the extra repository and run it as follows:

$ qemu-system-x86_64 -enable-kvm -net none -m 1024 -drive file=/usr/share/ovmf/ovmf_x64.bin,format=raw,if=pflash,readonly

As shorter alternative, ovmf can be loaded using -bios parameter

$ qemu-system-x86_64 -enable-kvm -m 1G -bios /usr/share/ovmf/ovmf_x64.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 [dead link 2016-08-21]. 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 [dead link 2016-08-21].

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

If you dual boot with Windows and your motherboard just boots Windows immediately instead of your chosen UEFI application, there are several possible causes and workarounds.

  • Ensure Fast Startup is disabled in your Windows power options
  • Ensure Secure Boot is disabled in your BIOS (if you are not using a signed boot loader)
  • Ensure your UEFI boot order does not have Windows Boot Manager set first e.g. using #efibootmgr and what you see in the configuration tool of the UEFI. Some motherboards override by default any settings set with efibootmgr by Windows if it detects it. This is confirmed in a Packard Bell laptop.
  • If your motherboard is booting the default UEFI path (\EFI\BOOT\BOOTX64.EFI), this file may have been overwritten with the Windows boot loader. Try setting the correct boot path e.g. using #efibootmgr.
  • If the previous steps do not work, you can tell the Windows boot loader to run a different UEFI application. From a Windows Administrator command prompt:
    # bcdedit /set {bootmgr} path \EFI\path\to\app.efi
  • Alternatively, you can set a startup script in Windows that ensures that the boot order is set correctly every time you boot Windows.
    1. Open a command prompt with admin privlages. Run bcdedit /enum firmware and find your desired boot entry.
    2. Copy the Identifier, including the brackets, e.g. {31d0d5f4-22ad-11e5-b30b-806e6f6e6963}
    3. Create a batch file with the command bcdedit /set {fwbootmgr} DEFAULT {copied boot identifier}
    4. Open gpedit and under Local Computer Policy > Computer Configuration > Windows Settings > Scripts(Startup/Shutdown), choose Startup
    5. Under the Scripts tab, choose the Add button, and select your batch file

USB media gets struck with black screen

This issue can occur due to KMS issue. Try Disabling KMS while booting the USB.

Booting 64-bit kernel on 32-bit UEFI

Both Official ISO (Archiso) and Archboot iso use EFISTUB (via systemd-boot 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

Tip: The given configuration entries can also be entered inside a GRUB command-shell.
  • Backup EFI/boot/loader.efi to EFI/boot/gummiboot.efi
  • Create EFI/boot/grub.cfg with the following contents (replace ARCH_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
}

UEFI boot loader does not show up in firmware menu

On certain UEFI motherboards like some 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