Unified Extensible Firmware Interface

Related articles
EFI system partition
GUID Partition Table
Secure Boot
Unified kernel image
The
Unified Extensible Firmware Interface
(UEFI)
is an 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
MBR boot code
method that was used by legacy
BIOS
systems. See
Arch boot process
for their differences and the boot process using UEFI. To set up UEFI boot loaders, see
Arch boot process#Boot loader
.
Note
Early vendor UEFI implementations may carry more bugs than their BIOS counterparts. Consider using legacy BIOS booting for such systems if you encounter unsolvable issues.
Apple UEFI implementation does not conform to the standard. Unless stated explicitly, these instructions are general and some of them may not work or may be different for
Macs
.
UEFI firmware bitness
Under UEFI, every program whether it is an operating system loader or a utility (e.g. a memory testing or recovery tool), should be an EFI application corresponding to the UEFI firmware bitness/architecture.
The vast majority of x86_64 systems, including recent Apple Macs, use x64 (64-bit) UEFI firmware. The only known devices that use IA32 (32-bit) UEFI are older (pre 2008) Apple Macs, Intel Atom System-on-Chip systems (as on 2 November 2013)
[1]
and some older Intel server boards that are known to operate on Intel EFI 1.10 firmware.
An x64 UEFI firmware does not include support for launching 32-bit EFI applications (unlike x86_64 Linux and Windows versions which include such support). Therefore the EFI application must be compiled for that specific firmware processor bitness/architecture.
Note
Systems with IA32 UEFI require using a
boot loader
that supports mixed mode booting.
Checking the firmware bitness
The firmware bitness can be checked from a booted operating system.
From Linux
On distributions running Linux kernel 4.0 or newer, the UEFI firmware bitness can be found via the sysfs interface. Run:
$ cat /sys/firmware/efi/fw_platform_size
It will return
64
for a 64-bit (x64) UEFI or
32
for a 32-bit (IA32) UEFI. If the file does not exist, you have not
booted in UEFI mode
.
From macOS
Pre-2008
Macs
mostly have IA32 EFI firmware while >=2008 Macs have mostly x64 EFI. All Macs capable of running Mac OS X Snow Leopard 64-bit Kernel have x64 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
, it is IA32 (32-bit) EFI firmware. If it returns
EFI64
, it is x64 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.
From Microsoft Windows
64-bit versions of Windows do not support booting on a 32-bit UEFI. So, if you have a 32-bit version of Windows booted in UEFI mode, you have a 32-bit UEFI.
To check the bitness run
msinfo32.exe
. In the
System Summary
section look at the values of "System Type" and "BIOS mode".
For 64-bit Windows on a 64-bit UEFI, it will be
System Type: x64-based PC
and
BIOS mode: UEFI
. For 32-bit Windows on a 32-bit UEFI—
System Type: x86-based PC
and
BIOS mode: UEFI
. If the "BIOS mode" is not
UEFI
, Windows is not booted in UEFI mode.
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 operating system only for early system start-up. UEFI runtime variables allow an operating system 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 --list
UEFI variables support in Linux kernel
Linux kernel exposes UEFI variables data to userspace via
efivarfs
(
EFI
VAR
iable
F
ile
S
ystem) 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
Kernel should be booted in UEFI mode via the
EFI boot stub
(optionally using a
boot manager
) or by a UEFI
boot loader
, not via BIOS or CSM (Compatibility Support Module), or Apple's Boot Camp which is also a CSM.
EFI Runtime Services support should be present in the kernel (
CONFIG_EFI=y
, check if present with
zgrep CONFIG_EFI /proc/config.gz
).
EFI Runtime Services in the kernel
should not
be disabled via the
kernel command line
, 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
/
--list
) the UEFI variables without any error.
If UEFI Variables support does not work even after the above conditions are satisfied, try the below workarounds:
If listing of the UEFI variables (
efivar -l
) leads to
efivar: error listing variables: Function not implemented
and the system is booted into a
realtime kernel
, add
efi=runtime
to the
kernel parameters
and reboot (efivarfs functionality is disabled by default on those kernels).
See
#Userspace tools are unable to modify UEFI variable data
for more troubleshooting steps
Mount efivarfs
If
efivarfs
is not automatically mounted at
/sys/firmware/efi/efivars
by
systemd
during boot, 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
(i.e. before)
and
inside
the
chroot
, if any.
See
efivarfs.html
for kernel documentation.
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/rhboot/efivar
||
efivar
efibootmgr
— Tool to manipulate UEFI Firmware Boot Manager Settings
https://github.com/rhboot/efibootmgr
||
efibootmgr
uefivars
— Dumps list of UEFI variables with some additional PCI related info (uses efibootmgr code internally)
https://github.com/fpmurphy/Various/tree/master/uefivars-2.0
||
uefivars-git
AUR
efitools
— Tools for manipulating UEFI secure boot platforms
https://git.kernel.org/pub/scm/linux/kernel/git/jejb/efitools.git
||
efitools
Ubuntu's Firmware Test Suite
— Test suite that performs sanity checks on Intel/AMD PC firmware
https://wiki.ubuntu.com/FirmwareTestSuite/
||
fwts-git
AUR
QEFI Entry Manager
— Qt-based GUI app for managing EFI boot entries and EFI system partitions
https://github.com/Inokinoki/QEFIEntryManager
||
qefientrymanager
AUR
efibootmgr
You will have to
install
the
efibootmgr
package.
Note
If
efibootmgr
does not work on your system, you can reboot into
#UEFI Shell
and use
bcfg
to create a boot entry for the boot loader.
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 firmwares have an "Add New Boot Option" choice which enables you to select a local EFI system partition and manually enter the EFI application location e.g.
\EFI\refind\refind_x64.efi
.
The below commands use
rEFInd
boot manager as example.
To add a new boot option using
efibootmgr
, you need to know three things:
The disk containing the
EFI system partition
(ESP). E.g.:
/dev/sda
,
/dev/nvme0n1
.
The partition number of the ESP on that disk. The
Y
in
/dev/sda
Y
or
/dev/nvme0n1p
Y
.
The path to the EFI application (relative to the root of the ESP)
For example, if you want to add a boot option for
/efi/EFI/refind/refind_x64.efi
where
/efi
is the mount point of the ESP, run
$ findmnt /efi
TARGET SOURCE    FSTYPE OPTIONS
/efi   /dev/sda1 vfat   rw,flush,tz=UTC
In this example,
findmnt(8)
indicates that the ESP is on disk
/dev/sda
and has partition number 1. The path to the EFI application relative to the root of the ESP is
/EFI/refind/refind_x64.efi
. So you would create the boot entry as follows:
# efibootmgr --create --disk /dev/sda --part 1 --loader '\EFI\refind\refind_x64.efi' --label 'rEFInd Boot Manager' --unicode
Get an overview of all boot entries and the boot order:
# efibootmgr --unicode
To set the boot order:
# efibootmgr --bootorder
XXXX
,
XXXX
--unicode
Where
XXXX
is the number that appears in the previous output of
efibootmgr
command.
Delete an unwanted entry:
# efibootmgr --delete-bootnum --bootnum
XXXX
--unicode
See
efibootmgr(8)
or
efibootmgr README
for more info.
Note
UEFI specification uses backward slash
\
as path separator but
efibootmgr
can automatically convert UNIX-style
/
path separators.
Disable UEFI variable access
Access to the UEFI can potentially cause harm beyond the running operating system level. There are dangerous UEFI exploits like
LogoFAIL
which allows a malicious actor to take full control over the machine. Even hardware-level bricking is possible in some cases of poor UEFI implementation
[2]
.
So, as the UEFI variables access is not required for daily system usage, you may want to disable it, to avoid potential security breaches or accidental harm.
Possible solutions are:
Mount
efivars
in read-only mode using
fstab
. For example:
efivarfs /sys/firmware/efi/efivars efivarfs ro,nosuid,nodev,noexec 0 0
Use the
noefi
kernel parameter
to completely disable OS access to UEFI.
Note
UEFI
userspace tools
cannot be used with a such setup, so perform the all necessary configurations before. Also UEFI-related commands (e.g.
systemctl reboot --firmware-setup
) will not work either.
UEFI Shell
The UEFI Shell is a shell/terminal for the firmware which allows launching EFI applications which include UEFI boot loaders. 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 obtain a BSD licensed UEFI Shell from the TianoCore EDK2 project:
Shell v2:
On the Arch install medium:
/shellx64.efi
. A copy of
/usr/share/edk2-shell/x64/Shell_Full.efi
from the time the ISO was built.
edk2-shell
provides x64 Shell for x64 (64-bit) UEFI and IA32 Shell for IA32 (32-bit) UEFI - compiled directly from latest TianoCore EDK2 release.
uefi-shell-git
AUR
provides x64 Shell for x64 (64-bit) UEFI and IA32 Shell for IA32 (32-bit) UEFI - compiled directly from latest TianoCore EDK2 source.
Shell v1:
Precompiled UEFI Shell v1 binaries
from TianoCore (not updated anymore upstream as of Jan 10, 2014).
Patched shells:
Precompiled UEFI Shell v2 binary with bcfg modified to work with UEFI pre-2.3 firmware
[
dead link
2023-07-30—HTTP 403]
- from Clover EFI boot loader.
Precompiled UEFI Shell v2 binary for compatibility with a broad range of firmwares
- from the OpenCore boot loader. In the release archive:
EFI/OC/Tools/OpenShell.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 information at
ShellPkg
and the EDK2 mailing list thread—
Inclusion of UEFI shell in Linux distro iso
.
Launching UEFI Shell
Few Asus and other AMI Aptio x64 UEFI firmware based motherboards (from Sandy Bridge onwards) provide an option called
Launch EFI Shell from filesystem device
. For those motherboards, copy the x64 UEFI Shell to the root of your EFI system partition, named as
shellx64.efi
.
Tip
The Arch Linux installation medium has
shellx64.efi
at the root of the volume.
rEFInd
and
systemd-boot
will automatically add a boot menu entry for the UEFI shell if
shellx64.efi
is in the root of the EFI system partition.
Systems with Phoenix SecureCore Tiano UEFI firmware is 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 the EFI binary copied as
/USB_drive_mointpoint
/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 internal commands. Available commands are either built into the shell or discrete EFI applications.
For more info see
Intel Scripting Guide 2008
[
dead link
2023-07-30—HTTP 404]
and
Intel "Course" 2011
[
dead link
2023-07-30—HTTP 404]
.
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 96 (Section 5.3) of the
UEFI Shell Specification 2.2
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 Boot Manager"
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 boot loader, see
EFI boot stub#bcfg
.
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
Press
Ctrl+e
for help.
UEFI drivers
This article or section needs expansion.
Reason:
Explain what are and how to use UEFI drivers. Add automatic UEFI driver loading setup with efibootmgr's
-r
/
--driver
option. (Discuss in
Talk:Unified Extensible Firmware Interface
)
UEFI drivers are pieces of software that support some functionality. For example, access to NTFS formatted partitions is usually not possible from a UEFI shell. The
efifs
package has drivers that support reading many more file systems from within an EFI shell. A usage example is to copy such driver to a partition that can be accessed from an UEFI shell. Then, from the UEFI shell, issuing commands such as:
Shell> load ntfs_x64.efi
Shell> map -r
After the map command has been executed, the user should be able to access NTFS formatted partitions from within a UEFI shell.
Tip
systemd-boot
automatically loads UEFI drivers from
esp
/EFI/systemd/drivers/
.
rEFInd
automatically loads UEFI drivers from the
drivers
and
drivers_x64
subdirectories of its own installation directory on the ESP. E.g.
esp
/EFI/refind/drivers_x64/
. It can be configured to scan additional directories.
UEFI bootable media
Remove UEFI boot support from optical media
Note
This section mentions removing UEFI boot support from a
CD/DVD only
(Optical Media booting via  EL Torito), not from a USB flash drive.
In order to hide the UEFI equipment on USB stick, use a partition editor after having copied the ISO to the flash drive. Remove the partition of type
EF
.
Do not
accept offers to convert to GPT.
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.
Extract the ISO skipping the UEFI-specific directories:
$ mkdir extracted_iso
$ bsdtar -x --exclude=EFI/ --exclude=loader/ -f archlinux-
version
-x86_64.iso -C extracted_iso
Then rebuild the ISO, excluding the UEFI optical media booting support, using
xorriso(1)
from
libisoburn
. Be sure to set the correct volume label, e.g.
ARCH_202103
; it can be acquired using
file(1)
on the original ISO.
$ xorriso -as mkisofs \
    -iso-level 3 \
    -full-iso9660-filenames \
    -joliet \
    -joliet-long \
    -rational-rock \
    -volid "ARCH_
YYYYMM
" \
    -appid "Arch Linux Live/Rescue CD" \
    -publisher "Arch Linux <
https://archlinux.org
>" \
    -preparer "prepared by $USER" \
    -eltorito-boot syslinux/isolinux.bin \
    -eltorito-catalog syslinux/boot.cat \
    -no-emul-boot -boot-load-size 4 -boot-info-table \
    -isohybrid-mbr "extracted_iso/syslinux/isohdpfx.bin" \
    -output archlinux-
version
-x86_64-noUEFI.iso extracted_iso/
Burn
archlinux-
version
-x86_64-noUEFI.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 and a separate non-volatile variable store for
QEMU
.
You can install
edk2-ovmf
from the extra repository.
It is
advised
to make a local copy of the non-volatile variable store for your virtual machine:
$ cp /usr/share/edk2/x64/OVMF_VARS.4m.fd my_OVMF_VARS.4m.fd
To use the OVMF firmware and this variable store, add following to your QEMU command:
-drive if=pflash,format=raw,readonly,file=/usr/share/edk2/x64/OVMF_CODE.4m.fd \
-drive if=pflash,format=raw,file=my_OVMF_VARS.4m.fd
For example:
$ qemu-system-x86_64 -enable-kvm -m 1G -drive if=pflash,format=raw,readonly,file=/usr/share/edk2/x64/OVMF_CODE.4m.fd -drive if=pflash,format=raw,file=my_OVMF_VARS.4m.fd …
DUET for BIOS only systems
DUET was a TianoCore project that enabled chainloading a full UEFI environment from a BIOS system, in a way similar to BIOS operating system booting. This method is being
discussed
extensively. Pre-build DUET images can be downloaded from one of the
repos
[
dead link
2023-04-07—404 Page Not Found]
. Read specific
instructions
[
dead link
2023-04-07—404 Page Not Found]
for setting up DUET. However, as of November 2018, the DUET code has been removed from TianoCore git repository.
You can also try
Clover
which provides modified DUET images that may contain some system specific fixes and is more frequently updated compared to the gitlab repos.
Troubleshooting
Boot back to Arch Linux when stuck with Windows
To boot back into Arch Linux when you are stuck with Windows, reach
Advanced startup
in Windows by the Windows PowerShell command
shutdown /r /o
, or via
Settings > Update & Security > Recovery > Advanced startup
and select
Restart now
. When you have reached the
Advanced startup
menu, choose
Use a device
, which actually contains your UEFI boot options (not limited to USB or CD, but can also boot operating system in hard drive), and choose "Arch Linux".
Enter firmware setup without function keys
On some laptops, like
Lenovo XiaoXin 15are 2020
, using keys like
F2
or
F12
does not do anything. This can possibly be fixed by returning laptops to OEM to repair mainboard information, but sometimes this is not possible or not desired. There are however other means to enter firmware setup:
With
systemctl
:
$ systemctl reboot --firmware-setup
This will reboot your computer to firmware setup.
With
GRUB
: Press
c
for command line and in GRUB command line use
fwsetup
to enter firmware setup.
In Windows: Enter
Advanced Startup
, see
#Boot back to Arch Linux when stuck with Windows
.
Userspace tools are unable to modify UEFI variable data
If any userspace tool is unable to modify UEFI variable 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 UEFI variable storage space check that may prevent writing/modification of UEFI variables.
Warning
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. See
FS#34641
for more information.
Cannot create a new boot entry with efibootmgr
Some kernel and
efibootmgr
version combinations might refuse to create new boot entries. This could be due to lack of free space in the NVRAM. You can try the solution at
#Userspace tools are unable to modify UEFI variable data
.
You can also try to
downgrade
your
efibootmgr
install to version 0.11.0. This version works with Linux version 4.0.6. See the bug discussion
FS#34641
, in particular the
closing comment
, for more information.
Windows changes boot order
If you
dual boot with Windows
and your motherboard just boots Windows immediately instead of your chosen EFI 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 firmware (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 boot 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 EFI application. From a Windows administrator command prompt
bcdedit /set "{bootmgr}" path "\EFI\
path
\
to
\
app.efi
"
Alternatively, deactivate the Windows Boot Manager by running
efibootmgr -A -b
bootnumber
as root. Replace
bootnumber
with the actual Windows Boot Manager boot number; you can see it by running
efibootmgr
with no options.
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 administrator privileges. Run
bcdedit /enum firmware
and find your desired boot entry.
Copy the identifier, including the brackets, e.g.
{31d0d5f4-22ad-11e5-b30b-806e6f6e6963}
Create a batch file with the command
bcdedit /set "{fwbootmgr}" DEFAULT "
{copied-boot-identifier}
"
Open
gpedit.msc
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
Note:
Windows 10 Home does not officially include gpedit.msc, although there are unsupported workarounds to install it manually.
Alternatively, Task Scheduler can be used to run a startup script in Windows:
Follow steps 1-3 above to create the batch file.
Run
taskschd.msc
, then choose
Create Task...
from the
Action
menu.
On the
General
tab:
Enter any suitable
Name
and
Description
.
Ensure the user account selected is an "Administrator", not a "Standard User".
Select "
Run whether user is logged in or not
".
Select "
Run with highest privileges
".
On the
Triggers
tab, choose "
At startup
" from the menu, then click
OK
.
On the
Actions
tab, click
New...
, then
Browse...
, and locate the batch file from step 1.
On the
Conditions tab
, untick the
Power
options so the script runs when on battery power (for laptops).
Click
OK
, and enter the password of the user account selected in step 4 when prompted.
USB media gets struck with black screen
This issue can occur due to
KMS
issue. Try
disabling KMS
while booting the USB.
UEFI boot loader does not show up in firmware menu
Some firmware do not support custom boot entries. They will instead only boot from hardcoded boot entries.
A typical workaround is to not rely on boot entries in the NVRAM and install the boot loader to one of the common fallback paths on the EFI system partition.
The following sections describe the fallback paths.
Default boot path for removable drives
The UEFI specification defines default file paths for EFI binaries for booting from removable media. The relevant ones are:
esp
/EFI/BOOT/BOOTx64.EFI
for x64 UEFI
esp
/EFI/BOOT/BOOTIA32.EFI
for IA32 UEFI.
While the specification defines these for removable drives only, most firmware support booting these from any drive.
See the appropriate
boot loader
article on how to install or migrate the boot loader to the default/fallback boot path.
Microsoft Windows boot loader location
On certain UEFI motherboards like some boards with an Intel Z77 chipset, adding entries with
efibootmgr
or
bcfg
from the UEFI 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:
Shell> mkdir FS1:\EFI\Microsoft
Shell> mkdir FS1:\EFI\Microsoft\Boot
Shell> 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.
UEFI/BIOS is stuck on loading screen
This is a recurring problem with Acer laptops, which occurs if
.efi
files have not been manually authorized. See
Laptop/Acer#Firmware Setup became inaccessible after Linux installation
.
Boot entries created with efibootmgr fail to show up in UEFI
efibootmgr
can fail to detect EDD 3.0 and as a result create unusable boot entries in NVRAM. See
efibootmgr issue 86
for the details.
To work around this, when creating boot entries manually, add the
-e 3
option to the
efibootmgr
command. E.g.
# efibootmgr --create --disk /dev/sda --part 1 --loader '\EFI\refind\refind_x64.efi' --label 'rEFInd Boot Manager' --unicode
-e 3
To fix boot loader installers, like
grub-install
and
refind-install
, create a wrapper script
/usr/local/bin/efibootmgr
and make it
executable
:
/usr/local/bin/efibootmgr
#!/bin/sh

exec /usr/bin/efibootmgr -e 3 "$@"
UEFI boot entry disappears after removing its referenced drive
Some firmware will remove boot entries referencing drives that are not present during boot. This could be an issue when frequently detaching/attaching drives or when booting from a removable drive.
The solution is to install the
boot loader
to
the default/fallback boot path
.
Boot entries are randomly removed
Some motherboards may remove boot entries due to lack of free space in the NVRAM instead of giving an error at creation. To prevent this from occurring, reduce the amount of boot entries being added by minimizing your entry creation process, as well as reducing the amount of automatic drive boot entries by the
Compatibility Support Module (CSM)
by disabling it from your UEFI settings. See
BBS#1608838
.
Another reason why boot entries might have been removed is the fact that UEFI specification allows OEMs to do "NVRAM maintenance" during boot process. Those manufacturers do it simply: they just look up for EFI applications in predefined, hardcoded paths on the device. If they fail to find any, they conclude there is no operating system on the device and wipe all boot entries from NVRAM associated with it, because they assume the NVRAM contains some corrupted or outdated data. If you do not plan to install Windows and still want to load the Linux kernel directly from the firmware, one possible workaround is to create an empty file
esp
/EFI/BOOT/BOOTx64.EFI
:
# mkdir -p
esp
/EFI/BOOT 
# touch
esp
/EFI/BOOT/BOOTx64.EFI
And restore the deleted boot entry. Now after reboot the motherboard will see the "Fake OS" and should not wipe other boot entries from NVRAM. You can change the fake operating system loader with an actual EFI application if you want, of course, as long as you keep the standard fallback name.
Lenovo ThinkPad: boot entries not persistent due to "OS Optimized Defaults"
This article or section is a candidate for merging with
Lenovo
.
Notes:
Brand-specific issues should be on the dedicated page. (Discuss in
Talk:Unified Extensible Firmware Interface
)
This article or section needs expansion.
Reason:
Missing links to the "user reports". (Discuss in
Talk:Unified Extensible Firmware Interface
)
On recent Lenovo ThinkPad laptops (e.g. T16 Gen 2 AMD models), users report that custom UEFI boot entries (created with
efibootmgr
or
bootctl
) are automatically deleted at each boot, with only Windows Boot Manager and Lenovo’s own entries (PXE, Recovery, Diagnostics) restored.
This is caused by the BIOS option "Restart / OS Optimized Defaults", which resets the UEFI boot variables at each reboot to defaults optimized for Windows.
Solution: Disable "OS Optimized Defaults" in the BIOS/UEFI setup. After doing so, manually created boot entries persist correctly, allowing systemd-boot or other custom boot managers to work as intended.
See also
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
Linux Kernel UEFI documentation for x86_64 platforms
Intel's page on EFI
Intel Architecture Firmware Resource Center
[
dead link
2023-07-30—HTTP 404]
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
[
dead link
2021-05-17—domain name not resolved]
LPC 2012 UEFI Tutorial : part 1
[
dead link
2021-05-17—domain name not resolved]
LPC 2012 UEFI Tutorial : part 2
[
dead link
2021-05-17—domain name not resolved]
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
The bootstrap process on EFI systems