EFISTUB

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Warning: A bug has been noticed where booting EFISTUB can fail depending on kernel version and motherboard model. See [1] and [2] for more information.

The Linux Kernel (linux>=3.3) supports EFISTUB (EFI BOOT STUB) booting. It is enabled by default on Arch Linux kernels or can be activated by setting CONFIG_EFI_STUB=y in the Kernel configuration (see The EFI Boot Stub for more information).

A single EFISTUB kernel is not capable of launching other kernels, hence each EFISTUB Kernel + Initramfs pair requires a separate boot menu entry. Because of this, when working with multiple kernels, it is recommended to use a UEFI Boot Manager.

Contents

Setting up EFISTUB

  1. Create a EFI System Partition.
  2. Mount the EFI System Partition either at /boot (recommended if you are planning to use Gummiboot or no boot manager) or some other location of your choice (most other distro's and tools use /boot/efi). The mountpoint will be mentioned as $esp hereafter.

Copying Kernel and Initramfs to ESP

Warning: The below steps are required only if you DID NOT use /boot as the EFISYS mountpoint. If you did choose /boot as mountpoint, you can continue to #Booting EFISTUB.
  1. Create $esp/EFI/arch/
  2. Copy the following files from source to destination
Boot File Source UEFI Destination
/boot/vmlinuz-linux $esp/EFI/arch/vmlinuz-arch.efi
/boot/initramfs-linux.img $esp/EFI/arch/initramfs-arch.img
/boot/initramfs-linux-fallback.img $esp/EFI/arch/initramfs-arch-fallback.img
Warning: The EFISTUB Kernel must be updated each time the kernel is updated (follow step 4 in #Setting up EFISTUB. Failure to do so will result in failure to boot. Alternatively one can automatically update the EFISTUB kernel using one of the following methods:

Using systemd

Systemd features event triggered tasks. In this particular case, the ability to detect a change in path is used to sync the EFISTUB kernel and initramfs files when they are updated in boot.

Warning: Since mkinitcpio takes time to build the kernel stub and the initramfs. It is possible for the following systemd services to copy older kernel stubs and initramfs instead of the new ones. To reduce the chance of this error, it is better to bind the efistub copying service to check if the initramfs-linux-fallback.img was changed (since it is the last thing built by mkinitcpio).
Tip: Save the following script as /etc/systemd/system/efistub-update.path
[Unit]
Description=Copy EFISTUB Kernel to UEFISYS Partition

[Path]
PathChanged=/boot/initramfs-linux-fallback.img

[Install]
WantedBy=multi-user.target
Tip: Save the following script as /etc/systemd/system/efistub-update.service
[Unit]
Description=Copy EFISTUB Kernel to UEFISYS Partition

[Service]
Type=oneshot
ExecStart=/usr/bin/cp -f /boot/vmlinuz-linux $esp/EFI/arch/vmlinuz-arch.efi
ExecStart=/usr/bin/cp -f /boot/initramfs-linux.img $esp/EFI/arch/initramfs-arch.img
ExecStart=/usr/bin/cp -f /boot/initramfs-linux-fallback.img $esp/EFI/arch/initramfs-arch-fallback.img
Tip: Enable these services with 
# systemctl enable efistub-update.path

Incron

incron can run a script to sync the EFISTUB Kernel after updates

Tip: Save the following script as /usr/local/bin/efistub-update.sh
#!/usr/bin/env bash
/usr/bin/cp -f /boot/vmlinuz-linux $esp/EFI/arch/vmlinuz-arch.efi
/usr/bin/cp -f /boot/initramfs-linux.img $esp/EFI/arch/initramfs-arch.img
/usr/bin/cp -f /boot/initramfs-linux-fallback.img $esp/EFI/arch/initramfs-arch-fallback.img
Tip: Save the following script as /etc/incron.d/efistub-update.conf
Note: The first parameter /boot/initramfs-linux-fallback.img is the file to watch. The second parameter IN_CLOSE_WRITE is the action to watch for. The third parameter /usr/local/bin/efistub-update.sh is the script to execute.
/boot/initramfs-linux-fallback.img IN_CLOSE_WRITE /usr/local/bin/efistub-update.sh
Tip: In order to use this method, incron must be activated, if it is not run 
# systemctl enable incrond.service

Mkinitcpio hook

Mkinitcpio can generate a hook that does not need a system level daemon to function. It spawns a background process which waits for the generation of vm-linuz, initramfs-linux.img, and initramfs-linux-fallback.img; then follows step 4 in Setting up EFISTUB

Tip: Save the following script as /usr/lib/initcpio/install/efistub-update
#!/usr/bin/env bash

build() {
	/root/watch.sh &
}

help() {
	cat <<HELPEOF
This hook waits for mkinitcpio to finish and copies the finished ramdisk and kernel to the ESP
HELPEOF
}
Tip: Save the following script as /root/watch.sh and make it executable
#!/usr/bin/env bash

while [[ -d "/proc/$PPID" ]]; do
	sleep 1
done

/usr/bin/cp -f /boot/vmlinuz-linux $esp/EFI/arch/vmlinuz-arch.efi
/usr/bin/cp -f /boot/initramfs-linux.img $esp/EFI/arch/initramfs-arch.img
/usr/bin/cp -f /boot/initramfs-linux-fallback.img $esp/EFI/arch/initramfs-arch-fallback.img

echo "Synced kernel with ESP"
Tip: Add efistub-update to the list of hooks in /etc/mkinitcpio.conf

/etc/fstab bind mount

Note:
  • The following method should work similarly with any distribution that does not symlink in /boot. See Warnings for caveats.
  • This involves no special scripts, services, or bootloader filesystem drivers.
  • This centralizes and organizes kernels and initrds across installations on one partition.
  • This avoids possible limitations imposed by firmware and/or the bootloader on boot device configuration as can often occur with RAID and/or LVM (excepting the standard FAT32 EFI system partition, of course).
  • Beyond initial configuration this should persist without special consideration or maintenance.
  • This should be transparent to any action normally affecting /boot and the files therein.
Warning:
  • This requires both a kernel and a bootloader compatible with the FAT32 filesystem.
  • Because the FAT32 filesystem cannot handle symlinks, this will not behave as intended with an installation that requires them in /boot.
  • Initial configuration requires root level access.
  • This may require a large EFI system partition in order to accomodate multiple installations.
  • All kernels will require at least a root=system root parameter passed at boot.
  • per rEFInd's author: OpenSUSE definitely uses symbolic links in /boot... Fedora, Ubuntu, and ... OpenSUSE all refuse a FAT partition as /boot in ... setup [which] can be worked around [in] /etc/fstab. Forum post [here].
Method
Whereas the general convention is to mount the EFI system partition to a /boot/efi subfolder, the following will achieve the opposite.
  • Create a ef00 type EFI system partition of FAT32 format as described elsewhere.
Tip:
  • It may be beneficial to make it several gigabytes in size to accomodate multiple installations.
  • Use the GPT partition name feature for added convenience. For example name the partition esp.
  • Create a mount-point and mount the EFI system partition somewhere on the filesystem. For example:
$ mkdir /esp
$ mount -L esp /esp
  • Create a folder in /EFI/boot on the EFI system partition to contain your system's /boot files. For example:
$ mkdir /esp/EFI/boot/arch64-laptop
Tip:
  • The refind bootloader automatically detects and adds EFI loadable kernel files installed to the EFI system partition in /EFI/boot/*/ by default.
  • Keying F2 on a highlighted refind boot menu entry enables adding the required root= kernel parameter to an auto-added or otherwise unconfigured menu entry.
  • Move all files in /boot to the newly created folder on your EFI system partition. For example:
$ mv /boot/* /esp/EFI/boot/arch64-laptop/
  • Bind mount the newly populated folder on your EFI system partition to /boot. For example:
$ mount --bind /esp/EFI/boot/arch64-laptop /boot
  • Verify your files are available as expected with $ ls /boot/ then persist the configuration by editing /etc/fstab. For example:
##/etc/fstab
LABEL=arch64-laptop_rootfs / ext4 defaults 0 0
LABEL=esp /esp vfat defaults 0 0
/esp/EFI/boot/arch64-laptop /boot none defaults,bind 0 0
  • Update your bootloader to apply the root= kernel boot parameter as necessary. For example:
##/boot/refind_linux.conf
... root=LABEL=arch64-laptop_rootfs ...
Note: As of refind-efi 0.2.7, refind automatically detects kernels in /boot. They do not have to be renamed to have a .efi extension either. Hence, the following sync scripts aren't needed if using refind. You do need to isntall an EFI driver to read the Linux filesystem on which the kernel is stored, though.

Booting EFISTUB

Warning: Linux Kernel EFISTUB initramfs path should be relative to the EFI System Partition's root. For example, if the initramfs is located in $esp/EFI/arch/initramfs-linux.img, the corresponding UEFI formatted line should be initrd=/EFI/arch/initramfs-linux.img or initrd=\EFI\arch\initramfs-linux.img.

EFISTUB kernel can be booted using one of the following ways :

Using gummiboot

Gummiboot is a UEFI Boot Manager which provides a nice menu for EFISTUB Kernels. It is available in [core] as gummiboot and is the recommended boot manager for EFISTUB booting. See gummiboot for more info.

Using rEFInd

rEFInd is a fork of rEFIt Boot Manager (used in Intel Macs) by Rod Smith (author of gdisk). rEFInd fixes many issues in rEFIt with respect to non-Mac UEFI booting and also has support for booting EFISTUB kernels and contains some features specific to them.

Tip: If you're new to EFISTUB and/or rEFInd, you need to read The rEFInd Boot Manager: Methods of Booting Linux before going any further. This section illustrates only one possible use-case which is not suitable for all configurations.
Note: refind-efi pkg includes a install script from upstream at /usr/bin/refind-install which does the job of setting-up of rEFInd similar to above steps.
Note: For 32-bit aka IA32 EFI, replace x64 with ia32 (case-sensitive) in the below commands.
  • Mount efivarfs 
# mount -t efivarfs efivarfs /sys/firmware/efi/efivars              # ignore if already mounted

# pacman -S refind-efi
  • Copy the following files from their source directory to their destination 
# cp /usr/share/refind/refind_x64.efi $esp/EFI/refind/refind_x64.efi
# cp /usr/share/refind/refind.conf-sample  $esp/EFI/refind/refind.conf
# cp /usr/share/refind/icons $esp/EFI/refind/icons
# cp /usr/share/refind/drivers_x64 $esp/EFI/refind/drivers
  • Edit rEFInd's config file at $esp/EFI/refind/refind.conf. The file is well commented and self explanatory.
  • Create a refind_linux.conf file inside the directory where the kernel and initramfs files and located. 
refind_linux.conf
"Boot with defaults" "root=PARTUUID=3518bb68-d01e-45c9-b973-0b5d918aae96 rw rootfstype=ext4 add_efi_memmap systemd.unit=graphical.target"
"Boot to Terminal"   "root=PARTUUID=3518bb68-d01e-45c9-b973-0b5d918aae96 rw rootfstype=ext4 add_efi_memmap systemd.unit=multi-user.target"
Tip: Each line of refind_linux.conf is displayed as a submenu by rEFInd. Access the submenu with "+" or "insert" keys.
Note: Replace the string after PARTUUID with your root's PARTUUID. Please note in the example above that PARTUUID/PARTLABEL identifies a GPT partition, and differs from UUID/LABEL, which identifies a filesystem. Using the PARTUUID/PARTLABEL is advantageous because it is invariant if you reformat the partition with another filesystem. It's also useful if you don't have a filesystem on the partition (or use LUKS, which doesn't support LABELs).
  • Create a boot entry in the UEFI boot menu using efibootmgr 
# efibootmgr -c -d /dev/sdX -p Y -l /EFI/refind/refind_x64.efi -L "rEFInd"
Note: As of refind-efi 0.2.7, refind can auto-detect kernels in /boot, if there are UEFI drivers for the filesystem used by /boot partition (or / partition if no separate /boot is used) in the ESP, and are loaded by rEFInd. This is enabled in the default configuration in refind.conf (you may need to include the PATH to the drivers folders in the ESP). See [3] for more info.

Systemd Automation

Tip: To automate the process of copying refind files and updating the nvram (if needed) use the following script
Note: Save this script as /usr/lib/systemd/scripts/refind_name_patchv2
Tip: If you want to change the directory that refind is installed in the UEFISYS partition, just change the value of $refind_dir in the script
#!/usr/bin/env bash
## COPYRIGHT 2013 : MARK E. LEE (BLUERIDER) : mlee24@binghamton.edu; mark@markelee.com

## LOG
## 1/17/2013 : Version 2 of refind_name_patch is released
##           : Supports long subdirectory location for refind
##           : Updates nvram when needed
##           : 10% speed boost
## 7/15/2013 : Changed arch to match 32-bit (ia32) and 64-bit (x64) naming scheme
##           : Changed directory copying in update-efi-dir to copy tools and drivers directories explicitly
##           : Changed efibootmgr writing code to be more concise and added (-w) to write the entry as per dusktreader's excellent guide : https://docs.google.com/document/d/1pvgm3BprpXoadsQi38FxqMOCUZhcSqFhZ26FZBkmn9I/edit
##           : Function to check if NVRAM boot entry was already listed was fixed to use awk and an if then clause
##           : ref_bin_escape was modified from : ref_bin_escape=${ref_bin//\//\\\\} to remove extra backslashes (error does not show up when using cmdline)
## 7/29/2013 : Changed location of tools,drivers, and binary directory to match capricious upstream move to /usr/share/refind

function main () {  ## main insertion function
  declare -r refind_dir="/boot/efi/EFI/refind"; ## set the refind directory
  arch=$(uname -m | awk -F'_' '{if ($1 == "x86") {print "x"$2} else if ($1 == "i686") {print "ia32"}}') &&  ## get bit architecture
  update-efi-dir;  ## updates or creates the refind directory
  update-efi-nvram;  ## updates nvram if needed
}

function update-efi-dir () {  ## setup the refind directory
  if [ ! -d $refind_dir ]; then  ## check if refind directory exists
    echo "Couldn't find $refind_dir";
    mkdir $refind_dir &&  ## make the refind directory if needed
    echo "Made $refind_dir";
  fi;
  if [ "$arch" ]; then  ## check if anything was stored in $arch
    cp -r /usr/share/refind/{refind_$arch.efi,keys,images,icons,fonts,docs,{tools,drivers}_$arch} $refind_dir/  && ## update the bins and dirs
    echo "Updated binaries and directory files for refind at $refind_dir";
   else
    echo "Failed to detect an x86 architecture";
    exit;
  fi;
}

function update-efi-nvram () { ## update the nvram with efibootmgr
  declare -r ref_bin=${refind_dir/\/boot\/efi}/refind_$arch.efi;  ## get path of refind binary (without /boot/efi)
  declare -r ref_bin_escape=${ref_bin//\//\\};  ## insert escape characters into $ref_bin
  [ "$(efibootmgr -v | awk "/${ref_bin_escape//\\/\\\\}/")" ] && ( ## check if boot entry is in nvram \
    echo "Found boot entry, no need to update nvram";
    ) || ( ## if boot entry is not in nvram; add it
    declare -r esp=$(mount -l | awk '/ESP/ {print $1}') &&  ## get ESP partition
    efibootmgr -cgw -d ${esp:0:8} -p ${esp:8} -L "rEFInd" -l $ref_bin_escape && ## update nvram
    echo "
    Updated nvram with entry rEFInd to boot $ref_bin
    Did not copy configuration files, please move refind.conf to $refind_dir/";
    )
}
main;  ## run the main insertion function
Note: As of refind-efi 0.2.7, refind automatically detects kernels in /boot. They do not have to be renamed to have a .efi extension either. Hence, the following sync scripts aren't needed if using refind. You do need to isntall an EFI driver to read the Linux filesystem on which the kernel is stored, though.
Note: Save the following service file as /usr/lib/systemd/system/refind_update.path
[Unit]
Description=Update rEFInd bootloader files

[Path]
PathChanged=/usr/share/refind/refind_<arch>.efi
Unit=refind_update.service

[Install]
WantedBy=multi-user.target
Note: Save the following service file as /usr/lib/systemd/system/refind_update.service
[Unit]
Description=Update rEFInd directories, binaries, and nvram

[Service]
Type=oneshot
ExecStart=/usr/bin/bash /usr/lib/systemd/scripts/refind_name_patchv2
RemainAfterExit=no
Tip: Enable the systemd path unit by running : 
# systemctl enable refind_update.path

Apple Macs

In case of Apple Macs, try mactel-boot for an experimental "bless" utility for Linux. If that does not work, use "bless" form within OSX to set rEFInd as default bootloader. Assuming UEFISYS partition is mounted at /mnt/efi within OSX, do 

$ sudo bless --setBoot --folder /mnt/efi/EFI/refind --file /mnt/efi/EFI/refind/refind_x64.efi

VirtualBox

In case of VirtualBox, see VirtualBox#Using_Arch_under_Virtualbox_EFI_mode.

Using UEFI Shell

It is possible to launch EFISTUB kernel form UEFI Shell as if it is a normal UEFI application. In this case the kernel parameters are passed as normal parameters to the launched EFISTUB kernel file. 

> fs0:
> cd \EFI\arch
> vmlinuz-arch.efi root=PARTUUID=3518bb68-d01e-45c9-b973-0b5d918aae96 ro rootfstype=ext4 add_efi_memmap initrd=EFI/arch/initramfs-arch.img

You can also write a simple archlinux.nsh file with your boot parameters and put it in your UEFI System Partition, then run it with: 

fs0:
archlinux

Example Script: 

echo -on
\EFI\arch\vmlinuz-arch.efi root=PARTUUID=3518bb68-d01e-45c9-b973-0b5d918aae96 rootfstype=ext4 add_efi_memmap initrd=/EFI/arch/initramfs-arch.img

This way you can specify UUID's without needing to remember the name or type out 20-30 characters.

Directly, using efibootmgr entry

Warning: Some kernel and efibootmgr combinations might not work without manual intervention [4]. You will be able to delete but not create boot entries.
Note: Some UEFI firmwares may not support embedding command line parameters to uefi applications in the boot entries.

It is possible to directly embed the kernel parameters within the boot entry created by efibootmgr. This means that you can use your UEFI boot order/GUI to directly boot Arch Linux without a separate bootloader like GRUB (below, the EFI System Partition is on /dev/sdX, partition Y). 

# mount -t efivarfs efivarfs /sys/firmware/efi/efivars              # ignore if already mounted
# efibootmgr -c -d /dev/sdX -p Y -l /EFI/arch/vmlinuz-arch.efi -L "Arch Linux (EFISTUB)" -u "$(cat /proc/cmdline)"

It is a good idea to run 

# efibootmgr -v

to verify that the resulting entry is correct. You should also consider reordering the boot options (efibootmgr -o) to place the Arch entry last, which could make the system easier to recover if it fails.

Tip: Save the command for creating your boot entry in a shell script somewhere, which makes it easier to modify (when changing kernel parameters, for example).

More info about efibootmgr at UEFI#efibootmgr. Forum post https://bbs.archlinux.org/viewtopic.php?pid=1090040#p1090040 .

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