How to install grub from windows

How do I chainload GRUB from Windows boot.ini

Other titles for this same problem.

• GRUB is a great but I prefer not to install it on my mbr.
• How do I chainload GRUB from Windows Vista
• I have Linux in my second hard disk and I follow other howto instructions but I cannot get it to be chainloaded from Windows.
• Is there a safe way to access Linux on the external drive and have xp on the internal drive while being able to disconnect the external drive from pc at any time? ([b]You should run Fix Boot of Windows[/b] for your internal hard disk before these steps.)

Advice

adrian15 advice for this kind of task is #Classical solution

Neogrub lazy solution

TODO: Talk about Neogrub that it is included with EasyBCD I think.

Classical solution

• Super Grub Disk (WITH HELP) :-)))
• English Super Grub Disk
• Windows
• Windows (Advanced)
• Windows chainloads Grub!
• Select the partition where GRUB it is found (i.e. stage1 is found).

Please continue reading at: Common Final Solution

Advanced solution

SITUATION WHEN GRUB FILES AND BOOT SECTOR ARE NOT THE SAME PARTITION

Problematic solution

TODO EXPLAIN THE USE OF LIVESWAP WHEN DETECTED HARD DISK ORDER IS NOT OK.

GRUB solution (on its own)

This method is only valid when you want to boot a Linux partition that it is found in the same hard disk as the windows one (i.e. the first hard disk).

This installs Stage1 of Grub to the first sector of partition containing the Grub folder.
To get started we need to identify the partition containing the Grub folder. (Usually the same as the Linux partition) Say it is (hd0,3) (Usually, but not always, identified in Linux as: /dev/sda4).

Boot with your grub disk or with your already installed grub.

Press ‘c’

At the grub> prompt type:

• root (hd0,3)
• setup (hd0,3)
• quit #(With Linux working)
• reboot #(From grub disk)

Please continue reading at: Common Final Solution

GRUB solution (Linux shell)

This installs Stage1 of Grub to the first sector of partition containing the Grub folder. We will use the «device» function of the grub-shell to ensure that Grub uses the correct map between the bios drives and linux devices, and also to ensure that Grub uses the hard drive numbers.

To get started we need to identify the partition containing the Grub folder. (Usually the same as the Linux partition) Say it is (hd2,3) and /dev/sdb4.
(The (hd2,3) must be how grub sees the partition during boot-up)

Open a terminal in Linux and type

• su #(use sudo -i in Ubuntu)
• grub

and at the «grub>»prompt

• device (hd2) /dev/sdb
• device (hd0) /dev/sdb
• root (hd2,3)
• setup (hd0,3)
• quit

Please continue reading at: Common Final Solution

GRUB2 solution (on its own)

As long as I know GRUB2 cannot install itself on its own.

GRUB2 solution (Linux shell)

This installs first part of Grub2 to the first sector of partition containing the Grub folder.

Let’s suppose that you know that your Linux partition is /dev/sda3

What you need to to is run:

Open a terminal in Linux and type

• su #(use sudo -i in Ubuntu)

• grub-install —force /dev/sda3

Please continue reading at: Common Final Solution

Common Final Solution

As a final solution we need somehow Windows to chainload our Linux partition. If we use easybcd we can avoid having to copy a file from a live cd to our Windows partition and setting up the boot. If we are geeks and classical we will have to edit boot.ini or the new Vista file manually in order to make
things work.

Windows Vista (with easybcd help)

1. Download and run EasyBCD 1.7.2(or any version i think)
2. If program ask for boot drive just select your windows partion
3. Choose Add/remove Entries
4. At «Add an Entry» select «Linux»
5. Change Type to «Linux»
6. Enter Name box with any name u want
7. At Drive Select Your Ubuntu Partion
8. Click «Add Entry»
9. Click «Save»
10. Restart, you have done ^ ^

Classical Final Solution

Once grub has been installed to a partition we need to get its boot sector to a file in order to boot it from Windows.

Let’s boot with a live cd and open a terminal.

Identify the partition containing the grub folder. (Usually the same one as the Linux partition)

In this example the identified grub partition is sda3.

Plugin your pendrive and open it.
Identify your plugged pendrive associated folder.

In this example:
Pendrive mount point is: /media/disk

From a terminal (Aplications -> System -> Terminal) please run:

• sudo -i | su

(When prompted enter your current user password or your root password in non-sudo systems such as Debian. If you do not know how to type | symbol please only type sudo -i)

• dd if=/dev/sda3 of=/media/disk/linux.bin count=1 bs=512
• sync
• Right Click on your pendrive icon in your desktop and click on umount or extract.

Now let’s boot into Windows.

Plug in your pendrive and copy the linux.bin file into c: folder.

Windows XP/Windows 2000/NT/Windows

Now let’s edit boot.ini and add this line at its bottom:

c:linux.bin="Linux"

Windows Vista (manually)

TODO

Now when rebooting if you boot windows you will get a Windows menu with two options: Windows and the new Linux option which will chainload GRUB.

Finally there is an optional step that it is removing grub so that it chainloads Windows menu in the first place automatically at boot.

Rescatux

This feature is not yet available at the Rescapp program. It is available at the Super Grub Disk included with Rescatux. If you want to have this feature at the Rescapp program please complain at the super grub disk mailing list.

Tecnical explanation

One thing you should know

• These methods only restore GRUB successfully if a stage1,stage2 (and optionally a stage1_5 file) is found. If you have deleted these files the GRUB solution (Linux shell) might help although it might be better to reinstall GRUB from a chroot environment got from a live cd.

If your Linux filesystem has errors GRUB might not be able to find its files even if they are there. So sometimes is advised to try to run the:

fsck -yc /dev/DEV

command as root where DEV is your linux partition device.

fsck -yc /dev/sda3 

will fix the third partition from an scsi or sata first disk (Although it might not actually be the first one).

• OpenSolaris GRUB cannot be restored to a partition which this method. You need to boot Linux and then use the install-grub command. See man install-grub for more info.

TIP

If you cannot get to restore grub this way you can always try to boot Linux and then use the Grub Solution (on its own) method or the Grub Solution (Linux shell) method.

Similar problems

External resources

TODO

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GRUB (GRand Unified Bootloader) is a boot loader. The current GRUB is also referred to as GRUB 2. The original GRUB, or GRUB Legacy, corresponds to versions 0.9x. This page exclusively describes GRUB 2.

Note: In the entire article esp denotes the mountpoint of the EFI system partition aka ESP.

UEFI systems

Installation

First, install the packages grub and efibootmgr: GRUB is the boot loader while efibootmgr is used by the GRUB installation script to write boot entries to NVRAM.

Then follow the below steps to install GRUB to your disk:

1. Mount the EFI system partition and in the remainder of this section, substitute esp with its mount point.
2. Choose a boot loader identifier, here named GRUB. A directory of that name will be created in esp/EFI/ to store the EFI binary and this is the name that will appear in the UEFI boot menu to identify the GRUB boot entry.
3. Execute the following command to install the GRUB EFI application grubx64.efi to esp/EFI/GRUB/ and install its modules to /boot/grub/x86_64-efi/.

Note:

• Make sure to install the packages and run the grub-install command from the system in which GRUB will be installed as the boot loader. That means if you are booting from the live installation environment, you need to be inside the chroot when running grub-install. If for some reason it is necessary to run grub-install from outside of the installed system, append the --boot-directory= option with the path to the mounted /boot directory, e.g --boot-directory=/mnt/boot.
• Some motherboards cannot handle bootloader-id with spaces in it.

# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=GRUB

https://wiki.archlinux.org/title/Unified_Extensible_Firmware_Interface/Secure_Boot#sbctl
After the above installation completed, the main GRUB directory is located at /boot/grub/. Read /Tips and tricks#Alternative install method for how to specify an alternative location. Note that grub-install also tries to create an entry in the firmware boot manager, named GRUB in the above example – this will, however, fail if your boot entries are full; use efibootmgr to remove unnecessary entries.

Remember to #Generate the main configuration file after finalizing the configuration.

Tip: If you use the option --removable then GRUB will be installed to esp/EFI/BOOT/BOOTX64.EFI (or esp/EFI/BOOT/BOOTIA32.EFI for the i386-efi target) and you will have the additional ability of being able to boot from the drive in case EFI variables are reset or you move the drive to another computer. Usually you can do this by selecting the drive itself similar to how you would using BIOS. If dual booting with Windows, be aware Windows usually places an EFI executable there, but its only purpose is to recreate the UEFI boot entry for Windows. If you are installing GRUB on a Mac, you will have to use this option.

See UEFI troubleshooting in case of problems. Additionally see /Tips and tricks#UEFI further reading.

Secure Boot support

Grub fully supports secure boot utilising either CA keys or shim, the installation command however is different depending on which you intend to use.

To make use of CA Keys the command is

# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=GRUB --modules="tpm" --disable-shim-lock

To make use of shim-lock the command is

# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=GRUB--modules="normal test efi_gop efi_uga search echo linux all_video gfxmenu gfxterm_background gfxterm_menu gfxterm loadenv configfile tpm"

After installation see Secure Boot for instructions on implementing it

BIOS systems

GUID Partition Table (GPT) specific instructions

On a BIOS/GPT configuration, a BIOS boot partition is required. GRUB embeds its core.img into this partition.

Create a mebibyte partition (+1M with fdisk or gdisk) on the disk with no file system and with partition type GUID 21686148-6449-6E6F-744E-656564454649.

• Select partition type BIOS boot for fdisk.
• Select partition type code ef02 for gdisk.
• For parted set/activate the flag bios_grub on the partition.

This partition can be in any position order but has to be on the first 2 TiB of the disk. This partition needs to be created before GRUB installation. When the partition is ready, install the boot loader as per the instructions below.

The space before the first partition can also be used as the BIOS boot partition though it will be out of GPT alignment specification. Since the partition will not be regularly accessed performance issues can be disregarded, though some disk utilities will display a warning about it. In fdisk or gdisk create a new partition starting at sector 34 and spanning to 2047 and set the type. To have the viewable partitions begin at the base consider adding this partition last.

Master Boot Record (MBR) specific instructions

Usually the post-MBR gap (after the 512 byte MBR region and before the start of the first partition) in many MBR partitioned systems is 31 KiB when DOS compatibility cylinder alignment issues are satisfied in the partition table. However a post-MBR gap of about 1 to 2 MiB is recommended to provide sufficient room for embedding GRUB’s core.img (FS#24103). It is advisable to use a partitioning tool that supports 1 MiB partition alignment to obtain this space as well as to satisfy other non-512-byte-sector issues (which are unrelated to embedding of core.img).

Installation

Install the grub package. (It will replace grub-legacy^AUR if that is already installed.) Then do:

# grub-install --target=i386-pc /dev/sdX

where i386-pc is deliberately used regardless of your actual architecture, and /dev/sdX is the disk (not a partition) where GRUB is to be installed. For example /dev/sda or /dev/nvme0n1, or /dev/mmcblk0. See Device file#Block device names for a description of the block device naming scheme.

Now you must generate the main configuration file.

If you use LVM for your /boot, you can install GRUB on multiple physical disks.

See grub-install(8) and GRUB Manual for more details on the grub-install command.

Configuration

On an installed system, GRUB loads the /boot/grub/grub.cfg configuration file each boot. You can follow #Generated grub.cfg for using a tool, or #Custom grub.cfg for a manual creation.

Generated grub.cfg

This section only covers editing the /etc/default/grub configuration file. See /Tips and tricks for more information.

Note: Remember to always generate the main configuration file after making changes to /etc/default/grub and/or files in /etc/grub.d/.

Warning: Update/reinstall the boot loader (see #UEFI systems or #BIOS systems) if a new GRUB version changes the syntax of the configuration file: mismatching configuration can result in an unbootable system.

Generate the main configuration file

After the installation, the main configuration file /boot/grub/grub.cfg needs to be generated. The generation process can be influenced by a variety of options in /etc/default/grub and scripts in /etc/grub.d/.

If you have not done additional configuration, the automatic generation will determine the root filesystem of the system to boot for the configuration file. For that to succeed it is important that the system is either booted or chrooted into.

Use the grub-mkconfig tool to generate /boot/grub/grub.cfg:

# grub-mkconfig -o /boot/grub/grub.cfg

By default the generation scripts automatically add menu entries for all installed Arch Linux kernels to the generated configuration.

To automatically add entries for other installed operating systems, see #Detecting other operating systems.

You can add additional custom menu entries by editing /etc/grub.d/40_custom and re-generating /boot/grub/grub.cfg. Or you can create /boot/grub/custom.cfg and add them there. Changes to /boot/grub/custom.cfg do not require re-running grub-mkconfig, since /etc/grub.d/41_custom adds the necessary source statement to the generated configuration file.

Tip: /etc/grub.d/40_custom can be used as a template to create /etc/grub.d/nn_custom, where nn defines the precedence, indicating the order the script is executed. The order scripts are executed determine the placement in the GRUB boot menu. nn should be greater than 06 to ensure necessary scripts are executed first.

See #Boot menu entry examples for custom menu entry examples.

Detecting other operating systems

To have grub-mkconfig search for other installed systems and automatically add them to the menu, install the os-prober package and mount the partitions from which the other systems boot. Then re-run grub-mkconfig. If you get the following output: Warning: os-prober will not be executed to detect other bootable partitions then edit /etc/default/grub and add/uncomment:

GRUB_DISABLE_OS_PROBER=false

Then try again.

Windows

For Windows installed in UEFI mode, make sure the EFI system partition containing the Windows Boot Manager (bootmgfw.efi) is mounted. Run os-prober as root to detect and generate an entry for it.

For Windows installed in BIOS mode, mount the Windows system partition (its file system label should be System Reserved or SYSTEM). Run os-prober as root to detect and generate an entry for it.

Additional arguments

To pass custom additional arguments to the Linux image, you can set the GRUB_CMDLINE_LINUX + GRUB_CMDLINE_LINUX_DEFAULT variables in /etc/default/grub. The two are appended to each other and passed to kernel when generating regular boot entries. For the recovery boot entry, only GRUB_CMDLINE_LINUX is used in the generation.

It is not necessary to use both, but can be useful. For example, you could use GRUB_CMDLINE_LINUX_DEFAULT="resume=UUID=uuid-of-swap-partition quiet" where uuid-of-swap-partition is the UUID of your swap partition to enable resume after hibernation. This would generate a recovery boot entry without the resume and without quiet suppressing kernel messages during a boot from that menu entry. Though, the other (regular) menu entries would have them as options.

By default grub-mkconfig determines the UUID of the root filesystem for the configuration. To disable this, uncomment GRUB_DISABLE_LINUX_UUID=true.

For generating the GRUB recovery entry you have to ensure that GRUB_DISABLE_RECOVERY is not set to true in /etc/default/grub.

See Kernel parameters for more info.

By default, grub-mkconfig sorts the included kernels using sort -V and uses the first kernel in that list as the top-level entry. This means that, for example, since /boot/vmlinuz-linux-lts is sorted before /boot/vmlinuz-linux, if you have both linux-lts and linux installed, the LTS kernel will be the top-level menu entry, which may not be desirable. This can be overridden by specifying GRUB_TOP_LEVEL=path_to_kernel" in /etc/default/grub. For example, to make the regular kernel be the top-level menu entry, you can use GRUB_TOP_LEVEL="/boot/vmlinuz-linux".

LVM

Warning: GRUB does not support thin-provisioned logical volumes.

If you use LVM for your /boot or / root partition, make sure that the lvm module is preloaded:

/etc/default/grub

GRUB_PRELOAD_MODULES="... lvm"

RAID

GRUB provides convenient handling of RAID volumes. You need to load GRUB modules mdraid09 or mdraid1x to allow you to address the volume natively:

/etc/default/grub

GRUB_PRELOAD_MODULES="... mdraid09 mdraid1x"

For example, /dev/md0 becomes:

set root=(md/0)

whereas a partitioned RAID volume (e.g. /dev/md0p1) becomes:

set root=(md/0,1)

To install grub when using RAID1 as the /boot partition (or using /boot housed on a RAID1 root partition), on BIOS systems, simply run grub-install on both of the drives, such as:

# grub-install --target=i386-pc --debug /dev/sda
# grub-install --target=i386-pc --debug /dev/sdb

Where the RAID 1 array housing /boot is housed on /dev/sda and /dev/sdb.

Note: GRUB supports booting from Btrfs RAID 0/1/10, but not RAID 5/6. You may use mdadm for RAID 5/6, which is supported by GRUB.

Encrypted /boot

GRUB also has special support for booting with an encrypted /boot. This is done by unlocking a LUKS blockdevice in order to read its configuration and load any initramfs and kernel from it. This option tries to solve the issue of having an unencrypted boot partition.

Tip: /boot is not required to be kept in a separate partition; it may also stay under the system’s root / directory tree.

Warning: GRUB 2.06 has limited support for LUKS2. See the #LUKS2 section below for details.

To enable this feature encrypt the partition with /boot residing on it using LUKS as normal. Then add the following option to /etc/default/grub:

/etc/default/grub

GRUB_ENABLE_CRYPTODISK=y

This option is used by grub-install to generate the grub core.img.

Make sure to install grub after modifying this option or encrypting the partition.

Without further changes you will be prompted twice for a passphrase: the first for GRUB to unlock the /boot mount point in early boot, the second to unlock the root filesystem itself as implemented by the initramfs. You can use a keyfile to avoid this.

Tip: You can use pacman hooks to automount your /boot when upgrades need to access related files.

LUKS2

• GRUB 2.06 has limited support for LUKS2. See GRUB bug #55093.
• Argon2id (cryptsetup default) and Argon2i PBKDFs are not supported (GRUB bug #59409), only PBKDF2 is.
• grub-install does not support creating a core image that could be used for unlocking LUKS2. See the comments below or on grub-git^AUR for a workaround.

Tip: You can use grub-improved-luks2-git^AUR that has been patched for LUKS2 as well as Argon support.

• Use grub-install as described in the #Installation section to populate the GRUB module directory. Do not forget to edit /etc/default/grub and run grub-mkconfig -o /boot/grub/grub.cfg, as described above. The generated EFI binary does not support LUKS2 and will be replaced in the next step.

• Create /boot/grub/grub-pre.cfg. Replace UUID with the LUKS encrypted device UUID. Use lvm/NameOfVolumeGroup-NameOfLogicalVolume instead of crypto0 if your root drive is on an LVM logical volume inside the LUKS volume, otherwise do not change crypto0, this is how GRUB names encrypted volumes.

/boot/grub/grub-pre.cfg

set crypto_uuid=UUID
cryptomount -u $crypto_uuid
set root=crypto0
set prefix=($root)/boot/grub
insmod normal
normal

Note: Whenever you make changes to grub-pre.cfg, you will have to do the following steps again.

Warning: If using Btrfs and /boot/grub is located on a subvolume, the prefix must include the full path from the top level Btrfs subvolume (subvolid = 5). For example, if /boot/grub is located on a subvolume called my_subvolume (subvolid ≠ 5), set the line to set prefix=($root)/my_subvolume/boot/grub. This is true even if you have set my_subvolume as default with btrfs subvolume set-default before.

• Add lvm if you use LVM. Replace ext2 with btrfs or another filesystem module, if needed. Depending on the settings of your key slot, replace gcry_sha256 with gcry_sha512 or gcry_whirlpool if need be:

$ grub-mkimage -p /boot/grub -O x86_64-efi -c grub-pre.cfg -o /tmp/grubx64.efi luks2 part_gpt cryptodisk gcry_rijndael pbkdf2 gcry_sha256 ext2

If it cannot find grub-pre.cfg, simply change to -c /boot/grub/grub-pre.cfg above.

• Copy to ESP:

# install -v /tmp/grubx64.efi esp/EFI/GRUB/grubx64.efi

If you enter an invalid passphrase during boot and end up at the GRUB rescue shell, try cryptomount -a to mount all (hopefully only one) encrypted partitions or use cryptomount -u $crypto_uuid to mount a specific one. Then proceed with insmod normal and normal as usual.

If you enter a correct passphrase, but an Invalid passphrase error is immediately returned, make sure that the right cryptographic modules are specified. Use cryptsetup luksDump /dev/nvme0n1p2 and check whether the hash function (SHA-256, SHA-512) matches the modules (gcry_sha256, gcry_sha512) installed and the PBKDF algorithm is pbkdf2. The hash and PBDKDF algorithms can be changed for existing keys by using cryptsetup luksConvertKey --hash sha256 --pbkdf pbkdf2 /dev/nvme0n1p2. Under normal circumstances it should take a few seconds before the passphrase is processed.

Custom grub.cfg

This section describes the manual creation of GRUB boot entries in /boot/grub/grub.cfg instead of relying on grub-mkconfig.

A basic GRUB config file uses the following options:

• (hdX,Y) is the partition Y on disk X, partition numbers starting at 1, disk numbers starting at 0
• set default=N is the default boot entry that is chosen after timeout for user action
• set timeout=M is the time M to wait in seconds for a user selection before default is booted
• menuentry "title" {entry options} is a boot entry titled title
• set root=(hdX,Y) sets the boot partition, where the kernel and GRUB modules are stored (boot need not be a separate partition, and may simply be a directory under the «root» partition (/)

Tip: These boot entries can also be used when using a /boot/grub/grub.cfg generated by grub-mkconfig. Add them to /etc/grub.d/40_custom and re-generate the main configuration file or add them to /boot/grub/custom.cfg.

For tips on managing multiple GRUB entries, for example when using both linux and linux-lts kernels, see /Tips and tricks#Multiple entries.

For Archiso and Archboot boot menu entries see Multiboot USB drive#Boot entries.

GRUB commands

menuentry "System shutdown" {
	echo "System shutting down..."
	halt
}

menuentry "System restart" {
	echo "System rebooting..."
	reboot
}

if [ ${grub_platform} == "efi" ]; then
	menuentry 'UEFI Firmware Settings' --id 'uefi-firmware' {
		fwsetup
	}
fi

EFI binaries

When launched in UEFI mode, GRUB can chainload other EFI binaries.

if [ ${grub_platform} == "efi" ]; then
	place UEFI-only menu entries here
fi

UEFI Shell

You can launch UEFI Shell by placing it in the root of the EFI system partition and adding this menu entry:

menuentry "UEFI Shell" {
	insmod fat
	insmod chain
	search --no-floppy --set=root --file /shellx64.efi
	chainloader /shellx64.efi
}

gdisk

Download the gdisk EFI application and copy gdisk_x64.efi to esp/EFI/tools/.

menuentry "gdisk" {
	insmod fat
	insmod chain
	search --no-floppy --set=root --file /EFI/tools/gdisk_x64.efi
	chainloader /EFI/tools/gdisk_x64.efi
}

Chainloading a unified kernel image

If you have a unified kernel image generated from following Secure Boot or other means, you can add it to the boot menu. For example:

menuentry "Arch Linux" {
	insmod fat
	insmod chain
	search --no-floppy --set=root --fs-uuid FILESYSTEM_UUID
	chainloader /EFI/Linux/Arch-linux.efi
}

Dual-booting

GNU/Linux

Assuming that the other distribution is on partition sda2:

menuentry "Other Linux" {
	set root=(hd0,2)
	linux /boot/vmlinuz (add other options here as required)
	initrd /boot/initrd.img (if the other kernel uses/needs one)
}

Alternatively let GRUB search for the right partition by UUID or file system label:

menuentry "Other Linux" {
        # assuming that UUID is 763A-9CB6
	search --no-floppy --set=root --fs-uuid 763A-9CB6

        # search by label OTHER_LINUX (make sure that partition label is unambiguous)
        #search --no-floppy --set=root --label OTHER_LINUX

	linux /boot/vmlinuz (add other options here as required, for example: root=UUID=763A-9CB6)
	initrd /boot/initrd.img (if the other kernel uses/needs one)
}

If the other distribution has already a valid /boot folder with installed GRUB, grub.cfg, kernel and initramfs, GRUB can be instructed to load these other grub.cfg files on-the-fly during boot. For example, for hd0 and the fourth GPT partition:

menuentry "configfile hd0,gpt4"  {
        insmod part_gpt
        insmod btrfs
        insmod ext2
        set root='hd0,gpt4'
        configfile /boot/grub/grub.cfg
}

When choosing this entry, GRUB loads the grub.cfg file from the other volume and displays that menu. Any environment variable changes made by the commands in file will not be preserved after configfile returns. Press Esc to return to the first GRUB menu.

Windows installed in UEFI/GPT mode

This mode determines where the Windows boot loader resides and chain-loads it after GRUB when the menu entry is selected. The main task here is finding the EFI system partition and running the bootloader from it.

if [ "${grub_platform}" == "efi" ]; then
	menuentry "Microsoft Windows Vista/7/8/8.1 UEFI/GPT" {
		insmod part_gpt
		insmod fat
		insmod chain
		search --no-floppy --fs-uuid --set=root $hints_string $fs_uuid
		chainloader /EFI/Microsoft/Boot/bootmgfw.efi
	}
fi

where $hints_string and $fs_uuid are obtained with the following two commands.

The $fs_uuid command determines the UUID of the EFI system partition:

# grub-probe --target=fs_uuid esp/EFI/Microsoft/Boot/bootmgfw.efi

1ce5-7f28

Alternatively one can run lsblk --fs and read the UUID of the EFI system partition from there.

The $hints_string command will determine the location of the EFI system partition, in this case harddrive 0:

# grub-probe --target=hints_string esp/EFI/Microsoft/Boot/bootmgfw.efi

--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1

These two commands assume the ESP Windows uses is mounted at esp. There might be case differences in the path to Windows’s EFI file, what with being Windows, and all.

Windows installed in BIOS/MBR mode

Note: GRUB supports booting bootmgr directly and chainloading of partition boot sector is no longer required to boot Windows in a BIOS/MBR setup.

Warning: It is the system partition that has /bootmgr, not your «real» Windows partition (usually C:). The system partition’s filesystem label is System Reserved or SYSTEM and the partition is only about 100 to 549 MiB in size. See Wikipedia:System partition and boot partition for more information.

Throughout this section, it is assumed your Windows partition is /dev/sda1. A different partition will change every instance of hd0,msdos1.

In both examples XXXX-XXXX is the filesystem UUID which can be found with command lsblk --fs.

For Windows Vista/7/8/8.1/10:

if [ "${grub_platform}" == "pc" ]; then
	menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS/MBR" {
		insmod part_msdos
		insmod ntfs
		insmod ntldr
		search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 XXXX-XXXX
		ntldr /bootmgr
	}
fi

For Windows XP:

if [ "${grub_platform}" == "pc" ]; then
	menuentry "Microsoft Windows XP" {
		insmod part_msdos
		insmod ntfs
		insmod ntldr
		search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 XXXX-XXXX
		ntldr /ntldr
	}
fi

X:> bootrec.exe /fixboot
X:> bootrec.exe /RebuildBcd

Using labels

It is possible to use file system labels, human-readable strings attached to file systems, by using the --label option to search. First of all, make sure your file system has a label.

Then, add an entry using labels. An example of this:

menuentry "Arch Linux, session texte" {
  search --label --set=root archroot
  linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro
  initrd /boot/initramfs-linux.img
}

Using the command shell

Since the MBR is too small to store all GRUB modules, only the menu and a few basic commands reside there. The majority of GRUB functionality remains in modules in /boot/grub/, which are inserted as needed. In error conditions (e.g. if the partition layout changes) GRUB may fail to boot. When this happens, a command shell may appear.

GRUB offers multiple shells/prompts. If there is a problem reading the menu but the bootloader is able to find the disk, you will likely be dropped to the «normal» shell:

grub>

If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the «rescue» shell:

grub rescue>

The rescue shell is a restricted subset of the normal shell, offering much less functionality. If dumped to the rescue shell, first try inserting the «normal» module, then starting the «normal» shell:

grub rescue> set prefix=(hdX,Y)/boot/grub
grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
rescue:grub> normal

GRUB supports pager for reading commands that provide long output (like the help command). This works only in normal shell mode and not in rescue mode. To enable pager, in GRUB command shell type:

sh:grub> set pager=1

Using the command shell environment to boot operating systems

grub>

The GRUB’s command shell environment can be used to boot operating systems.
A common scenario may be to boot Windows / Linux stored on a drive/partition via chainloading.

Chainloading means to load another boot-loader from the current one, ie, chain-loading.

The other bootloader may be embedded at the start of a partitioned disk (MBR), at the start of a partition or a partitionless disk (VBR), or as an EFI binary in the case of UEFI.

Chainloading a partition’s VBR

set root=(hdX,Y)
chainloader +1
boot

X=0,1,2…
Y=1,2,3…

For example to chainload Windows stored in the first partition of the first hard disk,

set root=(hd0,1)
chainloader +1
boot

Similarly GRUB installed to a partition can be chainloaded.

Chainloading a disk’s MBR or a partitionless disk’s VBR

set root=hdX
chainloader +1
boot

Chainloading Windows/Linux installed in UEFI mode

insmod fat
set root=(hd0,gpt4)
chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
boot

insmod fat is used for loading the FAT file system module for accessing the Windows bootloader on the EFI system partition.
(hd0,gpt4) or /dev/sda4 is the EFI system partition in this example.
The entry in the chainloader line specifies the path of the .efi file to be chain-loaded.

Normal loading

See the examples in #Using the rescue console

Using the rescue console

See #Using the command shell first. If unable to activate the standard shell, one possible solution is to boot using a live CD or some other rescue disk to correct configuration errors and reinstall GRUB. However, such a boot disk is not always available (nor necessary); the rescue console is surprisingly robust.

The available commands in GRUB rescue include insmod, ls, set, and unset. This example uses set and insmod. set modifies variables and insmod inserts new modules to add functionality.

Before starting, the user must know the location of their /boot partition (be it a separate partition, or a subdirectory under their root):

grub rescue> set prefix=(hdX,Y)/boot/grub

where X is the physical drive number and Y is the partition number.

Note: With a separate boot partition, omit /boot from the path (i.e. type set prefix=(hdX,Y)/grub).

To expand console capabilities, insert the linux module:

grub rescue> insmod i386-pc/linux.mod

or simply

grub rescue> insmod linux

This introduces the linux and initrd commands, which should be familiar.

An example, booting Arch Linux:

set root=(hd0,5)
linux /boot/vmlinuz-linux root=/dev/sda5
initrd /boot/initramfs-linux.img
boot

With a separate boot partition (e.g. when using UEFI), again change the lines accordingly:

Note: Since boot is a separate partition and not part of your root partition, you must address the boot partition manually, in the same way as for the prefix variable.

set root=(hd0,5)
linux (hdX,Y)/vmlinuz-linux root=/dev/sda6
initrd (hdX,Y)/initramfs-linux.img
boot

Note: If you experienced error: premature end of file /YOUR_KERNEL_NAME during execution of linux command, you can try linux16 instead.

After successfully booting the Arch Linux installation, users can correct grub.cfg as needed and then reinstall GRUB.

To reinstall GRUB and fix the problem completely, changing /dev/sda if needed. See #Installation for details.

GRUB removal

In general, in order to remove grub, one has to do the installation steps in reverse order. Perhaps cleaning any left over at the end. However, before doing anything, one has to decide if, and how, the machine will boot after the removal. Assuming one removes grub because they would like to use another boot loader, a safe, though a bit difficult, method is to make sure the other boot loader is working before removing grub.

In any case, even when removing grub before installing another boot loader, for the UEFI case, run:

$ efibootmgr

And verify the other boot loader is listed in the BootOrder line. If grub was not removed, the other boot loader should be listed before grub. If grub is already removed, grub should not be mentioned in that line. But note this is only a necessary, but not sufficient, condition for the machine to boot with the other boot loader. Neither it is a sufficient condition for the full removal of grub.

For both UEFI and non UEFI machines, grub-install was manually run as part of the installation of grub. One of its jobs for the UEFI case was to run the equivalent of efibootmgr --create. As part of grub removal, one has to remove the products of grub-install. The opposite of efibootmgr --create is efibootmgr --delete-bootnum, or an equivalent program. One way to obtain the number of the boot entry for the efibootmgr --delete-bootnum command is from the output of efibootmgr (with no arguments).

grub-install creates the /boot/grub directory that needs to be removed manually. Though some users will want to keep it, should they want to install grub again.

After migrating to GPT/UEFI one may want to remove the MBR boot code using dd:

# dd if=/dev/zero of=/dev/sdX bs=440 count=1

Troubleshooting

Unsupported file systems

In case that GRUB does not support the root file system, an alternative /boot partition with a supported file system must be created. In some cases, the development version of GRUB grub-git^AUR may have native support for the file system.

If GRUB is used with an unsupported file system it is not able to extract the UUID of your drive so it uses classic non-persistent /dev/sdXx names instead. In this case you might have to manually edit /boot/grub/grub.cfg and replace root=/dev/sdXx with root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX. You can use the blkid command to get the UUID of your device, see Persistent block device naming.

While GRUB supports F2FS since version 2.0.4, it cannot correctly read its boot files from an F2FS partition that was created with the extra_attr flag enabled.

Enable debug messages

Note: This change is overwritten when #Generate the main configuration file.

Add:

set pager=1
set debug=all

to grub.cfg.

msdos-style error message

grub-setup: warn: This msdos-style partition label has no post-MBR gap; embedding will not be possible!
grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.
            However, blocklists are UNRELIABLE and its use is discouraged.
grub-setup: error: If you really want blocklists, use --force.

This error may occur when you try installing GRUB in a VMware container. Read more about it here. It happens when the first partition starts just after the MBR (block 63), without the usual space of 1 MiB (2048 blocks) before the first partition. Read #Master Boot Record (MBR) specific instructions

UEFI

Common installation errors

• If you have a problem when running grub-install with sysfs or procfs and it says you must run modprobe efivarfs or it returns an error like Could not prepare Boot variable: Read-only file system, try mounting the efivarfs. Also see the Gentoo Wiki on installing the boot loader.
• Without --target or --directory option, grub-install cannot determine for which firmware to install. In such cases grub-install will print source_dir does not exist. Please specify --target or --directory.
• If after running grub-install you are told your partition does not look like an EFI partition then the partition is most likely not Fat32.

Create a GRUB entry in the firmware boot manager

grub-install automatically tries to create a menu entry in the boot manager. If it does not, then see UEFI#efibootmgr for instructions to use efibootmgr to create a menu entry. However, the problem is likely to be that you have not booted your CD/USB in UEFI mode, as in UEFI#Create UEFI bootable USB from ISO.

As another example of creating a GRUB entry in the firmware boot manager, consider efibootmgr -c. This assumes that /dev/sda1 is the EFI System Partition, and is mounted at /boot/efi. Which are the default behavior of efibootmgr. It creates a new boot option, called «Linux», and puts it at the top of the boot order list. Options may be passed to modify the default behavior. The default OS Loader is EFIarchgrub.efi.

Drop to rescue shell

If GRUB loads but drops into the rescue shell with no errors, it can be due to one of these two reasons:

• It may be because of a missing or misplaced grub.cfg. This will happen if GRUB UEFI was installed with --boot-directory and grub.cfg is missing,
• It also happens if the boot partition, which is hardcoded into the grubx64.efi file, has changed.

GRUB UEFI not loaded

An example of a working UEFI:

# efibootmgr -v

BootCurrent: 0000
Timeout: 3 seconds
BootOrder: 0000,0001,0002
Boot0000* GRUB HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(EFIGRUBgrubx64.efi)
Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(shellx64.efi)
Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI

If the screen only goes black for a second and the next boot option is tried afterwards, according to this post, moving GRUB to the partition root can help. The boot option has to be deleted and recreated afterwards. The entry for GRUB should look like this then:

Boot0000* GRUB HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(grubx64.efi)

Default/fallback boot path

Some UEFI firmwares require a bootable file at a known location before they will show UEFI NVRAM boot entries. If this is the case, grub-install will claim efibootmgr has added an entry to boot GRUB, however the entry will not show up in the VisualBIOS boot order selector. The solution is to install GRUB at the default/fallback boot path:

# grub-install --target=x86_64-efi --efi-directory=esp --removable

Alternatively you can move an already installed GRUB EFI executable to the default/fallback path:

# mv esp/EFI/grub esp/EFI/BOOT
# mv esp/EFI/BOOT/grubx64.efi esp/EFI/BOOT/BOOTX64.EFI

Invalid signature

If trying to boot Windows results in an «invalid signature» error, e.g. after reconfiguring partitions or adding additional hard drives, (re)move GRUB’s device configuration and let it reconfigure:

# mv /boot/grub/device.map /boot/grub/device.map-old
# grub-mkconfig -o /boot/grub/grub.cfg

grub-mkconfig should now mention all found boot options, including Windows. If it works, remove /boot/grub/device.map-old.

Boot freezes

If booting gets stuck without any error message after GRUB loading the kernel and the initial ramdisk, try removing the add_efi_memmap kernel parameter.

Arch not found from other OS

Some have reported that other distributions may have trouble finding Arch Linux automatically with os-prober. If this problem arises, it has been reported that detection can be improved with the presence of /etc/lsb-release. This file and updating tool is available with the package lsb-release.

Warning when installing in chroot

When installing GRUB on a LVM system in a chroot environment (e.g. during system installation), you may receive warnings like

/run/lvm/lvmetad.socket: connect failed: No such file or directory

or

WARNING: failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.

This is because /run is not available inside the chroot. These warnings will not prevent the system from booting, provided that everything has been done correctly, so you may continue with the installation.

GRUB loads slowly

GRUB can take a long time to load when disk space is low. Check if you have sufficient free disk space on your /boot or / partition when you are having problems.

error: unknown filesystem

GRUB may output error: unknown filesystem and refuse to boot for a few reasons. If you are certain that all UUIDs are correct and all filesystems are valid and supported, it may be because your BIOS Boot Partition is located outside the first 2 TiB of the drive [1]. Use a partitioning tool of your choice to ensure this partition is located fully within the first 2 TiB, then reinstall and reconfigure GRUB.

This error might also be caused by an ext4 filesystem having unsupported features set:

• large_dir — unsupported.
• metadata_csum_seed — will be supported in GRUB 2.11 (commit).

Warning: Make sure to check GRUB support for new file system features before you enable them on your /boot file system.

grub-reboot not resetting

GRUB seems to be unable to write to root Btrfs partitions [2]. If you use grub-reboot to boot into another entry it will therefore be unable to update its on-disk environment. Either run grub-reboot from the other entry (for example when switching between various distributions) or consider a different file system. You can reset a «sticky» entry by executing grub-editenv create and setting GRUB_DEFAULT=0 in your /etc/default/grub (do not forget grub-mkconfig -o /boot/grub/grub.cfg).

Old Btrfs prevents installation

If a drive is formatted with Btrfs without creating a partition table (eg. /dev/sdx), then later has partition table written to, there are parts of the BTRFS format that persist. Most utilities and OS’s do not see this, but GRUB will refuse to install, even with —force

# grub-install: warning: Attempting to install GRUB to a disk with multiple partition labels. This is not supported yet..
# grub-install: error: filesystem `btrfs' does not support blocklists.

You can zero the drive, but the easy solution that leaves your data alone is to erase the Btrfs superblock with wipefs -o 0x10040 /dev/sdx

Windows 8/10 not found

A setting in Windows 8/10 called «Hiberboot», «Hybrid Boot» or «Fast Boot» can prevent the Windows partition from being mounted, so grub-mkconfig will not find a Windows install. Disabling Hiberboot in Windows will allow it to be added to the GRUB menu.

VirtualBox EFI mode

For VirtualBox < 6.1, install GRUB to the default/fallback boot path.

See also VirtualBox#Installation in EFI mode on VirtualBox < 6.1.

GRUB rescue and encrypted /boot

When using an encrypted /boot, and you fail to input a correct password, you will be dropped in grub-rescue prompt.

This grub-rescue prompt has limited capabilities. Use the following commands to complete the boot:

grub rescue> cryptomount <partition>
grub rescue> insmod normal
grub rescue> normal

See this blog post for a better description.

Check /etc/default/grub if GRUB_TIMEOUT is set to 0, in which case set it to a positive number: it sets the number of seconds before the default GRUB entry is loaded. Also check if GRUB_TIMEOUT_STYLE is set to hidden and set it to menu, so that the menu will be shown by default. Then regenerate the main configuration file and reboot to check if it worked.

See also

• Wikipedia:GNU GRUB
• Official GRUB Manual
• Ubuntu wiki page for GRUB
• GRUB wiki page describing steps to compile for UEFI systems
• Wikipedia:BIOS Boot partition
• How to configure GRUB
• Detecting efi files and booting them from grub