GRUB: Difference between revisions
(→GUID Partition Table (GPT) specific instructions: fdisk's partition type numbers are irrelevant; "bios_grub" is a partition flag in parted not a partition type) |
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[[Install]] the {{Pkg|grub}} package. It will replace {{AUR|grub-legacy}}, where already installed. Then do: | [[Install]] the {{Pkg|grub}} package. It will replace {{AUR|grub-legacy}}, where already installed. Then do: | ||
# grub-install | # grub-install /dev/sd''X'' | ||
where {{ic|/dev/sd'' | where {{ic|/dev/sd''X''}} is the [[partition]]ed disk where grub is to be installed (for example, disk {{ic|/dev/sda}} and '''not''' partition {{ic|/dev/sda1}}). | ||
Now you must [[#Generate the main configuration file]]. | Now you must [[#Generate the main configuration file]]. | ||
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To install grub when using RAID1 as the {{ic|/boot}} partition (or using {{ic|/boot}} housed on a RAID1 root partition), on devices with GPT ef02/'BIOS boot partition', simply run ''grub-install'' on both of the drives, such as: | To install grub when using RAID1 as the {{ic|/boot}} partition (or using {{ic|/boot}} housed on a RAID1 root partition), on devices with GPT ef02/'BIOS boot partition', simply run ''grub-install'' on both of the drives, such as: | ||
# grub-install | # grub-install --debug /dev/sda | ||
# grub-install | # grub-install --debug /dev/sdb | ||
Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}. | Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}. |
Revision as of 17:17, 4 April 2018
GRUB (GRand Unified Bootloader) is a multi-boot loader. It is derived from PUPA which was a research project to develop the replacement of what is now known as GRUB Legacy. The latter had become too difficult to maintain and GRUB was rewritten from scratch with the aim to provide modularity and portability [1]. The current GRUB is also referred to as GRUB 2 while GRUB Legacy corresponds to versions 0.9x.
A boot loader is the first program that runs when a computer starts. It is responsible for selecting, loading and transferring control to an operating system kernel. The kernel, in turn, initializes the rest of the operating system.
esp
denotes the mountpoint of the EFI System Partition aka ESP.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.
- Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme. Read more on GUID partition tables.
- This additional partition is only needed on a GRUB, BIOS/GPT partitioning scheme. Previously, for a GRUB, BIOS/MBR partitioning scheme, GRUB used the Post-MBR gap for the embedding the
core.img
). GRUB for GPT, however, does not use the Post-GPT gap to conform to GPT specifications that require 1_megabyte/2048_sector disk boundaries. - For UEFI systems this extra partition is not required, since no embedding of boot sectors takes place in that case. However, UEFI systems still require an EFI System Partition.
Create a mebibyte partition (+1M
with fdisk or gdisk) on the disk with no file system and with partition type BIOS boot. Select partition type BIOS boot
for fdisk, 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 bootloader as per the instructions below.
The post-GPT gap 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 (or 'msdos' disklabel) 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-legacyAUR, where already installed. Then do:
# grub-install /dev/sdX
where /dev/sdX
is the partitioned disk where grub is to be installed (for example, disk /dev/sda
and not partition /dev/sda1
).
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.
UEFI systems
- It is recommended to read and understand the UEFI, GPT and UEFI Bootloaders pages.
- When installing to use UEFI it is important to start the install with your machine in UEFI mode. The Arch Linux install media must be UEFI bootable.
Check for GPT disk layout and an EFI System Partition
To boot from a disk using EFI, the recommended disk partition table is GPT and this is the layout that is assumed in this article. An EFI System Partition (ESP) is required on every bootable disk. If you are installing Arch Linux on an EFI-capable computer with an installed operating system, like Windows 10 for example, it is very likely that you already have an ESP.
To find out the disk partition scheme and the system partition, use parted
as root on the disk you want to boot from:
# parted /dev/sdx print
The command returns:
- The disk partition layout: if the disk is GPT, it indicates
Partition Table: gpt
. - The list of partitions on the disk: Look for the ESP in the list, it is a small (512 MiB or less) partition with a vfat or fat32 file system and with the flags boot and possibly esp enabled. To confirm this is the ESP, mount it and check whether it contains a directory named
EFI
, if it does this is definitely the ESP.
Once it is found, take note of the ESP partition number, it will be required for the GRUB installation. If you do not have an ESP, you will need to create one. See the EFI System Partition article.
Installation
First, install the packages grub and efibootmgr: GRUB is the bootloader while efibootmgr creates bootable .efi stub entries used by the GRUB installation script.
Then follow the below steps to install GRUB:
- Mount the EFI System Partition to either
/boot
or/boot/efi
and in the remainder of this section, substituteesp
with that mount point. - Choose a bootloader identifier, here named
arch
. A directory of that name will be created to store the EFI binary bootloader in the ESP and this is the name that will appear in the EFI boot menu to identify the GRUB boot entry. - Execute the following command to install the GRUB UEFI application to
esp/EFI/grub/
, install its modules to/boot/grub/x86_64-efi/
, and place the EFI binary bootloadergrubx64.efi
inesp/EFI/arch_grub/
.
# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=arch_grub
After the above install completed the main GRUB directory is located at /boot/grub/
. Note that grub-install
also tries to create an entry in the firmware boot manager, named arch_grub
in the above example.
Remember to #Generate the main configuration file after finalizing #Configuration.
--removable
then GRUB will be installed to esp/EFI/BOOT/BOOTX64.EFI
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 has a BOOT
folder inside the EFI
folder of the EFI partition, but its only purpose is to recreate the EFI boot option for Windows.- While some distributions require a
/boot/efi
or/boot/EFI
directory, Arch does not. --efi-directory
and--bootloader-id
are specific to GRUB UEFI,--efi-directory
replaces--root-directory
which is deprecated.- You might note the absence of a device_path option (e.g.:
/dev/sda
) in thegrub-install
command. In fact any device_path provided will be ignored by the GRUB UEFI install script. Indeed, UEFI bootloaders do not use a MBR or partition boot sector at all. - The section assumes you are installing GRUB for x86_64 systems (x86_64-efi). For 32-bit EFI systems (not to be confused with 32-bit CPUs), replace
x86_64-efi
withi386-efi
where appropriate.
See UEFI troubleshooting in case of problems. Additionally see GRUB/Tips and tricks#UEFI further reading.
Generate the main configuration file
After the installation, the main configuration file 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/
; see #Configuration.
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.
grub.cfg
has to be re-generated after any change to /etc/default/grub
or files in /etc/grub.d/
.Use the grub-mkconfig tool to generate grub.cfg
:
# grub-mkconfig -o /boot/grub/grub.cfg
By default the generation scripts automatically add menu entries for Arch Linux to any generated configuration. See Multiboot USB drive#Boot entries and #Dual-booting for custom menu entries for other systems.
- The default file path is
/boot/grub/grub.cfg
, not/boot/grub/i386-pc/grub.cfg
. The grub package includes a sample/boot/grub/grub.cfg
; ensure your intended changes are written to this file. - If you are trying to run grub-mkconfig in a chroot or systemd-nspawn container, you might notice that it does not work, complaining that grub-probe cannot get the "canonical path of /dev/sdaX". In this case, try using arch-chroot as described in the BBS post.
Configuration
This section only covers editing the /etc/default/grub
configuration file. See GRUB/Tips and tricks for more information.
Remember to always #Generate the main configuration file after making changes to /etc/default/grub
.
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=/dev/sdaX quiet"
where sdaX
is 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
.
You can also use GRUB_CMDLINE_LINUX="resume=UUID=uuid-of-swap-partition"
See Kernel parameters for more info.
Dual-booting
The best way to add other entries is editing /etc/grub.d/40_custom
or /boot/grub/custom.cfg
. The entries in this file will be automatically added after rerunning grub-mkconfig
.
menuentry "System shutdown" { echo "System shutting down..." halt }
menuentry "System restart" { echo "System rebooting..." reboot }
menuentry "Firmware setup" { fwsetup }
Assuming that the other distro 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 label:
menuentry "Other Linux" { # assuming that UUID is 763A-9CB6 search --set=root --fs-uuid 763A-9CB6 # search by label OTHER_LINUX (make sure that partition label is unambiguous) #search --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) }
This mode determines where the Windows bootloader resides and chain-loads it after Grub when the menu entry is selected. The main task here is finding the EFI 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 search_fs_uuid insmod chain search --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 partition:
# grub-probe --target=fs_uuid esp/EFI/Microsoft/Boot/bootmgfw.efi
1ce5-7f28
Alternatively one can run blkid
(as root) and read the UUID of the EFI partition from there.
The $hints_string
command will determine the location of the EFI partition, in this case harddrive 0:
# grub-probe --target=hints_string esp/EFI/Microsoft/Boot/bootmgfw.efi
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
These two commands assume the ESP Windows uses is mounted at esp
. There might be case differences in the path to Windows's EFI file, what with being Windows, and all.
Windows installed in BIOS-MBR mode
bootmgr
directly and chainloading of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup./bootmgr
, not your "real" Windows partition (usually C:). In blkid
output, the system partition is the one with LABEL="SYSTEM RESERVED"
or LABEL="SYSTEM"
and is only about 100 to 200 MB in size (much like the boot partition for Arch). See Wikipedia:System partition and boot partition for more info.Throughout this section, it is assumed your Windows partition is /dev/sda1
. A different partition will change every instance of hd0,msdos1. Add the below code to /etc/grub.d/40_custom
or /boot/grub/custom.cfg
and regenerate grub.cfg
with grub-mkconfig
as explained above to boot Windows (XP, Vista, 7, 8 or 10) installed in BIOS-MBR mode:
In both examples 69B235F6749E84CE is the filesystem UUID which can be found with command lsblk --fs.
For Windows Vista/7/8/8.1/10:
if [ "${grub_platform}" == "pc" ]; then menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS-MBR" { insmod part_msdos insmod ntfs insmod search_fs_uuid insmod ntldr search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE ntldr /bootmgr } fi
For Windows XP:
if [ "${grub_platform}" == "pc" ]; then menuentry "Microsoft Windows XP" { insmod part_msdos insmod ntfs insmod search_fs_uuid insmod ntldr search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE ntldr /ntldr } fi
\boot\bcd
(error code 0xc000000f
). You can fix it by going to Windows Recovery Console (cmd from install disk) and executing:
x:\> "bootrec.exe /fixboot" x:\> "bootrec.exe /RebuildBcd".
Do not use bootrec.exe /Fixmbr
because it will wipe GRUB out.
Or you can use Boot Repair function in the Troubleshooting menu - it will not wipe out GRUB but will fix most errors.
/etc/grub.d/40_custom
can be used as a template to create /etc/grub.d/nn_custom
. Where nn
defines the precendence, 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.LVM
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 add insmod mdraid09
or mdraid1x
which allows you to address the volume natively. 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 devices with GPT ef02/'BIOS boot partition', simply run grub-install on both of the drives, such as:
# grub-install --debug /dev/sda # grub-install --debug /dev/sdb
Where the RAID 1 array housing /boot
is housed on /dev/sda
and /dev/sdb
.
Multiple entries
For tips on managing multiple GRUB entries, for example when using both linux and linux-lts kernels, see GRUB/Tips and tricks#Multiple entries.
Encryption
Root partition
To encrypt a root filesystem to be used with GRUB, add the encrypt
hook or the sd-encrypt
hook (if using systemd hooks) to mkinitcpio. See dm-crypt/System configuration#mkinitcpio for details, and Mkinitcpio#Common hooks for alternative encryption hooks.
If using the encrypt
hook, add the cryptdevice
parameter to /etc/default/grub
. In the example below, the sda2
partition has been encrypted as /dev/mapper/cryptroot
:
/etc/default/grub
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:cryptroot"
If using the sd-encrypt
hook, add rd.luks.uuid
:
/etc/default/grub
GRUB_CMDLINE_LINUX="rd.luks.uuid=UUID"
where UUID is the UUID of the LUKS-encrypted device.
Be sure to #Generate the main configuration file when done.
For further information about bootloader configuration for encrypted devices, see Dm-crypt/System configuration#Boot loader.
/boot
either as a separate partition or part of the /
partition, further setup is required. See #Boot partition./boot/grub/menu.lst.pacsave
for the correct device/label to add. Look for them after the text kernel /vmlinuz-linux
.Boot partition
GRUB can be set to ask for a password to open 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. /boot
is not required to be kept in a separate partition; it may also stay under the system's root /
directory tree.
luks2
for the type parameter when creating the encrypted partition using cryptsetup luksFormat
.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
Be sure to #Generate the main configuration file while the partition containing /boot
is mounted.
Without further changes you will be prompted twice for a passhrase: the first for GRUB to unlock the /boot
mount point in early boot, the second to unlock the root filesystem itself as described in #Root partition. You can use a keyfile to avoid this.
- If you use a special keymap, a default GRUB installation will not know it. This is relevant for how to enter the passphrase to unlock the LUKS blockdevice.
- In order to perform system updates involving the
/boot
mount point, ensure that the encrypted/boot
is unlocked and mounted before performing an update. With a separate/boot
partition, this may be accomplished automatically on boot by using crypttab with a keyfile. - If you experience issues getting the prompt for a password to display (errors regarding cryptouuid, cryptodisk, or "device not found"), try reinstalling grub as below appending the following to the end of your installation command:
# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=grub --modules="part_gpt part_msdos"
Chainloading an Arch Linux .efi file
If you have an .efi file generated from following Secure Boot or other means, /etc/grub.d/40_custom
can be edited to add a new menu entry before regenerating grub.cfg
with grub-mkconfig
.
/etc/grub.d/40_custom
menuentry 'Arch Linux .efi' { insmod part_gpt insmod chain set root='(hdX,gptY)' chainloader /EFI/path/file.efi }
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
Pager support
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 starting of the disk(MBR) or at the starting of a partition or as an EFI file in the ESP in the case of UEFI.
Chainloading a partition
set root=(hdX,Y) chainloader +1 boot
X=0,1,2... Y=1,2,3...
For example to chainload Windows stored in the first partiton of the first hard disk,
set root=(hd0,1) chainloader +1 boot
Similarly GRUB installed to a partition can be chainloaded.
Chainloading a disk/drive
set root=hdX chainloader +1 boot
Chainloading Windows/Linux installed in UEFI mode
insmod ntfs set root=(hd0,gpt4) chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi boot
insmod ntfs used for loading the ntfs file system module for loading Windows. (hd0,gpt4) or /dev/sda4 is my EFI System Partition (ESP). 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.
/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 EFI), again change the lines accordingly:
set root=(hd0,5) linux (hdX,Y)/vmlinuz-linux root=/dev/sda6 initrd (hdX,Y)/initramfs-linux.img boot
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.
Troubleshooting
F2FS and other unsupported file systems
GRUB does not support F2FS file system. In case the root partition is on an unsupported file system, an alternative /boot
partition with a supported file system must be created. In some cases, the development version of GRUB grub-gitAUR may have native support for the file system.
Intel BIOS not booting GPT
MBR
Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.
This can be circumvented by using (for instance) fdisk to mark one of the GPT partitions (preferably the 1007 KiB partition you have created for GRUB already) bootable in the MBR. This can be achieved, using fdisk, by the following commands: Start fdisk against the disk you are installing, for instance fdisk /dev/sda
, then press a
and select the partition you wish to mark as bootable (probably #1) by pressing the corresponding number, finally press w
to write the changes to the MBR.
fdisk
or similar, not in GParted or others, as they will not set the bootable flag in the MBR.With cfdisk, the steps are similar, just cfdisk /dev/sda
, choose bootable (at the left) in the desired hard disk, and quit saving.
With recent version of parted, you can use disk_toggle pmbr_boot
option. Afterwards verify that Disk Flags show pmbr_boot.
# parted /dev/sdx disk_toggle pmbr_boot # parted /dev/sdx print
More information is available here
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
Enable debug messages
Add:
set pager=1 set debug=all
to grub.cfg
.
"No suitable mode found" error
If you get this error when booting any menuentry:
error: no suitable mode found Booting however
Then you need to initialize GRUB graphical terminal (gfxterm
) with proper video mode (gfxmode
) in GRUB. This video mode is passed by GRUB to the linux kernel via 'gfxpayload'. In case of UEFI systems, if the GRUB video mode is not initialized, no kernel boot messages will be shown in the terminal (atleast until KMS kicks in).
Copy /usr/share/grub/unicode.pf2
to ${GRUB_PREFIX_DIR} (/boot/grub/
in case of BIOS and UEFI systems). If GRUB UEFI was installed with --boot-directory=esp/EFI
set, then the directory is esp/EFI/grub/
:
# cp /usr/share/grub/unicode.pf2 ${GRUB_PREFIX_DIR}
If /usr/share/grub/unicode.pf2
does not exist, install bdf-unifont, create the unifont.pf2
file and then copy it to ${GRUB_PREFIX_DIR}
:
# grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
Then, in the grub.cfg
file, add the following lines to enable GRUB to pass the video mode correctly to the kernel, without of which you will only get a black screen (no output) but booting (actually) proceeds successfully without any system hang.
BIOS systems:
insmod vbe
UEFI systems:
insmod efi_gop insmod efi_uga
After that add the following code (common to both BIOS and UEFI):
insmod font
if loadfont ${prefix}/fonts/unicode.pf2 then insmod gfxterm set gfxmode=auto set gfxpayload=keep terminal_output gfxterm fi
As you can see for gfxterm (graphical terminal) to function properly, unicode.pf2
font file should exist in ${GRUB_PREFIX_DIR}
.
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 efivars
, try Unified Extensible Firmware Interface#Mount efivarfs. - Without
--target
or--directory
option, grub-install cannot determine for which firmware to install. In such casesgrub-install
will printsource_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
.
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
andgrub.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 EFI:
# efibootmgr -v
BootCurrent: 0000 Timeout: 3 seconds BootOrder: 0000,0001,0002 Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\efi\grub\grub.efi) Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\EfiShell.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(\grub.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 in the official repositories.
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 [2]. Use a partitioning tool of your choice to ensure this partition is located fully within the first 2 TiB, then reinstall and reconfigure GRUB.
grub-reboot not resetting
GRUB seems to be unable to write to root BTRFS partitions [3]. 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.