GRUB

Related articles
/EFI examples
/Tips and tricks
Arch boot process
GRUB Legacy
GUID Partition Table
Master Boot Record
Multiboot USB drive
Unified Extensible Firmware Interface
GRUB
(
GR
and
U
nified
B
ootloader) 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 mount point of the
EFI system partition
aka ESP.
Supported file systems
GRUB bundles its own support for
multiple file systems
, notably
FAT32
,
ext4
,
Btrfs
or
XFS
. See
#Unsupported file systems
for some caveats.
Warning
File systems can get new features not yet supported by GRUB, making them unsuitable for
/boot
unless disabling incompatible features. This can be typically avoided by using a separate
/boot partition
with a universally supported file system such as
FAT32
.
UEFI systems
Note
It is recommended to read and understand the
Unified Extensible Firmware Interface
,
Partitioning#GUID Partition Table
and
Arch boot process#UEFI 2
pages.
When installing to use UEFI it is important to boot the installation media in UEFI mode, otherwise
efibootmgr
will not be able to add the GRUB UEFI boot entry. Installing to the
fallback boot path
will still work even in BIOS mode since it does not touch the NVRAM.
To boot from a disk using UEFI, an EFI system partition is required. Follow
EFI system partition#Check for an existing partition
to find out if you have one already, otherwise you need to create it.
This whole article assumes that inserting additional GRUB2 modules via
insmod
is possible. As discussed in
#Shim-lock
, this is not the case on UEFI systems with Secure Boot enabled. If you want to use any additional GRUB module that is not included in the standard GRUB EFI file
grubx64.efi
on a Secure Boot system, you have to re-generate the GRUB EFI
grubx64.efi
with
grub-mkstandalone
or reinstall GRUB using
grub-install
with the additional GRUB modules included.
Installation
Note
UEFI firmwares are not implemented consistently across manufacturers. The procedure described below is intended to work on a wide range of UEFI systems but those experiencing problems despite applying this method are encouraged to share detailed information, and if possible the workarounds found, for their hardware-specific case. A
/EFI examples
article has been provided for such cases.
The section assumes you are installing GRUB for x64 (64-bit) UEFI. For IA32 (32-bit) UEFI (not to be confused with 32-bit CPUs), replace
x86_64-efi
with
i386-efi
where appropriate. Follow the instructions in
Unified Extensible Firmware Interface#Checking the firmware bitness
to figure out your UEFI's bitness.
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:
Mount the EFI system partition
and in the remainder of this section, substitute
esp
with its mount point.
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.
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.
EFI on
RAID
mdadm 1 version / metadata 0.90 or 1.0 ONLY!  So partitions start with a complete copy of the FAT filesystem then have mdadm label at the end.
grub-install
requires
--no-nvram
or else it errors with
efibootmgr: option requires an argument -- 'd'
. This is a
long open bug
(
Ubuntu discussion
).  The fastest workaround is to manually add the entry for each partition in the array with
efibootmgr
(
Gentoo wiki goes a little more in depth on efibootmgr use
)
# grub-install --target=x86_64-efi --efi-directory=
esp
--bootloader-id=GRUB
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 or the systems prevents the boot order from being manipulated (e.g. Thinkpad
firmware
has a setting called "Boot Order Lock" which needs to be disabled for efibootmgr to be able to add/remove entries); use
efibootmgr
to remove unnecessary entries.
Warning
Remember to
#Generate the main configuration file
after finalizing the configuration or else your os will not be in the grub menu.
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. Some desktop motherboards will only look for an EFI executable in this location, making this option mandatory, in particular with MSI boards.
If you execute a UEFI update, this update might delete the existing UEFI boot entries. Therefore, it is a potential fallback strategy to have the "removable" boot entry enabled.
Note
--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 the
grub-install
command. In fact any
device_path
provided will be ignored by the GRUB UEFI install script. Indeed, UEFI boot loaders do not use a MBR bootcode or partition boot sector at all.
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.
Warning
Incorrectly configuring
Secure Boot
can render your system unbootable. If for any reason you cannot boot after enabling secure boot then you should disable it in firmware and reboot the system.
Loading unnecessary modules in your
boot loader
has the potential to present a security risk, only use these commands if you need them.
CA Keys
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
Shim-lock
Note
Before following this section you should make sure you have followed the instructions at
Secure Boot#shim
and have
sbsigntools
set-up and ready to receive keys.
When using Shim-lock, GRUB can only be successfully booted in Secure Boot mode if its EFI binary includes all of the modules necessary to read the filesystem containing the
vmlinuz
and
initramfs
images.
Since GRUB version
2.06.r261.g2f4430cc0
, loading modules in Secure Boot Mode via
insmod
is no longer allowed, as this would violate the expectation to not sideload arbitrary code. If the GRUB modules are not embedded in the EFI binary, and GRUB tries to sideload/
insmod
them, GRUB will fail to boot with the message:
error: prohibited by secure boot policy
Ubuntu, according to
its official build script
, embeds the following GRUB modules in its signed GRUB EFI binary
grubx64.efi
:
the "basic" modules
, necessary for booting from a CD or from a simple-partitioned disk:
all_video
,
boot
,
btrfs
,
cat
,
chain
,
configfile
,
echo
,
efifwsetup
,
efinet
,
ext2
,
fat
,
font
,
gettext
,
gfxmenu
,
gfxterm
,
gfxterm_background
,
gzio
,
halt
,
help
,
hfsplus
,
iso9660
,
jpeg
,
keystatus
,
loadenv
,
loopback
,
linux
,
ls
,
lsefi
,
lsefimmap
,
lsefisystab
,
lssal
,
memdisk
,
minicmd
,
normal
,
ntfs
,
part_apple
,
part_msdos
,
part_gpt
,
password_pbkdf2
,
png
,
probe
,
reboot
,
regexp
,
search
,
search_fs_uuid
,
search_fs_file
,
search_label
,
sleep
,
smbios
,
squash4
,
test
,
true
,
video
,
xfs
,
zfs
,
zfscrypt
,
zfsinfo
the "platform-specific" modules
for x86_64-efi architecture, for example:
play
: to play sounds during boot
cpuid
: to the CPU at boot
tpm
: to support Measured Boot /
Trusted Platform Modules
the "advanced" modules
, consisting of modules:
cryptodisk
: to boot from
plain-mode encrypted
disks
gcry_
algorithm
: to support particular hashing and encryption algorithms
luks
: to boot from
LUKS
-encrypted disks:
lvm
: to boot from
LVM
logical volume disks
mdraid09
,
mdraid1x
,
raid5rec
,
raid6rec
: to boot from
RAID
virtual disks
You must construct your list of GRUB modules in the form of a shell variable that we denote as
GRUB_MODULES
. You can use the
latest Ubuntu script
as a starting point, and trim away modules that are not necessary on your system. Omitting modules will make the boot process relatively faster, and save some space on the ESP partition.
You also need a
Secure Boot Advanced Targeting (SBAT)
file/section included in the EFI binary, to improve the security; if GRUB is launched from the UEFI shim loader.  This SBAT file/section contains metadata about the GRUB binary (version, maintainer, developer, upstream URL) and makes it easier for shim to block certain GRUB versions from being loaded if they have security vulnerabilities
[1]
[2]
, as explained in the
UEFI shim boot loader secure boot life-cycle improvements
document from shim.
The first-stage UEFI
boot loader
shim will fail to launch
grubx64.efi
if the SBAT section from
grubx64.efi
is missing!
If GRUB is installed, a sample SBAT
.csv
file is provided under
/usr/share/grub/sbat.csv
.
Reinstall GRUB using the provided
/usr/share/grub/sbat.csv
file and all the needed
GRUB_MODULES
and sign it:
# grub-install --target=x86_64-efi --efi-directory=
esp
--modules="${GRUB_MODULES}" --sbat /usr/share/grub/sbat.csv
# sbsign --key MOK.key --cert MOK.crt --output
esp
/EFI/GRUB/grubx64.efi
esp
/EFI/GRUB/grubx64.efi
# cp
esp
/EFI/GRUB/grubx64.efi
esp
/EFI/BOOT/grubx64.efi
Reboot, select the key in
MokManager
, and Secure Boot should be working.
Using Secure Boot
After installation see
Secure Boot#Implementing Secure Boot
for instructions on enabling it.
If you are using the CA Keys method then key management, enrollment, and file signing can be automated by using
sbctl
, see
Secure Boot#Assisted process with sbctl
for details.
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.
Note
Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme. Read more on
Partitioning#GUID Partition Table
.
The BIOS boot partition is only needed by GRUB on a BIOS/GPT setup. On a BIOS/MBR setup, GRUB uses the post-MBR gap for the embedding the
core.img
. On GPT, however, there is no guaranteed unused space before the first partition.
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 GUID
21686148-6449-6E6F-744E-656564454649
.
fdisk
: Create a partition and use the
t
command to
change its partition type
to
BIOS boot
.
gdisk
: Create a partition with partition type
ef02
.
GNU Parted
: Create a partition and set the
bios_grub
flag on it.
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.
Tip
See
/Tips and tricks#Alternative installation methods
for other ways to install GRUB, such as to a USB stick.
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
re-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. For example, the new configuration might use a function unknown to the existing GRUB binary, causing unexpected behavior.
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/
. For the list of options in
/etc/default/grub
and a concise description of each refer to GNU's
documentation
.
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.
Note
The default file path is
/boot/grub/grub.cfg
, not
/boot/grub/i386-pc/grub.cfg
.
If you are trying to run
grub-mkconfig
in a
chroot
or
systemd-nspawn
container, you might notice that it does not work:
grub-probe: error: failed to get canonical path of
/dev/sdaX
. In this case, try using
arch-chroot
as described in the
BBS post
.
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.
Tip
After installing or removing a
kernel
, you just need to re-run the above
grub-mkconfig
command.
For tips on managing multiple GRUB entries, for example when using both
linux
and
linux-lts
kernels, see
/Tips and tricks#Multiple entries
.
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.
Note
The exact mount point does not matter,
os-prober
reads the
mtab
to identify places to search for bootable entries.
Remember to mount the partitions each time you run
grub-mkconfig
in order to include the other operating systems every time.
os-prober
might not work properly when run in a chroot. Try again after rebooting into the system if you experience this.
Tip
You might also want GRUB to remember the last chosen boot entry, see
/Tips and tricks#Recall previous entry
.
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.
Note
os-prober
might try to
grub-mount
a partition to probe whether the requisite
.efi
file exists. You need to install
fuse3
to make
grub-mount
work properly. Otherwise, you may fail to detect a Windows system.
NTFS partitions may not always be detected when mounted with the default Linux drivers. If GRUB is not detecting it, try installing
NTFS-3G
and remounting.
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.
Setting the top-level menu entry
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
This article or section is a candidate for merging with
#Installation
.
Notes:
grub-mkconfig is capable of detecting that it needs the
lvm
module, specifying it in
GRUB_PRELOAD_MODULES
is not required. Move warning to
#Installation
&
#Installation_2
or create a
Known issues section
and document it there. (Discuss in
Talk:GRUB
)
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
This article or section is a candidate for merging with
#Installation
.
Notes:
grub-mkconfig is capable of detecting that it needs the
mdraid09
and/or
mdraid1x
modules, specifying them in
GRUB_PRELOAD_MODULES
is not required. Summarize the double grub-install in a note and move it to
#Installation
; move
set root
stuff to
#Custom grub.cfg
. (Discuss in
Talk:GRUB
)
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 2.12rc1 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.
Warning
If you want to
generate the main configuration file
, make sure that
/boot
is mounted.
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
.
Note
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. See
/Tips and tricks#Manual configuration of core image for early boot
.
If you experience issues getting the prompt for a password to display (errors regarding cryptouuid, cryptodisk, or "device not found"), try reinstalling GRUB and appending
--modules="part_gpt part_msdos"
to the end of your
grub-install
command.
Tip
You can use
pacman hooks
to automount your
/boot
when upgrades need to access related files.
LUKS2
This article or section is out of date.
Reason:
Grub 2.14rc1 supports the Argon2i and Argon2id PBKDFs.
See upstream commit.
(Discuss in
Talk:GRUB#grub 2:2.14rc1 added support for LUKS2 + argon2 encryption.
)
Use
grub-install
as described in the
#Installation
section to create a bootable GRUB image with LUKS support. Note the following caveats:
Initial LUKS2 support was added to GRUB 2.06, but with several limitations that are only partially addressed in GRUB 2.12rc1. See
GRUB bug #55093
.
Since GRUB 2.12rc1,
grub-install
can create a core image to unlock LUKS2. However, it only supports PBKDF2, not Argon2.
Argon2id (
cryptsetup
default) and Argon2i PBKDFs are not supported (
GRUB bug #59409
), only PBKDF2 is.
Tip
You can use
grub-improved-luks2-git
AUR
that has been patched for LUKS2 as well as Argon2 support. Note the package's Argon2 support requires an UEFI system.
[3]
Note
Before GRUB 2.12rc1, you had to manually create an EFI binary using
grub-mkimage
with a custom GRUB config file. For example,
/boot/grub/grub-pre.cfg
, with calls to
cryptomount
,
insmod normal
, and
normal
. This is no longer needed,
grub-install
is sufficient. However, you may have to run
grub-mkconfig -o /boot/grub/grub.cfg
at least once after upgrading from 2.06.
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 $crypto_uuid
to mount a specific one. Then proceed with
insmod normal
and
normal
as usual.
If you enter a correct passphrase, but an
Invalid passphrase
error is immediately returned, make sure that the right cryptographic modules are specified. Use
cryptsetup luksDump
/dev/nvme0n1p2
and check whether the hash function (SHA-256, SHA-512) matches the modules (
gcry_sha256
,
gcry_sha512
) installed and the PBKDF algorithm is pbkdf2. The hash and PBDKDF algorithms can be changed for existing keys by using
cryptsetup luksConvertKey --hash
sha256
--pbkdf pbkdf2
/dev/nvme0n1p2
.  Under normal circumstances it should take a few seconds before the passphrase is processed.
Custom grub.cfg
This article or section needs expansion.
Reason:
Add instructions on how to write a custom
/boot/grub/grub.cfg
. See
User:Eschwartz/Grub
for a proposed draft. (Discuss in
Talk:GRUB#Manually generate grub.cfg
)
This section describes the manual creation of GRUB boot entries in
/boot/grub/grub.cfg
instead of relying on
grub-mkconfig
.
A basic GRUB config file uses the following options:
(hd
X
,
Y
)
is the partition
Y
on disk
X
, partition numbers starting at 1, disk numbers starting at 0
set default=
N
is the default boot entry that is chosen after timeout for user action
set timeout=
M
is the time
M
to wait in seconds for a user selection before default is booted
menuentry "title" {entry options}
is a boot entry titled
title
set root=(hd
X
,
Y
)
sets the boot partition, where the kernel and GRUB modules are stored (boot need not be a separate partition, and may simply be a directory under the "root" partition (
/
))
LoaderDevicePartUUID
For GRUB to set the
LoaderDevicePartUUID
UEFI variable required by
systemd-gpt-auto-generator(8)
for
GPT partition automounting
, load the
bli
module in
grub.cfg
:
if [ "$grub_platform" = "efi" ]; then
  insmod bli
fi
Boot menu entry examples
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
"Shutdown" menu entry
menuentry "System shutdown" {
	echo "System shutting down..."
	halt
}
"Restart" menu entry
menuentry "System restart" {
	echo "System rebooting..."
	reboot
}
"UEFI Firmware Settings" menu entry
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.
Tip
To show these menu entries only when GRUB is launched in UEFI mode, enclose them in the following
if
statement:
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/initramfs.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/initramfs.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
boot loader
from it.
Note
This menuentry will work only in UEFI boot mode and only if the Windows bitness matches the UEFI bitness. It will not work in BIOS installed GRUB. See
Dual boot with Windows#Windows UEFI vs BIOS limitations
and
Dual boot with Windows#Boot loader UEFI vs BIOS limitations
for more information.
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
$hints_string
command will determine the location of the EFI system partition, in this case harddrive 0:
# grub-probe --target=hints_string
esp
/EFI/Microsoft/Boot/bootmgfw.efi
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
These two commands assume the ESP Windows uses is mounted at
esp
. There might be case differences in the path to Windows's EFI file, what with being Windows, and all.
Windows installed in BIOS/MBR mode
Note
GRUB supports booting
bootmgr
directly and
chainloading
of partition boot sector is no longer required to boot Windows in a BIOS/MBR setup.
Warning
It is the
system partition
that has
/bootmgr
, not your "real" Windows partition (usually
C:
). The system partition's
filesystem label
is
System Reserved
or
SYSTEM
and the partition is only about 100 to 549 MiB in size. See
Wikipedia:System partition and boot partition
for more information.
Throughout this section, it is assumed your Windows partition is
/dev/sda1
. A different partition will change every instance of
hd0,msdos1
.
Note
These menu entries will work only in BIOS boot mode. It will not work in UEFI installed GRUB. See
Dual boot with Windows#Windows UEFI vs BIOS limitations
and
Dual boot with Windows#Boot loader UEFI vs BIOS limitations
.
In both examples
XXXX-XXXX
is the filesystem UUID which can be found with command
lsblk --fs
.
For Windows Vista/7/8/8.1/10:
if [ "${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
Note
In some cases, GRUB may be installed without a clean Windows 8, in which case you cannot boot Windows without having an error with
\boot\bcd
(error code
0xc000000f
). You can fix it by going to Windows Recovery Console (
cmd.exe
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.
Also you would better keep plugged in both the target hard drive and your bootable device
ONLY
. Windows usually fails to repair boot information if any other devices are connected.
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
boot loader
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
boot loader
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 /EFI/Microsoft/Boot/bootmgfw.efi
boot
insmod fat
is used for loading the FAT file system module for accessing the Windows
boot loader
on the UEFI system partition.
(hd0,gpt4)
or
/dev/sda4
is the UEFI 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=(hd
X
,
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=(hd
X
,
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 (hd
X
,
Y
)/vmlinuz-linux root=/dev/sda6
initrd (hd
X
,
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
UEFI systems
Before removing
grub
, make sure that some other boot loader is installed and configured to take over.
$ efibootmgr
BootOrder: 0003,0001,0000,0002
Boot0000* Windows Boot Manager  HD(2,GPT,4dabbedf-191b-4432-bc09-8bcbd1d7dabf,0x109000,0x32000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)
Boot0001* GRUB  HD(2,GPT,4dabbedf-191b-4432-bc09-8bcbd1d7dabf,0x109000,0x32000)/File(\EFI\GRUB\grubx64.efi)
Boot0002* Linux-Firmware-Updater        HD(2,GPT,5dabbedf-191b-4432-bc09-8bcbd1d7dabf,0x109000,0x32000)/File(\EFI\arch\fwupdx64.efi)
Boot0003* Linux Boot Manager    HD(2,GPT,4dabbedf-191b-4432-bc09-8bcbd1d7dabf,0x109000,0x32000)/File(\EFI\systemd\systemd-bootx64.efi)
If
BootOrder
has
grub
as the first entry, install another
boot loader
to put it in front, such as
systemd-boot
above.
grub
can then be removed using its
bootnum
.
# efibootmgr --delete-bootnum -b 1
Also delete the
esp
/EFI/grub
and
/boot/grub
directories.
BIOS systems
To replace
grub
with any other BIOS boot loader, simply install them, which will overwrite the
MBR boot code
.
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 UEFI/GPT one may want to
remove the MBR boot code using dd
.
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
An error that may occur on some UEFI devices is
Could not prepare Boot variable: Read-only file system
. You have to remount
/sys/firmware/efi/efivars
with read-write enabled.
# mount -o remount,rw,nosuid,nodev,noexec --types efivarfs efivarfs /sys/firmware/efi/efivars
See the
Gentoo Wiki
on installing the
boot loader
.
If you have a problem running
grub-install
with
sysfs
or
procfs
and it says you must run
modprobe efivarfs
try
mounting the efivarfs
with the command above.
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 get
error:
esp
doesn't look like an EFI partition
, then the partition is most likely not
FAT32
formatted.
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
Installation guide#Verify the boot mode
.
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
\EFI\arch\grub.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 -u
BootCurrent: 0000
Timeout: 3 seconds
BootOrder: 0000,0001,0002
Boot0000* GRUB HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\EFI\GRUB\grubx64.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 (e.g. MSI motherboards) 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
[4]
. 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
[5]
. 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.
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.
GRUB is installed but the menu is not shown at boot
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.
If it does not work, there may be incompatibility problems with the graphical terminal. Set
GRUB_TERMINAL_OUTPUT
to
console
in
/etc/default/grub
to disable the GRUB graphical terminal.
GRUB is installed, but receive "ERROR CODE 1962 - No operating system found" message on older Lenovo machines
See
Fixing Lenovo’s ERROR CODE 1962 by spoofing the EFI boot entries
.
See also
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