GRUB: Difference between revisions
(→Configuration: move multiple kernel management from #Boot menu entries to #Generate the main configuration file) |
(→Generate the main configuration file: add tip about re-running grub-mkconfig when installing/removing a kernel, see Talk:GRUB#Adding an additional entry to GRUB for a Custom Kernel) |
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# grub-mkconfig -o /boot/grub/grub.cfg | # grub-mkconfig -o /boot/grub/grub.cfg | ||
By default the generation scripts automatically add menu entries for Arch Linux and all installed [[kernel]]s to the generated configuration. For tips on managing multiple GRUB entries, for example when using both {{Pkg|linux}} and {{Pkg|linux-lts}} kernels, see [[GRUB/Tips and tricks#Multiple entries]]. | By default the generation scripts automatically add menu entries for Arch Linux and all installed [[kernel]]s 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 {{Pkg|linux}} and {{Pkg|linux-lts}} kernels, see [[GRUB/Tips and tricks#Multiple entries]]. | |||
}} | |||
To automatically add entries for other installed operating systems, see [[#Detecting other operating systems]]. | To automatically add entries for other installed operating systems, see [[#Detecting other operating systems]]. |
Revision as of 14:49, 29 November 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.
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 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
.
- 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 bootloader 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-legacyAUR, where already installed. Then do:
# grub-install --target=i386-pc /dev/sdX
where /dev/sdX
is the 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 Unified Extensible Firmware Interface, Partitioning#GUID Partition Table and Arch boot process#Under UEFI 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.
Installation
- 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 turnarounds found, for their hardware-specific case. A GRUB/EFI examples article has been provided for such cases.
- The section assumes you are installing GRUB for x86_64 systems. For IA32 (32-bit) EFI systems (not to be confused with 32-bit CPUs), replace
x86_64-efi
withi386-efi
where appropriate.
First, install the packages grub and efibootmgr: GRUB is the bootloader while efibootmgr is used by the GRUB installation script to write boot entries to NVRAM.
Then follow the below steps to install GRUB:
- Mount the EFI system partition and in the remainder of this section, substitute
esp
with its mount point. - Choose a bootloader identifier, here named
GRUB
. A directory of that name will be created inesp/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
toesp/EFI/GRUB/
and install its modules to/boot/grub/x86_64-efi/
.
# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=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 GRUB
in the above example.
Remember to #Generate the main configuration file after finalizing the configuration.
--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.--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 bootcode or partition boot sector at all.
See UEFI troubleshooting in case of problems. Additionally see GRUB/Tips and tricks#UEFI further reading.
Configuration
On an installed system, GRUB loads the /boot/grub/grub.cfg
configuration file each boot. You can use a #Generated grub.cfg or create a #Custom grub.cfg manually.
Generated grub.cfg
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
and/or files in /etc/grub.d/
.
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.
- Remember that
/boot/grub/grub.cfg
has to be re-generated after any change to/etc/default/grub
or files in/etc/grub.d/
. - 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, 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.
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 Arch Linux and all installed kernels to the generated configuration.
- 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 GRUB/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/40_custom
adds the necessary source
statement to the generated configuration file.
/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 entries 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 that contain the other systems. Then re-run grub-mkconfig.
MS Windows
Partitions containing Windows should be automatically discovered by os-prober. However, if the partition is encrypted, you may need to decrypt the partition before mounting. For BitLocker, this can be done with dislockerAUR. This should be sufficient for os-prober to add the correct entry.
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.
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 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
.
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.
/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
This option is used by grub-install to generate the grub core.img
, so make sure to install grub after modifying this option.
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 implemented by the initramfs. You can use a keyfile to avoid this.
- 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.
- 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.
- 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 yourgrub-install
command.
/boot
when upgrades need to access related files.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 0set default=N
is the default boot entry that is chosen after timeout for user actionset timeout=M
is the time M to wait in seconds for a user selection before default is bootedmenuentry "title" {entry options}
is a boot entry titledtitle
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 (/
)
/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 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 "Firmware setup" { fwsetup } fi
EFI binaries
When launched in UEFI mode, GRUB can chainload other EFI binaries.
if
statement:
if [ ${grub_platform} == "efi" ]; then place UEFI-only menu entries here fi
UEFI Shell
You can launch UEFI Shell by using placing it in the root of the EFI system partition and adding this menu entry:
menuentry "UEFI Shell" { insmod chain search --set=root --file /shellx64.efi chainloader /shellx64.efi }
gdisk
Download the gdisk EFI application and copy gdisk_x64.efi
to esp/EFI/tools/
.
menuentry "gdisk" { insmod chain search --set=root --file /EFI/tools/gdisk_x64.efi chainloader /EFI/tools/gdisk_x64.efi }
Chainloading an Arch Linux .efi file
If you have an .efi file generated from following Secure Boot or other means, you can add it to the boot menu. For example:
menuentry "Arch Linux .efi" { insmod chain search --set=root --fs-uuid FILESYSTEM_UUID chainloader /EFI/arch/vmlinuz.efi }
Dual-booting
GNU/Linux
Assuming that the other distribution is on partition sda2
:
menuentry "Other Linux" { set root=(hd0,2) linux /boot/vmlinuz (add other options here as required) initrd /boot/initrd.img (if the other kernel uses/needs one) }
Alternatively let GRUB search for the right partition by UUID or label:
menuentry "Other Linux" { # assuming that UUID is 763A-9CB6 search --set=root --fs-uuid 763A-9CB6 # search by label OTHER_LINUX (make sure that partition label is unambiguous) #search --set=root --label OTHER_LINUX linux /boot/vmlinuz (add other options here as required, for example: root=UUID=763A-9CB6) initrd /boot/initrd.img (if the other kernel uses/needs one) }
Windows installed in UEFI/GPT mode
This mode determines where the Windows bootloader resides and chain-loads it after GRUB when the menu entry is selected. The main task here is finding the EFI system partition and running the bootloader from it.
if [ "${grub_platform}" == "efi" ]; then menuentry "Microsoft Windows Vista/7/8/8.1 UEFI/GPT" { insmod part_gpt insmod fat insmod 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 system 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 system partition from there.
The $hints_string
command will determine the location of the EFI system partition, in this case harddrive 0:
# grub-probe --target=hints_string esp/EFI/Microsoft/Boot/bootmgfw.efi
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
These two commands assume the ESP Windows uses is mounted at esp
. There might be case differences in the path to Windows's EFI file, what with being Windows, and all.
Windows installed in BIOS/MBR mode
bootmgr
directly and chainloading of partition boot sector is no longer required to boot Windows in a BIOS/MBR setup./bootmgr
, not your "real" Windows partition (usually C:
). In blkid
output, the system partition is the one with LABEL="SYSTEM RESERVED"
or LABEL="SYSTEM"
and is only about 100 to 200 MiB in size (much like the boot partition for Arch). See Wikipedia:System partition and boot partition for more info.Throughout this section, it is assumed your Windows partition is /dev/sda1
. A different partition will change every instance of hd0,msdos1
.
In both examples XXXXXXXXXXXXXXXX
is the filesystem UUID which can be found with command lsblk --fs
.
For Windows Vista/7/8/8.1/10:
if [ "${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 XXXXXXXXXXXXXXXX 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 XXXXXXXXXXXXXXXX ntldr /ntldr } fi
\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 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 binary 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
is 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 UEFI), 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.
If GRUB is used with an unsupported filesystem 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.
Intel BIOS not booting GPT
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
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 UEFI:
# 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\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 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 [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.
VirtualBox EFI mode
Install GRUB to the default/fallback boot path.
See also VirtualBox#Installation in EFI mode.