GRUB
zh-CN:GRUB2 zh-TW:GRUB2 Template:Article summary start Template:Article summary text Template:Article summary heading Template:Article summary text Template:Article summary heading Template:Article summary wiki - BURG is a brand-new boot loader based on GRUB2. It can be built on a wider range of OS, and has a highly configurable menu system which works in both text and graphic mode. Template:Article summary wiki - previous Version, now obsolete. Template:Article summary heading Template:Article summary wiki Template:Article summary link Template:Article summary end GRUB - not to be confused with GRUB Legacy - is the next generation of the GRand Unified Bootloader. GRUB is derived from PUPA which was a research project to develop the next generation of what is now GRUB Legacy. GRUB has been rewritten from scratch to clean up everything and provide modularity and portability [1].
In brief, the bootloader is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the Linux kernel. The kernel, in turn, initializes the rest of the operating system.
Contents
- 1 Preface
- 2 Installation
- 3 Configuration
- 4 Using the command shell
- 5 GUI configuration tools
- 6 parttool for hide/unhide
- 7 Using the rescue console
- 8 Combining the use of UUIDs and basic scripting
- 9 Troubleshooting
- 10 References
- 11 External Links
Preface
- The name GRUB officially refers to version 2 of the software, see [2]. If you are looking for the article on the legacy version, see GRUB Legacy.
- GRUB supports Btrfs as root (without a separate
/boot
filesystem) compressed with either zlib or LZO.
Notes for current GRUB Legacy users
- Upgrade from GRUB Legacy to GRUB is the much same as fresh installing GRUB which is covered below.
- There are differences in the commands of GRUB Legacy and GRUB. Familiarize yourself with GRUB commands before proceeding (e.g. "find" has been replaced with "search").
- GRUB is now modular and no longer requires "stage 1.5". As a result, the bootloader itself is limited -- modules are loaded from the hard drive as needed to expand functionality (e.g. for LVM or RAID support).
- Device naming has changed between GRUB Legacy and GRUB. Partitions are numbered from 1 instead of 0 while drives are still numbered from 0, and prefixed with partition-table type. For example,
/dev/sda1
would be referred to as(hd0,msdos1)
(for MBR) or(hd0,gpt1)
(for GPT).
Backup Important Data
Although a GRUB installation should run smoothly, it is strongly recommended to keep the GRUB Legacy files before upgrading to GRUB2.
# mv /boot/grub /boot/grub-legacy
Backup the MBR which contains the boot code and partition table (Replace /dev/sdX
with your actual disk path)
# dd if=/dev/sdX of=/path/to/backup/mbr_backup bs=512 count=1
Only 446 bytes of the MBR contain boot code, the next 64 contain the partition table. If you do not want to overwrite your partition table when restoring, it is strongly advised to backup only the MBR boot code:
# dd if=/dev/sdX of=/path/to/backup/bootcode_backup bs=446 count=1
If unable to install GRUB2 correctly, see #Restore GRUB Legacy.
Preliminary Requirements
BIOS systems
GUID Partition Table (GPT) specific instructions
GRUB in BIOS-GPT configuration requires a BIOS Boot Partition to embed its core.img
in the absence of post-MBR gap in GPT partitioned systems (which is taken over by the GPT Primary Header and Primary Partition table). This partition is used by GRUB only in BIOS-GPT setups. No such partition type exists in case of MBR partitioning (at least not for GRUB). This partition is also not required if the system is UEFI based, as no embedding of bootsectors takes place in that case.
For a BIOS-GPT configuration, create a 1007 KiB partition at the beginning of the disk using cgdisk or GNU Parted with no filesystem. The size of 1007 KiB will allow for the following partition to be correctly alligned at 1024 KiB. If needed, the partition can also be located somewhere else on the disk, but it should be within the first 2 TiB region. Set the partition type to 0xEF02
in gdisk, EF02
in cgdisk or set <BOOT_PART_NUM> bios_grub on
in GNU Parted.
grub-install
or grub-setup
is run.Master Boot Record (MBR) specific instructions
Usually the post-MBR gap (after the 512 byte MBR region and before the start of the 1st 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 partitioner which supports 1 MiB partition alignment to obtain this space as well as satisfy other non-512 byte sector issues (which are unrelated to embedding of core.img
).
MBR partitioning has better support than GPT partitioning in some operating systems, such as older versions of Microsoft Windows (up to Windows 7) and Haiku. If you dual boot such an operating system, consider using MBR partitioning.
A MBR disk may be convertible to GPT if there is a small amount of extra space available. See GUID Partition Table#Convert from MBR to GPT.
UEFI systems
Create and Mount the UEFI System Partition
Follow Unified Extensible Firmware Interface#EFI System Partition for instructions on creating a UEFI System Partition. Then mount the UEFI System Partition at /boot/efi
. If you have mounted the UEFI System Partition at some other mountpoint, replace /boot/efi
in the below instructions with that mountpoint:
# mkdir -p /boot/efi # mount -t vfat <UEFI_SYSTEM_PARTITION> /boot/efi
Create a /boot/efi/EFI
directory:
# mkdir /boot/efi/EFI
Installation
BIOS systems
GRUB can be installed with the grub-bios package from the official repositories. It will replace grub-legacy or grub, if it is installed.
/boot/grub/i386-pc/core.img
file and the GRUB modules in /boot/grub/i386-pc
. You need to update them manually using grub-install
as explained below.Install boot files
There are 3 ways to install GRUB boot files in BIOS booting:
- #Install to GPT BIOS Boot Partition (recommended with GPT)
- #Install to 440-byte MBR boot code region (recommended with MBR)
- #Install to Partition or Partitionless Disk (not recommended)
- #Generate core.img alone (safest method, but requires another BIOS bootloader like GRUB Legacy or Syslinux to be installed to chainload
/boot/grub/i386-pc/core.img
)
Install to GPT BIOS Boot Partition
GUID Partition Table disks do not have a reserved "boot track". Therefore you must create a BIOS Boot Partition (0xEF02
) to hold the GRUB core image.
Using GNU Parted, you can set this using a command such as the following:
# parted /dev/disk set <partition-number> bios_grub on
If you are using gdisk, set the partition type to 0xEF02
. With partitioning programs that require setting the GUID directly, it should be ‘21686148-6449-6e6f-744e656564454649’
(stored on disk as "!haHdInotNeedEFI"
if interpreted as ASCII).
To setup grub-bios
on a GPT disk, populate the /boot/grub
directory, generate the /boot/grub/i386-pc/core.img
file, and embed it in the BIOS Boot Partition, run:
# modprobe dm-mod # grub-install --target=i386-pc --recheck --debug /dev/sda # mkdir -p /boot/grub/locale # cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
where /dev/sda
is the destination of the installation.
Install to 440-byte MBR boot code region
To setup grub-bios
in the 440-byte Master Boot Record boot code region, populate the /boot/grub
directory, generate the /boot/grub/i386-pc/core.img
file, embed it in the 31 KiB (minimum size - varies depending on partition alignment) post-MBR gap, and generate the configuration file, run:
# modprobe dm-mod # grub-install --recheck /dev/sda # grub-mkconfig -o /boot/grub/grub.cfg
where /dev/sda
is the destination of the installation (in this case the MBR of the first SATA disk). If you use LVM for your /boot
, you can install GRUB on multiple physical disks.
/boot
directory if you use the latter. Sometimes the boot-directory
parameter creates another /boot
folder inside of /boot
. A wrong install would look like: /boot/boot/grub/
.Install to Partition or Partitionless Disk
To set up grub-bios to a partition boot sector, to a partitionless disk (also called superfloppy) or to a floppy disk, run (using for example /dev/sdaX
as the /boot
partition):
# modprobe dm-mod # grub-install --target=i386-pc --recheck --debug --force /dev/sdaX # chattr -i /boot/grub/i386-pc/core.img # mkdir -p /boot/grub/locale # cp /usr/share/locale/en@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo # chattr +i /boot/grub/i386-pc/core.img
You need to use the --force
option to allow usage of blocklists and should not use --grub-setup=/bin/true
(which is similar to simply generating core.img
).
grub-install
will give out warnings like which should give you the idea of what might go wrong with this approach:
/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea. /sbin/grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists. However, blocklists are UNRELIABLE and their use is discouraged.
Without --force
you may get the below error and grub-setup
will not setup its boot code in the partition boot sector:
/sbin/grub-setup: error: will not proceed with blocklists
With --force
you should get:
Installation finished. No error reported.
The reason why grub-setup
does not by default allow this is because in case of partition or a partitionless disk is that grub-bios
relies on embedded blocklists in the partition bootsector to locate the /boot/grub/i386-pc/core.img
file and the prefix dir /boot/grub
. The sector locations of core.img
may change whenever the filesystem in the partition is being altered (files copied, deleted etc.). For more info see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915.
The workaround for this is to set the immutable flag on /boot/grub/i386-pc/core.img
(using chattr command as mentioned above) so that the sector locations of the core.img
file in the disk is not altered. The immutable flag on /boot/grub/i386-pc/core.img
needs to be set only if grub-bios
is installed to a partition boot sector or a partitionless disk, not in case of installation to MBR or simple generation of core.img
without embedding any bootsector (mentioned above).
Generate core.img alone
To populate the /boot/grub
directory and generate a /boot/grub/i386-pc/core.img
file without embedding any grub-bios
bootsector code in the MBR, post-MBR region, or the partition bootsector, add --grub-setup=/bin/true
to grub-install
:
# modprobe dm-mod # grub-install --target=i386-pc --grub-setup=/bin/true --recheck --debug /dev/sda # mkdir -p /boot/grub/locale # cp /usr/share/locale/en@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
You can then chainload GRUB's core.img
from GRUB Legacy or syslinux as a Linux kernel or a multiboot kernel.
Generate config file
Finally, generate a configuration for GRUB (this is explained in greater detail in the Configuration section):
# grub-mkconfig -o /boot/grub/grub.cfg
/boot/grub/grub.cfg
, NOT /boot/grub/i386-pc/grub.cfg
.If GRUB complains about "no suitable mode found" while booting, go to #Correct No Suitable Mode Found Error.
If grub-mkconfig
fails, convert your /boot/grub/menu.lst
file to /boot/grub/grub.cfg
using:
# grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
For example:
/boot/grub/menu.lst
default=0 timeout=5 title Arch Linux Stock Kernel root (hd0,0) kernel /vmlinuz-linux root=/dev/sda2 ro initrd /initramfs-linux.img title Arch Linux Stock Kernel Fallback root (hd0,0) kernel /vmlinuz-linux root=/dev/sda2 ro initrd /initramfs-linux-fallback.img
/boot/grub/grub.cfg
set default='0'; if [ x"$default" = xsaved ]; then load_env; set default="$saved_entry"; fi set timeout=5 menuentry 'Arch Linux Stock Kernel' { set root='(hd0,1)'; set legacy_hdbias='0' legacy_kernel '/vmlinuz-linux' '/vmlinuz-linux' 'root=/dev/sda2' 'ro' legacy_initrd '/initramfs-linux.img' '/initramfs-linux.img' } menuentry 'Arch Linux Stock Kernel Fallback' { set root='(hd0,1)'; set legacy_hdbias='0' legacy_kernel '/vmlinuz-linux' '/vmlinuz-linux' 'root=/dev/sda2' 'ro' legacy_initrd '/initramfs-linux-fallback.img' '/initramfs-linux-fallback.img' }
If you forgot to create a GRUB /boot/grub/grub.cfg
config file and simply rebooted into GRUB Command Shell, type:
sh:grub> insmod legacycfg sh:grub> legacy_configfile ${prefix}/menu.lst
Boot into Arch and re-create the proper GRUB /boot/grub/grub.cfg
config file.
Multiboot
Microsoft Windows installed in BIOS-MBR mode
bootmgr
directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.bootmgr
, not your "real" Windows partition (usually C:). When showing all UUIDs with blkid, the system partition is the one with LABEL="SYSTEM RESERVED"
and is only about 100 MB in size (much like the boot partition for Arch). See Wikipedia:System partition and boot partition for more info.Find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the bootmgr
and its files reside. For example, if Windows bootmgr
exists at /media/SYSTEM_RESERVED/bootmgr
:
For Windows Vista/7/8:
# grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr 69B235F6749E84CE
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1
bootmgr
with ntldr
in the above commands.Then, 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 or 8) installed in BIOS-MBR mode:
For Windows Vista/7/8:
menuentry "Microsoft Windows Vista/7/8 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 }
For Windows XP:
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 }
/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.UEFI systems
First detect which UEFI firmware arch you have (either x86_64 or i386). Depending on the result, install the appropriate package:
- For 64-bit aka x86_64 UEFI firmware, install grub-efi-x86_64
- For 32-bit aka i386 UEFI firmware, install grub-efi-i386
core.efi
file and the GRUB modules in the UEFI System Partition. You need to do this manually using grub-install
as explained below.Install boot files
Install to UEFI System Partition
grub-efi-x86_64
(for grub-efi-i386
replace x86_64
with i386
in the below commands).The UEFI system partition will need to be mounted at /boot/efi/
for the GRUB install script to detect it:
# mkdir -p /boot/efi # mount -t vfat /dev/sdXY /boot/efi
Install GRUB UEFI application to /boot/efi/EFI/arch_grub
and its modules to /boot/grub/x86_64-efi
(recommended) using:
# modprobe dm-mod # grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=arch_grub --recheck --debug # mkdir -p /boot/grub/locale # cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
--target
or --directory
option, grub-install cannot determine for which firmware GRUB is being installed. In such cases grub-install
will show source_dir doesn't exist. Please specify --target or --directory
message.If you want to install GRUB modules and grub.cfg
at the directory /boot/efi/EFI/grub
and the grubx64.efi
application at /boot/efi/EFI/arch_grub
(ie. all the GRUB UEFI files inside the UEFISYS partition itself) use:
# modprobe dm-mod # grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=arch_grub --boot-directory=/boot/efi/EFI --recheck --debug # mkdir -p /boot/efi/EFI/grub/locale # cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/efi/EFI/grub/locale/en.mo
The --efi-directory
option mentions the mountpoint of UEFI SYSTEM PARTITION , --bootloader-id
mentions the name of the directory used to store the grubx64.efi
file and --boot-directory
mentions the directory wherein the actual modules will be installed (and into which grub.cfg
should be created).
The actual paths are:
<efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi
<boot-directory>/grub/x86_64-efi/<all modules, grub.efi, core.efi, grub.cfg>
--bootloader-id
option does not change <boot-directory>/grub
, i.e. you cannot install the modules to <boot-directory>/<bootloader-id>
, the path is hard-coded to be <boot-directory>/grub
.In --efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=grub
:
<efi-directory>/<EFI or efi>/<bootloader-id> == <boot-directory>/grub == /boot/efi/EFI/grub
In --efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=arch_grub
:
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub <boot-directory>/grub == /boot/efi/EFI/grub
In --efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub
:
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub <boot-directory>/grub == /boot/grub
In --efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=grub
:
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/grub <boot-directory>/grub == /boot/grub
The <efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi
is an exact copy of <boot-directory>/grub/x86_64-efi/core.efi
.
grub-install
option --efi-directory
replaces --root-directory
and the latter is deprecated.--efi-directory
and --bootloader-id
are specific to GRUB UEFI.In all the cases the UEFI SYSTEM PARTITION should be mounted for grub-install
to install grubx64.efi
in it, which will be launched by the firmware (using the efibootmgr
created boot entry in non-Mac systems).
If you notice carefully, there is no <device_path> option (Eg: /dev/sda
) at the end of the grub-install
command unlike the case of setting up GRUB for BIOS systems. Any <device_path> provided will be ignored by the install script as UEFI bootloaders do not use MBR or Partition boot sectors at all.
You may now be able to UEFI boot your system by creating a grub.cfg
file by following #Generate UEFI Config file and #Create GRUB entry in the Firmware Boot Manager.
Generate config file
Finally, generate a configuration for GRUB (this is explained in greater detail in the Configuration section):
# grub-mkconfig -o <boot-directory>/grub/grub.cfg
<boot-directory>/grub/grub.cfg
, NOT <boot-directory>/grub/x86_64-efi/grub.cfg
.If you used --boot-directory=/boot
:
# grub-mkconfig -o /boot/grub/grub.cfg
If you used --boot-directory=/boot/efi/EFI
:
# grub-mkconfig -o /boot/efi/EFI/grub/grub.cfg
This is independent of the value of --bootloader-id
option.
If GRUB complains about "no suitable mode found" while booting, try #Correct No Suitable Mode Found Error.
Create GRUB entry in the Firmware Boot Manager
grub-install
automatically tries to create a menu entry in the boot manager. If it doesn't, then see Beginners' Guide#GRUB for instructions to use efibootmgr
to create a menu entry. However, the problem is likely to be that you haven't booted your CD/USB in UEFI mode, as in Unified Extensible Firmware Interface#Create UEFI bootable USB from ISO.
Create GRUB Standalone UEFI Application
It is possible to create a grubx64_standalone.efi
application which has all the modules embeddded in a memdisk within the UEFI application, thus removing the need for having a separate directory populated with all the GRUB UEFI modules and other related files. This is done using the grub-mkstandalone
command which is included in grub-common.
The easiest way to do this would be with the install command already mentioned before, but specifying the modules to include. For example:
# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \ --output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" <any extra files you want to include>
The grubx64_standalone.efi
file expects grub.cfg
to be within its $prefix which is (memdisk)/boot/grub
. The memdisk is embedded within the efi app. The grub-mkstandlone
script allow passing files to be included in the memdisk image to be as the arguments to the script (in <any extra files you want to include>).
If you have the grub.cfg
at /home/user/Desktop/grub.cfg
, then create a temporary /home/user/Desktop/boot/grub/
directory, copy the /home/user/Desktop/grub.cfg
to /home/user/Desktop/boot/grub/grub.cfg
, cd into /home/user/Desktop/boot/grub/
and run:
# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \ --output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" "boot/grub/grub.cfg"
The reason to cd into /home/user/Desktop/boot/grub/
and to pass the file path as boot/grub/grub.cfg
(notice the lack of a leading slash - boot/ vs /boot/ ) is because dir1/dir2/file
is included as (memdisk)/dir1/dir2/file
by the grub-mkstandalone
script.
If you pass /home/user/Desktop/grub.cfg
the file will be included as (memdisk)/home/user/Desktop/grub.cfg
. If you pass /home/user/Desktop/boot/grub/grub.cfg
the file will be included as (memdisk)/home/user/Desktop/boot/grub/grub.cfg
. That is the reason for cd'ing into /home/user/Desktop/boot/grub/
and passing boot/grub/grub.cfg
, to include the file as (memdisk)/boot/grub/grub.cfg
, which is what grub.efi
expects the file to be.
You need to create an UEFI Boot Manager entry for /boot/efi/EFI/arch_grub/grubx64_standalone.efi
using efibootmgr
. Follow #Create GRUB entry in the Firmware Boot Manager.
Multiboot
Microsoft Windows installed in UEFI-GPT mode
Find the UUID of the FAT32 filesystem in the UEFI SYSTEM PARTITION where the Windows UEFI Bootloader files reside. For example, if Windows bootmgfw.efi
exists at /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi
(ignore the upper-lower case differences since that is immaterial in FAT filesystem):
# grub-probe --target=fs_uuid /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi 1ce5-7f28
# grub-probe --target=hints_string /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
Then, add this code to /etc/grub.d/40_custom
to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode:
menuentry "Microsoft Windows Vista/7/8 x86_64 UEFI-GPT" { insmod part_gpt insmod fat insmod search_fs_uuid insmod chain search --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 1ce5-7f28 chainloader /efi/Microsoft/Boot/bootmgfw.efi }
Afterwards remake /boot/grub/grub.cfg
# grub-mkconfig -o /boot/grub/grub.cfg
Configuration
You can also choose to automatically generate or manually edit grub.cfg
.
--boot-directory
option set, the grub.cfg
file must be placed in the same directory as grubx64.efi
. Otherwise, the grub.cfg
file goes in /boot/grub/
, just like in GRUB BIOS.Automatically generating using grub-mkconfig
The GRUB menu.lst
equivalent configuration files are /etc/default/grub
and /etc/grub.d/*
. grub-mkconfig
uses these files to generate grub.cfg
. By default the script outputs to stdout. To generate a grub.cfg
file run the command:
# grub-mkconfig -o /boot/grub/grub.cfg
/etc/grub.d/10_linux
is set to automatically add menu items for Arch linux that work out of the box, to any generated configuration. Other operating systems may need to be added manually to /etc/grub.d/40_custom
or /boot/grub/custom.cfg
Additional arguments
To pass custom additional arguments to the Linux image, you can set the GRUB_CMDLINE_LINUX
variable in /etc/default/grub
.
For example, use GRUB_CMDLINE_LINUX="resume=/dev/sdaX"
where sdaX
is your swap partition to enable resume after hibernation.
You can also use GRUB_CMDLINE_LINUX="resume=/dev/disk/by-uuid/${swap_uuid}"
, where ${swap_uuid}
is the UUID of your swap partition.
Multiple entries are separated by spaces within the double quotes. So, for users who want both resume and systemd it would look like this:
GRUB_CMDLINE_LINUX="resume=/dev/sdaX init=/usr/lib/systemd/systemd"
See Kernel parameters for more info.
Manually creating grub.cfg
grub-mkconfig
command, and it is best to edit your /etc/default/grub
or one of the scripts in the /etc/grub.d
folder.A basic GRUB config file uses the following options
-
(hdX,Y)
is the partitionY
on diskX
, 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 timeM
to wait in seconds for a user selection before default is booted -
menuentry "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 (/
)
An example configuration:
/boot/grub/grub.cfg
# Config file for GRUB - The GNU GRand Unified Bootloader # /boot/grub/grub.cfg # DEVICE NAME CONVERSIONS # # Linux Grub # ------------------------- # /dev/fd0 (fd0) # /dev/sda (hd0) # /dev/sdb2 (hd1,2) # /dev/sda3 (hd0,3) # # Timeout for menu set timeout=5 # Set default boot entry as Entry 0 set default=0 # (0) Arch Linux menuentry "Arch Linux" { set root=(hd0,1) linux /vmlinuz-linux root=/dev/sda3 ro initrd /initramfs-linux.img } ## (1) Windows #menuentry "Windows" { # set root=(hd0,3) # chainloader +1 #}
Dual-booting
Using grub-mkconfig
The best way to add other entries is editing the /etc/grub.d/40_custom
or /boot/grub/custom.cfg
. The entries in this file will be automatically added when running grub-mkconfig
.
After adding the new lines, run:
# grub-mkconfig -o /boot/grub/grub.cfg
to generate an updated grub.cfg
.
With GNU/Linux
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) }
With FreeBSD
Requires that FreeBSD is installed on a single partition with UFS. Assuming it is installed on sda4
:
menuentry "FreeBSD" { set root=(hd0,4) chainloader +1 }
With Windows
This assumes that your Windows partition is sda3
. Remember you need to point set root and chainloader to the system reserve partition that windows made when it installed, not the actual partition windows is on. This example works if your system reserve partition is sda3
.
# (2) Windows XP menuentry "Windows XP" { set root=(hd0,3) chainloader (hd0,3)+1 }
If the Windows bootloader is on an entirely different hard drive than GRUB, it may be necessary to trick Windows into believing that it is the first hard drive. This was possible with drivemap
. Assuming GRUB is on hd0
and Windows is on hd2
, you need to add the following after set root
:
drivemap -s hd0 hd2
With Windows via EasyBCD and NeoGRUB
Since EasyBCD's NeoGRUB currently does not understand the GRUB menu format, chainload to it by replacing the contents of your C:\NST\menu.lst
file with lines similar to the following:
default 0 timeout 1
title Chainload into GRUB v2 root (hd0,7) kernel /boot/grub/i386-pc/core.img
Visual Configuration
In GRUB it is possible, by default, to change the look of the menu. Make sure to initialize, if not done already, GRUB graphical terminal, gfxterm, with proper video mode, gfxmode, in GRUB. This can be seen in the section #Correct No Suitable Mode Found Error. This video mode is passed by GRUB to the linux kernel via 'gfxpayload' so any visual configurations need this mode in order to be in effect.
Setting the framebuffer resolution
GRUB can set the framebuffer for both GRUB itself and the kernel. The old vga=
way is deprecated. The preferred method is editing /etc/default/grub
as the following sample:
GRUB_GFXMODE=1024x768x32 GRUB_GFXPAYLOAD_LINUX=keep
To generate the changes, run:
# grub-mkconfig -o /boot/grub/grub.cfg
The gfxpayload
property will make sure the kernel keeps the resolution.
gfxmode="1024x768x32"
by vbemode="0x105"
. Remember to replace the specified resolution with one suitable for your screen.# hwinfo --framebuffer
(hwinfo is available in [community]), while at GRUB prompt you can use the vbeinfo
command.If this method does not work for you, the deprecated vga=
method will still work. Just
add it next to the "GRUB_CMDLINE_LINUX_DEFAULT="
line in /etc/default/grub
for eg: "GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"
will give you a 1024x768
resolution.
You can choose one of these resolutions: 640×480
, 800×600
, 1024×768
, 1280×1024
, 1600×1200
, 1920×1200
915resolution hack
Some times for Intel graphic adapters neither # hwinfo --framebuffer
nor vbeinfo
will show you the desired resolution. In this case you can use 915resolution
hack. This hack will temporarily modify video BIOS and add needed resolution. See 915resolution's home page
First you need to find a video mode which will be modified later. For that we need the GRUB command shell:
sh:grub> 915resolution -l
Intel 800/900 Series VBIOS Hack : version 0.5.3 [...] Mode 30 : 640x480, 8 bits/pixel [...]
Next, we overwrite the Mode 30
with 1440x900
resolution:
/etc/grub.d/00_header
[...] 915resolution 30 1440 900 # Inserted line set gfxmode=${GRUB_GFXMODE} [...]
Lastly we need to set GRUB_GFXMODE
as described earlier, regenerate GRUB configuration file and reboot to test changes:
# grub-mkconfig -o /boot/grub/grub.cfg # reboot
Background image and bitmap fonts
GRUB comes with support for background images and bitmap fonts in pf2
format. The unifont font is included in the grub-common package under the filename unicode.pf2
, or, as only ASCII characters under the name ascii.pf2
.
Image formats supported include tga, png and jpeg, providing the correct modules are loaded. The maximum supported resolution depends on your hardware.
Make sure you have set up the proper framebuffer resolution.
Edit /etc/default/grub
like this:
GRUB_BACKGROUND="/boot/grub/myimage" #GRUB_THEME="/path/to/gfxtheme" GRUB_FONT="/path/to/font.pf2"
/boot/grub/myimage
becomes /grub/myimage
.To generate the changes and add the information into grub.cfg
, run:
# grub-mkconfig -o /boot/grub/grub.cfg
If adding the splash image was successful, the user will see "Found background image..."
in the terminal as the command is executed.
If this phrase is not seen, the image information was probably not incorporated into the grub.cfg
file.
If the image is not displayed, check:
- The path and the filename in
/etc/default/grub
are correct. - The image is of the proper size and format (tga, png, 8-bit jpg).
- The image was saved in the RGB mode, and is not indexed.
- The console mode is not enabled in
/etc/default/grub
. - The command
grub-mkconfig
must be executed to place the background image information into the/boot/grub/grub.cfg
file.
Theme
Here is an example for configuring Starfield theme which was included in GRUB package.
Edit /etc/default/grub
GRUB_THEME="/usr/share/grub/themes/starfield/theme.txt"
Generate the changes:
# grub-mkconfig -o /boot/grub/grub.cfg
If configuring the theme was successful, you'll see Found theme: /usr/share/grub/themes/starfield/theme.txt
in the terminal.
Your splash image will usually not be displayed when using a theme.
Menu colors
You can set the menu colors in GRUB. The available colors for GRUB can be found in the GRUB Manual. Here is an example:
Edit /etc/default/grub
:
GRUB_COLOR_NORMAL="light-blue/black" GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
Generate the changes:
# grub-mkconfig -o /boot/grub/grub.cfg
One of the unique features of GRUB is hiding/skipping the menu and showing it by holding Template:Keypress when needed. You can also adjust whether you want to see the timeout counter.
Edit /etc/default/grub
as you wish. Here is an example where the comments from the beginning of the two lines have been removed to enable the feature, the timeout has been set to five seconds and to be shown to the user:
GRUB_HIDDEN_TIMEOUT=5 GRUB_HIDDEN_TIMEOUT_QUIET=false
and run:
# grub-mkconfig -o /boot/grub/grub.cfg
Disable framebuffer
Users who use NVIDIA proprietary driver might wish to disable GRUB's framebuffer as it can cause problems with the binary driver.
To disable framebuffer, edit /etc/default/grub
and uncomment the following line:
GRUB_TERMINAL_OUTPUT=console
and run:
# grub-mkconfig -o /boot/grub/grub.cfg
Another option if you want to keep the framebuffer in GRUB is to revert to text mode just before starting the kernel. To do that modify the variable in /etc/default/grub
:
GRUB_GFXPAYLOAD_LINUX=text
and rebuild the configuration as before.
Other Options
LVM
If you use LVM for your /boot
, add the following before menuentry lines:
insmod lvm
and specify your root in the menuentry as:
set root=lvm/lvm_group_name-lvm_logical_boot_partition_name
Example:
# (0) Arch Linux menuentry "Arch Linux" { insmod lvm set root=lvm/VolumeGroup-lv_boot # you can only set following two lines linux /vmlinuz-linux root=/dev/mapper/VolumeGroup-root ro initrd /initramfs-linux.img }
RAID
GRUB provides convenient handling of RAID volumes. You need to add insmod mdraid
which allows you to address the volume natively. For example, /dev/md0
becomes:
set root=(md0)
whereas a partitioned RAID volume (e.g. /dev/md0p1
) becomes:
set root=(md0,1)
Persistent block device naming
One naming scheme for Persistent block device naming is the use of globally unique UUIDs to detect partitions instead of the "old" /dev/sd*
. Advantages are covered up in the above linked article.
Persistent naming via filesystem UUIDs are used by default in GRUB.
/boot/grub.cfg
file needs regeneration with the new UUID in /etc/default/grub
every time a relevant filesystem is resized or recreated. Remember this when modifying partitions & filesystems with a Live-CD.Whether to use UUIDs is controlled by an option in /etc/default/grub
:
# GRUB_DISABLE_LINUX_UUID=true
Either way, do not forget to generate the changes:
# grub-mkconfig -o /boot/grub/grub.cfg
Using Labels
It is possible to use labels, human-readable strings attached to filesystems, by using the --label
option to search
. First of all, label your existing partition:
# tune2fs -L <LABEL> <PARTITION>
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 }
Recall previous entry
GRUB can remember the last entry you booted from and use this as the default entry to boot from next time. This is useful if you have multiple kernels (i.e., the current Arch one and the LTS kernel as a fallback option) or operating systems. To do this, edit /etc/default/grub
and change the setting of GRUB_DEFAULT
:
GRUB_DEFAULT=saved
This ensures that GRUB will default to the saved entry. To enable saving the selected entry, add the following line to /etc/default/grub
:
GRUB_SAVEDEFAULT=true
/etc/grub.d/40_custom
or /boot/grub/custom.cfg
, will need savedefault
added. Remember to regenerate your configuration file.Security
If you want to secure GRUB so it is not possible for anyone to change boot parameters or use the command line, you can add a user/password combination to GRUB's configuration files. To do this, run the command grub-mkpasswd-pbkdf2
. Enter a password and confirm it:
grub-mkpasswd-pbkdf2
[...] Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A
Then, add the following to /etc/grub.d/00_header
:
/etc/grub.d/00_header
cat << EOF set superusers="username" password_pbkdf2 username <password> EOF
where <password>
is the string generated by grub-mkpasswd_pbkdf2
.
Regenerate your configuration file. Your GRUB command line, boot parameters and all boot entries are now protected.
This can be relaxed and further customized with more users as described in the "Security" part of the GRUB manual.
Root Encryption
To let GRUB automatically add the kernel parameters for root encryption,
add cryptdevice=/dev/yourdevice:label
to GRUB_CMDLINE_LINUX
in /etc/default/grub
.
Example with root mapped to /dev/mapper/root
:
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:root"
Also, disable the usage of UUIDs for the rootfs:
GRUB_DISABLE_LINUX_UUID=true
Regenerate the configuration.
Boot non-default entry only once
The command grub-reboot
is very helpful to boot another entry than the default only once. GRUB loads the entry passed in the first command line argument, when the system is rebooted the next time. Most importantly GRUB returns to loading the default entry for all future booting. Changing the configuration file or selecting an entry in the GRUB menu is not necessary.
GRUB_DEFAULT=saved
in /etc/default/grub
(and then regenerating grub.cfg
) or, in case of hand-made grub.cfg
, the line set default="${saved_entry}"
.Booting an ISO Directly From GRUB
Edit /etc/grub.d/40_custom
or /boot/grub/custom.cfg
to add an entry for the target ISO. When finished, update the GRUB menu as with the usual grub-mkconfig -o /boot/grub/grub.cfg
(as root).
Arch ISO
/archives
on hd0,6
.(hd1,$partition)
and either /dev/sdbY
for the img_dev
parameter or a persistent name, e.g. img_dev=/dev/disk/by-label/CORSAIR
.x86_64
menuentry "Archlinux-2013.05.01-dual.iso" --class iso { set isofile="/archives/archlinux-2013.05.01-dual.iso" set partition="6" loopback loop (hd0,$partition)/$isofile linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201305 img_dev=/dev/sda$partition img_loop=$isofile earlymodules=loop initrd (loop)/arch/boot/x86_64/archiso.img }
i686
menuentry "Archlinux-2013.05.01-dual.iso" --class iso { set isofile="/archives/archlinux-2013.05.01-dual.iso" set partition="6" loopback loop (hd0,$partition)/$isofile linux (loop)/arch/boot/i686/vmlinuz archisolabel=ARCH_201305 img_dev=/dev/sda$partition img_loop=$isofile earlymodules=loop initrd (loop)/arch/boot/i686/archiso.img }
Ubuntu ISO
/archives
on hd0,6
. Users must adjust the location and hdd/partition in the lines below to match their systems.menuentry "ubuntu-13.04-desktop-amd64.iso" { set isofile="/archives/ubuntu-13.04-desktop-amd64.iso" loopback loop (hd0,6)/$isofile linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash -- initrd (loop)/casper/initrd.lz }
menuentry "ubuntu-12.04-desktop-amd64.iso" { set isofile="/archives/ubuntu-12.04-desktop-amd64.iso" loopback loop (hd0,6)/$isofile linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash -- initrd (loop)/casper/initrd.lz }
Other ISOs
Other working configurations from link Source.
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:
sh: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
GUI configuration tools
Following package may be installed from AUR
- grub-customizerAUR (requires gettext gksu gtkmm hicolor-icon-theme openssl)
- Customize the bootloader (GRUB or BURG)
- grub2-editorAUR (requires kdelibs)
- A KDE4 control module for configuring the GRUB bootloader
- kcm-grub2AUR (requires kdelibs python2-qt kdebindings-python)
- This Kcm module manages the most common settings of GRUB.
- startupmanagerAUR (requires gnome-python imagemagick yelp python2 xorg-xrandr)
- GUI app for changing the settings of GRUB Legacy, GRUB, Usplash and Splashy
parttool for hide/unhide
If you have a Windows 9x paradigm with hidden C:\ disks GRUB can hide/unhide it using parttool
. For example, to boot the third C:\ disk of three Windows 9x installations on the CLI enter the CLI and:
parttool hd0,1 hidden+ boot- parttool hd0,2 hidden+ boot- parttool hd0,3 hidden- boot+ set root=hd0,3 chainloader +1 boot
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.
To expand console capabilities, insert the linux
module:
grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
/boot
from the path, (i.e. type set prefix=(hdX,Y)/grub
and insmod (hdX,Y)/grub/linux.mod
).This introduces the linux
and initrd
commands, which should be familiar (see #Configuration).
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, again change the lines accordingly:
set root=(hd0,5) linux /vmlinuz-linux root=/dev/sda6 initrd /initramfs-linux.img boot
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 #Bootloader installation for details.
Combining the use of UUIDs and basic scripting
If you like the idea of using UUIDs to avoid unreliable BIOS mappings or are struggling with GRUB's syntax, here is an example boot menu item that uses UUIDs and a small script to direct GRUB to the proper disk partitions for your system. All you need to do is replace the UUIDs in the sample with the correct UUIDs for your system. The example applies to a system with a boot and root partition. You will obviously need to modify the GRUB configuration if you have additional partitions:
menuentry "Arch Linux 64" { # Set the UUIDs for your boot and root partition respectively set the_boot_uuid=ece0448f-bb08-486d-9864-ac3271bd8d07 set the_root_uuid=c55da16f-e2af-4603-9e0b-03f5f565ec4a # (Note: This may be the same as your boot partition) # Get the boot/root devices and set them in the root and grub_boot variables search --fs-uuid --set=root $the_root_uuid search --fs-uuid --set=grub_boot $the_boot_uuid # Check to see if boot and root are equal. # If they are, then append /boot to $grub_boot (Since $grub_boot is actually the root partition) if [ $the_boot_uuid == $the_root_uuid] ; then set grub_boot=$grub_boot/boot fi # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd linux ($grub_boot)/vmlinuz-linux root=/dev/disk/by-uuid/$uuid_os_root ro initrd ($grub_boot)/initramfs-linux.img }
Troubleshooting
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've created for GRUB already) bootable in the MBR. This can be achieved, using fdisk, by the following commands: Start fdisk against the disk you're installing, for instance fdisk /dev/sda
, then press Template:Keypress and select the partition you wish to mark as bootable (probably #1) by pressing the corresponding number, finally press Template:Keypress 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.More information is available here
Enable debug messages
Add:
set pager=1 set debug=all
to grub.cfg
.
Correct 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=/boot/efi/EFI
set, then the directory is /boot/efi/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 won't 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
GRUB UEFI drops to shell
If GRUB loads but drops you into the rescue shell with no errors, 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 OR if the partition number of the boot partition changed (which is hard-coded into the grubx64.efi
file).
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.
Restore GRUB Legacy
- Move GRUB2 files out of the way:
# mv /boot/grub /boot/grub.nonfunctional
- Copy GRUB Legacy back to
/boot
:
# cp -af /boot/grub-legacy /boot/grub
- Replace MBR and next 62 sectors of sda with backed up copy
# dd if=/path/to/backup/first-sectors of=/dev/sdX bs=512 count=1
A safer way is to restore only the MBR boot code use:
# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=446 count=1
References
- Official GRUB Manual - https://www.gnu.org/software/grub/manual/grub.html
- Ubuntu wiki page for GRUB - https://help.ubuntu.com/community/Grub2
- GRUB wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
- Wikipedia's page on BIOS Boot partition