Difference between revisions of "GRUB"

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(Use standard mount paths.)
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Assume your USB stick's first partition is FAT32 and it's partition is /dev/sdy1
Assume your USB stick's first partition is FAT32 and it's partition is /dev/sdy1
  #  mkdir -p /tmp/y ; mount /dev/sdy1 /tmp/y
  #  mkdir -p /mnt/usb ; mount /dev/sdy1 /mnt/usb
  # grub-install --target=i386-pc --recheck --debug --boot-directory=/tmp/y/boot /dev/sdy
  # grub-install --target=i386-pc --recheck --debug --boot-directory=/mnt/usb/boot /dev/sdy
  # grub-mkconfig -o /tmp/y/boot/grub/grub.cfg
  # grub-mkconfig -o /mnt/usb/boot/grub/grub.cfg
  # optional, backup config files of grub.cfg
  # optional, backup config files of grub.cfg
  # mkdir -p /tmp/y/etc/default
  # mkdir -p /mnt/usb/etc/default
  # cp /etc/default/grub /tmp/y/etc/default
  # cp /etc/default/grub /mnt/usb/etc/default
  # cp -a /etc/grub.d /tmp/y/etc
  # cp -a /etc/grub.d /mnt/usb/etc
  #  sync ; umount /tmp/y
  #  sync ; umount /mnt/usb
===== Install to partition or partitionless disk =====
===== Install to partition or partitionless disk =====

Revision as of 22:34, 20 September 2014


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.



  • 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 file system) compressed with either zlib or LZO
  • GRUB does not support F2fs as root so you will need a separate /boot with a supported file system.

Notes for GRUB Legacy users

  • Upgrading from GRUB Legacy to GRUB is much the same as freshly installing GRUB. This topic is covered here.
  • 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).
  • GRUB is noticeably bigger than GRUB legacy (occupies ~13 MB in /boot). If you are booting from a separate /boot partition, and this partition is smaller than 32 MB, you will run into disk space issues, and pacman will refuse to install new kernels.

Backup important data

Although a GRUB installation should run smoothly, it is strongly recommended to keep the GRUB Legacy files before upgrading to GRUB v2.

# 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

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

  • Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme, read more on GUID partition tables.
  • This additional partition is only needed on a GRUB, BIOS/GPT partitioning scheme. Previously, for a GRUB, BIOS/MBR partitioning scheme, GRUB used the Post-MBR gap for the embedding the core.img). GRUB for GPT, however, does not use the Post-GPT gap to confirm to GPT specifications that require 1_mebibyte/2048_sector disk boundaries.
  • For UEFI systems this extra partition is not required as no embedding of boot sectors takes place in that case.

Create a mebibyte partition {+1MiB with gdisk) on the disk with no file system and type ef02 (or bios_grub in parted). 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 and be sure to include the --target=i386-pc option (as GRUB may mistaken the configuration as EFI-GPT).

The Post-GPT gap can also be used as the BIOS boot partition though it will be out of GPT alignment specification. Since the partition will not be regularly accessed performance issues can be disregarded (though some disk utilities will display a warning about it). In gdisk create a new partition starting at sector 34 and spanning to 2047 and set the type. To 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 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).

UEFI systems

Note: It is recommended to read and understand the UEFI, GPT and UEFI Bootloaders pages.
Check if you have GPT and an ESP

An EFI System Partition (ESP) is needed on every disc you want to boot using EFI. GPT is not strictly necessary, but it is highly recommended and is the only method currently supported in this article. If you are installing Arch Linux on an EFI-capable computer with an already-working operating system, like Windows 8 for example, it is very likely that you already have an ESP. To check for GPT and for an ESP, use parted as root to print the partition table of the disk you want to boot from. (We are calling it /dev/sda.)

# parted /dev/sda print

For GPT, you are looking for "Partition Table: GPT". For EFI, you are looking for a small (512 MiB or less) partition with a vfat file system and the boot flag enabled. On it, there should be a directory named "EFI". If these criteria are met, this is your ESP. Make note of the partition number. You will need to know which one it is, so you can mount it later on while installing GRUB to it.

Create an ESP

If you do not have an ESP, you will need to create it. Follow UEFI#EFI System Partition for instructions on creating an ESP.


Note: If you are performing an initial installation from the Arch live CD, make sure you have chrooted into the installed system before installing grub. Using the CD's own grub installation scripts may result in an invalid grub.cfg, or other problems that will prevent the system from booting.

BIOS systems

GRUB can be installed with the grub package from the official repositories. It will replace grub-legacyAUR , if it is installed.

Note: Simply installing the package will not update the /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 4 ways to install GRUB boot files in BIOS booting:

Install to disk
Note: The method is specific to installing GRUB to a partitioned (MBR or GPT) disk, with GRUB files installed to /boot/grub and its first stage code installed to the 440-byte MBR boot code region (not to be confused with MBR partition table). For partitionless disk (super-floppy) please refer to #Install to partition or partitionless disk

To set up GRUB in the 440-byte Master Boot Record boot code region, populate the /boot/grub directory, generate the /boot/grub/i386-pc/core.img file, and embed it in the 31 KiB (minimum size - varies depending on partition alignment) post-MBR gap in case of MBR partitioned disk (or BIOS Boot Partition in case of GPT partitioned disk, denoted by bios_grub flag in parted and EF02 type code in gdisk), run:

# grub-install --target=i386-pc --recheck --debug /dev/sdx
# grub-mkconfig -o /boot/grub/grub.cfg

Note: --target=i386-pc instructs grub-install to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in grub-install.

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

Install to external USB stick

Assume your USB stick's first partition is FAT32 and it's partition is /dev/sdy1

#  mkdir -p /mnt/usb ; mount /dev/sdy1 /mnt/usb 
# grub-install --target=i386-pc --recheck --debug --boot-directory=/mnt/usb/boot /dev/sdy
# grub-mkconfig -o /mnt/usb/boot/grub/grub.cfg
# optional, backup config files of grub.cfg
# mkdir -p /mnt/usb/etc/default
# cp /etc/default/grub /mnt/usb/etc/default
# cp -a /etc/grub.d /mnt/usb/etc
#  sync ; umount /mnt/usb
Install to partition or partitionless disk
Note: GRUB does not encourage installation to a partition boot sector or a partitionless disk like GRUB Legacy or Syslinux does. This kind of setup is prone to breakage, especially during updates, and is not supported by Arch devs.

To set up grub 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):

# chattr -i /boot/grub/i386-pc/core.img
# grub-install --target=i386-pc --recheck --debug --force /dev/sdaX
# chattr +i /boot/grub/i386-pc/core.img
  • /dev/sdaX used for example only.
  • --target=i386-pc instructs grub-install to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in grub-install.

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 relies on embedded blocklists in the partition bootsector to locate the /boot/grub/i386-pc/core.img file and the prefix directory /boot/grub. The sector locations of core.img may change whenever the file system 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 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).

Unfortunately, the grub.cfg file that is created will not contain the proper UUID in order to boot, even if it reports no errors. see https://bbs.archlinux.org/viewtopic.php?pid=1294604#p1294604. In order to fix this issue the following commands:

# mount /dev/sdxY /mnt        #Your root partition.
# mount /dev/sdxZ /mnt/boot   #Your boot partition (if you have one).
# arch-chroot /mnt
# pacman -S linux
# grub-mkconfig -o /boot/grub/grub.cfg
Generate core.img alone

To populate the /boot/grub directory and generate a /boot/grub/i386-pc/core.img file without embedding any GRUB bootsector code in the MBR, post-MBR region, or the partition bootsector, add --grub-setup=/bin/true to grub-install:

# grub-install --target=i386-pc --grub-setup=/bin/true --recheck --debug /dev/sda
  • /dev/sda used for example only.
  • --target=i386-pc instructs grub-install to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in grub-install.

You can then chainload GRUB's core.img from GRUB Legacy or syslinux as a Linux kernel or as a multiboot kernel.

UEFI systems

Note: It is well known that different motherboard manufactures implement UEFI differently. Users experiencing problems getting GRUB or EFI to work properly are encouraged to share detailed steps for hardware-specific cases where UEFI booting does not work as described below. In an effort to keep the parent GRUB article neat and tidy, see the GRUB EFI Examples page for these special cases.

First install the grub, dosfstools, and efibootmgr packages, then follow the instructions below. (The last two packages are required for EFI support in grub.)

Note: Simply installing the package will not update the core.efi file and the GRUB modules in the ESP. You need to do this manually using grub-install as explained below.

Install boot files

Recommended method
  • The below commands assume you are using installing GRUB for x86_64-efi (for IA32-efi replace x86_64-efi with i386-efi in the below commands)
  • To do this, you need to be booted using UEFI and not BIOS, or grub-install will show errors.

First, mount the ESP at your preferred mountpoint (usually /boot/efi, hereafter referred to as $esp). On a first install, you will need to mkdir /boot/efi, if that's where you want to mount it.

Now, install the GRUB UEFI application to $esp/EFI/grub and its modules to /boot/grub/x86_64-efi:

# grub-install --target=x86_64-efi --efi-directory=$esp --bootloader-id=grub --recheck --debug
  • If you have a problem when running grub-install with sysfs or procfs and it says you have to "modprobe efivars", try Unified_Extensible_Firmware_Interface#Switch_to_efivarfs.
  • 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.
  • 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.
  • --efi-directory and --bootloader-id are specific to GRUB UEFI. --efi-directory specifies the mountpoint of the ESP. It replaces --root-directory, which is deprecated. --bootloader-id specifies the name of the directory used to store the grubx64.efi file.
  • 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.

GRUB is now installed. Do not forget to generate the main configuration file.

Alternative method

If you want to keep all of the GRUB boot files inside the EFI System Partition itself, add --boot-directory=$esp/EFI to the grub-install command:

# grub-install --target=x86_64-efi --efi-directory=$esp --bootloader-id=grub --boot-directory=$esp/EFI --recheck --debug

This puts the GRUB modules in $esp/EFI/grub. ('/grub' is hard coded onto the end of this path.) Using this method, grub.cfg is kept on the EFI System Partition as well, so make sure you point grub-mkconfig to the right place in the configuration phase:

# grub-mkconfig -o $esp/EFI/grub/grub.cfg

Configuration is otherwise the same.

Create a GRUB entry in the firmware boot manager

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

GRUB Standalone

It is possible to create a grubx64_standalone.efi application which has all the modules embedded in a tar archive within the UEFI application, thus removing the need for having a separate directory populated with all of the GRUB UEFI modules and other related files. This is done using the grub-mkstandalone command (included in grub) as follows:

# echo 'configfile ${cmdpath}/grub.cfg' > /tmp/grub.cfg                                ## use single quotes, ${cmdpath}/grub.cfg should be present as it is
# grub-mkstandalone -d /usr/lib/grub/x86_64-efi/ -O x86_64-efi --modules="part_gpt part_msdos" --fonts="unicode" --locales="en@quot" --themes="" -o "$esp/EFI/grub/grubx64_standalone.efi"  "boot/grub/grub.cfg=/tmp/grub.cfg" -v

Then copy the GRUB config file to $esp/EFI/grub/grub.cfg and create a UEFI Boot Manager entry for $esp/EFI/grub/grubx64_standalone.efi using efibootmgr.

Note: The option --modules="part_gpt part_msdos" (with the quotes) is necessary for the ${cmdpath} feature to work properly.
Warning: You may find that the grub.cfg file is not loaded due to ${cmdpath} missing a slash (i.e. (hd1,msdos2)EFI/Boot instead of (hd1,msdos2)/EFI/Boot) and so you are dropped into a GRUB shell. If this happens determine what ${cmdpath} is set to (echo ${cmdpath} ) and then load the config file manually (e.g. configfile (hd1,msdos2)/EFI/Boot/grub.cfg).
GRUB Standalone - Technical Info

The GRUB EFI file always expects its config file to be at ${prefix}/grub.cfg. However in the standalone GRUB EFI file, the ${prefix} is located inside a tar archive and embedded inside the standalone GRUB EFI file itself (inside the GRUB environment, it is denoted by "(memdisk)", without quotes). This tar archive contains all the files that would be stored normally at /boot/grub in case of a normal GRUB EFI install.

Due to this embedding of /boot/grub contents inside the standalone image itself, it does not rely on actual (external) /boot/grub for anything. Thus in case of standalone GRUB EFI file ${prefix}==(memdisk)/boot/grub and the standalone GRUB EFI file reads expects the config file to be at ${prefix}/grub.cfg==(memdisk)/boot/grub/grub.cfg.

Hence to make sure the standalone GRUB EFI file reads the external grub.cfg located in the same directory as the EFI file (inside the GRUB environment, it is denoted by ${cmdpath} ), we create a simple /tmp/grub.cfg which instructs GRUB to use ${cmdpath}/grub.cfg as its config (configfile ${cmdpath}/grub.cfg command in (memdisk)/boot/grub/grub.cfg). We then instruct grub-mkstandalone to copy this /tmp/grub.cfg file to ${prefix}/grub.cfg (which is actually (memdisk)/boot/grub/grub.cfg) using the option "boot/grub/grub.cfg=/tmp/grub.cfg".

This way, the standalone GRUB EFI file and actual grub.cfg can be stored in any directory inside the EFI System Partition (as long as they are in the same directory), thus making them portable.

Generating main configuration file

After the installation, the main configuration file grub.cfg needs to be generated. The generation process can be influenced by a variety of options in /etc/default/grub and scripts in /etc/grub.d/, this is covered in the #Basic configuration and #Advanced configuration sections.

Note: Remember that grub.cfg has to be re-generated after any change to /etc/default/grub or /etc/grub.d/*.

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

# grub-mkconfig -o /boot/grub/grub.cfg
  • The 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 here.
  • When generating the GRUB config file on a LVM system in a chroot environment (even arch-chroot, 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.

By default the generation scripts automatically add menu entries for Arch Linux to any generated configuration. However, entries for other operating systems do not work out of the box. On BIOS systems, you may want to install os-prober, which detects other operating systems installed on your machine and adds entries for them into grub.cfg. If installed, it will be executed when running grub-mkconfig. See #Dual-booting for advanced configuration.

Converting GRUB Legacy's config file to the new format

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
Note: This option works only in BIOS systems, not in UEFI systems.

For example:


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
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.

Basic configuration

This section covers only editing the /etc/default/grub configuration file. See #Advanced configuration if you need more.

Note: Remember to always re-generate the main configuration file after you make changes to /etc/default/grub.

Additional arguments

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

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

For generating the GRUB recovery entry you also have to comment out #GRUB_DISABLE_RECOVERY=true in /etc/default/grub.

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.

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 #"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:


To generate the changes, run:

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

The gfxpayload property will make sure the kernel keeps the resolution.

  • If this example does not work for you try to replace gfxmode="1024x768x32" by vbemode="0x105". Remember to replace the specified resolution with one suitable for your screen
  • To show all the modes you can use # 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 example: "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:

915resolution 30 1440 900  # Inserted line
set gfxmode=${GRUB_GFXMODE}

Lastly we need to set GRUB_GFXMODE as described earlier, regenerate grub.cfg and reboot to test changes.

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 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:

Note: If you have installed GRUB on a separate partition, /boot/grub/myimage becomes /grub/myimage.

Re-generate grub.cfg to apply the changes. 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


Here is an example for configuring Starfield theme which was included in GRUB package.

Edit /etc/default/grub


Re-generate grub.cfg to apply the changes. If configuring the theme was successful, you will 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:


Hidden menu

One of the unique features of GRUB is hiding/skipping the menu and showing it by holding Esc 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 is how many seconds before displaying menu. You also need to set GRUB_TIMEOUT=0 if you want to hide menu.

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:


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:


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 file system UUIDs are used by default in GRUB.

Note: The /boot/grub.cfg file needs regeneration with the new UUID in /etc/default/grub every time a relevant file system is resized or recreated. Remember this when modifying partitions & file systems with a Live-CD.

Whether to use UUIDs is controlled by an option in /etc/default/grub:


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 value of GRUB_DEFAULT:


This ensures that GRUB will default to the saved entry. To enable saving the selected entry, add the following line to /etc/default/grub:

Note: Manually added menu items, e.g. Windows in /etc/grub.d/40_custom or /boot/grub/custom.cfg, will need savedefault added.

Changing the default menu entry

To change the default selected entry, edit /etc/default/grub and change the value of GRUB_DEFAULT:

Using numbers :


Grub identifies entries in generated menu counted from zero. That means 0 for the first entry which is the default value, 1 for the second and so on.

Or using menu titles :

GRUB_DEFAULT='Arch Linux, with Linux core repo kernel'

Disable Submenu

If you have multiple kernels installed, say linux and linux-lts, by default grub-mkconfig groups them in a submenu. If you do not like this behaviour you can go back to one single menu by adding the following line to /etc/default/grub:


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.

See Dm-crypt/System Configuration#Boot loader for more details.

Tip: If you are upgrading from a working GRUB Legacy configuration, check /boot/grub/menu.lst.pacsave for the correct device/label to add. Look for them after the text kernel /vmlinuz-linux.

Example with root mapped to /dev/mapper/root:


Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: The following step was added with [3], but there is not a clear reason to disable the usage of UUIDs for the root file system. (Discuss in Talk:GRUB#)

Also, disable the usage of UUIDs for the rootfs:


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.

Note: This requires 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}".

Advanced configuration

This section covers manual editing of grub.cfg, writing custom scripts in /etc/grub.d/ and other advanced settings.

Manually creating grub.cfg

Warning: Editing this file is strongly discouraged. The file is generated by the grub-mkconfig command, and it is best to edit your /etc/default/grub or one of the scripts in the /etc/grub.d directory.

A basic GRUB config file uses the following options:

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

An example configuration:

# Config file for GRUB - The GNU GRand Unified Bootloader
# /boot/grub/grub.cfg

#  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


Tip: If you want GRUB to automatically search for other systems, you may wish to install os-prober.

Automatically generating using /etc/grub.d/40_custom and 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

or, for UEFI-GPT Mode (as per alternate method):

# grub-mkconfig -o /boot/efi/EFI/GRUB/grub.cfg

to generate an updated grub.cfg.

For example, a typical /etc/grub.d/40_custom file, could appear similar to the following one, created for HP Pavilion 15-e056sl Notebook PC, originally with Microsoft Windows 8 preinstalled. Each menuentry should mantain a structure similar to the following ones. Note that the UEFI partition /dev/sda2 within GRUB is called hd0,gpt2 and ahci0,gpt2 (see here for more info).

exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry "HP / Microsoft Windows 8.1" {
	echo "Loading HP / Microsoft Windows 8.1..."
	insmod part_gpt
	insmod fat
	insmod search_fs_uuid
	insmod chain
	search --fs-uuid --no-floppy --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2 763A-9CB6
	chainloader /EFI/Microsoft/Boot/bootmgfw.efi

menuentry "HP / Microsoft Control Center" {
	echo "Loading HP / Microsoft Control Center..."
	insmod part_gpt
	insmod fat
	insmod search_fs_uuid
	insmod chain
	search --fs-uuid --no-floppy --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2 763A-9CB6
	chainloader /EFI/HP/boot/bootmgfw.efi

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

menuentry "System restart" {
	echo "System rebooting..."
GNU/Linux menu entry

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)
FreeBSD menu entry

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
Windows XP menu entry

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 +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
Windows installed in UEFI-GPT Mode menu entry
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(2). See this and this for more info.
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

where $hints_string and $fs_uuid are obtained with the following two commands. $fs_uuid's command:

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

$hints_string's command:

# 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.

"Shutdown" menu entry
menuentry "System shutdown" {
	echo "System shutting down..."
"Restart" menu entry
menuentry "System restart" {
	echo "System rebooting..."
Windows installed in BIOS-MBR mode

Tango-edit-clear.pngThis article or section needs language, wiki syntax or style improvements. See Help:Style for reference.Tango-edit-clear.png

Reason: This section does not fit into the others, should be slimmed down a bit. (Discuss in Talk:GRUB#)
Note: GRUB supports booting bootmgr directly and chainload 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:). In blkid output, the system partition is the one with LABEL="SYSTEM RESERVED" or LABEL="SYSTEM" and is only about 100 to 200 MB in size (much like the boot partition for Arch). See Wikipedia:System partition and boot partition for more info.

Throughout this section, it is assumed your Windows partition is /dev/sda1. A different partition will change every instance of hd0,msdos1. First, find the UUID of the NTFS file system 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/7/8/8.1:

# grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr
--hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1
Note: For Windows XP, replace bootmgr with NTLDR in the above commands. And note that there may not be a separate SYSTEM_RESERVED partition; just probe the file NTLDR on your Windows partition.

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:

Note: These menuentries will work only in Legacy BIOS boot mode. It WILL NOT WORK in uefi installed grub(2). See Windows_and_Arch_Dual_Boot#Windows_UEFI_vs_BIOS_limitations and Windows_and_Arch_Dual_Boot#Bootloader_UEFI_vs_BIOS_limitations.

For Windows Vista/7/8/8.1:

if [ "${grub_platform}" == "pc" ]; then
  menuentry "Microsoft Windows Vista/7/8/8.1 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:

if [ "${grub_platform}" == "pc" ]; then
  menuentry "Microsoft Windows XP" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
    ntldr /bootmgr
Note: In some cases, mine I have installed GRUB before a clean Windows 8, you cannot boot Windows having an error with \boot\bcd (error code 0xc000000f). You can fix it going to Windows Recovery Console (cmd from install disk) and executing:
x:\> "bootrec.exe /fixboot" 
x:\> "bootrec.exe /RebuildBcd".
Do not use bootrec.exe /Fixmbr because it will wipe GRUB out.

/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.

Note: nn should be greater than 06 to ensure necessary scripts are executed first.

With Windows via EasyBCD and NeoGRUB

Merge-arrows-2.pngThis article or section is a candidate for merging with NeoGRUB.Merge-arrows-2.png

Notes: New page has been created, so this section should be merged there. (Discuss in Talk:GRUB#)

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

Finally, recreate your grub.cfg using grub-mkconfig.

Booting ISO9660 image file directly via GRUB

GRUB supports booting from ISO images directly via loopback devices, see Multiboot USB drive#Using GRUB and loopback devices for examples.


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


# (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


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=(md/0)

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

set root=(md/0,1)

To install grub when using RAID1 as the /boot partition (or using /boot housed on a RAID1 root partition), on devices with GPT ef02/'BIOS boot partition', simply run grub-install on both of the drives, such as:

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

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

Using labels

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

Password protection of GRUB menu

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:

Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A

Then, add the following to /etc/grub.d/40_custom:

cat << EOF

set superusers="username"
password_pbkdf2 username <password>


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.

Hide GRUB unless the Shift key is held down

In order to achieve the fastest possible boot, instead of having GRUB wait for a timeout, it is possible for GRUB to hide the menu, unless the Shift key is held down during GRUB's start-up.

In order to achieve this, you should add the following line to /etc/default/grub:


And the following file should be created and made executable:

#! /bin/sh
set -e

# grub-mkconfig helper script.
# Copyright (C) 2006,2007,2008,2009  Free Software Foundation, Inc.
# GRUB is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# GRUB is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with GRUB.  If not, see <http://www.gnu.org/licenses/>.


export TEXTDOMAIN=grub
export TEXTDOMAINDIR="${datarootdir}/locale"
source "${datarootdir}/grub/grub-mkconfig_lib"


make_timeout () {

  if [ "x${GRUB_FORCE_HIDDEN_MENU}" = "xtrue" ] ; then 
    if [ "x${1}" != "x" ] ; then
      if [ "x${GRUB_HIDDEN_TIMEOUT_QUIET}" = "xtrue" ] ; then
    verbose=" --verbose"

      if [ "x${1}" = "x0" ] ; then
    cat <<EOF
if [ "x\${timeout}" != "x-1" ]; then
  if keystatus; then
    if keystatus --shift; then
      set timeout=-1
      set timeout=0
    if sleep$verbose --interruptible 3 ; then
      set timeout=0
    cat << EOF
if [ "x\${timeout}" != "x-1" ]; then
  if sleep$verbose --interruptible ${GRUB_HIDDEN_TIMEOUT} ; then
    set timeout=0

adjust_timeout () {
  if [ "x$GRUB_BUTTON_CMOS_ADDRESS" != "x" ]; then
    cat <<EOF
if cmostest $GRUB_BUTTON_CMOS_ADDRESS ; then
    echo else
    make_timeout "${GRUB_HIDDEN_TIMEOUT}" "${GRUB_TIMEOUT}"
    echo fi
    make_timeout "${GRUB_HIDDEN_TIMEOUT}" "${GRUB_TIMEOUT}"


    cat <<EOF
if [ "x\${timeout}" != "x-1" ]; then
  if keystatus; then
    if keystatus --shift; then
      set timeout=-1
      set timeout=0
    if sleep$verbose --interruptible 3 ; then
      set timeout=0

Make that file executable and then regenerate your grub config:

chmod a+x /etc/grub.d/31_hold_shift
grub-mkconfig -o /boot/grub/grub.cfg

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 $the_root_uuid --set=root
    search --fs-uuid $the_boot_uuid --set=grub_boot

    # 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
        set grub_boot=($grub_boot)

    # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd
    linux $grub_boot/vmlinuz-linux root=/dev/disk/by-uuid/$the_root_uuid ro
    initrd $grub_boot/initramfs-linux.img

Using the command shell

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

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


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


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.

Chainloading a partition

set root=(hdX,Y)
chainloader +1

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

Similarly GRUB installed to a partition can be chainloaded.

Chainloading a disk/drive

set root=hdX
chainloader +1

Chainloading Windows/Linux installed in UEFI mode

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

insmod ntfs used for loading the ntfs file system module for loading Windows. (hd0,gpt4) or /dev/sda4 is my EFI System Partition (ESP). The entry in the chainloader line specifies the path of the .efi file to be chain-loaded.

Normal loading

See the examples in #Using_the_rescue_console

GUI configuration tools

Following package may be installed:

  • grub-customizer — Customize the bootloader (GRUB or BURG)
https://launchpad.net/grub-customizer || grub-customizerAUR
  • grub2-editor — KDE4 control module for configuring the GRUB bootloader
http://kde-apps.org/content/show.php?content=139643 || grub2-editorAUR
  • startupmanager — GUI app for changing the settings of GRUB Legacy, GRUB, Usplash and Splashy (abandonned)
http://sourceforge.net/projects/startup-manager/ || startupmanagerAUR

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

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 i386-pc/linux.mod
Note: With a separate boot partition, omit /boot from the path, (i.e. type set prefix=(hdX,Y)/grub).

This introduces the linux and initrd commands, which should be familiar (see #Advanced configuration).

An example, booting Arch Linux:

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

With a separate boot partition, again change the lines accordingly:

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


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.

Note: The bootable-marking must be done in 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.

More information is available here

EFI 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 place a file at one of the known locations. Assuming the EFI partition is at /boot/efi/ this will work:

mkdir /boot/efi/EFI/boot
cp /boot/efi/EFI/grub/grubx64.efi /boot/efi/EFI/boot/bootx64.efi

This solution worked for an Intel DH87MC motherboard with firmware dated Jan 2014.

Enable debug messages


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
    insmod gfxterm
    set gfxmode=auto
    set gfxpayload=keep
    terminal_output gfxterm

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

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 GRUB v2 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
Warning: This command also restores the partition table, so be careful of overwriting a modified partition table with the old one. It will mess up your system.
# 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

Arch not found from other OS

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

See also

  1. Official GRUB Manual - https://www.gnu.org/software/grub/manual/grub.html
  2. Ubuntu wiki page for GRUB - https://help.ubuntu.com/community/Grub2
  3. GRUB wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
  4. Wikipedia's page on BIOS Boot partition
  5. http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html - quite complete description of how to configure GRUB