# GRUB

Related articles

- GRUB Legacy
- Arch boot process
- Boot loaders
- Master Boot Record
- GUID Partition Table
- Unified Extensible Firmware Interface
- GRUB EFI Examples

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.

## 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` 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

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 boot sectors takes place in that case.

For a BIOS-GPT configuration, create a 1007 KiB partition at the beginning of the disk using gdisk, cgdisk or GNU Parted with no file system. The size of 1007 KiB, plus the size of the preceding GPT of 17 KiB, will allow for the following partition to be correctly aligned 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 `ef02` in (c)gdisk or `set BOOT_PART_NUM bios_grub on` in GNU Parted.

The GPT partition also creates a protective MBR partition to stop unsupported tools from modifying it. You may need to set a bootable flag on this protective MBR e.g., using cfdisk, or some BIOSes/EFIs will refuse to boot.

Note:

- You will probably need to explicitly set the `grub-install` target to `i386-pc` using `--target=i386-pc`. Otherwise `grub-install` sometimes guesses that your configuration is EFI-GPT.
- This partition should be created before `grub-install` or `grub-setup` is run
- gdisk will only allow you to create this partition on the position which will waste the least amount of space (sector 34-2047) if you create it last, after all the other partitions. This is because gdisk will auto-align partitions to 2048-sector boundaries if possible

##### 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.

## Installation

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-legacy , 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 3 ways to install GRUB boot files in BIOS booting:

- Install to disk (recommended)
- Install to partition or partitionless disk (not recommended)
- Generate core.img alone (safest method, but requires another BIOS bootloader like Syslinux to be installed to chainload `/boot/grub/i386-pc/core.img`)

Note: See https://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html for additional documentation.

##### 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 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

Note:

- `/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 partiton (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

Note:

- `/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

Note:

- 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

Note:

- 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.

Finally, do not forget to generate GRUB's config file :

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

Note:

- Should you forget this line, you may find yourself with a `unaligned pointer 0x22` at boot time.

GRUB is now installed.

##### 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

Note:

- 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:

    /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.

## 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:

    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.

Note:

- 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:

    /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.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:

    GRUB_BACKGROUND="/boot/grub/myimage"
    #GRUB_THEME="/path/to/gfxtheme"
    GRUB_FONT="/path/to/font.pf2"

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

#### 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"

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`:

    GRUB_COLOR_NORMAL="light-blue/black"
    GRUB_COLOR_HIGHLIGHT="light-cyan/blue"

#### 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_TIMEOUT=0
    GRUB_HIDDEN_TIMEOUT=5
    GRUB_HIDDEN_TIMEOUT_QUIET=false

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:

    GRUB_TERMINAL_OUTPUT=console

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

### 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`:

    GRUB_DISABLE_LINUX_UUID=true

### 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`:

    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

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_DEFAULT=0

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`:

     GRUB_DISABLE_SUBMENU=y

### 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`:

    GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:root"

Also, disable the usage of UUIDs for the rootfs:

    GRUB_DISABLE_LINUX_UUID=true

### 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:

    /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

Note: 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).

    /etc/grub.d/40_custom

    #!/bin/sh
    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..."
    	halt
    }

    menuentry "System restart" {
    	echo "System rebooting..."
    	reboot
    }

##### 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
    	}
    fi

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
    1ce5-7f28

`$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..."
    	halt
    }

##### "Restart" menu entry

    menuentry "System restart" {
    	echo "System rebooting..."
    	reboot
    }

##### Windows installed in BIOS-MBR mode

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
    69B235F6749E84CE

    # 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
      }
    fi

For Windows XP:

    if [ "${grub_platform}" == "pc" ]; then
      menuentry "Microsoft Windows XP" {
        insmod part_msdos
        insmod ntfs
        insmod search_fs_uuid
        insmod ntldr
        search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
        ntldr /bootmgr
      }
    fi

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

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

Edit `/etc/grub.d/40_custom` or `/boot/grub/custom.cfg` to add an entry for the target ISO image file and update the boot menu accordingly, for example:

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

Here are some examples about booting different distributions' LiveCD.

Note:

- The following examples assume the ISO image exists at `/boot/iso` on `hd1,2`(i.e.`/dev/sdb2`).
- Not all distributions' ISO image can boot that way (e.g. CentOS), so when you try to boot other distribution's ISO which is or not listed here and it is stuck, please looking for related documentation and wiki pages or ask for help in the related community.
- The prefix `(hd1,2)` before `$isofile`(also `$initrdfile` and any other similar) can be omitted when the grub directory(the directory includes GRUB config files and modules, e.g. `/boot/grub`) and the ISO images are in the same partition. This is recommended for thumbdrives.

#### Arch Linux

Tip: If you want to boot into a 32-bit system, replace `x86_64` with `i686`.

##### monthly release

    menuentry "[loopback]archlinux-2014.06.01-dual.iso" {
    	set isofile="/boot/iso/archlinux-2014.06.01-dual.iso"
    	loopback loop (hd1,2)$isofile
    	linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201406 img_dev=/dev/sdb2 img_loop=$isofile earlymodules=loop
    	initrd (loop)/arch/boot/x86_64/archiso.img
    }

Note:

- It's recommend for thumbdrives to use a persistent name instead of `/dev/sdxY` for the `img_dev` parameter, e.g. `img_dev=/dev/disk/by-label/MYUSBSTICK` (or `img_label=MYUSBSTICK`).
- As the official monthly release build script defines, you need to edit the label string after `archisolabel=` when you use a newer monthly released ISO image.

##### archboot

    menuentry "[loopback]archlinux-2014.06-1-archboot" {
    	set isofile="/boot/iso/archlinux-2014.06-1-archboot.iso"
    	loopback (hd1,2)$isofile
    	linux (loop)/boot/vmlinuz_x86_64 iso_loop_dev=/dev/sdb2 iso_loop_path=$isofile
    	initrd (loop)/boot/initramfs_x86_64.img
    }

Tip: The parameter `iso_loop_dev` is similar to fstab's first field(fs_spec):

- `iso_loop_dev=/dev/sdxY`
- `iso_loop_dev=LABEL=MYUSBSTICK`
- `iso_loop_dev=UUID=00000000-0000-0000-0000-0000deadbeef`

#### Debian

##### Stock install medium

Note: To install debian from any stock install medium on a hard disk(or usb stick), it's necessary to use a different initramfs instead of the default one on the installation medium(as 7.5.0 it is located at `/install.amd/initrd.gz`). If you boot with the default one, the debian-installer will unable to find or mount the proper iso image for installation. Please download the initramfs for hard disk installation from an official mirror site, put it in the same directory with the image file and give it a suitable name(`debian-7.5.0-amd64-DVD-1.hdd.initrd.gz` in this example).

    menuentry '[loopback]debian-7.5.0-amd64-DVD-1' {
    	set isofile="/boot/iso/debian-7.5.0-amd64-DVD-1.iso"
    	set initrdfile="/boot/iso/debian-7.5.0-amd64-DVD-1.hdd.initrd.gz"
    	loopback loop (hd1,2)$isofile
    	linux (loop)/install.amd/vmlinuz vga=791 iso-scan/ask_second_pass=true iso-scan/filename=$isofile
    	initrd (hd1,2)$initrdfile
    }

##### Live install medium

    menuentry "[loopback]debian-live-7.5.0-amd64-xfce-desktop" {
    	set isofile="/boot/iso/debian-live-7.5.0-amd64-xfce-desktop.iso"
    	loopback loop (hd1,2)$isofile
    	linux (loop)/live/vmlinuz boot=live config fromiso=/dev/sdb2/$isofile
    	initrd (loop)/live/initrd.img
    }

Note: It's also OK to use `findiso=$isofile` instead of the longer `fromiso=/dev/disk/by-.../.../$isofile`. Anyway, using `fromiso=` instead of `findiso=` may speed up the initialization progress because it avoids unnecessary mounting.

#### Fedora

##### Stock installation medium

    menuentry '[loopback]Fedora-20-x86_64-DVD' {
    	set isofile='/boot/iso/Fedora-20-x86_64-DVD.iso'
    	loopback loop (hd1,2)$isofile
    	linux (loop)/isolinux/vmlinuz noeject repo=hd:/dev/sdb2:/$isofile
    	initrd (loop)/isolinux/initrd.img
    }

Tip: The parameter `repo=hd:` is similar to fstab's first field(fs_spec):

- `repo=hd:/dev/sdxY`
- `repo=hd:/dev/disk/by-label/MYUSBSTICK`
- `repo=hd:LABEL=MYUSBSTICK`
- `repo=hd:UUID=00000000-0000-0000-0000-0000deadbeef`

##### Desktop live medium

    menuentry '[loopback]Fedora-Live-Desktop-x86_64-20-1' {
    	set isofile='/boot/iso/Fedora-Live-Desktop-x86_64-20-1.iso'
    	loopback loop (hd1,2)$isofile
    	linux (loop)/isolinux/vmlinuz0 root=live:CDLABEL=Fedora-Live-Desktop-x86_64-20-1 iso-scan/filename=$isofile
    	initrd (loop)/isolinux/initrd0.img
    }

#### Kali Linux

    menuentry "[loopback]kali-linux-1.0.6-amd64" {
    	insmod loopback
    	set isofile="/boot/iso/kali-linux-1.0.6-amd64.iso"
    	loopback loop (hd1,2)$isofile
    	linux (loop)/live/vmlinuz boot=live findiso=$isofile noconfig=sudo username=root hostname=kali noswap
    	initrd (loop)/live/initrd.img
    }

#### openSUSE

    menuentry "[loopback]openSUSE-13.1-DVD-x86_64" {
    	set isofile="/boot/iso/openSUSE-13.1-DVD-x86_64.iso"
    	loopback loop (hd1,2)$isofile
    	linux (loop)/boot/x86_64/loader/linux install=hd:$isofile
    	initrd (loop)/boot/x86_64/loader/initrd
    }

#### Sabayon

    menuentry "[loopback]Sabayon_Linux_14.05_amd64_KDE" {
    	set isofile="/boot/iso/Sabayon_Linux_14.05_amd64_KDE.iso"
    	loopback loop (hd1,2)$isofile
    	linux (loop)/boot/sabayon root=/dev/ram0 aufs cdroot locale=en_US loop=/livecd.squashfs looptype=squashfs isoboot=$isofile
    	initrd (loop)/boot/sabayon.igz
    }

#### Slackware Linux

    menuentry '[loopback]slackware64-14.1-install-dvd' {
    	set isofile='/boot/iso/slackware64-14.1-install-dvd.iso'
    	loopback loop (hd1,2)$isofile
    	linux (loop)/kernels/huge.s/bzImage printk.time=0
    	initrd (loop)/isolinux/initrd.img
    }

#### Ubuntu

    menuentry "[loopback]ubuntu-14.04-desktop-amd64" {
    	set isofile="/boot/iso/ubuntu-14.04-desktop-amd64.iso"
    	loopback loop (hd1,2)$isofile
    	linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile locale=en_US.UTF-8
    	initrd (loop)/casper/initrd.lz
    }

### 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=(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:

    # 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
    }

### 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:

    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.

### 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`:

     GRUB_FORCE_HIDDEN_MENU="true"

And the following file should be created and made executable:

    /etc/grub.d/31_hold_shift

    #! /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
    # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    # 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/>.

    prefix="/usr"
    exec_prefix="${prefix}"
    datarootdir="${prefix}/share"

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

    found_other_os=

    make_timeout () {

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

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

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

      adjust_timeout

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

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
        else
            set grub_boot=($grub_boot)
        fi

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

    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

### Using the command shell environment to boot operating systems

    grub>

The GRUB's command shell environment can be used to boot operating systems. A common scenario may be to boot Windows / Linux stored on a drive/partition via chainloading.

Chainloading means to load another boot-loader from the current one, ie, chain-loading.

The other bootloader may be embedded at the starting of the disk(MBR) or at the starting of a partition.

#### Chainloading a partition

    set root=(hdX,Y)
    chainloader +1
    boot

X=0,1,2... Y=1,2,3...

For example to chainload Windows stored in the first partiton of the first hard disk,

    set root=(hd0,1)
    chainloader +1
    boot

Similarly GRUB installed to a partition can be chainloaded.

#### Chainloading a disk/drive

    set root=hdX
    chainloader +1
    boot

#### Chainloading Windows/Linux installed in UEFI mode

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

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

#### Normal loading

See the examples in #Using_the_rescue_console

## GUI configuration tools

Following package may be installed:

- grub-customizer — Customize the bootloader (GRUB or BURG)

  https://launchpad.net/grub-customizer || grub-customizer

- grub2-editor — KDE4 control module for configuring the GRUB bootloader

  http://kde-apps.org/content/show.php?content=139643 || grub2-editor

- startupmanager — GUI app for changing the settings of GRUB Legacy, GRUB, Usplash and Splashy (abandonned)

  http://sourceforge.net/projects/startup-manager/ || startupmanager

## 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 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
    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

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.

## Troubleshooting

### Intel BIOS not booting GPT

#### MBR

Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.

This can be circumvented by using (for instance) fdisk to mark one of the GPT partitions (preferably the 1007 KiB partition you have created for GRUB already) bootable in the MBR. This can be achieved, using fdisk, by the following commands: Start fdisk against the disk you are installing, for instance `fdisk /dev/sda`, then press `a` and select the partition you wish to mark as bootable (probably #1) by pressing the corresponding number, finally press `w` to write the changes to the MBR.

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.

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

Add:

    set pager=1
    set debug=all

to `grub.cfg`.

### "No suitable mode found" error

If you get this error when booting any menuentry:

    error: no suitable mode found
    Booting however

Then you need to initialize GRUB graphical terminal (`gfxterm`) with proper video mode (`gfxmode`) in GRUB. This video mode is passed by GRUB to the linux kernel via 'gfxpayload'. In case of UEFI systems, if the GRUB video mode is not initialized, no kernel boot messages will be shown in the terminal (atleast until KMS kicks in).

Copy `/usr/share/grub/unicode.pf2` to ${GRUB_PREFIX_DIR} (`/boot/grub/` in case of BIOS and UEFI systems). If GRUB UEFI was installed with `--boot-directory=$esp/EFI` set, then the directory is `$esp/EFI/grub/`:

    # cp /usr/share/grub/unicode.pf2 ${GRUB_PREFIX_DIR}

If `/usr/share/grub/unicode.pf2` does not exist, install bdf-unifont, create the `unifont.pf2` file and then copy it to `${GRUB_PREFIX_DIR}`:

    # grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf

Then, in the `grub.cfg` file, add the following lines to enable GRUB to pass the video mode correctly to the kernel, without of which you will only get a black screen (no output) but booting (actually) proceeds successfully without any system hang.

BIOS systems:

    insmod vbe

UEFI systems:

    insmod efi_gop
    insmod efi_uga

After that add the following code (common to both BIOS and UEFI):

    insmod font

    if loadfont ${prefix}/fonts/unicode.pf2
    then
        insmod gfxterm
        set gfxmode=auto
        set gfxpayload=keep
        terminal_output gfxterm
    fi

As you can see for gfxterm (graphical terminal) to function properly, `unicode.pf2` font file should exist in `${GRUB_PREFIX_DIR}`.

### msdos-style error message

    grub-setup: warn: This msdos-style partition label has no post-MBR gap; embedding will not be possible!
    grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.
                However, blocklists are UNRELIABLE and its use is discouraged.
    grub-setup: error: If you really want blocklists, use --force.

This error may occur when you try installing GRUB in a VMware container. Read more about it here. It happens when the first partition starts just after the MBR (block 63), without the usual space of 1 MiB (2048 blocks) before the first partition. Read #Master Boot Record (MBR) specific instructions

### 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

Category:

- Boot loaders