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If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks. | If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks. | ||
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===== Install to partition or partitionless disk ===== | ===== Install to partition or partitionless disk ===== |
Revision as of 13:15, 22 November 2013
GRUB - not to be confused with GRUB Legacy - is the next generation of the GRand Unified Bootloader. GRUB is derived from PUPA which was a research project to develop the next generation of what is now GRUB Legacy. GRUB has been rewritten from scratch to clean up everything and provide modularity and portability [1].
In brief, the bootloader is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the Linux kernel. The kernel, in turn, initializes the rest of the operating system.
Contents
- 1 Preface
- 2 Installation
- 3 Generating main configuration file
- 4 Basic configuration
- 5 Advanced configuration
- 5.1 Manually creating grub.cfg
- 5.2 Dual-booting
- 5.3 Booting an ISO directly from GRUB
- 5.4 LVM
- 5.5 RAID
- 5.6 Using labels
- 5.7 Password protection of GRUB menu
- 5.8 Hide GRUB unless the Shift key is held down
- 5.9 Combining the use of UUIDs and basic scripting
- 6 Using the command shell
- 7 GUI configuration tools
- 8 parttool for hide/unhide
- 9 Using the rescue console
- 10 Troubleshooting
- 11 See also
Preface
- The name GRUB officially refers to version 2 of the software, see [2]. If you are looking for the article on the legacy version, see GRUB Legacy.
- GRUB supports Btrfs as root (without a separate
/boot
filesystem) compressed with either zlib or LZO - GRUB does not support F2fs as root so you will need a separate
/boot
with a supported filesystem.
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 bootsectors 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 filesystem. The size of 1007 KiB will allow for the following partition to be correctly alligned at 1024 KiB. If needed, the partition can also be located somewhere else on the disk, but it should be within the first 2 TiB region. Set the partition type to 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.
- This partition should be created before
grub-install
orgrub-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
Check if you have GPT and an ESP
An EFI System Partition (ESP) is needed on every disc you wan 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 Archlinux 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 filesystem and the 'boot' flag enabled. On it, there should be a folder called "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
BIOS systems
GRUB can be installed with the grub package from the official repositories. It will replace grub-legacyAUR , if it is installed.
/boot/grub/i386-pc/core.img
file and the GRUB modules in /boot/grub/i386-pc
. You need to update them manually using grub-install
as explained below.Install boot files
There are 3 ways to install GRUB boot files in BIOS booting:
- Install to 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
)
Install to disk
/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 diskTo setup 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/sda
-
/dev/sda
used for example only. -
--target=i386-pc
instructsgrub-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.
Continue with #Generating main configuration file. The GRUB config file is not generated by grub-install
command.
Install to partition or partitionless disk
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
instructsgrub-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 dir /boot/grub
. The sector locations of core.img
may change whenever the filesystem in the partition is being altered (files copied, deleted etc.). For more info see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915.
The workaround for this is to set the immutable flag on /boot/grub/i386-pc/core.img
(using chattr command as mentioned above) so that the sector locations of the core.img
file in the disk is not altered. The immutable flag on /boot/grub/i386-pc/core.img
needs to be set only if grub
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).
Continue with #Generate config file. The GRUB config file is not generated by grub-install
command.
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
instructsgrub-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
First install the grub, dosfstools, and efibootmgr packages, then follow the instructions below. (The last two packages are required for EFI support in grub.)
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
(forIA32-efi
replacex86_64-efi
withi386-efi
in the below commands) - To do this, you need to boot using UEFI and not BIOS. If you booted by just copying the ISO file to the USB drive, you have booted using BIOS. You will need to create a UEFI bootable USB device and reboot with it 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.
- Without
--target
or--directory
option, grub-install cannot determine for which firmware to install. In such casesgrub-install
will printsource_dir does not exist. Please specify --target or --directory
. -
--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 thegrubx64.efi
file. - If you notice carefully, there is no <device_path> option (Eg:
/dev/sda
) at the end of thegrub-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. You may proceed to configuration.
Alternate 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 Beginners' Guide#GRUB 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 the GRUB UEFI modules and other related files. This is done using the grub-mkstandalone
command (included in grub) as follows"
# mkdir -p /tmp/boot/grub # echo 'configfile ${cmdpath}/grub.cfg' > /tmp/boot/grub/grub.cfg ## use single quotes, ${cmdpath} should be present as it is # cd /tmp # grub-mkstandalone -d /usr/lib/grub/x86_64-efi/ -O x86_64-efi --modules="part_gpt part_msdos" --fonts="unicode" -o "$esp/EFI/grub/grubx64_standalone.efi" "boot/grub/grub.cfg"
The grubx64_standalone.efi
file expects grub.cfg
to be within its $prefix which is (memdisk)/boot/grub
. Hence we create a simple (memdisk)/boot/grub/grub.cfg
which redirects to ${cmdpath}/grub.cfg
(ie. in the same dir as grubx64_standalone.efi
).
The reason to cd
into /tmp
and to pass the file path as boot/grub/grub.cfg
(notice the lack of a leading slash - boot/
vs. /boot/
) is because dir1/dir2/file
is included as (memdisk)/dir1/dir2/file
by the grub-mkstandalone
script.
You need to create a UEFI Boot Manager entry for $esp/EFI/arch_grub/grubx64_standalone.efi
using efibootmgr
. Follow UEFI#efibootmgr.
grubx64_standalone.efi
looks for grub.cfg
in the same dir as it is located, not in /boot/grub
.Generating main configuration file
After the installation, the main configuration file grub.cfg
needs to be generated. The generation process can be influenced by a variety of options in /etc/default/grub
and scripts in /etc/grub.d/
, this is covered in the #Configuration section.
grub.cfg
has to be re-generated after any change to /etc/default/grub
or /etc/grub.d/*
.Use the grub-mkconfig tool to generate grub.cfg
:
# grub-mkconfig -o /boot/grub/grub.cfg
- The file path for BIOS systems is
/boot/grub/grub.cfg
, NOT/boot/grub/i386-pc/grub.cfg
. - For EFI systems, if GRUB was installed with the
--boot-directory=$esp/EFI
option set, thegrub.cfg
file must be placed in the same directory asgrubx64.efi
. Otherwise, thegrub.cfg
file goes in/boot/grub/
, just like in BIOS systems. - 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.
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
. It can detect only systems on mounted partitions, so mount them before 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
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 ${prefix}/menu.lst
Boot into Arch and re-create the proper GRUB /boot/grub/grub.cfg
config file.
Basic configuration
This section covers only editing the /etc/default/grub
configuration file. See #Advanced configuration if you need more.
/etc/default/grub
.Additional arguments
To pass custom additional arguments to the Linux image, you can set the GRUB_CMDLINE_LINUX
+ GRUB_CMDLINE_LINUX_DEFAULT
variables in /etc/default/grub
. The two are appended to each other and passed to kernel when generating regular boot entries. For the recovery boot entry, only GRUB_CMDLINE_LINUX
is used in the generation.
It is not necessary to use both, but can be useful. For example, you could use GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sdaX quiet"
where sdaX
is your swap partition to enable resume after hibernation. This would generate a recovery boot entry without the resume and without quiet suppressing kernel messages during a boot from that menu entry. Though, the other (regular) menu entries would have them as options.
For generating the GRUB recovery entry you also have to comment out #GRUB_DISABLE_RECOVERY=true
in /etc/default/grub
.
You can also use GRUB_CMDLINE_LINUX="resume=/dev/disk/by-uuid/${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.
- If this example does not work for you try to replace
gfxmode="1024x768x32"
byvbemode="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 thevbeinfo
command
If this method does not work for you, the deprecated vga=
method will still work. Just
add it next to the "GRUB_CMDLINE_LINUX_DEFAULT="
line in /etc/default/grub
for eg: "GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"
will give you a 1024x768
resolution.
You can choose one of these resolutions: 640×480
, 800×600
, 1024×768
, 1280×1024
, 1600×1200
, 1920×1200
915resolution hack
Some times for Intel graphic adapters neither # hwinfo --framebuffer
nor vbeinfo
will show you the desired resolution. In this case you can use 915resolution
hack. This hack will temporarily modify video BIOS and add needed resolution. See 915resolution's home page
First you need to find a video mode which will be modified later. For that we need the GRUB command shell:
sh:grub> 915resolution -l
Intel 800/900 Series VBIOS Hack : version 0.5.3 [...] Mode 30 : 640x480, 8 bits/pixel [...]
Next, we overwrite the Mode 30
with 1440x900
resolution:
/etc/grub.d/00_header
[...] 915resolution 30 1440 900 # Inserted line set gfxmode=${GRUB_GFXMODE} [...]
Lastly we need to set GRUB_GFXMODE
as described earlier, regenerate grub.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"
/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"
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=5 GRUB_HIDDEN_TIMEOUT_QUIET=false
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 filesystem UUIDs are used by default in GRUB.
/boot/grub.cfg
file needs regeneration with the new UUID in /etc/default/grub
every time a relevant filesystem is resized or recreated. Remember this when modifying partitions & filesystems with a Live-CD.Whether to use UUIDs is controlled by an option in /etc/default/grub
:
GRUB_DISABLE_LINUX_UUID=true
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
/etc/grub.d/40_custom
or /boot/grub/custom.cfg
, will need savedefault
added.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'
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
.
/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.
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
grub-mkconfig
command, and it is best to edit your /etc/default/grub
or one of the scripts in the /etc/grub.d
folder.A basic GRUB config file uses the following options:
-
(hdX,Y)
is the 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 titledtitle
-
set root=(hdX,Y)
sets the boot partition, where the kernel and GRUB modules are stored (boot need not be a separate partition, and may simply be a directory under the "root" partition (/
)
An example configuration:
/boot/grub/grub.cfg
# Config file for GRUB - The GNU GRand Unified Bootloader # /boot/grub/grub.cfg # DEVICE NAME CONVERSIONS # # Linux Grub # ------------------------- # /dev/fd0 (fd0) # /dev/sda (hd0) # /dev/sdb2 (hd1,2) # /dev/sda3 (hd0,3) # # Timeout for menu set timeout=5 # Set default boot entry as Entry 0 set default=0 # (0) Arch Linux menuentry "Arch Linux" { set root=(hd0,1) linux /vmlinuz-linux root=/dev/sda3 ro initrd /initramfs-linux.img } ## (1) Windows #menuentry "Windows" { # set root=(hd0,3) # chainloader +1 #}
Dual-booting
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:
# 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 infos).
/etc/grub.d/40_custom:
#!/bin/sh exec tail -n +3 $0 # This file provides an easy way to add custom menu entries. Simply type the # menu entries you want to add after this comment. Be careful not to change # the 'exec tail' line above. menuentry "HP / Microsoft Windows 8.1" { echo "Loading HP / Microsoft Windows 8.1..." insmod part_gpt insmod fat insmod search_fs_uuid insmod chain search --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2 763A-9CB6 chainloader (${root})/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 --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2 763A-9CB6 chainloader (${root})/EFI/HP/boot/bootmgfw.efi } menuentry "System shutdown" { echo "System shutting down..." halt } menuentry "System restart" { echo "System rebooting..." reboot }
Assuming that the other distro is on partition sda2
:
menuentry "Other Linux" { set root=(hd0,2) linux /boot/vmlinuz (add other options here as required) initrd /boot/initrd.img (if the other kernel uses/needs one) }
Requires that FreeBSD is installed on a single partition with UFS. Assuming it is installed on sda4
:
menuentry "FreeBSD" { set root=(hd0,4) chainloader +1 }
This assumes that your Windows partition is sda3
. Remember you need to point set root and chainloader to the system reserve partition that windows made when it installed, not the actual partition windows is on. This example works if your system reserve partition is sda3
.
# (2) Windows XP menuentry "Windows XP" { set root="(hd0,3)" chainloader +1 }
If the Windows bootloader is on an entirely different hard drive than GRUB, it may be necessary to trick Windows into believing that it is the first hard drive. This was possible with drivemap
. Assuming GRUB is on hd0
and Windows is on hd2
, you need to add the following after set root
:
drivemap -s hd0 hd2
if [ "${grub_platform}" == "efi" ]; then menuentry "Microsoft Windows Vista/7/8 x86_64 UEFI-GPT" { insmod part_gpt insmod fat insmod search_fs_uuid insmod chain search --fs-uuid --set=root $hints_string $uuid chainloader /EFI/Microsoft/Boot/bootmgfw.efi } fi
where $hints_string
and $uuid
are obtained with the following two commands. $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 $esp
. There might be case differences in the path to Windows's EFI file, what with being Windows, and all.
menuentry "System shutdown" { echo "System shutting down..." halt }
menuentry "System restart" { echo "System rebooting..." reboot }
Windows installed in BIOS-MBR mode
bootmgr
directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.bootmgr
, not your "real" Windows partition (usually C:). When showing all UUIDs with blkid, the system partition is the one with LABEL="SYSTEM RESERVED"
or LABEL="SYSTEM"
and is only about 100 to 200 MB in size (much like the boot partition for Arch). See Wikipedia:System partition and boot partition for more info.Throughout this section, it is assumed your Windows partition is /dev/sda1
. A different partition will change every instance of hd0,msdos1. First, find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the bootmgr
and its files reside. For example, if Windows bootmgr
exists at /media/SYSTEM_RESERVED/bootmgr
:
For Windows Vista/7/8:
# grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr 69B235F6749E84CE
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1
bootmgr
with NTLDR
in the above commands. And note that there may not be a separate SYSTEM_RESERVED partition; just probe the file NTLDR on your Windows partition.Then, add the below code to /etc/grub.d/40_custom
or /boot/grub/custom.cfg
and regenerate grub.cfg
with grub-mkconfig
as explained above to boot Windows (XP, Vista, 7 or 8) installed in BIOS-MBR mode:
For Windows Vista/7/8:
if [ "${grub_platform}" == "pc" ]; then menuentry "Microsoft Windows Vista/7/8 BIOS-MBR" { insmod part_msdos insmod ntfs insmod search_fs_uuid insmod ntldr search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE ntldr /bootmgr } fi
For Windows XP:
if [ "${grub_platform}" == "pc" ]; then menuentry "Microsoft Windows XP" { insmod part_msdos insmod ntfs insmod search_fs_uuid insmod ntldr search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE ntldr /bootmgr } fi
\boot\bcd
(error code 0xc000000f
). You can fix it going to Windows Recovery Console (cmd from install disk) and executing:
x:\> "bootrec.exe /fixboot" x:\> "bootrec.exe /RebuildBcd".Do not use
bootrec.exe /Fixmbr
because it will wipe GRUB out./etc/grub.d/40_custom
can be used as a template to create /etc/grub.d/nn_custom
. Where nn
defines the precendence, indicating the order the script is executed. The order scripts are executed determine the placement in the grub boot menu.
nn
should be greater than 06 to ensure necessary scripts are executed first.With Windows via EasyBCD and NeoGRUB
Since EasyBCD's NeoGRUB currently does not understand the GRUB menu format, chainload to it by replacing the contents of your C:\NST\menu.lst
file with lines similar to the following:
default 0 timeout 1
title Chainload into GRUB v2 root (hd0,7) kernel /boot/grub/i386-pc/core.img
Finally, recreate your grub.cfg
using grub-mkconfig
.
Booting an ISO directly from GRUB
Edit /etc/grub.d/40_custom
or /boot/grub/custom.cfg
to add an entry for the target ISO. When finished, update the GRUB menu as with the usual grub-mkconfig -o /boot/grub/grub.cfg
(as root).
Arch ISO
/archives
on hd0,6
.(hd1,$partition)
and either /dev/sdbY
for the img_dev
parameter or a persistent name, e.g. img_dev=/dev/disk/by-label/CORSAIR
.x86_64
menuentry "Archlinux-2013.05.01-dual.iso" --class iso { set isofile="/archives/archlinux-2013.05.01-dual.iso" set partition="6" loopback loop (hd0,$partition)/$isofile linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201305 img_dev=/dev/sda$partition img_loop=$isofile earlymodules=loop initrd (loop)/arch/boot/x86_64/archiso.img }
i686
menuentry "Archlinux-2013.05.01-dual.iso" --class iso { set isofile="/archives/archlinux-2013.05.01-dual.iso" set partition="6" loopback loop (hd0,$partition)/$isofile linux (loop)/arch/boot/i686/vmlinuz archisolabel=ARCH_201305 img_dev=/dev/sda$partition img_loop=$isofile earlymodules=loop initrd (loop)/arch/boot/i686/archiso.img }
Ubuntu ISO
/archives
on hd0,6
. Users must adjust the location and hdd/partition in the lines below to match their systems.menuentry "ubuntu-13.04-desktop-amd64.iso" { set isofile="/archives/ubuntu-13.04-desktop-amd64.iso" loopback loop (hd0,6)/$isofile linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash -- initrd (loop)/casper/initrd.lz }
menuentry "ubuntu-12.04-desktop-amd64.iso" { set isofile="/archives/ubuntu-12.04-desktop-amd64.iso" loopback loop (hd0,6)/$isofile linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash -- initrd (loop)/casper/initrd.lz }
Other ISOs
Other working configurations from link Source.
LVM
If you use LVM for your /boot
, add the following before menuentry lines:
insmod lvm
and specify your root in the menuentry as:
set root=lvm/lvm_group_name-lvm_logical_boot_partition_name
Example:
# (0) Arch Linux menuentry "Arch Linux" { insmod lvm set root=lvm/VolumeGroup-lv_boot # you can only set following two lines linux /vmlinuz-linux root=/dev/mapper/VolumeGroup-root ro initrd /initramfs-linux.img }
RAID
GRUB provides convenient handling of RAID volumes. You need to add insmod mdraid
which allows you to address the volume natively. For example, /dev/md0
becomes:
set root=(md0)
whereas a partitioned RAID volume (e.g. /dev/md0p1
) becomes:
set root=(md0,1)
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 RAID1 array housing /boot
is housed on /dev/sda
and /dev/sdb
.
Using labels
It is possible to use labels, human-readable strings attached to filesystems, by using the --label
option to search
. First of all, label your existing partition:
# tune2fs -L LABEL PARTITION
Then, add an entry using labels. An example of this:
menuentry "Arch Linux, session texte" { search --label --set=root archroot linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro initrd /boot/initramfs-linux.img }
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:
/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
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 environemnt 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
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)
- grub2-editor — KDE4 control module for configuring the GRUB bootloader
- kcm-grub2 — This Kcm module manages the most common settings of GRUB
- startupmanager — GUI app for changing the settings of GRUB Legacy, GRUB, Usplash and Splashy (abandonned)
parttool for hide/unhide
If you have a Windows 9x paradigm with hidden C:\
disks GRUB can hide/unhide it using parttool
. For example, to boot the third C:\
disk of three Windows 9x installations on the CLI enter the CLI and:
parttool hd0,1 hidden+ boot- parttool hd0,2 hidden+ boot- parttool hd0,3 hidden- boot+ set root=hd0,3 chainloader +1 boot
Using the rescue console
See #Using the command shell first. If unable to activate the standard shell, one possible solution is to boot using a live CD or some other rescue disk to correct configuration errors and reinstall GRUB. However, such a boot disk is not always available (nor necessary); the rescue console is surprisingly robust.
The available commands in GRUB rescue include insmod
, ls
, set
, and unset
. This example uses set
and insmod
. set
modifies variables and insmod
inserts new modules to add functionality.
Before starting, the user must know the location of their /boot
partition (be it a separate partition, or a subdirectory under their root):
grub rescue> set prefix=(hdX,Y)/boot/grub
where X is the physical drive number and Y is the partition number.
To expand console capabilities, insert the linux
module:
grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
/boot
from the path, (i.e. type set prefix=(hdX,Y)/grub
and insmod (hdX,Y)/grub/linux.mod
).This introduces the linux
and initrd
commands, which should be familiar (see #Configuration).
An example, booting Arch Linux:
set root=(hd0,5) linux /boot/vmlinuz-linux root=/dev/sda5 initrd /boot/initramfs-linux.img boot
With a separate boot partition, again change the lines accordingly:
set root=(hd0,5) linux /vmlinuz-linux root=/dev/sda6 initrd /initramfs-linux.img boot
After successfully booting the Arch Linux installation, users can correct grub.cfg
as needed and then reinstall GRUB.
To reinstall GRUB and fix the problem completely, changing /dev/sda
if needed. See #Bootloader installation for details.
Troubleshooting
Intel BIOS not booting GPT
Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.
This can be circumvented by using (for instance) fdisk to mark one of the GPT partitions (preferably the 1007 KiB partition you have created for GRUB already) bootable in the MBR. This can be achieved, using fdisk, by the following commands: Start fdisk against the disk you are installing, for instance fdisk /dev/sda
, then press a
and select the partition you wish to mark as bootable (probably #1) by pressing the corresponding number, finally press w
to write the changes to the MBR.
fdisk
or similar, not in GParted or others, as they will not set the bootable flag in the MBR.More information is available here
Enable debug messages
Add:
set pager=1 set debug=all
to grub.cfg
.
"No suitable mode found" error
If you get this error when booting any menuentry:
error: no suitable mode found Booting however
Then you need to initialize GRUB graphical terminal (gfxterm
) with proper video mode (gfxmode
) in GRUB. This video mode is passed by GRUB to the linux kernel via 'gfxpayload'. In case of UEFI systems, if the GRUB video mode is not initialized, no kernel boot messages will be shown in the terminal (atleast until KMS kicks in).
Copy /usr/share/grub/unicode.pf2
to ${GRUB_PREFIX_DIR} (/boot/grub/
in case of BIOS and UEFI systems). If GRUB UEFI was installed with --boot-directory=$esp/EFI
set, then the directory is $esp/EFI/grub/
:
# cp /usr/share/grub/unicode.pf2 ${GRUB_PREFIX_DIR}
If /usr/share/grub/unicode.pf2
does not exist, install bdf-unifont, create the unifont.pf2
file and then copy it to ${GRUB_PREFIX_DIR}
:
# grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
Then, in the grub.cfg
file, add the following lines to enable GRUB to pass the video mode correctly to the kernel, without of which you will only get a black screen (no output) but booting (actually) proceeds successfully without any system hang.
BIOS systems:
insmod vbe
UEFI systems:
insmod efi_gop insmod efi_uga
After that add the following code (common to both BIOS and UEFI):
insmod font
if loadfont ${prefix}/fonts/unicode.pf2 then insmod gfxterm set gfxmode=auto set gfxpayload=keep terminal_output gfxterm fi
As you can see for gfxterm (graphical terminal) to function properly, unicode.pf2
font file should exist in ${GRUB_PREFIX_DIR}
.
msdos-style error message
grub-setup: warn: This msdos-style partition label has no post-MBR gap; embedding will not be possible! grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists. However, blocklists are UNRELIABLE and its use is discouraged. grub-setup: error: If you really want blocklists, use --force.
This error may occur when you try installing GRUB in a VMware container. Read more about it here. It happens when the first partition starts just after the MBR (block 63), without the usual space of 1 MiB (2048 blocks) before the first partition. Read #Master Boot Record (MBR) specific instructions
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
# 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
- Official GRUB Manual - https://www.gnu.org/software/grub/manual/grub.html
- Ubuntu wiki page for GRUB - https://help.ubuntu.com/community/Grub2
- GRUB wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
- Wikipedia's page on BIOS Boot partition
- http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html - quite complete description of how to configure GRUB