Difference between revisions of "GRUB"

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[[Category:Boot loaders (English)]]
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[[Category:Boot loaders]]
{{i18n|GRUB2}}
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[[ar:GRUB]]
[[fr:GRUB2]]
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[[cs:GRUB]]
{{Article summary start}}
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[[de:GRUB]]
{{Article summary text|Covers various aspects of the next generation of the GRand Unified Bootloader (GRUB2).}}
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[[el:GRUB]]
{{Article summary heading|Overview}}
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[[es:GRUB]]
{{Article summary text|{{Boot process overview}}}}
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[[fa:گراب]]
{{Article summary heading|Related}}
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[[fr:GRUB]]
{{Article summary wiki|Burg}} - Burg is a brand-new boot loader based on GRUB2. It uses a new object format which allows it to be built in a wider range of OS, including Linux/Windows/OSX/Solaris/FreeBSD, etc. It also has a highly configurable menu system which works in both text and graphic mode.
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[[he:GRUB]]
{{Article summary heading|Resources}}
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[[id:GRUB]]
{{Article summary link|GNU GRUB -- GNU Project|http://www.gnu.org/software/grub/}}
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[[it:GRUB]]
{{Article summary end}}
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[[ja:GRUB]]
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[[nl:GRUB]]
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[[pt:GRUB]]
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[[ru:GRUB]]
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[[zh-hans:GRUB]]
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[[zh-hant:GRUB]]
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{{Related articles start}}
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{{Related|Arch boot process}}
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{{Related|Boot loaders}}
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{{Related|Master Boot Record}}
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{{Related|GUID Partition Table}}
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{{Related|Unified Extensible Firmware Interface}}
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{{Related|GRUB Legacy}}
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{{Related|GRUB/EFI examples}}
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{{Related|GRUB/Tips and tricks}}
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{{Related|Multiboot USB drive}}
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{{Related articles end}}
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[https://www.gnu.org/software/grub/ GRUB] (GRand Unified Bootloader) is a [[:Category:Boot loaders|multi-boot loader]]. It is derived from [http://www.nongnu.org/pupa/ PUPA] which was a research project to develop the replacement of what is now known as [[GRUB Legacy]]. The latter had become too difficult to maintain and GRUB was rewritten from scratch with the aim to provide modularity and portability [https://www.gnu.org/software/grub/grub-faq.html#q1]. The current GRUB is also referred to as GRUB 2 while GRUB Legacy corresponds to versions 0.9x.
  
[http://www.gnu.org/software/grub/ GRUB2] is the next generation of the GRand Unified Bootloader (GRUB). GRUB2 is derived from [http://www.nongnu.org/pupa/ PUPA] which was a research project to investigate the next generation of GRUB. GRUB2 has been rewritten from scratch to clean up everything and provide modularity and portability [http://www.gnu.org/software/grub/grub-faq.en.html#q1].
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{{Note|In the entire article {{ic|''esp''}} denotes the mountpoint of the [[EFI system partition]] aka ESP.}}
  
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.
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== BIOS systems ==
  
{{Note|From 1.99-6 onwards GRUB2 supports Btrfs as root (without a separate {{ic|/boot}} filesystem) compressed with either zlib or LZO.}}
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=== GUID Partition Table (GPT) specific instructions ===
  
{{Note|[[Archboot]] iso is required for {{Pkg|grub2-bios}} and {{Pkg|grub2-efi-x86_64}} installation. The official installer AIF (Arch Installation Framework) based [[Archiso]] does not support it.}}
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On a BIOS/[[GPT]] configuration, a [https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation BIOS boot partition] is required.  GRUB embeds its {{ic|core.img}} into this partition.
  
== Preface ==
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{{Note|
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* Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme. Read more on [[Partitioning#GUID_Partition_Table|GUID partition tables]].
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* This additional partition is only needed on a GRUB, BIOS/GPT partitioning scheme.  Previously, for a GRUB, BIOS/MBR partitioning scheme, GRUB used the Post-MBR gap for the embedding the {{ic|core.img}}). On GPT, however, there is no guaranteed unused space before the first partition.
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* For [[UEFI]] systems this extra partition is not required, since no embedding of boot sectors takes place in that case. However, UEFI systems still require an [[EFI system partition]].
 +
}}
  
Although, [[GRUB]] (i.e. version 0.9x) is the standard bootloader of Arch Linux, it is considered 'legacy' by upstream. It is being replaced by GRUB2 and [[Syslinux]] in many distributions. Upstream recommends GRUB2 >=1.99 over GRUB Legacy, even for current GRUB Legacy users.
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Create a mebibyte partition ({{ic|1=+1M}} with ''fdisk'' or ''gdisk'') on the disk with no file system and with partition type GUID {{ic|21686148-6449-6E6F-744E-656564454649}}.
  
=== Notes for current GRUB Legacy users ===
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* Select partition type {{ic|BIOS boot}} for [[fdisk]], {{ic|ef02}} for [[gdisk]].
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* For [[parted]] set/activate the flag {{ic|bios_grub}} on the partition.
  
* There are differences in the commands of GRUB and GRUB2. Familiarize yourself with [http://www.gnu.org/software/grub/manual/grub.html#Commands GRUB2 commands] before proceeding (e.g. "find" has been replaced with "search").
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This partition can be in any position order but has to be on the first 2 TiB of the disk. This partition needs to be created before GRUB installation. When the partition is ready, install the bootloader as per the instructions below.
  
* GRUB2 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).
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The space before the first partition can also be used as the BIOS boot partition though it will be out of GPT alignment specification.  Since the partition will not be regularly accessed performance issues can be disregarded, though some disk utilities will display a warning about it.  In ''fdisk'' or ''gdisk'' create a new partition starting at sector 34 and spanning to 2047 and set the type. To have the viewable partitions begin at the base consider adding this partition last.
  
* Device naming has changed between GRUB and GRUB2. Partitions are numbered from 1 instead of 0 while drives are still numbered from 0, and prefixed with partition-table type. For example, {{ic|/dev/sda1}} would be referred to as {{ic|(hd0,msdos1)}} (for MBR) or {{ic|(hd0,gpt1)}} (for GPT) using GRUB2.
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=== Master Boot Record (MBR) specific instructions ===
  
=== Preliminary Requirements for GRUB2 ===
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Usually the post-[[MBR]] gap (after the 512 byte MBR region and before the start of the first 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 {{ic|core.img}} ({{bug|24103}}). It is advisable to use a partitioning tool that supports 1 MiB partition alignment to obtain this space as well as to satisfy other non-512 byte sector issues (which are unrelated to embedding of {{ic|core.img}}).
  
==== BIOS systems ====
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=== Installation ===
  
===== [[GPT]] specific instructions =====
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[[Install]] the {{Pkg|grub}} package. It will replace {{AUR|grub-legacy}}, where already installed. Then do:
  
GRUB2 in BIOS-GPT configuration requires a BIOS Boot Partition to embed its {{ic|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 GRUB2 only in BIOS-GPT setups. No such partition type exists in case of MBR partitioning (at least not for GRUB2). This partition is also not required if the system is UEFI based, as no embedding of bootsectors takes place in that case. Syslinux does not require this partition.
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# grub-install --target=i386-pc /dev/sd'''X'''
  
For a BIOS-GPT configuration, create a 2 MiB partition using cgdisk or GNU Parted with no filesystem. The location of the partition in the partition table does not matter but it should be within the first 2 TiB region of the disk. It is advisable to put it somewhere in the beginning of the disk before the /boot partition. Set the partition type to "EF02" in cgdisk or {{ic|set <BOOT_PART_NUM> bios_grub on}} in GNU Parted.
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where {{ic|/dev/sd'''X'''}} is the disk where grub is to be installed (for example, disk {{ic|/dev/sda}} and '''not''' partition {{ic|/dev/sda1}}).
  
{{Note|This partition should be created before {{ic|grub-install}} or {{ic|grub-setup}} is run or before the '''Install Bootloader''' step of the Archlinux installer (if GRUB2 BIOS is selected as bootloader).}}
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Now you must [[#Generate the main configuration file]].
  
===== [[MBR]] aka msdos partitioning specific instructions =====
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If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks.
  
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 32 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 GRUB2's {{ic|core.img}} ([https://bugs.archlinux.org/task/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 {{ic|core.img}}).
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{{Tip|See [[GRUB/Tips and tricks#Alternative installation methods]] for other ways to install GRUB, such as to a USB stick.}}
  
If you do not dual-boot with MS Windows (any version) in BIOS systems, it is advisable to switch to GPT partitioning - [[GUID_Partition_Table#Convert_from_MBR_to_GPT_without_data_loss]]
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See {{man|8|grub-install}} and [https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation GRUB Manual] for more details on the ''grub-install'' command.
  
{{Note|Create the 2MiB partition mentioned above BEFORE you convert to GPT. If you do not, gparted will not resize your boot partition to allow its creation, and when you reboot GRUB2 will not know where to look.}}
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== UEFI systems ==
  
==== UEFI systems ====
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{{Note|
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* It is recommended to read and understand the [[UEFI]], [[GPT]] and [[Arch boot process#Under UEFI]] pages.
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* When installing to use UEFI it is important to start the install with your machine in UEFI mode. The Arch Linux install media must be UEFI bootable.
 +
}}
  
===== Create and Mount the UEFI SYSTEM PARTITION =====
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=== Check for an EFI System Partition ===
  
Follow [[Unified_Extensible_Firmware_Interface#Create_an_UEFI_SYSTEM_PARTITION_in_Linux]] for instructions on creating a UEFI SYSTEM PARTITION. Then mount the UEFI SYSTEM PARTITION at {{ic|/boot/efi}}. It should be FAT32 formatted and should be >=200 MiB in size. If you have mounted the UEFISYS partition in some other mountpoint, replace {{ic|/boot/efi}} in the below instructions with that mountpoint:
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To boot from a disk using UEFI, the recommended disk partition table is GPT and this is the layout that is assumed in this article. An [[EFI system partition]] (ESP) is required on every bootable disk. If you are installing Arch Linux on an UEFI-capable computer with an installed operating system, like Windows 10 for example, it is very likely that you already have an ESP.
  
# mkdir -p /boot/efi
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To find out the disk partition scheme and the system partition, use {{ic|parted}} as root on the disk you want to boot from:
# mount -t vfat <UEFISYS_PART_DEVICE> /boot/efi
 
  
Create a <UEFI_SYSTEM_PARTITION>{{ic|/efi}} directory, if it does not exist:
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# parted /dev/sd''x'' print
  
# mkdir -p /boot/efi/efi
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The command returns:
  
== Installation ==
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* The disk partition layout: if the disk is GPT, it indicates {{ic|Partition Table: gpt}}.
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* The list of partitions on the disk: Look for the EFI system partition in the list, it is a small (usually about 100-550 MiB) partition with a {{ic|fat32}} file system and with the flag {{ic|esp}} enabled. To confirm this is the ESP, mount it and check whether it contains a directory named {{ic|EFI}}, if it does this is definitely the ESP.
  
=== During Arch Linux installation ===
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Once it is found, '''take note of the partition number''', it will be required for the [[#Installation_2|GRUB installation]]. If you do not have an ESP, you will need to create one. See the [[EFI system partition]] article.
  
* Skip the '''Install Bootloader''' step and exit the installer.
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=== Installation ===
* Configure the network:
 
# aif -p partial-configure-network
 
This will bring up a prompt; put in the network interface to use, (e.g., {{ic|eth0}}) and use DHCP for easy configuration.
 
* If you did not configure the installed system's {{ic|/etc/resolv.conf}} file during installation (for instance, if you plan to let DHCP generate it later), you will need to copy the one generated by AIF when it configured the network:
 
# cp /etc/resolv.conf /mnt/etc/resolv.conf
 
* If you run into network issues in the pacman update step below, you may have needed to install the {{Pkg|net-tools}} package.
 
* Check and see if the dm_mod module is loaded. If it is not, load it manually (you might need {{Pkg|grub2-bios}}).:
 
# lsmod | grep dm_mod
 
# modprobe dm-mod
 
{{Note|This is necessary at this point, and cannot be postponed after the chroot. If you try to use modprobe in a chroot environment that has a later kernel version from that of the installing device (at the time of writing, 2.6.33), modprobe will fail. This happens routinely using the Arch "net" installations.}}
 
* From the installer's live shell, chroot to the installed system:
 
# mount -o bind /dev /mnt/dev
 
# mount -t proc /proc /mnt/proc/
 
# mount -t sysfs /sys /mnt/sys/
 
# chroot /mnt bash
 
* Update pacman's database:
 
# pacman-db-upgrade
 
* Refresh the package list (with an extra {{ic|-y}} flag to force a refresh of all package lists even if they appear to be up to date):
 
# pacman -Syy
 
* Install the GRUB2 package as mentioned in the section [[#From a running Arch Linux]] (Note that the {{ic|dm-mod}} module has already been loaded, no need to do that again).
 
  
=== From a running Arch Linux ===
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{{Note|
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* UEFI firmwares are not implemented consistently across manufacturers. The procedure described below is intended to work on a wide range of UEFI systems but those experiencing problems despite applying this method are encouraged to share detailed information, and if possible the turnarounds found, for their hardware-specific case. A [[GRUB/EFI examples]] article has been provided for such cases.
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* The section assumes you are installing GRUB for x86_64 systems. For IA32 (32-bit) EFI systems (not to be confused with 32-bit CPUs), replace {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
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}}
  
==== BIOS systems ====
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First, [[install]] the packages {{Pkg|grub}} and {{Pkg|efibootmgr}}: ''GRUB'' is the bootloader while ''efibootmgr'' is used by the GRUB installation script to write boot entries to NVRAM.
  
===== Backup Important Data =====
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Then follow the below steps to install GRUB:
  
Though a GRUB2 installation should run smoothly, it is strongly recommended to make a backup before installing {{Pkg|grub2-bios}}.
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# [[EFI system partition#Mount the partition|Mount the EFI System Partition]] and in the remainder of this section, substitute {{ic|''esp''}} with its mount point.
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# Choose a bootloader identifier, here named {{ic|'''''GRUB'''''}}. A directory of that name will be created to store the EFI binary in the ESP and this is the name that will appear in the UEFI boot menu to identify the GRUB boot entry.
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# Execute the following command to install the GRUB EFI application {{ic|grubx64.efi}} to {{ic|''esp''/EFI/'''''GRUB'''''/}} and install its modules to {{ic|/boot/grub/x86_64-efi/}}.
  
* copy GRUB modules and configuration
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# grub-install --target=x86_64-efi --efi-directory=''esp'' --bootloader-id='''''GRUB'''''
  
# cp -a /boot/grub /path/to/backup/
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After the above install completed the main GRUB directory is located at {{ic|/boot/grub/}}. Note that {{ic|grub-install}} also tries to [[GRUB/Tips_and_tricks#Create_a_GRUB_entry_in_the_firmware_boot_manager|create an entry in the firmware boot manager]], named {{ic|'''''GRUB'''''}} in the above example.
  
* backup the MBR and GRUB Legacy stage 1.5
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Remember to [[#Generate the main configuration file]] after finalizing [[#Configuration]].  
  
# dd if=/dev/sdX of=/path/to/backup/first-sectors bs=512 count=63
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{{Tip|If you use the option {{ic|--removable}} then GRUB will be installed to {{ic|''esp''/EFI/BOOT/BOOTX64.EFI}} (or {{ic|''esp''/EFI/BOOT/BOOTIA32.EFI}} for the {{ic|i386-efi}} target) and you will have the additional ability of being able to boot from the drive in case EFI variables are reset or you move the drive to another computer. Usually you can do this by selecting the drive itself similar to how you would using BIOS. If dual booting with Windows, be aware Windows usually has a {{ic|BOOT}} folder inside the {{ic|EFI}} folder of the EFI system partition, but its only purpose is to recreate the UEFI boot entry for Windows.}}
  
Replace /dev/sdaX with your actual disk path.
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{{Note|
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* While some distributions require a {{ic|/boot/efi}} or {{ic|/boot/EFI}} directory, Arch does not.
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* {{ic|--efi-directory}} and {{ic|--bootloader-id}} are specific to GRUB UEFI, {{ic|--efi-directory}} replaces {{ic|--root-directory}} which is deprecated.
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* You might note the absence of a ''device_path'' option (e.g.: {{ic|/dev/sda}}) in the {{ic|grub-install}} command. In fact any ''device_path'' provided will be ignored by the GRUB UEFI install script. Indeed, UEFI bootloaders do not use a MBR bootcode or partition boot sector at all.
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}}
  
{{Note|This command backs up the partition table too. Be careful while restoring if you've changed your partition setup in the meantime}}
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See [[#UEFI|UEFI troubleshooting]] in case of problems. Additionally see [[GRUB/Tips and tricks#UEFI further reading]].
  
To backup only the MBR boot code use:
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== Generate the main configuration file ==
  
# dd if=/dev/sdX of=/path/to/backup/mbr-boot-code bs=440 count=1
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After the installation, the main configuration file {{ic|grub.cfg}} needs to be generated. The generation process can be influenced by a variety of options in {{ic|/etc/default/grub}} and scripts in {{ic|/etc/grub.d/}}; see [[#Configuration]].
  
You may now lightly remove {{ic|/boot/grub}} with:
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If you have not done additional configuration, the automatic generation will determine the root filesystem of the system to boot for the configuration file. For that to succeed it is important that the system is either booted or chrooted into.
  
# rm -rf /boot/grub
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{{Note|Remember that {{ic|grub.cfg}} has to be re-generated after any change to {{ic|/etc/default/grub}} or files in {{ic|/etc/grub.d/}}.}}
  
and follow the instructions below. You know that if things get nasty, you could reboot your system thanks to an installation media and:
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Use the ''grub-mkconfig'' tool to generate {{ic|grub.cfg}}:
 
 
* move old GRUB Legacy or GRUB2 files out of the way
 
 
 
# mv /boot/grub /boot/grub.nonfunctional
 
 
 
* copy GRUB Legacy back to {{ic|/boot}}
 
 
 
# cp -a /path/to/backup/grub /boot/
 
 
 
* replace MBR and next 62 sectors of sda with backed up copy (DANGEROUS!)
 
 
 
# dd if=/path/to/backup/first-sectors of=/dev/sdX bs=512 count=63
 
 
 
{{Note|This command also restores the partition table so be careful.}}
 
 
 
To restore only the MBR boot code use:
 
 
 
# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=440 count=1
 
 
 
===== Install grub2-bios package =====
 
 
 
The GRUB2 package can be installed with pacman (and will replace {{Pkg|grub}}, if it is installed).
 
 
# pacman -S grub2-bios
 
 
 
{{Note|Simply installing the package won't update the {{ic|/boot/grub/i386-pc/core.img}} file and the GRUB2 modules in {{ic|/boot/grub/i386-pc}}. You need to update them manually using {{ic|grub-install}} as explained below.}}
 
 
 
Also load the device-mapper kernel module without which {{ic|grub-probe}} does not reliably detect disks and partitions:
 
 
 
# modprobe dm-mod
 
 
 
===== Install grub2-bios boot files =====
 
 
 
There are 3 ways to install GRUB2 boot files in BIOS booting:
 
*[[#Install_to_440-byte_MBR_boot_code_region]] (recommended) ,
 
*[[#Install_to_Partition_or_Partitionless_Disk]] (not recommended),
 
*[[#Generate_core.img_alone]] (safest method, but requires another BIOS bootloader like [[grub-legacy]] or [[syslinux]] to be installed to chainload {{ic|/boot/grub/i386-pc/core.img}} ).
 
 
 
====== Install to 440-byte MBR boot code region ======
 
 
 
To setup {{ic|grub2-bios}} in the 440-byte Master Boot Record boot code region, populate the {{ic|/boot/grub}} directory, generate the {{ic|/boot/grub/i386-pc/core.img}} file, and embed it in the 32 KiB (minimum size - varies depending on partition alignment) post-MBR gap (MBR disks) or in BIOS Boot Partition (GPT disks), run:
 
 
 
# grub-install --directory=/usr/lib/grub/i386-pc --target=i386-pc --boot-directory=/boot --recheck --debug /dev/sda
 
 
 
where {{ic|/dev/sda}} is the destination of the installation (in this case the MBR of the first SATA disk). If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB2 on multiple physical disks.
 
 
 
The {{ic|--no-floppy}} tells {{ic|grub2-bios}} utilities not to search for any floppy devices which reduces the overall execution time of {{ic|grub-install}} on many systems (it will also prevent the issue below from occurring). Otherwise you get an error that looks like this:
 
 
 
grub-probe: error: Cannot get the real path of '/dev/fd0'
 
Auto-detection of a filesystem module failed.
 
Please specify the module with the option '--modules' explicitly.
 
 
 
{{Note|{{ic|--no-floppy}} has been removed from {{ic|grub-install}} in 2.00~beta2 upstream release, and replaced with {{ic|--allow-floppy}}.}}
 
 
 
{{Warning|Make sure to check the {{ic|/boot}} directory if you use the latter. Sometimes the {{ic| boot-directory}} parameter creates another {{ic|/boot}} folder inside of {{ic|/boot}}. A wrong install would look like: {{ic|/boot/boot/grub/}}.}}
 
 
 
====== Install to Partition or Partitionless Disk ======
 
 
 
{{Note|{{ic|grub2-bios}} (any version - including upstream Bazaar repo) does not encourage installation to a partition boot sector or a partitionless disk like GRUB Legacy or syslinux does. Neither do the Arch devs.}}
 
 
 
To setup {{ic|grub2-bios}} to a partition boot sector, to a partitionless disk (also called superfloppy) or to a floppy disk, run (using for example /dev/sda1 as the /boot partition)
 
 
# chattr -i /boot/grub/i386-pc/core.img
 
# grub-install --directory=/usr/lib/grub/i386-pc --target=i386-pc --boot-directory=/boot --recheck --force --debug /dev/sda1
 
# chattr +i /boot/grub/i386-pc/core.img
 
 
 
You need to use the {{ic|--force}} option to allow usage of blocklists and should not use {{ic|1=--grub-setup=/bin/true}} (which is similar to simply generating {{ic|core.img}}).
 
 
 
{{ic|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 {{ic|--force}} you may get the below error and {{ic|grub-setup}} will not setup its boot code in the partition boot sector.
 
 
/sbin/grub-setup: error: will not proceed with blocklists
 
 
 
With {{ic|--force}} you should get
 
 
 
Installation finished. No error reported.
 
 
 
The reason why {{ic|grub-setup}} does not by default allow this is because in case of partition or a partitionless disk is that {{ic|grub2-bios}} relies on embedded blocklists in the partition bootsector to locate the {{ic|/boot/grub/i386-pc/core.img}} file and the prefix dir {{ic|/boot/grub}}. The sector locations of {{ic|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 {{ic|/boot/grub/i386-pc/core.img}} (using chattr command as mentioned above) so that the sector locations of the {{ic|core.img}} file in the disk is not altered. The immutable flag on {{ic|/boot/grub/i386-pc/core.img}} needs to be set only if {{ic|grub2-bios}} is installed to a partition boot sector or a partitionless disk, not in case of installtion to MBR or simple generation of {{ic|core.img}} without embedding any bootsector (mentioned above).
 
 
 
====== Generate core.img alone ======
 
 
 
To populate the {{ic|/boot/grub}} directory and generate a {{ic|/boot/grub/i386-pc/core.img}} file '''without''' embedding any {{ic|grub2-bios}} bootsector code in the MBR, post-MBR region, or the partition bootsector, add {{ic|1=--grub-setup=/bin/true}} to {{ic|grub-install}}:
 
 
# grub-install --directory=/usr/lib/grub/i386-pc --target=i386-pc --grub-setup=/bin/true --boot-directory=/boot --recheck --debug /dev/sda
 
 
 
You can then chainload GRUB2's {{{ic|core.img}} from GRUB Legacy or syslinux as a Linux kernel or a multiboot kernel.
 
 
 
===== Generate GRUB2 BIOS Config file =====
 
 
 
Finally, generate a configuration for GRUB2 (this is explained in greater detail in the Configuration section):
 
  
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 
  # grub-mkconfig -o /boot/grub/grub.cfg
  
{{Note|The file path is {{ic|/boot/grub/grub.cfg}}, NOT {{ic|/boot/grub/i386-pc/grub.cfg}}.}}
+
By default the generation scripts automatically add menu entries for Arch Linux to any generated configuration. See [[Multiboot USB drive#Boot entries]] and [[#Dual-booting]] for custom menu entries for other systems.
  
If grub2 complains about "no suitable mode found" while booting, go to [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]].
+
{{Tip|To have ''grub-mkconfig'' search for other installed systems and automatically add them to the menu, [[install]] the {{Pkg|os-prober}} package and [[mount]] the partitions that contain other systems.}}
  
If {{ic|grub-mkconfig}} fails, convert your {{ic|/boot/grub/menu.lst}} file to {{ic|/boot/grub/grub.cfg}} using:
+
{{Note|
 +
* The default file path is {{ic|/boot/grub/grub.cfg}}, not {{ic|/boot/grub/i386-pc/grub.cfg}}. The {{Pkg|grub}} package includes a sample {{ic|/boot/grub/grub.cfg}}; ensure your intended changes are written to this file.
 +
* If you are trying to run ''grub-mkconfig'' in a chroot or ''systemd-nspawn'' container, you might notice that it does not work, complaining that ''grub-probe'' cannot get the "canonical path of /dev/sdaX". In this case, try using ''arch-chroot'' as described in the [https://bbs.archlinux.org/viewtopic.php?pid&#61;1225067#p1225067 BBS post].
 +
}}
  
# grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
+
== Configuration ==
  
For example:
+
This section only covers editing the {{ic|/etc/default/grub}} configuration file. See [[GRUB/Tips and tricks]] for more information.
  
{{hc|/boot/grub/menu.lst|<nowiki>
+
Remember to always [[#Generate the main configuration file]] after making changes to {{ic|/etc/default/grub}}.
default=0
 
timeout=5
 
  
title  Arch Linux Stock Kernel
+
=== Additional arguments ===
root  (hd0,0)
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux.img
 
  
title  Arch Linux Stock Kernel Fallback
+
To pass custom additional arguments to the Linux image, you can set the {{ic|GRUB_CMDLINE_LINUX}} + {{ic|GRUB_CMDLINE_LINUX_DEFAULT}} variables in {{ic|/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 {{ic|GRUB_CMDLINE_LINUX}} is used in the generation.
root  (hd0,0)
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux-fallback.img
 
</nowiki>}}
 
  
{{hc|/boot/grub/grub.cfg|<nowiki>
+
It is not necessary to use both, but can be useful. For example, you could use {{ic|1=GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sdaX quiet"}} where {{ic|sda'''X'''}} is your swap partition to enable resume after hibernation. This would generate a recovery boot entry without the resume and without {{ic|quiet}} suppressing kernel messages during a boot from that menu entry. Though, the other (regular) menu entries would have them as options.
set default='0'; if [ x"$default" = xsaved ]; then load_env; set default="$saved_entry"; fi
 
set timeout=5
 
  
menuentry 'Arch Linux Stock Kernel' {
+
By default ''grub-mkconfig'' determines the [[UUID]] of the root filesystem for the configuration. To disable this, uncomment {{ic|1=GRUB_DISABLE_LINUX_UUID=true}}.  
  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' {
+
For generating the GRUB recovery entry you have to ensure that {{ic|GRUB_DISABLE_RECOVERY}} is not set to {{ic|true}} in {{ic|/etc/default/grub}}.
  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'
 
}
 
</nowiki>}}
 
  
If you forgot to create a GRUB2 {{ic|/boot/grub/grub.cfg}} config file and simply rebooted into GRUB2 Command Shell, type:
+
You can also use {{ic|1=GRUB_CMDLINE_LINUX="resume=UUID=''uuid-of-swap-partition''"}}
  
sh:grub> insmod legacycfg
+
See [[Kernel parameters]] for more info.
sh:grub> legacy_configfile ${prefix}/menu.lst
 
  
Boot into Arch and re-create the proper GRUB2 {{ic|/boot/grub/grub.cfg}} config file.
+
=== LVM ===
  
{{Note|This option works only in BIOS systems, not in UEFI systems.}}
+
If you use [[LVM]] for your {{ic|/boot}} or {{ic|/}} root partition, make sure that the {{ic|lvm}} module is preloaded:
  
===== Multiboot in BIOS =====
+
{{hc|/etc/default/grub|2=
 +
GRUB_PRELOAD_MODULES="... lvm"
 +
}}
  
====== Boot Microsoft Windows installed in BIOS-MBR mode ======
+
=== RAID ===
  
{{Note|GRUB2 supports booting {{ic|bootmgr}} directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.}}
+
GRUB provides convenient handling of [[RAID]] volumes. You need to load GRUB modules {{ic|mdraid09}} or {{ic|mdraid1x}} to allow you to address the volume natively:
  
Find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the {{ic|bootmgr}} and its files reside. For example, if Windows {{ic|bootmgr}} exists at {{ic|/media/Windows/bootmgr}}:
+
{{hc|/etc/default/grub|2=
 +
GRUB_PRELOAD_MODULES="... mdraid09 mdraid1x"
 +
}}
  
# grub-probe --target=fs_uuid /media/Windows/bootmgr
+
For example, {{ic|/dev/md0}} becomes:
69B235F6749E84CE
 
  
Then, add the below code to {{ic|/etc/grub.d/40_custom}} and regenerate {{ic|grub.cfg}} with {{ic|grub-mkconfig}} as explained above to chainload Windows (Vista, 7 or 8) installed in BIOS-MBR mode:
+
set root=(md/0)
  
menuentry "Microsoft Windows 7 BIOS-MBR" {
+
whereas a partitioned RAID volume (e.g. {{ic|/dev/md0p1}}) becomes:
    insmod part_msdos
 
    insmod ntfs
 
    insmod search_fs_uuid
 
    insmod ntldr   
 
    search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
 
    ntldr /bootmgr
 
}
 
  
For Windows XP
+
set root=(md/0,1)
  
menuentry "Microsoft Windows XP" {
+
To install grub when using RAID1 as the {{ic|/boot}} partition (or using {{ic|/boot}} housed on a RAID1 root partition), on BIOS systems, simply run ''grub-install'' on both of the drives, such as:
    insmod part_msdos
 
    insmod ntfs
 
    insmod search_fs_uuid
 
    insmod ntldr   
 
    search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
 
    ntldr /ntldr
 
}
 
  
==== [[UEFI]] systems ====
+
# grub-install --target=i386-pc --debug /dev/sda
 +
# grub-install --target=i386-pc --debug /dev/sdb
  
===== Install grub2-uefi package =====
+
Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}.
  
{{Note|Unless specified as EFI 1.x , EFI and UEFI terms are used interchangeably to denote UEFI 2.x firmware. Also unless stated explicitely, the instructions are general and not Mac specific. Some of them may not work or may be different in Macs. Apple's EFI implementation is neither a EFI 1.x version nor UEFI 2.x version but mixes up both. This kind of firmware does not fall under any one UEFI Specification version and is therefore not a standard UEFI firmware.}}
+
{{Note|GRUB supports booting from [[Btrfs]] RAID 0/1/10, but ''not'' RAID 5/6. You may use [[mdadm]] for RAID 5/6, which is supported by GRUB.}}
  
GRUB2 UEFI bootloader is available in Arch Linux only from version 1.99~rc1. To install, first [https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interface#Detecting_UEFI_Firmware_Arch Detect which UEFI firmware arch] you have (either x86_64 or i386).
+
=== Encryption ===
  
Depending on that, install the appropriate package
+
==== Root partition ====
  
For 64-bit aka x86_64 UEFI firmware:
+
To encrypt a root filesystem to be used with GRUB, add the {{ic|encrypt}} hook or the {{ic|sd-encrypt}} hook (if using systemd hooks) to [[mkinitcpio]]. See [[dm-crypt/System configuration#mkinitcpio]] for details, and [[Mkinitcpio#Common hooks]] for alternative encryption hooks.
# pacman -S grub2-efi-x86_64
 
  
For 32-bit aka i386 UEFI firmware:
+
If using the {{ic|encrypt}} hook, add the {{ic|cryptdevice}} parameter to {{ic|/etc/default/grub}}.
# pacman -S grub2-efi-i386
 
  
{{Note|Simply installing the package won't update the {{ic|grub.efi}} file and the GRUB2 modules in the UEFI System Partition. You need to do this manually using {{ic|grub-install}} as explained below.}}
+
{{hc|/etc/default/grub|2=
 +
GRUB_CMDLINE_LINUX="cryptdevice=UUID=''device-UUID'':cryptroot"
 +
}}
  
Also load the device-mapper kernel module without which {{ic|grub-probe}} does not reliably detect disks and partitions:
+
If using the {{ic|sd-encrypt}} hook, add {{ic|rd.luks.name}}:
  
# modprobe dm-mod
+
{{hc|/etc/default/grub|2=
 +
GRUB_CMDLINE_LINUX="rd.luks.name=''device-UUID''=cryptroot"
 +
}}
  
===== Install grub2-uefi boot files =====
+
where ''device-UUID'' is the UUID of the LUKS-encrypted device.
  
====== Install to UEFI SYSTEM PARTITION ======
+
Be sure to [[#Generate the main configuration file|generate the main configuration file]] when done.
  
{{Note|The below commands assume you are using {{ic|grub2-efi-x86_64}} (for {{ic|grub2-efi-i386}} replace {{ic|x86_64}} with {{ic|i386}} in the below commands).}}
+
For further information about bootloader configuration for encrypted devices, see [[Dm-crypt/System configuration#Boot loader]].
  
The UEFI system partition will need to be mounted at {{ic|/boot/efi/}} for the GRUB2 install script to detect it.
+
{{Note|If you wish to encrypt {{ic|/boot}} either as a separate partition or part of the {{ic|/}} partition, further setup is required. See [[#Boot partition]].}}
  
# mkdir -p /boot/efi
+
{{Tip|If you are upgrading from a working GRUB Legacy configuration, check {{ic|/boot/grub/menu.lst.pacsave}} for the correct device/label to add. Look for them after the text {{ic|kernel /vmlinuz-linux}}.}}
# mount -t vfat /dev/sdXY /boot/efi
 
  
Install GRUB UEFI application to {{ic|/boot/efi/efi/arch_grub}} and its modules to {{ic|/boot/grub/x86_64-efi}} (recommended) using
+
==== Boot partition ====
  
# grub-install --directory=/usr/lib/grub/x86_64-efi --target=x86_64-efi --root-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub --recheck --debug
+
GRUB can be set to ask for a password to open a [[LUKS]] blockdevice in order to read its configuration and load any [[initramfs]] and [[kernel]] from it. This option tries to solve the issue of having an [[Dm-crypt/Specialties#Securing the unencrypted_boot partition|unencrypted boot partition]]. {{ic|/boot}} is '''not''' required to be kept in a separate partition; it may also stay under the system's root {{ic|/}} directory tree.
  
If you want to install grub2 modules and {{ic|grub.cfg}} at the directory {{ic|/boot/efi/efi/grub}} and the {{ic|grubx64.efi}} application at {{ic|/boot/efi/efi/arch_grub}} use
+
{{Warning|GRUB does not support LUKS2 headers. Make sure you do not specify {{ic|luks2}} for the type parameter when creating the encrypted partition using {{ic|cryptsetup luksFormat}}.}}
  
# grub-install --directory=/usr/lib/grub/x86_64-efi --target=x86_64-efi --root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=arch_grub --recheck --debug
+
To enable this feature encrypt the partition with {{ic|/boot}} residing on it using [[LUKS]] as normal. Then add the following option to {{ic|/etc/default/grub}}:
  
In this case {{ic|grub2-efi-x86_64}} will be installed into {{ic|/boot/grub}}, making the behavior consistent with the BIOS verion of GRUB2, but this is not recommended if you use both {{ic|grub2-bios}} and {{ic|grub2-efi-x86_64}} in your system, as this will overwrite {{ic|grub2-bios }}modules in {{ic|/boot/grub}}.
+
{{hc|/etc/default/grub|output=
 +
GRUB_ENABLE_CRYPTODISK=y
 +
}}
  
The {{ic|--root-directory}} option mentions the mountpoint of UEFI SYSTEM PARTITION , {{ic|--bootloader-id}} mentions the name of the directory used to store the {{ic|grubx64.efi}} file and {{ic|--boot-directory}} mentions the directory wherein the actual modules will be installed (and into which {{ic|grub.cfg}} should be created).
+
Be sure to [[#Generate the main configuration file]] while the partition containing {{ic|/boot}} is mounted.  
  
The actual paths are:
+
Without further changes you will be prompted twice for a passhrase: the first for GRUB to unlock the {{ic|/boot}} mount point in early boot, the second to unlock the root filesystem itself as described in [[#Root partition]]. You can use a [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs|keyfile]] to avoid this.
  
<root-directory>/<efi or EFI>/<bootloader-id>/grubx64.efi
+
{{Note|
 +
* If you use a special keymap, a default GRUB installation will not know it. This is relevant for how to enter the passphrase to unlock the LUKS blockdevice.
 +
* In order to perform system updates involving the {{ic|/boot}} mount point, ensure that the encrypted {{ic|/boot}} is unlocked and mounted before performing an update. With a separate {{ic|/boot}} partition, this may be accomplished automatically on boot by using [[crypttab]] with a [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs|keyfile]].
 +
* If you experience issues getting the prompt for a password to display (errors regarding cryptouuid, cryptodisk, or "device not found"), try reinstalling grub as below appending the following to the end of your installation command:
 +
{{bc|1=# grub-install --target=x86_64-efi --efi-directory=''esp'' --bootloader-id=grub '''--modules="part_gpt part_msdos"'''}}
 +
}}
  
<boot-directory>/grub/x86_64-efi/<all modules, grub.efi, core.efi, grub.cfg>
+
=== Multiple entries ===
  
{{Note|the {{ic|--bootloader-id}} option does not change {{ic|<boot-directory>/grub}}, i.e. you cannot install the modules to {{ic|<boot-directory>/<bootloader-id>}}, the path is hard-coded to {{ic|<boot-directory>/grub}}.}}
+
For tips on managing multiple GRUB entries, for example when using both {{Pkg|linux}} and {{Pkg|linux-lts}} kernels, see [[GRUB/Tips and tricks#Multiple entries]].
  
In {{ic|<nowiki>--root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=grub</nowiki>}}
+
=== Chainloading an Arch Linux .efi file ===
  
<root-directory>/<efi or EFI>/<bootloader-id> == <boot-directory>/grub == /boot/efi/efi/grub
+
If you have an ''.efi'' file generated from following [[Secure Boot]] or other means, {{ic|/etc/grub.d/40_custom}} can be edited to add a new menu entry before regenerating {{ic|grub.cfg}} with {{ic|grub-mkconfig}}.
  
In {{ic|<nowiki>--root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=arch_grub</nowiki>}}
+
{{hc|/etc/grub.d/40_custom|output=
 +
menuentry 'Arch Linux .efi' {
 +
insmod part_gpt
 +
insmod chain
 +
set root='(hdX,gptY)'
 +
chainloader /EFI/''path''/''file''.efi
 +
}
 +
}}
  
<root-directory>/<efi or EFI>/<bootloader-id> == /boot/efi/efi/arch_grub
+
=== Dual-booting ===
<boot-directory>/grub == /boot/efi/efi/grub
 
  
In {{ic|<nowiki>--root-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub</nowiki>}}
+
{{Merge|Multiboot USB drive|Same topic, substituting USB drives for SATA drives is trivial.}}
  
<root-directory>/<efi or EFI>/<bootloader-id> == /boot/efi/efi/arch_grub
+
The best way to add other entries is editing {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}}. The entries in this file will be automatically added after rerunning {{ic|grub-mkconfig}}.
<boot-directory>/grub == /boot/grub
 
  
In {{ic|<nowiki>--root-directory=/boot/efi --boot-directory=/boot --bootloader-id=grub</nowiki>}}
+
==== "Shutdown" menu entry ====
  
<root-directory>/<efi or EFI>/<bootloader-id> == /boot/efi/efi/grub
+
{{bc|menuentry "System shutdown" {
<boot-directory>/grub == /boot/grub
+
echo "System shutting down..."
 +
halt
 +
}
 +
}}
  
The {{ic|<nowiki><root-directory>/<efi or EFI>/<bootloader-id>/grubx64.efi</nowiki>}} is an exact copy of {{ic|<nowiki><boot-directory>/grub/x86_64-efi/core.efi</nowiki>}}.
+
==== "Restart" menu entry ====
  
{{Note|This behavior of {{ic|--root-directory}}, {{ic|--boot-directory}}, and {{ic|--bootloader-id}} options are specific to UEFI systems and does not occur is BIOS mode. In {{ic|grub-install}}, {{ic|--root-directory}} is deprecated and {{ic|--bootloader-id}} does not exist.}}
+
{{bc|menuentry "System restart" {
+
echo "System rebooting..."
In all the cases the UEFI SYSTEM PARTITION should be mounted for {{ic|grub-install}} to install {{ic|grubx64.efi}} in it, which will be launched by the firmware (using the efibootmgr created boot entry in non-Mac systems).
+
reboot
 +
}
 +
}}
  
If you notice carefully, there is no <device_path> option (Eg: {{ic|/dev/sda}}) at the end of the {{ic|grub-install}} command unlike the case of setting up GRUB2 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.
+
==== "Firmware setup" menu entry (UEFI only) ====
  
You may now be able to UEFI boot your system by creating a {{ic|grub.cfg}} file by following [[#Generate_GRUB2_UEFI_Config_file]] and [[#Create_GRUB2_entry_in_the_Firmware_Boot_Manager]].
+
{{bc|menuentry "Firmware setup" {
 +
fwsetup
 +
}
 +
}}
  
===== Create GRUB2 entry in the Firmware Boot Manager =====
+
==== GNU/Linux menu entry ====
  
====== Non-Mac UEFI systems ======
+
Assuming that the other distribution is on partition {{ic|sda2}}:
  
{{ic|grub-install}} will ensure that {{ic|/boot/efi/efi/arch_grub/grubx64.efi}} is launched by default if it detects {{ic|efibootmgr}} and if it is able to access UEFI Runtime Services. Follow [[Unified_Extensible_Firmware_Interface#efibootmgr]] for more info.
+
{{bc|1=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)
 +
}
 +
}}
  
If you have problems running GRUB2 in UEFI mode you can try the following (worked on an ASUS Z68 mainboard):
+
Alternatively let grub search for the right partition by ''UUID'' or ''label'':
 
# cp /boot/efi/efi/arch_grub/grubx64.efi /boot/efi/shellx64.efi
 
  
or
+
{{bc|1=menuentry "Other Linux" {
+
        # assuming that UUID is 763A-9CB6
# cp /boot/efi/efi/arch_grub/grubx64.efi /boot/efi/efi/shellx64.efi
+
search --set=root --fs-uuid 763A-9CB6
  
or
+
        # search by label OTHER_LINUX (make sure that partition label is unambiguous)
 +
        #search --set=root --label OTHER_LINUX
  
# cp /boot/efi/efi/arch_grub/grubx64.efi /boot/efi/efi/shell/shellx64.efi
+
linux /boot/vmlinuz (add other options here as required, for example: root=UUID=763A-9CB6)
 +
initrd /boot/initrd.img (if the other kernel uses/needs one)
 +
}
 +
}}
  
After this launch the UEFI Shell from the UEFI setup/menu (in ASUS UEFI BIOS, switch to advanced mode, press Exit in the top right corner and choose "Launch EFI shell from filesystem device"). The GRUB2 menu will show up and you can boot into your system. Afterwards you can use efibootmgr to setup a menu entry (see above).
+
==== Windows installed in UEFI/GPT Mode menu entry ====
  
====== Apple Mac EFI systems ======
+
This mode determines where the Windows bootloader resides and chain-loads it after Grub when the menu entry is selected. The main task here is finding the EFI partition and running the bootloader from it.
  
{{Note|TODO: GRUB upstream Bazaar mactel branch http://bzr.savannah.gnu.org/lh/grub/branches/mactel/changes}}
+
{{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. See [[Dual boot with Windows#Windows UEFI vs BIOS limitations]] and [[Dual boot with Windows#Bootloader UEFI vs BIOS limitations]] for more information.}}
{{Note|TODO: Fedora's mactel-boot ( https://bugzilla.redhat.com/show_bug.cgi?id&#61;755093 )}}
 
  
Use bless command from within Mac OS X to set {{ic|grubx64.efi}} as the default boot option. You can also boot from the Mac OS X install disc and launch a Terminal there if you only have Linux installed. In the Terminal, create a directory and mount the EFI System Partition:
+
{{bc|1=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
 +
}}
  
# cd /Volumes
+
where {{ic|$hints_string}} and {{ic|$fs_uuid}} are obtained with the following two commands.
# mkdir efi
 
# mount -t msdos /dev/disk0s1 /Volumes/efi
 
  
Then run bless on {{ic|grub.efi}} and on the EFI partition to set them as the default boot options.
+
The {{ic|$fs_uuid}} command determines the UUID of the EFI partition:
  
# bless --folder=/Volumes/efi --file=/Volumes/efi/efi/arch_grub/grubx64.efi --setBoot
+
{{hc|1=# grub-probe --target=fs_uuid ''esp''/EFI/Microsoft/Boot/bootmgfw.efi|2=
# bless --mount=/Volumes/efi --file=/Volumes/efi/efi/arch_grub/grubx64.efi --setBoot
+
1ce5-7f28
 +
}}
  
More info at https://help.ubuntu.com/community/UEFIBooting#Apple_Mac_EFI_systems_.28both_EFI_architecture.29.
+
Alternatively one can run {{ic|blkid}} (as root) and read the UUID of the EFI system partition from there.
  
===== Generate GRUB2 UEFI Config file =====
+
The {{ic|$hints_string}} command will determine the location of the EFI system partition, in this case harddrive 0:
  
Finally, generate a configuration for GRUB2 (this is explained in greater detail in the Configuration section):
+
{{hc|1=# grub-probe --target=hints_string ''esp''/EFI/Microsoft/Boot/bootmgfw.efi|2=
 +
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
 +
}}
  
# grub-mkconfig -o <boot-directory>/grub/grub.cfg
+
These two commands assume the ESP Windows uses is mounted at {{ic|''esp''}}. There might be case differences in the path to Windows's EFI file, what with being Windows, and all.
  
{{Note|The file path is {{ic|<boot-directory>/grub/grub.cfg}}, NOT {{ic|<boot-directory>/grub/x86_64-efi/grub.cfg}}.}}
+
==== Windows installed in BIOS/MBR mode ====
  
If you used {{ic|<nowiki>--boot-directory=/boot</nowiki>}} :
+
{{Note|GRUB supports booting {{ic|bootmgr}} directly and [https://www.gnu.org/software/grub/manual/grub.html#Chain_002dloading chainloading] of partition boot sector is no longer required to boot Windows in a BIOS/MBR setup.}}
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
{{Warning|It is the '''system partition''' that has {{ic|/bootmgr}}, not your "real" Windows partition (usually C:). In {{ic|blkid}} output, the system partition is the one with {{ic|LABEL&#61;"SYSTEM RESERVED"}} or {{ic|LABEL&#61;"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.}}
  
If you used {{ic|<nowiki>--boot-directory=/boot/efi/efi</nowiki>}} :
+
Throughout this section, it is assumed your Windows partition is {{ic|/dev/sda1}}. A different partition will change every instance of hd0,msdos1. Add the below code to {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} and regenerate {{ic|grub.cfg}} with {{ic|grub-mkconfig}} as explained above to boot Windows (XP, Vista, 7, 8 or 10) installed in BIOS/MBR mode:
  
# grub-mkconfig -o /boot/efi/efi/grub/grub.cfg
+
{{Note|These menu entries will work only in BIOS boot mode. It will not work in UEFI installed GRUB. See [[Dual boot with Windows#Windows UEFI vs BIOS limitations]] and [[Dual boot with Windows#Bootloader UEFI vs BIOS limitations]] .}}
  
This is independent of the value of {{ic|--bootloader-id}} option.
+
In both examples {{ic|''XXXXXXXXXXXXXXXX''}} is the filesystem UUID which can be found with command {{ic|lsblk --fs}}.
  
If grub2-uefi complains about "no suitable mode found" while booting, try [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]].
+
For Windows Vista/7/8/8.1/10:
  
===== Create GRUB2 Standalone UEFI Application =====
+
if [ "${grub_platform}" == "pc" ]; then
 +
  menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS/MBR" {
 +
    insmod part_msdos
 +
    insmod ntfs
 +
    insmod search_fs_uuid
 +
    insmod ntldr   
 +
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 ''XXXXXXXXXXXXXXXX''
 +
    ntldr /bootmgr
 +
  }
 +
fi
  
It is possible to create a {{ic|grubx64_standalone.efi}} application which has all the modules embeddded in a memdisk within the uefi application, thus removing the need for having a separate directory populated with all the GRUB2 uefi modules and other related files. This is done using the {{ic|grub-mkstandalone}} command which is included in {{Pkg|grub2-common}} >= 1:1.99-6 package.
+
For Windows XP:
  
The easiest way to do this would be with the install command already mentioned before, but specifying the modules to include. For example:
+
  if [ "${grub_platform}" == "pc" ]; then
 
+
  menuentry "Microsoft Windows XP" {
  # grub-mkstandlone --directory="/usr/lib/grub-x86_64-efi" --format="x86_64-efi" --compression="xz" \
+
     insmod part_msdos
--output="/boot/efi/efi/arch_grub/grubx64_standalone.efi" <any extra files you want to include>
+
     insmod ntfs
 
 
The {{ic|grubx64_standalone.efi}} file expects {{ic|grub.cfg}} to be within its $prefix which is {{ic|(memdisk)/boot/grub}}. The memdisk is embedded within the efi app. The {{ic|grub-mkstandlone}} script allow passing files to be included in the memdisk image to be as the arguments to the script (in <any extra files you want to include>).
 
 
 
If you have the {{ic|grub.cfg}} at {{ic|/home/user/Desktop/grub.cfg}}, then create a temporary {{ic|/home/user/Desktop/boot/grub/}} directory, copy the {{ic|/home/user/Desktop/grub.cfg}} to {{ic|/home/user/Desktop/boot/grub/grub.cfg}}, cd into {{ic|/home/user/Desktop/boot/grub/}} and run
 
 
 
# grub-mkstandlone --directory="/usr/lib/grub-x86_64-efi" --format="x86_64-efi" --compression="xz" \
 
--output="/boot/efi/efi/arch_grub/grubx64_standalone.efi" "boot/grub/grub.cfg"
 
 
 
The reason to cd into {{ic|/home/user/Desktop/boot/grub/}} and to pass the file path as {{ic|boot/grub/grub.cfg}} (notice the lack of a leading slash - boot/ vs /boot/ ) is because {{ic|dir1/dir2/file}} is included as {{ic|(memdisk)/dir1/dir2/file}} by the {{ic|grub-mkstandalone}} script.
 
 
 
If you pass {{ic|/home/user/Desktop/grub.cfg}} the file will be included as {{ic|(memdisk)/home/user/Desktop/grub.cfg}}. If you pass {{ic|/home/user/Desktop/boot/grub/grub.cfg}} the file will be included as {{ic|(memdisk)/home/user/Desktop/boot/grub/grub.cfg}}. That is the reason for cd'ing into {{ic|/home/user/Desktop/boot/grub/}} and passing {{ic|boot/grub/grub.cfg}}, to includ the file as {{ic|(memdisk)/boot/grub/grub.cfg}}, which is what {{ic|grub.efi}} expects the file to be.
 
 
 
You need to create an UEFI Boot Manager entry for {{ic|/boot/efi/efi/arch_grub/grubx64_standalone.efi}} using {{ic|efibootmgr}}. Follow [[#Create GRUB2 entry in the Firmware Boot Manager]].
 
 
 
===== Multiboot in UEFI =====
 
 
 
====== Chainload Microsoft Windows x86_64 UEFI-GPT ======
 
 
 
Find the UUID of the FAT32 filesystem in the UEFI SYSTEM PARTITION where the Windows UEFI Bootloader files reside. For example, if Windows {{ic|bootmgfw.efi}} exists at {{ic|/boot/efi/efi/Microsoft/Boot/bootmgfw.efi}} (ignore the upper-lower case differences since that is immaterial in FAT filesystem):
 
 
 
# grub-probe --target=fs_uuid /boot/efi/efi/Microsoft/Boot/bootmgfw.efi
 
1ce5-7f28
 
 
 
# grub-probe --target=hints_string /boot/efi/efi/Microsoft/Boot/bootmgfw.efi
 
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
 
 
 
Then, add this code to {{ic|/boot/grub/grub.cfg}} OR {{ic|/boot/efi/efi/grub/grub.cfg}} to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode:
 
 
 
menuentry "Microsoft Windows x86_64 UEFI-GPT" {
 
     insmod part_gpt
 
     insmod fat
 
 
     insmod search_fs_uuid
 
     insmod search_fs_uuid
     insmod chain
+
     insmod ntldr   
     search --fs-uuid --no-floppy --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 1ce5-7f28
+
     search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 ''XXXXXXXXXXXXXXXX''
     chainloader /efi/Microsoft/Boot/bootmgfw.efi
+
     ntldr /ntldr
  }
+
  }
 +
  fi
  
== Configuration ==
+
{{Note|In some cases, GRUB may be installed without a clean Windows 8, in which case you cannot boot Windows without having an error with {{ic|\boot\bcd}} (error code {{ic|0xc000000f}}). You can fix it by going to Windows Recovery Console ({{ic|cmd.exe}} from install disk) and executing:
  
You can also choose to automatically generate or manually edit {{ic|grub.cfg}}.
+
X:\> bootrec.exe /fixboot
 +
X:\> bootrec.exe /RebuildBcd
  
{{Note|If GRUB2 was installed with the {{ic|--boot-directory}} option set, the {{ic|grub.cfg}} file must be placed in the same directory as {{ic|grubx64.efi}}. Otherwise, the {{ic|grub.cfg}} file goes in {{ic|/boot/grub/}}, just like in the BIOS version of GRUB2.}}
+
Do '''not''' use {{ic|bootrec.exe /Fixmbr}} because it will wipe GRUB out.
 +
Or you can use Boot Repair function in the Troubleshooting menu - it will not wipe out GRUB but will fix most errors.
 +
Also you would better keep plugged in both the target hard drive and your bootable device '''ONLY'''. Windows usually fails to repair boot information if any other devices are connected.
 +
}}
  
=== Automatically generating using grub-mkconfig (Recommended) ===
+
{{ic|/etc/grub.d/40_custom}} can be used as a template to create {{ic|/etc/grub.d/''nn''_custom}}. Where {{ic|''nn''}} defines the precedence, indicating the order the script is executed.  The order scripts are executed determine the placement in the grub boot menu.
  
The GRUB2 {{ic|menu.lst}} equivalent configuration files are {{ic|/etc/default/grub}} and {{ic|/etc/grub.d/*}}. {{ic|grub-mkconfig}} uses these files to generate {{ic|grub.cfg}}. By default the script outputs to stdout. To generate a {{ic|grub.cfg}} file run the command:
+
{{Note|{{ic|nn}} should be greater than 06 to ensure necessary scripts are executed first.}}
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
== Using the command shell ==
  
{{ic|/etc/grub.d/10_linux}} is set to automatically add menu items for Arch linux that work out of the box, to any generated configuration. Other operating systems may need to be added manually by editing {{ic|/etc/grub.d/40_custom}}
+
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 {{ic|/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.
  
=== Manually creating grub.cfg ===
+
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:
  
A basic GRUB config file uses the following options
+
grub>
* {{ic|(hdX,Y)}} is the partition {{ic|Y}} on disk {{ic|X}}, partition numbers starting at 1, disk numbers starting at 0
 
* {{ic|1=set default=N}} is the default boot entry that is chosen after timeout for user action
 
* {{ic|1=set timeout=M}} is the time {{ic|M}} to wait in seconds for a user selection before default is booted
 
* {{ic|<nowiki>menuentry "title" {entry options}</nowiki>}} is a boot entry titled {{ic|title}}
 
* {{ic|1=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 ({{ic|/}})
 
  
An example configuration:
+
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
  
{{hc
+
grub rescue>
|/boot/grub/grub.cfg
 
|<nowiki>
 
# Config file for GRUB2 - The GNU GRand Unified Bootloader
 
# /boot/grub/grub.cfg
 
  
# DEVICE NAME CONVERSIONS
+
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:
#
 
#  Linux          Grub
 
# -------------------------
 
#  /dev/fd0        (fd0)
 
#  /dev/sda        (hd0)
 
#  /dev/sdb2      (hd1,2)
 
#  /dev/sda3      (hd0,3)
 
#
 
  
# Timeout for menu
+
grub rescue> set prefix=(hdX,Y)/boot/grub
set timeout=5
+
grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
 +
rescue:grub> normal
  
# Set default boot entry as Entry 0
+
=== Pager support ===
set default=0
 
  
# (0) Arch Linux
+
GRUB supports pager for reading commands that provide long output (like the {{ic|help}} command). This works only in normal shell mode and not in rescue mode. To enable pager, in GRUB command shell type:
menuentry "Arch Linux" {
 
    set root=(hd0,1)
 
    linux /vmlinuz-linux root=/dev/sda3 ro
 
    initrd /initramfs-linux.img
 
}
 
  
## (1) Windows
+
sh:grub> set pager=1
#menuentry "Windows" {
 
#set root=(hd0,3)
 
#chainloader +1
 
#}
 
</nowiki>}}
 
  
=== Dual-booting ===
+
=== Using the command shell environment to boot operating systems ===
  
{{Note|If you want GRUB2 to automatically search for other systems, you may wish to install {{Pkg|os-prober}}.}}
+
grub>
  
==== Using grub-mkconfig ====
+
The GRUB's command shell environment can be used to boot operating systems.
The best way to add other entries is editing the {{ic|/etc/grub.d/40_custom}}. The entries in this file will be automatically added when running {{ic|grub-mkconfig}}.
+
A common scenario may be to boot Windows / Linux stored on a drive/partition via '''chainloading'''.
After adding the new lines, run:
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
to generate an updated {{ic|grub.cfg}}.
 
  
===== With GNU/Linux =====
+
''Chainloading'' means to load another boot-loader from the current one, ie, chain-loading.
  
Assuming that the other distro is on partition {{ic|sda2}}:
+
The other bootloader may be embedded at the starting of the disk (MBR) or at the starting of a partition or as an EFI binary in the ESP in the case of UEFI.
  
menuentry "Other Linux" {
+
==== Chainloading a partition ====
set root=(hd0,2)
 
linux /boot/vmlinuz (add other options here as required)
 
initrd /boot/initrd.img (if the other kernel uses/needs one)
 
}
 
  
===== With FreeBSD =====
+
  set root=(hdX,Y)
 
 
Requires that FreeBSD is installed on a single partition with UFS. Assuming it is installed on {{ic|sda4}}:
 
 
 
menuentry "FreeBSD" {
 
  set root=(hd0,4)
 
 
  chainloader +1
 
  chainloader +1
  }
+
  boot
  
===== With Windows =====
+
X=0,1,2...
 +
Y=1,2,3...
  
This assumes that your Windows partition is {{ic|sda3}}.
+
For example to chainload Windows stored in the first partiton of the first hard disk,
  
  # (2) Windows XP
+
  set root=(hd0,1)
menuentry "Windows XP" {
+
chainloader +1
    set root=(hd0,3)
+
  boot
    chainloader (hd0,3)+1
 
  }
 
  
If the Windows Bootloader is on an entirely different harddrive than GRUB, it may be necessary to trick Windows into believing that it is in fact the first harddrive. This was possible in the old GRUB with {{ic|map}} and is now done with {{ic|drivemap}}. Assume GRUB is on {{ic|hd0}} and windows on {{ic|hd2}}, you need to add the following after {{ic|set root}}:
+
Similarly GRUB installed to a partition can be chainloaded.
  
drivemap -s hd0 hd2
+
==== Chainloading a disk/drive ====
  
==== With Windows via EasyBCD and NeoGRUB ====
+
set root=hdX
 +
chainloader +1
 +
boot
  
Since EasyBCD's NeoGRUB currently does not understand the GRUB2 menu format, chainload to it by replacing the contents of your {{ic|C:\NST\menu.lst}} file with lines similar to the following:
+
==== Chainloading Windows/Linux installed in UEFI mode ====
  
  default 0
+
  insmod ntfs
  timeout 1
+
  set root=(hd0,gpt4)
 +
chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
 +
boot
  
title      Chainload into GRUB v2
+
{{ic|insmod ntfs}} is used for loading the ntfs file system module for loading Windows.
root        (hd0,7)
+
(hd0,gpt4) or /dev/sda4 is my EFI system partition (ESP).
kernel      /boot/grub/i386-pc/core.img
+
The entry in the ''chainloader'' line specifies the path of the ''.efi'' file to be chain-loaded.
  
===Visual Configuration===
+
==== Normal loading ====
  
In GRUB2 it is possible, by default, to change the look of the menu. Make sure to initialize, if not done already, GRUB2 graphical terminal, gfxterm, with proper video mode, gfxmode, in GRUB2. This can be seen in the section [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]]. This video mode is passed by GRUB2 to the linux kernel via 'gfxpayload' so any visual configurations need this mode in order to be in effect.
+
See the examples in [[#Using the rescue console]]
  
====Setting the framebuffer resolution ====
+
=== Using the rescue console ===
  
GRUB2 can set the framebuffer for both GRUB2 itself and the kernel. The old ''vga='' way is deprecated. The preferred method is editing {{ic|/etc/default/grub}} as the following sample:
+
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.
  
GRUB_GFXMODE=1024x768x32
+
The available commands in GRUB rescue include {{ic|insmod}}, {{ic|ls}}, {{ic|set}}, and {{ic|unset}}. This example uses {{ic|set}} and {{ic|insmod}}. {{ic|set}} modifies variables and {{ic|insmod}} inserts new modules to add functionality.
GRUB_GFXPAYLOAD_LINUX=keep
 
  
To generate the changes, run:  
+
Before starting, the user must know the location of their {{ic|/boot}} partition (be it a separate partition, or a subdirectory under their root):
grub-mkconfig -o /boot/grub/grub.cfg
 
  
The {{ic|gfxpayload}} property will make sure the kernel keeps the resolution.
+
grub rescue> set prefix=(hdX,Y)/boot/grub
  
{{Note|If this example does not work for you try to replace {{ic|1=gfxmode="1024x768x32"}} by {{ic|1=vbemode="0x105"}}. Remember to replace the specified resolution with one suitable for your screen.}}
+
where X is the physical drive number and Y is the partition number.
{{Note|To show all the modes you can use {{ic|1=# hwinfo --framebuffer}} (hwinfo is available in [community]), while at GRUB2 prompt you can use the {{ic|1=vbeinfo}} command.}}
 
  
If this method does not work for you, the deprecated {{ic|1=vga=}} method will still work. Just
+
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}}).}}
add it next to the {{ic|1="GRUB_CMDLINE_LINUX_DEFAULT="}} line in {{ic|/etc/default/grub}}
 
for eg: {{ic|1="GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"}} will give you a {{ic|1024x768}} resolution.
 
  
You can choose one of these resolutions: {{ic|640×480}}, {{ic|800×600}}, {{ic|1024×768}}, {{ic|1280×1024}}, {{ic|1600×1200}}
+
To expand console capabilities, insert the {{ic|linux}} module:
  
====915resolution hack ====
+
grub rescue> insmod i386-pc/linux.mod
  
Some times for Intel graphic adapters neither {{ic|1=# hwinfo --framebuffer}} nor {{ic|1=vbeinfo}} will show you the desired resolution. In this case you can use {{ic|915resolution}} hack. This hack will temporarily modify video BIOS and add needed resolution. See [http://915resolution.mango-lang.org/ 915resolution's home page]
+
or simply
  
In the following I will proceed with the example for my system. Please adjust the recipe for your needs. First you need to find a video mode which will be modified later. For that, run {{ic|915resolution}} in GRUB2 command shell.
+
  grub rescue> insmod linux
  915resolution -l
 
The output will be something like:
 
Intel 800/900 Series VBIOS Hack : version 0.5.3
 
...
 
Mode 30 : 640x480, 8 bits/pixel
 
...
 
Next, our purpose is to overwrite mode 30. (You can choose what ever mode you want.) In the file {{ic|/etc/grub.d/00_header}} just before the {{ic|set gfxmode&#61;${GRUB_GFXMODE} }} line insert
 
915resolution 30 1440 900
 
Here we are overwriting the mode {{ic|30}} with {{ic|1440x900}} resolution. Lastly we need to set {{ic|GRUB_GFXMODE}} as described earlier, regenerate GRUB2 configuration file and reboot to test changes.
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
# reboot
 
  
====Background image and bitmap fonts====
+
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar.
  
GRUB2 comes with support for background images and bitmap fonts in {{ic|pf2}} format. The unifont font is included in the {{Pkg|grub2-common}} package under the filename {{ic|unicode.pf2}}, or, as only ASCII characters under the name {{ic|ascii.pf2}}.
+
An example, booting Arch Linux:
  
Image formats supported include tga, png and jpeg, providing the correct modules are loaded. The maximum supported resolution depends on your hardware.
+
set root=(hd0,5)
 +
linux /boot/vmlinuz-linux root=/dev/sda5
 +
initrd /boot/initramfs-linux.img
 +
boot
  
Make sure you have set up the proper [https://wiki.archlinux.org/index.php/GRUB2#Setting_the_framebuffer_resolution framebuffer resolution].
+
With a separate boot partition (e.g. when using UEFI), again change the lines accordingly:  
  
Edit {{ic|/etc/default/grub}} like this:
+
{{Note|Since boot is a separate partition and not part of your root partition, you must address the boot partition manually, in the same way as for the prefix variable.}}
GRUB_BACKGROUND="/boot/grub/archlinux.tga"
 
#GRUB_THEME="/path/to/gfxtheme"
 
  
(archlinux.tga is a placeholder; put your file name there)
+
set root=(hd0,5)
 +
linux (hdX,Y)/vmlinuz-linux root=/dev/sda6
 +
initrd (hdX,Y)/initramfs-linux.img
 +
boot
  
{{Note|If you have installed GRUB on a separate partition, {{ic|/boot/grub/archlinux.tga}} becomes {{ic|/grub/archlinux.tga}}.}}
+
{{Note|If you experienced {{ic|error: premature end of file /YOUR_KERNEL_NAME}} during execution of {{ic|linux}} command, you can try {{ic|linux16}} instead.}}
  
To generate the changes and add the information into {{ic|grub.cfg}}, run:
+
After successfully booting the Arch Linux installation, users can correct {{ic|grub.cfg}} as needed and then reinstall GRUB.
grub-mkconfig -o /boot/grub/grub.cfg
 
  
If adding the splash image was successful, the user will see {{ic|"Found background image..."}} in the terminal as the command is executed.
+
To reinstall GRUB and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Installation]] for details.
If this phrase is not seen, the image information was probably not incorporated into the {{ic|grub.cfg}} file.
 
 
If the image is not displayed, check:
 
* The path and the filename in {{ic|/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 {{ic|/etc/default/grub}}.
 
* The command {{ic|grub-mkconfig}} must be executed to place the background image information into the {{ic|/boot/grub/grub.cfg}} file.
 
  
====Theme====
+
== Troubleshooting ==
  
Here is an example for configuring Starfield theme which was included in GRUB2 package.
+
=== F2FS and other unsupported file systems ===
  
Edit {{ic|/etc/default/grub}}
+
GRUB does not support [[F2FS]] file system. In case the root partition is on an unsupported file system, an alternative {{ic|/boot}} partition with a supported file system must be created. In some cases, the development version of GRUB {{aur|grub-git}} may have native support for the file system.
GRUB_THEME="/boot/grub/themes/starfield/theme.txt"
 
  
Generate the changes:
+
=== Intel BIOS not booting GPT ===
grub-mkconfig -o /boot/grub/grub.cfg
 
  
If configuring the theme was successful, you'll see {{ic|Found theme: /boot/grub/themes/starfield/theme.txt}} in the terminal.
+
Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.
  
====Menu colors====
+
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 {{ic|fdisk /dev/sda}}, then press {{ic|a}} and select the partition you wish to mark as bootable (probably #1) by pressing the corresponding number, finally press {{ic|w}} to write the changes to the MBR.
  
As in GRUB Legacy (0.9x), you can change the menu colors in GRUB2. The available colors for GRUB2 are at http://www.gnu.org/software/grub/manual/html_node/Theme-file-format.html#Theme-file-format.
+
{{Note|The bootable-marking must be done in {{ic|fdisk}} or similar, not in GParted or others, as they will not set the bootable flag in the MBR.}}
Here is an example:
 
  
Edit {{ic|/etc/default/grub}}:
+
With cfdisk, the steps are similar, just {{ic|cfdisk /dev/sda}}, choose bootable (at the left) in the desired hard disk, and quit saving.
GRUB_COLOR_NORMAL="light-blue/black"
 
GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
 
  
Generate the changes:
+
With recent version of parted, you can use {{ic|disk_toggle pmbr_boot}} option. Afterwards verify that Disk Flags show pmbr_boot.
grub-mkconfig -o /boot/grub/grub.cfg
 
  
====Hidden menu====
+
# parted /dev/sd''x'' disk_toggle pmbr_boot
 +
# parted /dev/sd''x'' print
  
One of the unique features of GRUB2 is hiding/skipping the menu and showing it by holding "Shift" when needed. You can also adjust whether you want to see the timeout counter.
+
More information is available [http://www.rodsbooks.com/gdisk/bios.html here]
  
Edit {{ic|/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:
+
=== Enable debug messages ===
GRUB_HIDDEN_TIMEOUT=5
 
GRUB_HIDDEN_TIMEOUT_QUIET=false
 
  
and run:
+
{{Note|This change is overwritten when [[#Generate the main configuration file]].}}
grub-mkconfig -o /boot/grub/grub.cfg
 
  
=== Other Options ===
+
Add:
  
==== LVM ====
+
set pager=1
 +
set debug=all
  
If you use [[LVM]] for your {{ic|/boot}}, add the following before menuentry lines:
+
to {{ic|grub.cfg}}.
  
insmod lvm
+
=== "No suitable mode found" error ===
  
and specify your root in the menuentry as:
+
If you get this error when booting any menuentry:
  
  set root=(''lvm_group_name''-''lvm_logical_boot_partition_name'')
+
  error: no suitable mode found
 +
Booting however
  
Example:
+
Then you need to initialize GRUB graphical terminal ({{ic|gfxterm}}) with proper video mode ({{ic|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).
  
# (0) Arch Linux
+
Copy {{ic|/usr/share/grub/unicode.pf2}} to {{ic|${GRUB_PREFIX_DIR}}} ({{ic|/boot/grub/}} in case of BIOS and UEFI systems). If GRUB UEFI was installed with {{ic|1=--boot-directory=''esp''/EFI}} set, then the directory is {{ic|''esp''/EFI/grub/}}:
menuentry "Arch Linux" {
 
insmod lvm
 
set root=(VolumeGroup-lv_boot)
 
# you can only set following two lines
 
linux /vmlinuz-linux root=/dev/mapper/VolumeGroup-root ro
 
initrd /initramfs-linux.img
 
}
 
  
==== Raid ====
+
# cp /usr/share/grub/unicode.pf2 ${GRUB_PREFIX_DIR}
  
GRUB2 provides convenient handling of raid-volumes. You need to add:
+
If {{ic|/usr/share/grub/unicode.pf2}} does not exist, install {{Pkg|bdf-unifont}}, create the {{ic|unifont.pf2}} file and then copy it to {{ic|1=${GRUB_PREFIX_DIR}}}:
insmod raid
 
  
which allows you to address the volume natively. E.g. {{ic|/dev/md0}} becomes:
+
# grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
set root=(md0)
 
  
whereas a partitioned raid-volume (e.g. {{ic|/dev/md0p1}}) becomes:
+
Then, in the {{ic|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.
set root=(md0,1)
 
  
==== Persistent block device naming ====
+
BIOS systems:
You can use UUIDs to detect partitions instead of the "old" {{ic|/dev/sd*}} and {{ic|/dev/hd*}} scheming. It has the advantage of detecting partitions by their unique UUIDs, which is needed by some people booting with complicated partition setups.
 
  
UUIDs are used by default in the recent versions of GRUB2 - there is no downside in it anyway except that you need to re-generate the {{ic|grub.cfg}} file every time you resize or reformat your partitions. Remember this when modifying partitions with Live-CD.
+
insmod vbe
  
The recent versions of GRUB2 use UUIDs by default. You can re-enable the use of UUIDS by simply commenting the UUID line (this is also what it looks like by default):
+
UEFI systems:
#GRUB_DISABLE_LINUX_UUID=true
 
you can also just set the value as {{ic|false}} as shown here:
 
GRUB_DISABLE_LINUX_UUID=false
 
  
Either way, do not forget to generate the changes:
+
insmod efi_gop
  grub-mkconfig -o /boot/grub/grub.cfg
+
  insmod efi_uga
  
==== Using Labels ====
+
After that add the following code (common to both BIOS and UEFI):
  
It is possible to use labels, human-readable strings attached to filesystems, by using the {{ic|--label}} option to {{ic|search}}. First of all, label your existing partition:
+
  insmod font
  # tune2fs -L a <LABEL> <PARTITION>
 
  
Then, add an entry using labels. An example of this:
+
if loadfont ${prefix}/fonts/unicode.pf2
 +
then
 +
    insmod gfxterm
 +
    set gfxmode=auto
 +
    set gfxpayload=keep
 +
    terminal_output gfxterm
 +
fi
  
menuentry "Arch Linux, session texte" {
+
As you can see for gfxterm (graphical terminal) to function properly, {{ic|unicode.pf2}} font file should exist in {{ic|1=${GRUB_PREFIX_DIR}}}.
    search --label --no-floppy --set=root archroot
 
    linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro
 
    initrd /boot/initramfs-linux.img
 
}
 
  
==== Recall previous entry ====
+
=== msdos-style error message ===
  
GRUB2 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 {{ic|/etc/default/grub}} and change the setting of {{ic|GRUB_DEFAULT}}:
+
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.
  
GRUB_DEFAULT=saved
+
This error may occur when you try installing GRUB in a VMware container. Read more about it [https://bbs.archlinux.org/viewtopic.php?pid=581760#p581760 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]]
  
This ensures that GRUB will default to the saved entry. To enable saving the selected entry, add the following line to {{ic|/etc/default/grub}}:
+
=== UEFI ===
  
GRUB_SAVEDEFAULT=true
+
==== Common installation errors ====
  
{{Note|Manually added menu items, eg Windows in {{ic|/etc/grub.d/40_custom}}, will need {{ic|savedefault}} added. Remember to regenerate your configuration file.}}
+
* If you have a problem when running ''grub-install'' with ''sysfs'' or ''procfs'' and it says you must run {{ic|modprobe efivars}}, try [[Unified Extensible Firmware Interface#Mount efivarfs]].
 +
* Without {{ic|--target}} or {{ic|--directory}} option, grub-install cannot determine for which firmware to install. In such cases {{ic|grub-install}} will print {{ic|source_dir does not exist. Please specify --target or --directory}}.
 +
* If after running grub-install you are told your partition does not look like an EFI partition then the partition is most likely not {{ic|Fat32}}.
  
==== Security ====
+
==== Drop to rescue shell ====
  
If you want to secure GRUB2 so it is not possible for anyone to change boot parameters or use the command line, you can add a user/password combination to GRUB2's configuration files. To do this, run the command {{ic|grub-mkpasswd_pbkdf2}}. Enter a password and confirm it. The output will look like this:
+
If GRUB loads but drops into the rescue shell with no errors, it can be due to one of these two reasons:
  
{{bc|<nowiki>
+
* It may be because of a missing or misplaced {{ic|grub.cfg}}. This will happen if GRUB UEFI was installed with {{ic|--boot-directory}} and {{ic|grub.cfg}} is missing,
Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A</nowiki>}}Then, add the following to {{ic|/etc/grub.d/00_header}}:
+
* It also happens if the boot partition, which is hardcoded into the {{ic|grubx64.efi}} file, has changed.
{{bc|<nowiki>cat << EOF
 
  
set superusers="username"
+
==== GRUB UEFI not loaded ====
password_pbkdf2 username <password>
 
  
EOF</nowiki>}}
+
An example of a working EFI:
where <password> is the string generated by {{ic|grub-mkpasswd_pbkdf2}}.
 
  
Regenerate your configuration file. Your GRUB2 command line and boot parameters are now protected.
+
{{hc|# 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
 +
}}
  
==== Root Encryption ====
+
If the screen only goes black for a second and the next boot option is tried afterwards, according to [https://bbs.archlinux.org/viewtopic.php?pid=981560#p981560 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:
  
To let GRUB2 automatically add the kernel parameters for root encryption,
+
Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\grub.efi)
add {{ic|1=cryptdevice=/dev/yourdevice:label}} to {{ic|GRUB_CMDLINE_LINUX}} in {{ic|/etc/defaults/grub}}.
 
  
Example with root mapped to {{ic|/dev/mapper/root}}:
+
==== Default/fallback boot path ====
  
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:root"
+
Some UEFI firmwares require a bootable file at a known location before they will show UEFI NVRAM boot entries. If this is the case, {{ic|grub-install}} will claim {{ic|efibootmgr}} has added an entry to boot GRUB, however the entry will not show up in the VisualBIOS boot order selector. The solution is to install GRUB at the default/fallback boot path:
  
Also, disable the usage of UUIDs for the rootfs:
+
# grub-install --target=x86_64-efi --efi-directory=''esp'' '''--removable'''
  
GRUB_DISABLE_LINUX_UUID=true
+
Alternatively you can move an already installed GRUB EFI executable to the default/fallback path:
  
Regenerate the configuration.
+
# mv ''esp''/EFI/grub ''esp''/EFI/BOOT
 +
# mv ''esp''/EFI/BOOT/grubx64.efi ''esp''/EFI/BOOT/BOOTX64.EFI
  
=== Booting an ISO Directly From GRUB2 ===
+
=== Invalid signature ===
Edit {{ic|/etc/grub.d/40_custom}} to add an entry for the target ISO. When finished, update the GRUB menu as with the usual {{ic|grub-mkconfig -o /boot/grub/grub.cfg}} (as root).
 
  
==== Arch ISO ====
+
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:
{{Note|Be sure to adjust the "hdX,Y" in the third line to point to the correct disk/partition number of the isofile. Also adjust the img_dev line to match this same location.}}
 
  
  menuentry "Archlinux-2011.08.19-netinstall-x86_64.iso" {
+
  # mv /boot/grub/device.map /boot/grub/device.map-old
    set isofile="/archives/archlinux-2011.08.19-netinstall-x86_64.iso"
+
# grub-mkconfig -o /boot/grub/grub.cfg
    loopback loop (hd0,7)$isofile
 
    linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201108 img_dev=/dev/sda7 img_loop=$isofile earlymodules=loop
 
    initrd (loop)/arch/boot/x86_64/archiso.img
 
}
 
  
==== Ubuntu ISO ====
+
{{ic|grub-mkconfig}} should now mention all found boot options, including Windows. If it works, remove {{ic|/boot/grub/device.map-old}}.
{{Note|Be sure to adjust the "hdX,Y" in the third line to point to the correct disk/partition number of the isofile. }}
 
  
menuentry "ubuntu-11.04-desktop-amd64.iso" {
+
=== Boot freezes ===
    set isofile="/path/to/ubuntu-11.04-desktop-amd64.iso"
 
    loopback loop (hdX,Y)$isofile
 
    linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
 
    initrd (loop)/casper/initrd.lz
 
}
 
  
== Using the command shell ==
+
If booting gets stuck without any error message after GRUB loading the kernel and the initial ramdisk, try removing the {{ic|add_efi_memmap}} kernel parameter.
  
Since the MBR is too small to store all GRUB2 modules, only the menu and a few basic commands reside there. The majority of GRUB2 functionality remains in modules in {{ic|/boot/grub}}, which are inserted as needed. In error conditions (e.g. if the partition layout changes) GRUB2 may fail to boot. When this happens, a command shell may appear.
+
=== Arch not found from other OS ===
  
GRUB2 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:
+
Some have reported that other distributions may have trouble finding Arch Linux automatically with {{ic|os-prober}}. If this problem arises, it has been reported that detection can be improved with the presence of {{ic|/etc/lsb-release}}. This file and updating tool is available with the package {{Pkg|lsb-release}}.
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:
+
=== Warning when installing in chroot ===
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:
+
When installing GRUB on a LVM system in a chroot environment (e.g. during system installation), you may receive warnings like
grub rescue> set prefix=(hdX,Y)/boot/grub
 
grub rescue> insmod (hdX,Y)/boot/grub/normal.mod
 
rescue:grub> normal
 
  
=== Pager support ===
+
/run/lvm/lvmetad.socket: connect failed: No such file or directory
  
GRUB2 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 GRUB2 command shell type:
+
or
sh:grub> set pager=1
 
  
== GUI configuration tools ==
+
WARNING: failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.
  
Following package may be installed from [[AUR]]
+
This is because {{ic|/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.
* [https://aur.archlinux.org/packages.php?ID=44020 grub-customizer] (requires gettext gksu gtkmm hicolor-icon-theme openssl)
 
*:Customize the bootloader (GRUB2 or BURG)
 
* [http://kde-apps.org/content/show.php?content=139643 grub2-editor] (requires kdelibs)
 
*:A KDE4 control module for configuring the GRUB2 bootloader
 
* [http://kde-apps.org/content/show.php?content=137886 kcm-grub2] (requires kdelibs python2-qt kdebindings-python)
 
*:This Kcm module manages the most common settings of Grub2.
 
* [http://sourceforge.net/projects/startup-manager/ startupmanager] (requires gnome-python imagemagick yelp python2 xorg-xrandr)
 
*:GUI app for changing the settings of GRUB, GRUB2, Usplash and Splashy
 
  
== parttool or legacy hide/unhide ==
+
=== GRUB loads slowly ===
  
If you have a win9x paradigm with hidden C disks GRUB Legacy had the hide/unhide feature. In GRUB2 this has been replaced by parttool. For example, to boot the third C disk of three win9x installations on the CLI enter the CLI and:
+
GRUB can take a long time to load when disk space is low. Check if you have sufficient free disk space on your {{ic|/boot}} or {{ic|/}} partition when you are having problems.
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 ==
+
=== error: unknown filesystem ===
  
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.
+
GRUB may output {{ic|error: unknown filesystem}} and refuse to boot for a few reasons. If you are certain that all [[UUID]]s are correct and all filesystems are valid and supported, it may be because your [[#GUID Partition Table (GPT) specific instructions|BIOS Boot Partition]] is located outside the first 2 TiB of the drive [https://bbs.archlinux.org/viewtopic.php?id=195948]. Use a partitioning tool of your choice to ensure this partition is located fully within the first 2 TiB, then reinstall and reconfigure GRUB.
  
The available commands in GRUB rescue include {{ic|insmod}}, {{ic|ls}}, {{ic|set}}, and {{ic|unset}}. This example uses {{ic|set}} and {{ic|insmod}}. {{ic|set}} modifies variables and {{ic|insmod}} inserts new modules to add functionality.
+
=== grub-reboot not resetting ===
  
Before starting, the user must know the location of their {{ic|/boot}} partition (be it a separate partition, or a subdirectory under their root):
+
GRUB seems to be unable to write to root BTRFS partitions [https://bbs.archlinux.org/viewtopic.php?id=166131]. If you use grub-reboot to boot into another entry it will therefore be unable to update its on-disk environment. Either run grub-reboot from the other entry (for example when switching between various distributions) or consider a different file system. You can reset a "sticky" entry by executing {{ic|grub-editenv create}} and setting {{ic|1=GRUB_DEFAULT=0}} in your {{ic|/etc/default/grub}} (do not forget {{ic|grub-mkconfig -o /boot/grub/grub.cfg}}).
grub rescue> set prefix=(hdX,Y)/boot/grub
 
  
where X is the physical drive number and Y is the partition number.
+
=== Old BTRFS prevents installation ===
 
 
To expand console capabilities, insert the {{ic|linux}} module:
 
grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
 
  
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path, (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}} and {{ic|insmod (hdX,Y)/grub/linux.mod}}).}}
+
If a drive is formatted with BTRFS without creating a partition table (eg. /dev/sdx), then later has partition table written to, there are parts of the BTRFS format that persist. Most utilities and OS's do not see this, but GRUB will refuse to install, even with --force
  
This introduces the "linux" and "initrd" commands, which should be familiar (see [[#Configuration]]).
+
# grub-install: warning: Attempting to install GRUB to a disk with multiple partition labels. This is not supported yet..
 +
# grub-install: error: filesystem `btrfs' does not support blocklists.
  
An example, booting Arch Linux:
+
You can zero the drive, but the easy solution that leaves your data alone is to erase the BTRFS superblock with {{ic|wipefs -o 0x10040 /dev/sdx}}
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:
+
=== Windows 8/10 not found ===
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 {{ic|grub.cfg}} as needed and then reinstall GRUB2.
+
A setting in Windows 8/10 called "Hiberboot", "Hybrid Boot" or "Fast Boot" can prevent the Windows partition from being mounted, so {{ic|grub-mkconfig}} will not find a Windows install. Disabling Hiberboot in Windows will allow it to be added to the GRUB menu.
  
to reinstall GRUB2 and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Bootloader installation]] for details.
+
=== VirtualBox EFI mode ===
 
 
== Combining the use of UUID's and basic scripting  ==
 
 
 
If you like the idea of using UUID's to avoid unreliable BIOS mappings or are struggling with GRUB's syntax, here is an example boot menu item that uses UUID's and a small script to direct GRUB to the proper disk partitions for your system. All you need to do is replace the UUID's in the sample with the correct UUID's 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 --no-floppy --set=root $the_root_uuid     
 
      search --fs-uuid --no-floppy --set=grub_boot $the_boot_uuid
 
   
 
      # Check to see if boot and root are equal.
 
      # If they are, then append /boot to $grub_boot (Since $grub_boot is actually the root partition)
 
      if [ $the_boot_uuid == $the_root_uuid] ; then
 
          set grub_boot=$grub_boot/boot
 
      fi
 
   
 
      # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd
 
      linux ($grub_boot)/vmlinuz-linux root=/dev/disk/by-uuid/$uuid_os_root ro
 
      initrd ($grub_boot)/initramfs-linux.img
 
  }
 
 
 
== Troubleshooting ==
 
 
 
Any troubleshooting should be added here.
 
 
 
=== Enable GRUB2 debug messages ===
 
 
 
Add
 
 
set pager=1
 
set debug=all
 
 
 
to {{ic|grub.cfg}}.
 
 
 
=== Correct GRUB2 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 GRUB2 graphical terminal (gfxterm) with proper video mode (gfxmode) in GRUB2. This video mode is passed by GRUB2 to the linux kernel via 'gfxpayload'. In case of UEFI systems, if the GRUB2 video mode is not initialized, no kernel boot messages will be shown in the terminal (atleast until KMS kicks in)
 
 
 
Copy {{ic|/usr/share/grub/unicode.pf2}} to ${GRUB2_PREFIX_DIR} ({{ic|/boot/grub/}} in case of BIOS and UEFI systems. If GRUB2 UEFI was installed with {{ic|1=--boot-directory=/boot/efi/efi}} set, then the directory is {{ic|/boot/efi/efi/grub/}}.
 
 
 
# cp /usr/share/grub/unicode.pf2 ${GRUB2_PREFIX_DIR}
 
 
 
If {{ic|/usr/share/grub/unicode.pf2}} does not exist, install {{Pkg|bdf-unifont}}, create the {{ic|unifont.pf2}} file and then copy it to ${GRUB2_PREFIX_DIR}.
 
 
 
# grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
 
 
 
Then, in the {{ic|grub.cfg}} file, add the following lines to enable GRUB2 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, {{ic|unicode.pf2}} font file should exist in ${GRUB2_PREFIX_DIR}.
 
 
 
=== msdos-style error message ===
 
 
 
grub-setup: warn: This msdos-style partition label has no post-MBR gap; embedding won't be possible!
 
grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.
 
            However, blocklists are UNRELIABLE and its use is discouraged.
 
grub-setup: error: If you really want blocklists, use --force.
 
 
 
This error may occur when you try installing GRUB2 in a VMware container. Read more about it [http://bbs.archlinux.org/viewtopic.php?pid=581760#p581760 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 [[#MBR_aka_msdos_partitioning_specific_instructions]]
 
 
 
=== UEFI GRUB2 drops to shell ===
 
 
 
If grub loads but drop you into the rescue shell with no errors, it may be because of a missing or misplaced {{ic|grub.cfg}}. This will happen if GRUB2 UEFI was installed with {{ic|--boot-directory}} and {{ic|grub.cfg}} is missing OR if the partition number of the boot partition changed (which is hard-coded into the {{ic|grubx64.efi}} file).
 
 
 
=== UEFI GRUB2 not loaded ===
 
In some cases the EFI may fail to load GRUB correctly. Provided everything is set up correctly, the output of
 
efibootmgr -v
 
might look something like this:
 
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 everything works correctly, the EFI would now automatically load grub.<br>
 
If the screen only goes black for a second and the next boot option is tried afterwards, according to [https://bbs.archlinux.org/viewtopic.php?pid=981560#p981560 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
 
{{ic|grub-mkconfig}} should now mention all found boot options including windows. If it works, remove {{ic|/boot/grub/device.map-old}}.
 
  
== References ==
+
Install GRUB to the [[#Default/fallback boot path|default/fallback boot path]].
  
# Official GRUB2 Manual - http://www.gnu.org/software/grub/manual/grub.html
+
See also [[VirtualBox#Installation in EFI mode]].
# Ubuntu wiki page for Grub2 - https://help.ubuntu.com/community/Grub2
 
# GRUB2 wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
 
# Wikipedia's page on [http://en.wikipedia.org/wiki/BIOS_Boot_partition BIOS Boot Partition]
 
  
== External Links ==
+
== See also ==
  
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub/grub_bios.sh A Linux Bash Shell script to compile and install GRUB2 for BIOS from BZR Source]
+
* [https://www.gnu.org/software/grub/manual/grub.html Official GRUB Manual]
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub/grub_uefi.sh A Linux Bash Shell script to compile and install GRUB2 for UEFI from BZR Source]
+
* [https://help.ubuntu.com/community/Grub2 Ubuntu wiki page for GRUB]
 +
* [https://help.ubuntu.com/community/UEFIBooting GRUB wiki page describing steps to compile for UEFI systems]
 +
* [[Wikipedia:BIOS Boot partition]]
 +
* [http://web.archive.org/web/20160424042444/http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html#Editing_etcgrub.d05_debian_theme How to configure GRUB]
 +
* [http://www.linuxjournal.com/article/4622 Boot with GRUB]

Latest revision as of 09:54, 15 July 2018

GRUB (GRand Unified Bootloader) is a multi-boot loader. It is derived from PUPA which was a research project to develop the replacement of what is now known as GRUB Legacy. The latter had become too difficult to maintain and GRUB was rewritten from scratch with the aim to provide modularity and portability [1]. The current GRUB is also referred to as GRUB 2 while GRUB Legacy corresponds to versions 0.9x.

Note: In the entire article esp denotes the mountpoint of the EFI system partition aka ESP.

Contents

BIOS systems

GUID Partition Table (GPT) specific instructions

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

Note:
  • Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme. Read more on GUID partition tables.
  • This additional partition is only needed on a GRUB, BIOS/GPT partitioning scheme. Previously, for a GRUB, BIOS/MBR partitioning scheme, GRUB used the Post-MBR gap for the embedding the core.img). On GPT, however, there is no guaranteed unused space before the first partition.
  • For UEFI systems this extra partition is not required, since no embedding of boot sectors takes place in that case. However, UEFI systems still require an EFI system partition.

Create a mebibyte partition (+1M with fdisk or gdisk) on the disk with no file system and with partition type GUID 21686148-6449-6E6F-744E-656564454649.

  • Select partition type BIOS boot for fdisk, ef02 for gdisk.
  • For parted set/activate the flag bios_grub on the partition.

This partition can be in any position order but has to be on the first 2 TiB of the disk. This partition needs to be created before GRUB installation. When the partition is ready, install the bootloader as per the instructions below.

The space before the first partition can also be used as the BIOS boot partition though it will be out of GPT alignment specification. Since the partition will not be regularly accessed performance issues can be disregarded, though some disk utilities will display a warning about it. In fdisk or gdisk create a new partition starting at sector 34 and spanning to 2047 and set the type. To have the viewable partitions begin at the base consider adding this partition last.

Master Boot Record (MBR) specific instructions

Usually the post-MBR gap (after the 512 byte MBR region and before the start of the first partition) in many MBR (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 partitioning tool that supports 1 MiB partition alignment to obtain this space as well as to satisfy other non-512 byte sector issues (which are unrelated to embedding of core.img).

Installation

Install the grub package. It will replace grub-legacyAUR, where already installed. Then do:

# grub-install --target=i386-pc /dev/sdX

where /dev/sdX is the disk where grub is to be installed (for example, disk /dev/sda and not partition /dev/sda1).

Now you must #Generate the main configuration file.

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

Tip: See GRUB/Tips and tricks#Alternative installation methods for other ways to install GRUB, such as to a USB stick.

See grub-install(8) and GRUB Manual for more details on the grub-install command.

UEFI systems

Note:
  • It is recommended to read and understand the UEFI, GPT and Arch boot process#Under UEFI pages.
  • When installing to use UEFI it is important to start the install with your machine in UEFI mode. The Arch Linux install media must be UEFI bootable.

Check for an EFI System Partition

To boot from a disk using UEFI, the recommended disk partition table is GPT and this is the layout that is assumed in this article. An EFI system partition (ESP) is required on every bootable disk. If you are installing Arch Linux on an UEFI-capable computer with an installed operating system, like Windows 10 for example, it is very likely that you already have an ESP.

To find out the disk partition scheme and the system partition, use parted as root on the disk you want to boot from:

# parted /dev/sdx print

The command returns:

  • The disk partition layout: if the disk is GPT, it indicates Partition Table: gpt.
  • The list of partitions on the disk: Look for the EFI system partition in the list, it is a small (usually about 100-550 MiB) partition with a fat32 file system and with the flag esp enabled. To confirm this is the ESP, mount it and check whether it contains a directory named EFI, if it does this is definitely the ESP.

Once it is found, take note of the partition number, it will be required for the GRUB installation. If you do not have an ESP, you will need to create one. See the EFI system partition article.

Installation

Note:
  • UEFI firmwares are not implemented consistently across manufacturers. The procedure described below is intended to work on a wide range of UEFI systems but those experiencing problems despite applying this method are encouraged to share detailed information, and if possible the turnarounds found, for their hardware-specific case. A GRUB/EFI examples article has been provided for such cases.
  • The section assumes you are installing GRUB for x86_64 systems. For IA32 (32-bit) EFI systems (not to be confused with 32-bit CPUs), replace x86_64-efi with i386-efi where appropriate.

First, install the packages grub and efibootmgr: GRUB is the bootloader while efibootmgr is used by the GRUB installation script to write boot entries to NVRAM.

Then follow the below steps to install GRUB:

  1. Mount the EFI System Partition and in the remainder of this section, substitute esp with its mount point.
  2. Choose a bootloader identifier, here named GRUB. A directory of that name will be created to store the EFI binary in the ESP and this is the name that will appear in the UEFI boot menu to identify the GRUB boot entry.
  3. Execute the following command to install the GRUB EFI application grubx64.efi to esp/EFI/GRUB/ and install its modules to /boot/grub/x86_64-efi/.
# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=GRUB

After the above install completed the main GRUB directory is located at /boot/grub/. Note that grub-install also tries to create an entry in the firmware boot manager, named GRUB in the above example.

Remember to #Generate the main configuration file after finalizing #Configuration.

Tip: If you use the option --removable then GRUB will be installed to esp/EFI/BOOT/BOOTX64.EFI (or esp/EFI/BOOT/BOOTIA32.EFI for the i386-efi target) and you will have the additional ability of being able to boot from the drive in case EFI variables are reset or you move the drive to another computer. Usually you can do this by selecting the drive itself similar to how you would using BIOS. If dual booting with Windows, be aware Windows usually has a BOOT folder inside the EFI folder of the EFI system partition, but its only purpose is to recreate the UEFI boot entry for Windows.
Note:
  • While some distributions require a /boot/efi or /boot/EFI directory, Arch does not.
  • --efi-directory and --bootloader-id are specific to GRUB UEFI, --efi-directory replaces --root-directory which is deprecated.
  • You might note the absence of a device_path option (e.g.: /dev/sda) in the grub-install command. In fact any device_path provided will be ignored by the GRUB UEFI install script. Indeed, UEFI bootloaders do not use a MBR bootcode or partition boot sector at all.

See UEFI troubleshooting in case of problems. Additionally see GRUB/Tips and tricks#UEFI further reading.

Generate the 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/; see #Configuration.

If you have not done additional configuration, the automatic generation will determine the root filesystem of the system to boot for the configuration file. For that to succeed it is important that the system is either booted or chrooted into.

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

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

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

By default the generation scripts automatically add menu entries for Arch Linux to any generated configuration. See Multiboot USB drive#Boot entries and #Dual-booting for custom menu entries for other systems.

Tip: To have grub-mkconfig search for other installed systems and automatically add them to the menu, install the os-prober package and mount the partitions that contain other systems.
Note:
  • The default file path is /boot/grub/grub.cfg, not /boot/grub/i386-pc/grub.cfg. The grub package includes a sample /boot/grub/grub.cfg; ensure your intended changes are written to this file.
  • If you are trying to run grub-mkconfig in a chroot or systemd-nspawn container, you might notice that it does not work, complaining that grub-probe cannot get the "canonical path of /dev/sdaX". In this case, try using arch-chroot as described in the BBS post.

Configuration

This section only covers editing the /etc/default/grub configuration file. See GRUB/Tips and tricks for more information.

Remember to always #Generate the main configuration file after making changes to /etc/default/grub.

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.

By default grub-mkconfig determines the UUID of the root filesystem for the configuration. To disable this, uncomment GRUB_DISABLE_LINUX_UUID=true.

For generating the GRUB recovery entry you have to ensure that GRUB_DISABLE_RECOVERY is not set to true in /etc/default/grub.

You can also use GRUB_CMDLINE_LINUX="resume=UUID=uuid-of-swap-partition"

See Kernel parameters for more info.

LVM

If you use LVM for your /boot or / root partition, make sure that the lvm module is preloaded:

/etc/default/grub
GRUB_PRELOAD_MODULES="... lvm"

RAID

GRUB provides convenient handling of RAID volumes. You need to load GRUB modules mdraid09 or mdraid1x to allow you to address the volume natively:

/etc/default/grub
GRUB_PRELOAD_MODULES="... mdraid09 mdraid1x"

For example, /dev/md0 becomes:

set root=(md/0)

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

set root=(md/0,1)

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

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

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

Note: GRUB supports booting from Btrfs RAID 0/1/10, but not RAID 5/6. You may use mdadm for RAID 5/6, which is supported by GRUB.

Encryption

Root partition

To encrypt a root filesystem to be used with GRUB, add the encrypt hook or the sd-encrypt hook (if using systemd hooks) to mkinitcpio. See dm-crypt/System configuration#mkinitcpio for details, and Mkinitcpio#Common hooks for alternative encryption hooks.

If using the encrypt hook, add the cryptdevice parameter to /etc/default/grub.

/etc/default/grub
GRUB_CMDLINE_LINUX="cryptdevice=UUID=device-UUID:cryptroot"

If using the sd-encrypt hook, add rd.luks.name:

/etc/default/grub
GRUB_CMDLINE_LINUX="rd.luks.name=device-UUID=cryptroot"

where device-UUID is the UUID of the LUKS-encrypted device.

Be sure to generate the main configuration file when done.

For further information about bootloader configuration for encrypted devices, see Dm-crypt/System configuration#Boot loader.

Note: If you wish to encrypt /boot either as a separate partition or part of the / partition, further setup is required. See #Boot partition.
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.

Boot partition

GRUB can be set to ask for a password to open a LUKS blockdevice in order to read its configuration and load any initramfs and kernel from it. This option tries to solve the issue of having an unencrypted boot partition. /boot is not required to be kept in a separate partition; it may also stay under the system's root / directory tree.

Warning: GRUB does not support LUKS2 headers. Make sure you do not specify luks2 for the type parameter when creating the encrypted partition using cryptsetup luksFormat.

To enable this feature encrypt the partition with /boot residing on it using LUKS as normal. Then add the following option to /etc/default/grub:

/etc/default/grub
GRUB_ENABLE_CRYPTODISK=y

Be sure to #Generate the main configuration file while the partition containing /boot is mounted.

Without further changes you will be prompted twice for a passhrase: the first for GRUB to unlock the /boot mount point in early boot, the second to unlock the root filesystem itself as described in #Root partition. You can use a keyfile to avoid this.

Note:
  • If you use a special keymap, a default GRUB installation will not know it. This is relevant for how to enter the passphrase to unlock the LUKS blockdevice.
  • In order to perform system updates involving the /boot mount point, ensure that the encrypted /boot is unlocked and mounted before performing an update. With a separate /boot partition, this may be accomplished automatically on boot by using crypttab with a keyfile.
  • If you experience issues getting the prompt for a password to display (errors regarding cryptouuid, cryptodisk, or "device not found"), try reinstalling grub as below appending the following to the end of your installation command:
# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=grub --modules="part_gpt part_msdos"

Multiple entries

For tips on managing multiple GRUB entries, for example when using both linux and linux-lts kernels, see GRUB/Tips and tricks#Multiple entries.

Chainloading an Arch Linux .efi file

If you have an .efi file generated from following Secure Boot or other means, /etc/grub.d/40_custom can be edited to add a new menu entry before regenerating grub.cfg with grub-mkconfig.

/etc/grub.d/40_custom
menuentry 'Arch Linux .efi' {
insmod part_gpt
insmod chain
set root='(hdX,gptY)'
chainloader /EFI/path/file.efi
}

Dual-booting

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

Notes: Same topic, substituting USB drives for SATA drives is trivial. (Discuss in Talk:GRUB#)

The best way to add other entries is editing /etc/grub.d/40_custom or /boot/grub/custom.cfg. The entries in this file will be automatically added after rerunning grub-mkconfig.

"Shutdown" menu entry

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

"Restart" menu entry

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

"Firmware setup" menu entry (UEFI only)

menuentry "Firmware setup" {
	fwsetup
}

GNU/Linux menu entry

Assuming that the other distribution is on partition sda2:

menuentry "Other Linux" {
	set root=(hd0,2)
	linux /boot/vmlinuz (add other options here as required)
	initrd /boot/initrd.img (if the other kernel uses/needs one)
}

Alternatively let grub search for the right partition by UUID or label:

menuentry "Other Linux" {
        # assuming that UUID is 763A-9CB6
	search --set=root --fs-uuid 763A-9CB6

        # search by label OTHER_LINUX (make sure that partition label is unambiguous)
        #search --set=root --label OTHER_LINUX

	linux /boot/vmlinuz (add other options here as required, for example: root=UUID=763A-9CB6)
	initrd /boot/initrd.img (if the other kernel uses/needs one)
}

Windows installed in UEFI/GPT Mode menu entry

This mode determines where the Windows bootloader resides and chain-loads it after Grub when the menu entry is selected. The main task here is finding the EFI partition and running the bootloader from it.

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. See Dual boot with Windows#Windows UEFI vs BIOS limitations and Dual boot with Windows#Bootloader UEFI vs BIOS limitations for more information.
if [ "${grub_platform}" == "efi" ]; then
	menuentry "Microsoft Windows Vista/7/8/8.1 UEFI/GPT" {
		insmod part_gpt
		insmod fat
		insmod search_fs_uuid
		insmod chain
		search --fs-uuid --set=root $hints_string $fs_uuid
		chainloader /EFI/Microsoft/Boot/bootmgfw.efi
	}
fi

where $hints_string and $fs_uuid are obtained with the following two commands.

The $fs_uuid command determines the UUID of the EFI partition:

# grub-probe --target=fs_uuid esp/EFI/Microsoft/Boot/bootmgfw.efi
1ce5-7f28

Alternatively one can run blkid (as root) and read the UUID of the EFI system partition from there.

The $hints_string command will determine the location of the EFI system partition, in this case harddrive 0:

# grub-probe --target=hints_string esp/EFI/Microsoft/Boot/bootmgfw.efi
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1

These two commands assume the ESP Windows uses is mounted at esp. There might be case differences in the path to Windows's EFI file, what with being Windows, and all.

Windows installed in BIOS/MBR mode

Note: GRUB supports booting bootmgr directly and chainloading 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. 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, 8 or 10) installed in BIOS/MBR mode:

Note: These menu entries will work only in BIOS boot mode. It will not work in UEFI installed GRUB. See Dual boot with Windows#Windows UEFI vs BIOS limitations and Dual boot with Windows#Bootloader UEFI vs BIOS limitations .

In both examples XXXXXXXXXXXXXXXX is the filesystem UUID which can be found with command lsblk --fs.

For Windows Vista/7/8/8.1/10:

if [ "${grub_platform}" == "pc" ]; then
  menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS/MBR" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 XXXXXXXXXXXXXXXX
    ntldr /bootmgr
  }
fi

For Windows XP:

if [ "${grub_platform}" == "pc" ]; then
  menuentry "Microsoft Windows XP" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 XXXXXXXXXXXXXXXX
    ntldr /ntldr
  }
fi
Note: In some cases, GRUB may be installed without a clean Windows 8, in which case you cannot boot Windows without having an error with \boot\bcd (error code 0xc000000f). You can fix it by going to Windows Recovery Console (cmd.exe from install disk) and executing:
X:\> bootrec.exe /fixboot
X:\> bootrec.exe /RebuildBcd

Do not use bootrec.exe /Fixmbr because it will wipe GRUB out. Or you can use Boot Repair function in the Troubleshooting menu - it will not wipe out GRUB but will fix most errors. Also you would better keep plugged in both the target hard drive and your bootable device ONLY. Windows usually fails to repair boot information if any other devices are connected.

/etc/grub.d/40_custom can be used as a template to create /etc/grub.d/nn_custom. Where nn defines the precedence, indicating the order the script is executed. The order scripts are executed determine the placement in the grub boot menu.

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

Using the command shell

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

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

grub>

If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:

grub rescue>

The rescue shell is a restricted subset of the normal shell, offering much less functionality. If dumped to the rescue shell, first try inserting the "normal" module, then starting the "normal" shell:

grub rescue> set prefix=(hdX,Y)/boot/grub
grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
rescue:grub> normal

Pager support

GRUB supports pager for reading commands that provide long output (like the help command). This works only in normal shell mode and not in rescue mode. To enable pager, in GRUB command shell type:

sh:grub> set pager=1

Using the command shell environment to boot operating systems

grub>

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

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

The other bootloader may be embedded at the starting of the disk (MBR) or at the starting of a partition or as an EFI binary in the ESP in the case of UEFI.

Chainloading a partition

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

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

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

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

Similarly GRUB installed to a partition can be chainloaded.

Chainloading a disk/drive

set root=hdX
chainloader +1
boot

Chainloading Windows/Linux installed in UEFI mode

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

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

Normal loading

See the examples in #Using the rescue console

Using the rescue console

See #Using the command shell first. If unable to activate the standard shell, one possible solution is to boot using a live CD or some other rescue disk to correct configuration errors and reinstall GRUB. However, such a boot disk is not always available (nor necessary); the rescue console is surprisingly robust.

The available commands in GRUB rescue include insmod, ls, set, and unset. This example uses set and insmod. set modifies variables and insmod inserts new modules to add functionality.

Before starting, the user must know the location of their /boot partition (be it a separate partition, or a subdirectory under their root):

grub rescue> set prefix=(hdX,Y)/boot/grub

where X is the physical drive number and Y is the partition number.

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

To expand console capabilities, insert the linux module:

grub rescue> insmod i386-pc/linux.mod

or simply

grub rescue> insmod linux

This introduces the linux and initrd commands, which should be familiar.

An example, booting Arch Linux:

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

With a separate boot partition (e.g. when using UEFI), again change the lines accordingly:

Note: Since boot is a separate partition and not part of your root partition, you must address the boot partition manually, in the same way as for the prefix variable.
set root=(hd0,5)
linux (hdX,Y)/vmlinuz-linux root=/dev/sda6
initrd (hdX,Y)/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

F2FS and other unsupported file systems

GRUB does not support F2FS file system. In case the root partition is on an unsupported file system, an alternative /boot partition with a supported file system must be created. In some cases, the development version of GRUB grub-gitAUR may have native support for the file system.

Intel BIOS not booting GPT

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

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

Note: The bootable-marking must be done in fdisk or similar, not in GParted or others, as they will not set the bootable flag in the MBR.

With cfdisk, the steps are similar, just cfdisk /dev/sda, choose bootable (at the left) in the desired hard disk, and quit saving.

With recent version of parted, you can use disk_toggle pmbr_boot option. Afterwards verify that Disk Flags show pmbr_boot.

# parted /dev/sdx disk_toggle pmbr_boot
# parted /dev/sdx print

More information is available here

Enable debug messages

Note: This change is overwritten when #Generate the main configuration file.

Add:

set pager=1
set debug=all

to grub.cfg.

"No suitable mode found" error

If you get this error when booting any menuentry:

error: no suitable mode found
Booting however

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

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

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

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

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

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

BIOS systems:

insmod vbe

UEFI systems:

insmod efi_gop
insmod efi_uga

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

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

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

msdos-style error message

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

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

UEFI

Common installation errors

  • If you have a problem when running grub-install with sysfs or procfs and it says you must run modprobe efivars, try Unified Extensible Firmware Interface#Mount efivarfs.
  • Without --target or --directory option, grub-install cannot determine for which firmware to install. In such cases grub-install will print source_dir does not exist. Please specify --target or --directory.
  • If after running grub-install you are told your partition does not look like an EFI partition then the partition is most likely not Fat32.

Drop to rescue shell

If GRUB loads but drops into the rescue shell with no errors, it can be due to one of these two reasons:

  • It may be because of a missing or misplaced grub.cfg. This will happen if GRUB UEFI was installed with --boot-directory and grub.cfg is missing,
  • It also happens if the boot partition, which is hardcoded into the grubx64.efi file, has changed.

GRUB UEFI not loaded

An example of a working 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)

Default/fallback boot path

Some UEFI firmwares require a bootable file at a known location before they will show UEFI NVRAM boot entries. If this is the case, grub-install will claim efibootmgr has added an entry to boot GRUB, however the entry will not show up in the VisualBIOS boot order selector. The solution is to install GRUB at the default/fallback boot path:

# grub-install --target=x86_64-efi --efi-directory=esp --removable

Alternatively you can move an already installed GRUB EFI executable to the default/fallback path:

# mv esp/EFI/grub esp/EFI/BOOT
# mv esp/EFI/BOOT/grubx64.efi esp/EFI/BOOT/BOOTX64.EFI

Invalid signature

If trying to boot Windows results in an "invalid signature" error, e.g. after reconfiguring partitions or adding additional hard drives, (re)move GRUB's device configuration and let it reconfigure:

# mv /boot/grub/device.map /boot/grub/device.map-old
# grub-mkconfig -o /boot/grub/grub.cfg

grub-mkconfig should now mention all found boot options, including Windows. If it works, remove /boot/grub/device.map-old.

Boot freezes

If booting gets stuck without any error message after GRUB loading the kernel and the initial ramdisk, try removing the add_efi_memmap kernel parameter.

Arch not found from other OS

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

Warning when installing in chroot

When installing GRUB on a LVM system in a chroot environment (e.g. during system installation), you may receive warnings like

/run/lvm/lvmetad.socket: connect failed: No such file or directory

or

WARNING: failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.

This is because /run is not available inside the chroot. These warnings will not prevent the system from booting, provided that everything has been done correctly, so you may continue with the installation.

GRUB loads slowly

GRUB can take a long time to load when disk space is low. Check if you have sufficient free disk space on your /boot or / partition when you are having problems.

error: unknown filesystem

GRUB may output error: unknown filesystem and refuse to boot for a few reasons. If you are certain that all UUIDs are correct and all filesystems are valid and supported, it may be because your BIOS Boot Partition is located outside the first 2 TiB of the drive [2]. Use a partitioning tool of your choice to ensure this partition is located fully within the first 2 TiB, then reinstall and reconfigure GRUB.

grub-reboot not resetting

GRUB seems to be unable to write to root BTRFS partitions [3]. If you use grub-reboot to boot into another entry it will therefore be unable to update its on-disk environment. Either run grub-reboot from the other entry (for example when switching between various distributions) or consider a different file system. You can reset a "sticky" entry by executing grub-editenv create and setting GRUB_DEFAULT=0 in your /etc/default/grub (do not forget grub-mkconfig -o /boot/grub/grub.cfg).

Old BTRFS prevents installation

If a drive is formatted with BTRFS without creating a partition table (eg. /dev/sdx), then later has partition table written to, there are parts of the BTRFS format that persist. Most utilities and OS's do not see this, but GRUB will refuse to install, even with --force

# grub-install: warning: Attempting to install GRUB to a disk with multiple partition labels. This is not supported yet..
# grub-install: error: filesystem `btrfs' does not support blocklists.

You can zero the drive, but the easy solution that leaves your data alone is to erase the BTRFS superblock with wipefs -o 0x10040 /dev/sdx

Windows 8/10 not found

A setting in Windows 8/10 called "Hiberboot", "Hybrid Boot" or "Fast Boot" can prevent the Windows partition from being mounted, so grub-mkconfig will not find a Windows install. Disabling Hiberboot in Windows will allow it to be added to the GRUB menu.

VirtualBox EFI mode

Install GRUB to the default/fallback boot path.

See also VirtualBox#Installation in EFI mode.

See also