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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[[Category:GNU]]
[[fr:GRUB2]]
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[[ar:GRUB]]
{{Article summary start}}
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[[cs:GRUB]]
{{Article summary text|Covers various aspects of the next generation of the GRand Unified Bootloader (GRUB2).}}
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[[de:GRUB]]
{{Article summary heading|Overview}}
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[[el:GRUB]]
{{Article summary text|{{Boot process overview}}}}
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[[es:GRUB]]
{{Article summary heading|Related}}
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[[fa:گراب]]
{{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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[[fr:GRUB]]
{{Article summary heading|Resources}}
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[[he:GRUB]]
{{Article summary link|GNU GRUB -- GNU Project|http://www.gnu.org/software/grub/}}
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[[id:GRUB]]
{{Article summary link|GNU GRUB Wiki|http://grub.enbug.org/}}{{Linkrot|2011|09|05}}
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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|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 [[Boot loader|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. GRUB 2 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.}}
  
Briefly, 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 ==
  
== Preface ==
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=== GUID Partition Table (GPT) specific instructions ===
  
Although, [[GRUB]] (i.e. version 0.9x) is the de facto standard bootloader of Linux, it is considered 'legacy' by upstream. It is being replaced by GRUB2 in many distributions. Upstream recommends GRUB2 >=1.99~rc2 over grub-legacy, even for current grub-legacy users.
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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.
  
{{Note|grub2 from 1.99~rc2 and later supports btrfs as root (without a separate /boot filesystem).}}
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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]].
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* The BIOS boot partition is only needed by GRUB on a BIOS/GPT setup. On a BIOS/MBR setup, GRUB uses 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]].
 +
}}
  
=== Notes 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}}.
  
* 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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* Select partition type {{ic|BIOS boot}} for [[fdisk]].
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* Select partition type code {{ic|ef02}} for [[gdisk]].
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* For [[parted]] set/activate the flag {{ic|bios_grub}} on the partition.
  
* 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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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.
  
* 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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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.
  
=== Preliminary Requirements for GRUB2 ===
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=== Master Boot Record (MBR) specific instructions ===
  
==== BIOS systems ====
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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 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 [[Partitioning#Partition alignment|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}}).
  
===== [[GPT]] specific instructions =====
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=== Installation ===
  
GRUB2 in BIOS-GPT configuration requires a BIOS Boot Partition to embed its core.img in the absence of post-MBR gap in GPT partitioned systems (which is taken over by the GPT Primary Header and Primary Partition table).  This partition is used by 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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[[Install]] the {{Pkg|grub}} package. (It will replace {{AUR|grub-legacy}} if that is already installed.) Then do:
  
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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# grub-install --target=i386-pc /dev/sd'''X'''
  
{{Note|This partition should be created before grub_bios-install or 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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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}}).
  
===== [[MBR]] aka msdos partitioning specific instructions =====
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Now you must [[#Generate the main configuration file]].
  
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 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 core.img).
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If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks.
  
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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{{Tip|See [[GRUB/Tips and tricks#Alternative installation methods]] for other ways to install GRUB, such as to a USB stick.}}
  
{{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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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.
  
==== UEFI systems ====
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== UEFI systems ==
  
===== Create and Mount the UEFI SYSTEM PARTITION =====
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{{Note|
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* It is recommended to read and understand the [[Unified Extensible Firmware Interface]], [[Partitioning#GUID Partition Table]] and [[Arch boot process#Under UEFI]] pages.
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* When installing to use UEFI it is important to boot the installation media in UEFI mode, otherwise ''efibootmgr'' will not be able to add the GRUB UEFI boot entry. Installing to the [[#Default/fallback boot path|fallback boot path]] will still work even in BIOS mode since it does not touch the NVRAM.
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* To boot from a disk using UEFI, an EFI system partition is required. Follow [[EFI system partition#Check for an existing partition]] to find out if you have one already, otherwise you need to create it.
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}}
  
Follow [[Unified_Extensible_Firmware_Interface#Creating_a_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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=== Installation ===
  
# mkdir -p /boot/efi
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{{Note|
# mount -t vfat <UEFISYS_PART_DEVICE> /boot/efi
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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) UEFI systems (not to be confused with 32-bit CPUs), replace {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
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}}
  
Create a <UEFI_SYSTEM_PARTITION>/efi directory if it does not exist:
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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.
  
# mkdir -p /boot/efi/efi
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Then follow the below steps to install GRUB:
  
== Installation ==
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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 in {{ic|''esp''/EFI/}} to store the EFI binary 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/}}.
  
=== During Arch Linux installation ===
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# grub-install --target=x86_64-efi --efi-directory=''esp'' --bootloader-id=GRUB
  
* Skip the '''Install Bootloader''' step and exit the installer.
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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.
* Configure the network:
 
# aif -p partial-configure-network
 
This will bring up a prompt; put in the network interface to use, (e.g., 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 /tmp/install/etc/resolv.conf
 
* If you run into network issues in the pacman update step below, you may have needed to install the net-tools package.
 
* Load the dm-mod module (you might need grub2-bios; install the package if needed):
 
# 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 -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 dm-mod module has already been loaded, no need to do that again.
 
  
=== From a running Arch Linux ===
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Remember to [[#Generate the main configuration file]] after finalizing the configuration.
  
==== BIOS systems ====
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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 places an EFI executable there, but its only purpose is to recreate the UEFI boot entry for Windows.}}
  
===== Make a backup of your precious data =====
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{{Note|
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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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}}
  
In general, a grub installation should run smoothly . Sometimes it could mess up your system. You're strongly advised to make a backup before installing grub2-bios.
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See [[#UEFI|UEFI troubleshooting]] in case of problems. Additionally see [[GRUB/Tips and tricks#UEFI further reading]].
  
* copy grub modules and configuration
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== Configuration ==
  
# cp -a /boot/grub /path/to/backup/
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On an installed system, GRUB loads the {{ic|/boot/grub/grub.cfg}} configuration file each boot. You can follow [[#Generated grub.cfg]] for using a tool, or [[#Custom grub.cfg]] for a manual creation.
  
* backup the MBR and GRUB-Legacy stage 1.5
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=== Generated grub.cfg ===
  
# dd if=/dev/sdX of=/path/to/backup/first-sectors bs=512 count=63
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This section only covers editing the {{ic|/etc/default/grub}} configuration file. See [[GRUB/Tips and tricks]] for more information.
  
Replace /dev/sdaX with you disk path (mostly /dev/sda).
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Remember to always [[#Generate the main configuration file]] after making changes to {{ic|/etc/default/grub}} and/or files in {{ic|/etc/grub.d/}}.
  
{{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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==== Generate the main configuration file ====
  
To backup only the MBR boot code use:
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After the installation, the main configuration file {{ic|/boot/grub/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/}}.
  
# dd if=/dev/sdX of=/path/to/backup/mbr-boot-code bs=440 count=1
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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.
  
You could now lightly remove {{ic|/boot/grub}} with:
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{{Note|
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* Remember that {{ic|/boot/grub/grub.cfg}} has to be re-generated after any change to {{ic|/etc/default/grub}} or files in {{ic|/etc/grub.d/}}.
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* The default file path is {{ic|/boot/grub/grub.cfg}}, not {{ic|/boot/grub/i386-pc/grub.cfg}}.
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* 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].
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* If you are installing GRUB in chroot environment using LVM and the {{ic|grub-mkconfig}} hangs indefinitely, see [[#Device /dev/xxx not initialized in udev database even after waiting 10000000 microseconds]].
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}}
  
# rm -rf /boot/grub
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Use the ''grub-mkconfig'' tool to generate {{ic|/boot/grub/grub.cfg}}:
  
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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# grub-mkconfig -o /boot/grub/grub.cfg
  
* move old grub-legacy or grub2 files out of the way
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By default the generation scripts automatically add menu entries for all installed Arch Linux [[kernel]]s to the generated configuration.
  
# mv /boot/grub /boot/grub.nonfunctional
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{{Tip|
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* After installing or removing a [[kernel]], you just need to re-run the above ''grub-mkconfig'' command.
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* 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]].
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}}
  
* copy grub back to /boot
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To automatically add entries for other installed operating systems, see [[#Detecting other operating systems]].
  
# cp -a /path/to/backup/grub /boot/
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You can add additional custom menu entries by editing {{ic|/etc/grub.d/40_custom}} and re-generating {{ic|/boot/grub/grub.cfg}}. Or you can create {{ic|/boot/grub/custom.cfg}} and add them there. Changes to {{ic|/boot/grub/custom.cfg}} do not require re-running ''grub-mkconfig'', since {{ic|/etc/grub.d/40_custom}} adds the necessary {{ic|source}} statement to the generated configuration file.
  
* replace MBR and next 62 sectors of sda with backed up copy (DANGEROUS!)
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{{Tip|{{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. {{ic|''nn''}} should be greater than {{ic|06}} to ensure necessary scripts are executed first.}}
  
# dd if=/path/to/backup/first-sectors of=/dev/sdX bs=512 count=63
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See [[#Boot menu entry examples]] for custom menu entry examples.
  
{{Note|This command also restores the partition table. Be careful.}}
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==== Detecting other operating systems ====
  
To restore only the MBR boot code use:
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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 the other systems. Then re-run ''grub-mkconfig''.
  
# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=440 count=1
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===== MS Windows =====
  
===== Before grub_bios-install =====
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Often, partitions containing Windows will be automatically discovered by {{Pkg|os-prober}}. However, NTFS partitions may not always be detected when mounted with the default Linux drivers. If GRUB is not detecting it, try installing {{Pkg|ntfs-3g}} and remounting.
  
The GRUB2 package can be installed with pacman (and will replace {{Pkg|grub}}, if it is installed):
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Encrypted Windows partitions may need to be decrypted before mounting. For BitLocker, this can be done with {{AUR|dislocker}}. This should be sufficient for {{Pkg|os-prober}} to add the correct entry.
 
# pacman -S grub2-bios
 
  
{{Note|Installing grub2-common (a dependency of grub2-bios) 1.99~rc1 or later, may take forever in some systems since the post_install script runs grub-mkconfig and this script does not provide the option {{ic|--no-floppy}}. For more details search this option in the article.}}
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==== Additional arguments ====
  
{{Note|Simply installing the package won't update the /boot/grub/core.img file and the grub2 modules in /boot/grub . You need to update the core.img file and the grub2 modules manually using grub_bios-install as explained below.}}
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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.
  
Also load the device-mapper kernel module without which grub-probe does not reliably detect disks and partitions:
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It is not necessary to use both, but can be useful. For example, you could use {{ic|1=GRUB_CMDLINE_LINUX_DEFAULT="resume=UUID=''uuid-of-swap-partition'' quiet"}} where {{ic|''uuid-of-swap-partition''}} is the [[UUID]] of 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.
  
# modprobe dm-mod
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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}}.
  
===== Run grub_bios-install =====
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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}}.
  
There are 3 ways to install grub2 in BIOS booting - [[#Install_to_440-byte_MBR_boot_code_region]] (recommended) , [[#Install_to_Partition_or_Partitionless_Disk]] (not recommended) or [[#Generate_core.img_alone]] (safest method, but requires another BIOS bootloader like [[grub-legacy]] or [[syslinux]] to be installed to chainload {{ic|/boot/grub/core.img}} ). For all the ways [[#Before_grub_bios-install]] step is needed.
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See [[Kernel parameters]] for more info.
  
====== Install to 440-byte MBR boot code region ======
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==== LVM ====
  
To setup grub2-bios in the 440-byte Master Boot Record boot code region, populate the {{ic|/boot/grub}} directory, generate the {{ic|/boot/grub/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:
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{{Merge|#Installation|grub-mkconfig is capable of detecting that it needs the {{ic|lvm}} module, specifying it in {{ic|GRUB_PRELOAD_MODULES}} is not required. Move warning to [[#Installation]] & [[#Installation_2]] or create a [[Help:Style#"Known issues" section|Known issues section]] and document it there.}}
  
# grub_bios-install --boot-directory=/boot --no-floppy --recheck /dev/sda
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{{Warning|GRUB does not support thin-provisioned logical volumes.}}
  
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.
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If you use [[LVM]] for your {{ic|/boot}} or {{ic|/}} root partition, make sure that the {{ic|lvm}} module is preloaded:
  
The {{ic|--no-floppy}} tells grub2-bios utilities not to search for any floppy devices which reduces the overall execution time of grub_bios-install on many systems (it will also prevent the issue below from occurring). Otherwise you get an error like this:
+
{{hc|/etc/default/grub|2=
 +
GRUB_PRELOAD_MODULES="... lvm"
 +
}}
  
grub-probe: error: Cannot get the real path of '/dev/fd0'
+
==== RAID ====
Auto-detection of a filesystem module failed.
 
Please specify the module with the option '--modules' explicitly.
 
  
Follow [[#Generate_GRUB2_BIOS_Config_file]] or if that fails, convert your {{ic|/boot/grub/menu.lst}} file to {{ic|/boot/grub/grub.cfg}} using:
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{{Merge|#Installation|grub-mkconfig is capable of detecting that it needs the {{ic|mdraid09}} and/or {{ic|mdraid1x}} modules, specifying them in {{ic|GRUB_PRELOAD_MODULES}} is not required. Summarize the double grub-install in a note and move it to [[#Installation]]; move {{ic|set root}} stuff to [[#Custom grub.cfg]].}}
  
# grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
+
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:
  
For example:
+
{{hc|/etc/default/grub|2=
 +
GRUB_PRELOAD_MODULES="... mdraid09 mdraid1x"
 +
}}
  
{{hc|/boot/grub/menu.lst|<nowiki>
+
For example, {{ic|/dev/md0}} becomes:
default=0
 
timeout=5
 
  
title Arch Linux Stock Kernel
+
  set root=(md/0)
root   (hd0,0)
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux.img
 
  
title  Arch Linux Stock Kernel Fallback
+
whereas a partitioned RAID volume (e.g. {{ic|/dev/md0p1}}) becomes:
root  (hd0,0)
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux-fallback.img
 
</nowiki>}}
 
  
{{hc|/boot/grub/grub.cfg|<nowiki>
+
set root=(md/0,1)
set default='0'; if [ x"$default" = xsaved ]; then load_env; set default="$saved_entry"; fi
 
set timeout=5
 
  
menuentry 'Arch Linux Stock Kernel' {
+
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:
  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' {
+
# grub-install --target=i386-pc --debug /dev/sda
  set root='(hd0,1)'; set legacy_hdbias='0'
+
# grub-install --target=i386-pc --debug /dev/sdb
  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}} configfile and simply rebooted into GRUB2 Command Shell, type:
+
Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}.
  
sh:grub> insmod legacycfg
+
{{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.}}
sh:grub> legacy_configfile ${prefix}/menu.lst
 
  
Boot into Arch and re-create the proper GRUB2 {{ic|/boot/grub/grub.cfg}} configfile.
+
==== Encrypted /boot ====
  
{{Note|This option works only in BIOS systems, not in UEFI systems.}}
+
GRUB also has special support for booting with an encrypted {{ic|/boot}}. This is done by unlocking 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]].
  
====== Install to Partition or Partitionless Disk ======
+
{{Note|{{ic|/boot}} is '''not''' required to be kept in a separate partition; it may also stay under the system's root {{ic|/}} directory tree.}}
  
{{Note|grub2-bios (any version - including upstream bzr 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.}}
+
{{Warning|GRUB does not support LUKS2 headers; see [https://savannah.gnu.org/bugs/?55093 GRUB bug #55093]. Make sure to specify {{ic|1=--type luks1}} when creating the encrypted partition using {{ic|cryptsetup luksFormat}}.}}
  
To setup 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)
+
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}}:
 
# chattr -i /boot/grub/core.img
 
# grub_bios-install --boot-directory=/boot --no-floppy --recheck --force /dev/sda1
 
# chattr +i /boot/grub/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 core.img).
+
{{hc|/etc/default/grub|output=
 +
GRUB_ENABLE_CRYPTODISK=y
 +
}}
  
grub_bios-install will give out warnings like which should give you the idea of what might go wrong with this approach.
+
This option is used by grub-install to generate the grub {{ic|core.img}}, so make sure to [[#Installation|install grub]] after modifying this option.
  
/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea.
+
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 implemented by the initramfs. You can use a [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs|keyfile]] to avoid this.
/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 grub-setup will not setup its boot code in the partition boot sector.
+
{{Warning|
+
* If you want to [[#Generate the main configuration file|generate the main configuration file]], make sure that {{ic|/boot}} is mounted.
/sbin/grub-setup: error: will not proceed with blocklists
+
* 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]].
 +
}}
  
With {{ic|--force}} you should get
+
{{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.
 +
* If you experience issues getting the prompt for a password to display (errors regarding cryptouuid, cryptodisk, or "device not found"), try reinstalling GRUB and appending {{ic|1=--modules="part_gpt part_msdos"}} to the end of your {{ic|grub-install}} command.
 +
}}
  
Installation finished. No error reported.
+
{{Tip|1=You can use [https://bbs.archlinux.org/viewtopic.php?id=234607 pacman hooks]to automount your {{ic|/boot}} when upgrades need to access related files.}}
  
The reason why grub-setup does not by default allow this is because in case of partition or a partitionless disk is that grub2-bios relies on embedded blocklists in the partition bootsector to locate the {{ic|/boot/grub/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 .
+
=== Custom grub.cfg ===
  
The workaround for this is to set the immutable flag on {{ic|/boot/grub/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/core.img}} needs to be set only if 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).
+
{{Expansion|Add instructions on how to write a custom {{ic|/boot/grub/grub.cfg}}. See [[User:Eschwartz/Grub]] for a proposed draft.|section=Manually generate grub.cfg}}
  
====== Generate core.img alone ======
+
This section describes the manual creation of GRUB boot entries in {{ic|/boot/grub/grub.cfg}} instead of relying on ''grub-mkconfig''.
  
To populate the {{ic|/boot/grub}} directory and generate a {{ic|/boot/grub/core.img}} file WITHOUT embedding any grub2-bios bootsector code in the MBR, post-MBR region, or the partition bootsector, add {{ic|1=--grub-setup=/bin/true}} to grub_bios-install:
+
A basic GRUB config file uses the following options:
 
# grub_bios-install --grub-setup=/bin/true --boot-directory=/boot --no-floppy --recheck /dev/sda
 
  
You can then chainload grub2's core.img from grub-legacy or syslinux as a Linux kernel or a multiboot kernel.
+
* {{ic|(hd''X'',''Y'')}} is the partition ''Y'' on disk ''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 ''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=(hd''X'',''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|/}})
  
===== After grub_bios-install =====
+
==== Boot menu entry examples ====
  
====== Generate GRUB2 BIOS Config file ======
+
{{Tip|These boot entries can also be used when using a {{ic|/boot/grub/grub.cfg}} generated by ''grub-mkconfig''. Add them to {{ic|/etc/grub.d/40_custom}} and [[#Generate the main configuration file|re-generate the main configuration file]] or add them to {{ic|/boot/grub/custom.cfg}}.}}
  
Finally, generate a configuration for grub2 (this is explained in greater detail in the Configuration section):
+
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]].
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
For [[Archiso]] and [[Archboot]] boot menu entries see [[Multiboot USB drive#Boot entries]].
  
If grub2 complains about "no suitable mode found" while booting, go to [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]] .
+
===== GRUB commands =====
  
===== Multiboot in BIOS =====
+
====== "Shutdown" menu entry ======
  
====== Boot Microsoft Windows installed in BIOS-MBR mode ======
+
{{bc|
 +
menuentry "System shutdown" {
 +
echo "System shutting down..."
 +
halt
 +
}
 +
}}
  
{{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.}}
+
====== "Restart" menu entry ======
  
Find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the bootmgr and its files reside. For example, if Windows {{ic|bootmgr}} exists at {{ic|/media/Windows/bootmgr}}:
+
{{bc|
 +
menuentry "System restart" {
 +
echo "System rebooting..."
 +
reboot
 +
}
 +
}}
  
# grub-probe --target=fs_uuid /media/Windows/bootmgr
+
====== "Firmware setup" menu entry (UEFI only) ======
69B235F6749E84CE
 
  
Then, add the below code to {{ic|/etc/grub.d/40_custom}} and regenerate grub.cfg with grub-mkconfig as explained above to chainload Windows (Vista, 7 or 8) installed in BIOS-MBR mode:
+
{{bc|1=
 +
if [ ${grub_platform} == "efi" ]; then
 +
menuentry "Firmware setup" {
 +
fwsetup
 +
}
 +
fi
 +
}}
  
menuentry "Microsoft Windows 7 BIOS-MBR" {
+
===== EFI binaries =====
    insmod part_msdos
 
    insmod ntfs
 
    insmod search_fs_uuid
 
    insmod ntldr   
 
    search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
 
    ntldr (${root})/bootmgr
 
}
 
  
For Windows XP
+
When launched in UEFI mode, GRUB can chainload other EFI binaries.
  
menuentry "Microsoft Windows XP" {
+
{{Tip|1=To show these menu entries only when GRUB is launched in UEFI mode, enclose them in the following {{ic|if}} statement:
    insmod part_msdos
 
    insmod ntfs
 
    insmod search_fs_uuid
 
    insmod ntldr   
 
    search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
 
    ntldr (${root})/ntldr
 
}
 
  
==== [[UEFI]] systems ====
+
{{bc|1=
 +
if [ ${grub_platform} == "efi" ]; then
 +
''place UEFI-only menu entries here''
 +
fi
 +
}}
  
===== Before grub_efi_${UEFI_ARCH}-install =====
+
}}
  
{{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.}}
+
====== UEFI Shell ======
  
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).
+
You can launch [[Unified Extensible Firmware Interface#UEFI Shell|UEFI Shell]] by using placing it in the root of the [[EFI system partition]] and adding this menu entry:
  
Depending on that, install the appropriate package
+
{{bc|1=
 +
menuentry "UEFI Shell" {
 +
insmod fat
 +
insmod chain
 +
search --no-floppy --set=root --file /shellx64.efi
 +
chainloader /shellx64.efi
 +
}
 +
}}
  
For 64-bit aka x86_64 UEFI firmware:
+
====== gdisk ======
# pacman -S grub2-efi-x86_64
 
  
For 32-bit aka i386 UEFI firmware:
+
Download the [[gdisk#gdisk EFI application|gdisk EFI application]] and copy {{ic|gdisk_x64.efi}} to {{ic|''esp''/EFI/tools/}}.
# pacman -S grub2-efi-i386
 
  
{{Note|Installing grub2-common (a dependency of grub2-bios) 1.99~rc1 or later, may take forever in some systems since the post_install script runs grub-mkconfig and this script does not provide the option {{ic|--no-floppy}}. For more details search this option in the article.}}
+
{{bc|1=
 +
menuentry "gdisk" {
 +
insmod fat
 +
insmod chain
 +
search --no-floppy --set=root --file /EFI/tools/gdisk_x64.efi
 +
chainloader /EFI/tools/gdisk_x64.efi
 +
}
 +
}}
  
{{Note|Simply installing the package won't update the grub.efi file and the grub2 modules in the UEFI System Partition . You need to update the grub.efi file and the grub2 modules in the UEFI System Partition manually using grub_efi_${UEFI_ARCH}-install as explained below.}}
+
====== Chainloading an Arch Linux .efi file ======
  
Also load the device-mapper kernel module without which grub-probe does not reliably detect disks and partitions
+
If you have an ''.efi'' file generated from following [[Secure Boot]] or other means, you can add it to the boot menu. For example:
  
# modprobe dm-mod
+
{{bc|1=
 +
menuentry "Arch Linux .efi" {
 +
insmod fat
 +
insmod chain
 +
search --no-floppy --set=root --fs-uuid ''FILESYSTEM_UUID''
 +
chainloader /EFI/arch/vmlinuz.efi
 +
}
 +
}}
  
===== Run grub_efi_${UEFI_ARCH}-install =====
+
===== Dual-booting =====
  
====== Install to UEFI SYSTEM PARTITION ======
+
====== GNU/Linux ======
  
{{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).}}
+
Assuming that the other distribution is on partition {{ic|sda2}}:
  
# grub_efi_x86_64-install --root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=grub --no-floppy --recheck
+
{{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)
 +
}
 +
}}
  
The {{ic|grub_efi_x86_64-install}} automatically generates a {{ic|grub.efi}} while setting up the {{ic|/boot/efi/efi/grub/}} directory.
+
Alternatively let GRUB search for the right partition by ''UUID'' or ''label'':
  
If you notice carefully, there is no <device_path> option (Eg: {{ic|/dev/sda}}) at the end of the {{ic|grub_efi_x86_64-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.
+
{{bc|1=
 +
menuentry "Other Linux" {
 +
        # assuming that UUID is 763A-9CB6
 +
search --no-floppy --set=root --fs-uuid 763A-9CB6
  
You may now be able to UEFI boot your system by creating a grub.cfg file using grub-mkconfig and copying /boot/efi/efi/grub/grub.efi to /boot/efi/efi/boot/bootx64.efi.
+
        # search by label OTHER_LINUX (make sure that partition label is unambiguous)
 +
        #search --no-floppy --set=root --label OTHER_LINUX
  
===== After grub_efi_${UEFI_ARCH}-install =====
+
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)
 +
}
 +
}}
  
====== Launch GRUB2 as default in non-Mac UEFI systems ======
+
====== Windows installed in UEFI/GPT mode ======
  
{{Note|The below steps will not work if the system has been booted in BIOS mode and will not work if the UEFI processor architecture does not match the kernel one, i.e. x86_64 UEFI + ix86 32-bit Kernel and vice-versa config will not work. This is true only for efivars kernel module and efibootmgr step. The previous steps can be done even in BIOS/Legacy boot mode.}}
+
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 system partition and running the bootloader from it.
  
{{Warning|Using {{ic|efibootmgr}} in Apple Macs will brick the firmware and may need reflash of the motherboard ROM. There have been bug reports regarding this in Ubuntu/Launchpad bug tracker. Use bless command alone in case of Macs (see chapter regarding Apple systems}}
+
{{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.}}
  
 +
{{bc|1=
 +
if [ "${grub_platform}" == "efi" ]; then
 +
menuentry "Microsoft Windows Vista/7/8/8.1 UEFI/GPT" {
 +
insmod part_gpt
 +
insmod fat
 +
insmod chain
 +
search --no-floppy --fs-uuid --set=root $hints_string $fs_uuid
 +
chainloader /EFI/Microsoft/Boot/bootmgfw.efi
 +
}
 +
fi
 +
}}
  
grub_efi_${UEFI_ARCH}-install will ensure {{ic|/boot/efi/efi/grub/grub.efi}} is launched by default if it detects {{ic|efibootmgr}} and if it is able to access UEFI Runtime Services. {{ic|efibootmgr}} command will work only if you have booted the system in UEFI mode itself, since it '''requires access to UEFI Runtime Variables''' which are '''available only in UEFI boot mode''' (with "noefi" kernel parameter NOT being used).  Initially the user is required to manually launch {{ic|/boot/efi/efi/grub/grub.efi}} from the firmware itself (using maybe the UEFI Shell) if grub2-efi was installed in BIOS mode. Then {{ic|efibootmgr}} should be run to make grub2 as the default entry in the UEFI Boot Manager
+
where {{ic|$hints_string}} and {{ic|$fs_uuid}} are obtained with the following two commands.  
  
First boot into UEFI mode manually either using the firmware boot menu, UEFI shell, or using any UEFI capable bootable iso (Archboot or Ubuntu non-Mac iso). Use grub probe to determine the device path of your EFI System Partition:
+
The {{ic|$fs_uuid}} command determines the UUID of the EFI system partition:
# grub-probe --target=device /boot/efi/efi/grub/grub.efi
 
  
It should give something like {{ic|/dev/sda1}} (used as example in the remaining steps). Load 'efivars' kernel module:
+
{{hc|1=# grub-probe --target=fs_uuid ''esp''/EFI/Microsoft/Boot/bootmgfw.efi|2=
# modprobe efivars
+
1ce5-7f28
 +
}}
  
If you get '''no such device found''' error for this command, that means you have not booted in UEFI mode or due to some reason the kernel is unable to access UEFI Runtime Variables.
+
Alternatively one can run {{ic|blkid}} (as root) and read the UUID of the EFI system partition from there.
  
Verify whether there are files in ''/sys/firmware/efi/vars/'' directory. This directory and its contents are created by "efivars" kernel module and it will exist only if you have booted in UEFI mode without the "noefi" kernel parameter.
+
The {{ic|$hints_string}} command will determine the location of the EFI system partition, in this case harddrive 0:
 
# ls -1 /sys/firmware/efi/vars/
 
  
Sample output (x86_64-UEFI 2.3.1 in x86_64 Kernel:
+
{{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
# ls -1 /sys/firmware/efi/vars/
+
}}
Boot0000-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
BootCurrent-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
BootOptionSupport-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
  ConIn-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
ConInDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
ConOut-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
ConOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
ErrOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
Lang-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
LangCodes-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
MTC-eb704011-1402-11d3-8e77-00a0c969723b/
 
MemoryTypeInformation-4c19049f-4137-4dd3-9c10-8b97a83ffdfa/
 
PlatformLang-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
PlatformLangCodes-8be4df61-93ca-11d2-aa0d-00e098032b8c/
 
RTC-378d7b65-8da9-4773-b6e4-a47826a833e1/
 
del_var
 
new_var
 
  
If ''/sys/firmware/efi/vars/'' directory is empty or does not exist, then {{ic|efibootmgr}} command will not work. If you are unable to make the ISO/CD/DVD/USB boot in UEFI mode try https://gitorious.org/tianocore_uefi_duet_builds/pages/Linux_Windows_BIOS_UEFI_boot_USB .
+
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.
  
If ''/sys/firmware/efi/vars/'' directory (along with the exists then run {{ic|efibootmgr}} and reboot:
+
====== Windows installed in BIOS/MBR mode ======
 
# efibootmgr --create --gpt --disk /dev/sda --part 1 --write-signature --label "GRUB2" --loader "\\EFI\\grub\\grub.efi"
 
  
In the above command, {{ic|/boot/efi/efi/grub/grub.efi}} can be split up as {{ic|/boot/efi}} and {{ic|/efi/grub/grub.efi}}, which translates to {{ic|(/dev/sda)}} -> partition 1 -> {{ic|\\EFI\\grub\\grub.efi}}.
+
{{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.}}
  
FAT32 filesystem is case-insensitive since it does not use UTF-8 encoding by default. In that case the firmware uses capital 'EFI' instead of small 'efi', therefore using {{ic|\\EFI\\grub\\grub.efi}} or {{ic|\\efi\\grub\\grub.efi}} does not matter (this will change if the filesystem encoding is UTF-8). UEFI uses backward slash as path separatoir (similar to Windows paths). In the above command "double" backward slashes are used instead of single ones, since a backward slash is used as a escape character by sh shells, the first backward slash escapes the second one so that the path {{ic|\EFI\grub\grub.efi}} is passed to {{ic|efibootmgr}}.
+
{{Warning|It is the '''system partition''' that has {{ic|/bootmgr}}, not your "real" Windows partition (usually {{ic|C:}}). The system partition's [[Persistent block device naming#by-label|filesystem label]] is {{ic|System Reserved}} or {{ic|SYSTEM}} and the partition is only about 100 to 549 MiB in size. See [[Wikipedia:System partition and boot partition]] for more information.}}
  
The 'label' is the name of the menu entry shown in the UEFI boot menu. This name is user's choice and does not affect the booting of the system. More info can be obtained from [http://linux.dell.com/cgi-bin/gitweb/gitweb.cgi?p=efibootmgr.git;a=blob_plain;f=README;hb=HEAD efibootmgr GIT README]
+
Throughout this section, it is assumed your Windows partition is {{ic|/dev/sda1}}. A different partition will change every instance of {{ic|hd0,msdos1}}.
  
If you have problems running GRUB2 in UEFI mode you can try the following (worked on an ASUS Z68 mainboard):
+
{{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]] .}}
 
# cp /boot/efi/efi/grub/grub.efi /boot/efi/shellx64.efi
 
  
or
+
In both examples {{ic|''XXXXXXXXXXXXXXXX''}} is the filesystem UUID which can be found with command {{ic|lsblk --fs}}.
 
# cp /boot/efi/efi/grub/grub.efi /boot/efi/efi/shellx64.efi
 
or
 
  
# cp /boot/efi/efi/grub/grub.efi /boot/efi/efi/shell/shellx64.efi
+
For Windows Vista/7/8/8.1/10:
  
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).
+
{{bc|1=
 +
if [ "${grub_platform}" == "pc" ]; then
 +
menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS/MBR" {
 +
insmod part_msdos
 +
insmod ntfs
 +
insmod ntldr   
 +
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 ''XXXXXXXXXXXXXXXX''
 +
ntldr /bootmgr
 +
}
 +
fi
 +
}}
  
====== Launch GRUB2 as default in Apple Mac EFI systems ======
+
For Windows XP:
  
Use bless command from within Mac OS X to set {{ic|grub.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}" == "pc" ]; then
 +
menuentry "Microsoft Windows XP" {
 +
insmod part_msdos
 +
insmod ntfs
 +
insmod ntldr   
 +
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 ''XXXXXXXXXXXXXXXX''
 +
ntldr /ntldr
 +
}
 +
fi
 +
}}
  
# cd /Volumes
+
{{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:
# 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.
+
X:\> bootrec.exe /fixboot
 +
X:\> bootrec.exe /RebuildBcd
  
# bless --folder=/Volumes/efi --file=/Volumes/efi/efi/grub/grub.efi --setBoot
+
Do '''not''' use {{ic|bootrec.exe /Fixmbr}} because it will wipe GRUB out.
# bless --mount=/Volumes/efi --file=/Volumes/efi/efi/grub/grub.efi --setBoot
+
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.
 +
}}
  
More info at https://help.ubuntu.com/community/UEFIBooting#Apple_Mac_EFI_systems_.28both_EFI_architecture.29 .
+
== Using the command shell ==
  
====== Generate GRUB2 UEFI Config file ======
+
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.
  
Finally, generate a configuration for grub2 (this is explained in greater detail in the Configuration section):
+
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-mkconfig -o /boot/efi/efi/grub/grub.cfg
+
  grub>
  
If grub2-uefi complains about "no suitable mode found" while booting, go to [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]] .
+
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
  
===== Generate a custom GRUB2 UEFI Application =====
+
grub rescue>
  
If you want, you can create a custom {{ic|grub_custom.efi}} app using:
+
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-mkimage -d /usr/lib/grub/x86_64-efi -O x86_64-efi -p "" -o /boot/efi/efi/grub/grub_custom.efi <GRUB2_Modules_to_be_included>
 
  
{{Note|The '''-p''' option is important for creating a portable {{ic|grub_custom.efi}} app.}}
+
grub rescue> set prefix=(hdX,Y)/boot/grub
 +
grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
 +
rescue:grub> normal
  
There is no file-size restriction on {{ic|grub_custom.efi}} either due to GRUB2 or due to the UEFI firmware. Therefore you can include any number of modules you want.
+
=== Pager support ===
  
A "{{ic|grub.cfg}}" created for BIOS based GRUB2 will be sufficient for the UEFI GRUB2 as long as all the paths in the config are absolute paths. The {{ic|grub.cfg}} file should exist in the same directory as {{ic|grub.efi}} or {{ic|grub_custom.efi}}.
+
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:
  
The {{ic|grub.efi}} UEFI application can be launched using the firmware's "Boot Manager", "Boot from file" option or using the [https://wiki.archlinux.org/index.php/UEFI#UEFI_Shell UEFI Shell].
+
sh:grub> set pager=1
  
Alternatively, you can also setup {{ic|/boot/efi/efi/grub}} directory by copying all the files in {{ic|/usr/lib/grub/x86_64-efi}} to {{ic|/boot/efi/efi/grub}} and using the above grub-mkimage command to create a {{ic|grub_custom.efi}} application. Just make sure you have the required modules embedded in {{ic|grub_custom.efi}} to enable it to access the EFI SYSTEM PARTITION.
+
=== Using the command shell environment to boot operating systems ===
  
A basic {{ic|grub_custom.efi}} can be generated using the following command:
+
  grub>
  # sudo grub-mkimage -d /usr/lib/grub/x86_64-efi -O x86_64-efi -p "" -o /boot/efi/efi/grub/grub_custom.efi part_gpt fat iso9660 udf normal chain linux \
 
ls search search_fs_file search_fs_uuid search_label help boot configfile echo efi_gop
 
  
===== Multiboot in UEFI =====
+
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'''.
  
====== Chainload Microsoft Windows x86_64 UEFI-GPT ======
+
''Chainloading'' means to load another boot-loader from the current one, ie, chain-loading.
  
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):
+
The other bootloader may be embedded at the start of a partitioned disk (MBR), at the start of a partition or a partitionless disk (VBR), or as an EFI binary in the case of UEFI.
  
# grub-probe --target=fs_uuid /boot/efi/efi/Microsoft/Boot/bootmgfw.efi
+
==== Chainloading a partition's VBR ====
1ce5-7f28
 
  
Then, add this code to {{ic|/boot/efi/efi/grub/grub.cfg}} to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode:
+
set root=(hdX,Y)
 +
chainloader +1
 +
boot
  
menuentry "Microsoft Windows x86_64 UEFI-GPT" {
+
X=0,1,2...
    insmod part_gpt
+
Y=1,2,3...
    insmod fat
 
    insmod search_fs_uuid
 
    insmod chain
 
    search --fs-uuid --no-floppy --set=root 1ce5-7f28
 
    chainloader (${root})/efi/Microsoft/Boot/bootmgfw.efi
 
}
 
  
== Manual Compilation ==
+
For example to chainload Windows stored in the first partition of the first hard disk,
  
=== For BIOS Systems ===
+
set root=(hd0,1)
 +
chainloader +1
 +
boot
  
GRUB2 for BIOS systems should be compiled as follows:
+
Similarly GRUB installed to a partition can be chainloaded.
{{bc|<nowiki>
 
./autogen.sh
 
  
./configure --with-platform=pc --prefix=/usr
+
==== Chainloading a disk's MBR or a partitionless disk's VBR ====
  
make
+
set root=hdX
 +
chainloader +1
 +
boot
  
make install
+
==== Chainloading Windows/Linux installed in UEFI mode ====
</nowiki>}}
 
  
The {{ic|1=--with-platform=pc}} generates grub2 for bios alone irrespective of the firmware of the build system.
+
insmod fat
 +
set root=(hd0,gpt4)
 +
chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
 +
boot
  
=== For UEFI Systems ===
+
{{ic|insmod fat}} is used for loading the FAT file system module for accessing the Windows bootloader on the EFI system partition.
 +
{{ic|(hd0,gpt4)}} or {{ic|/dev/sda4}} is the EFI system partition in this example.
 +
The entry in the {{ic|chainloader}} line specifies the path of the ''.efi'' file to be chain-loaded.
  
First [https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interface#Detecting_UEFI_Firmware_Arch Detect which UEFI Firmware arch] you have and then follow the compile instructions below:
+
==== Normal loading ====
{{bc|<nowiki>
 
./autogen.sh
 
  
./configure --with-platform=efi --target=TARGET_UEFI_ARCH --prefix=/usr
+
See the examples in [[#Using the rescue console]]
  
make
+
=== Using the rescue console ===
  
make install
+
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.
</nowiki>}}
 
  
The "--target" option denotes the UEFI firmware arch. for which grub2 should be compiled, not the architecture of the linux kernel grub2 may boot.  
+
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.
  
It is possible to use UEFI 64-bit firmware + GRUB2 as x86_64-EFI app loading a i686 linux kernel, as long as the kernel does not try to access UEFI Runtime Services. Vice-versa situation is also possible. But a x86_64 UEFI firmware cannot launch GRUB2 i386-efi app (unlike x86_64 Operating Systems), and a i386 UEFI firmware will not launch GRUB2 {{ic|x86_64-efi}} app. It is important to compile GRUB2 to match the architecture of the UEFI firmware.
+
Before starting, the user must know the location of their {{ic|/boot}} partition (be it a separate partition, or a subdirectory under their root):
  
== Configuration ==
+
grub rescue> set prefix=(hdX,Y)/boot/grub
  
You can also choose to automatically generate or manually edit {{ic|grub.cfg}}.
+
where X is the physical drive number and Y is the partition number.
  
{{Note|If using UEFI {{ic|grub.cfg}} must be placed alongside {{ic|grub.efl}} on the UEFI system partition. The easiest way is to copy the configuration file created below from {{ic|/boot/grub/grub.cfg}} to {{ic|/boot/efi/EFI/grub}} where {{ic|/boot/efi}} is the mounted UEFI partition. }}
+
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}}).}}
  
=== Automatically generating using grub-mkconfig (Recommended) ===
+
To expand console capabilities, insert the {{ic|linux}} module:
  
The GRUB2 {{ic|menu.1st}} equivalent configuration files are {{ic|/etc/default/grub}} and {{ic|/etc/grub.d/*}}. 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:
+
  grub rescue> insmod i386-pc/linux.mod
  # grub-mkconfig -o /boot/grub/grub.cfg
 
{{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}}
 
  
=== Manually creating grub.cfg ===
+
or simply
  
A basic grub file uses the following options
+
grub rescue> insmod linux
* {{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:
+
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar.
  
{{hc
+
An example, booting Arch Linux:
|/boot/grub/grub.cfg
 
|<nowiki>
 
# Config file for GRUB2 - The GNU GRand Unified Bootloader
 
# /boot/grub/grub.cfg
 
  
# DEVICE NAME CONVERSIONS
+
  set root=(hd0,5)
#
+
  linux /boot/vmlinuz-linux root=/dev/sda5
#  Linux          Grub
+
  initrd /boot/initramfs-linux.img
# -------------------------
+
boot
# /dev/fd0        (fd0)
 
# /dev/sda        (hd0)
 
/dev/sdb2      (hd1,2)
 
# /dev/sda3      (hd0,3)
 
#
 
  
# Timeout for menu
+
With a separate boot partition (e.g. when using UEFI), again change the lines accordingly:
set timeout=5
 
  
# Set default boot entry as Entry 0
+
{{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 default=0
 
  
# (0) Arch Linux
+
set root=(hd0,5)
menuentry "Arch Linux" {
+
linux (hdX,Y)/vmlinuz-linux root=/dev/sda6
set root=(hd0,1)
+
initrd (hdX,Y)/initramfs-linux.img
linux /vmlinuz-linux root=/dev/sda3 ro
+
boot
initrd /initramfs-linux.img
 
}
 
  
## (1) Windows
+
{{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.}}
#menuentry "Windows" {
 
#set root=(hd0,3)
 
#chainloader +1
 
#}
 
</nowiki>}}
 
  
=== Dual-booting ===
+
After successfully booting the Arch Linux installation, users can correct {{ic|grub.cfg}} as needed and then reinstall GRUB.
  
''NOTE: If you want GRUB2 to automatically search for other systems, for example as in Ubuntu. Then you may need to download {{AUR|os-prober}} from the [[AUR]].''
+
To reinstall GRUB and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Installation]] for details.
  
==== Using grub-mkconfig ====
+
== Troubleshooting ==
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 '''grub-mkconfig'''.
 
After adding the new lines, run:
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
to generate an updated {{ic|grub.cfg}}.
 
  
===== With GNU/Linux =====
+
=== F2FS and other unsupported file systems ===
  
Assuming that the other distro is on partition {{ic|sda2}}:
+
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.
  
menuentry "Other Linux" {
+
If GRUB is used with an unsupported filesystem it is not able to extract the [[UUID]] of your drive so it uses classic non-persistent {{ic|/dev/''sdXx''}} names instead. In this case you might have to manually edit {{ic|/boot/grub/grub.cfg}} and replace {{ic|1=root=/dev/''sdXx''}} with {{ic|1=root=UUID=''XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX''}}. You can use the {{ic|blkid}} command to get the UUID of your device, see [[Persistent block device naming]].
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 Windows =====
+
=== Intel BIOS not booting GPT ===
  
This assumes that your Windows partition is {{ic|sda3}}.
+
Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.
  
# (2) Windows XP
+
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.
menuentry "Windows XP" {
 
    set root=(hd0,3)
 
    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}}:
+
{{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.}}
  
drivemap -s hd0 hd2
+
With cfdisk, the steps are similar, just {{ic|cfdisk /dev/sda}}, choose bootable (at the left) in the desired hard disk, and quit saving.
  
==== With Windows via EasyBCD and NeoGRUB ====
+
With recent version of parted, you can use {{ic|disk_toggle pmbr_boot}} option. Afterwards verify that Disk Flags show pmbr_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:
+
# parted /dev/sd''x'' disk_toggle pmbr_boot
 +
# parted /dev/sd''x'' print
  
default 0
+
More information is available [http://www.rodsbooks.com/gdisk/bios.html here]
timeout 1
 
  
title      Chainload into GRUB v2
+
=== Enable debug messages ===
root        (hd0,7)
 
kernel      /boot/grub/core.img
 
  
===Visual Configuration===
+
{{Note|This change is overwritten when [[#Generate the main configuration file]].}}
  
In GRUB2 it is possible, by default, to change the look of the menu.
+
Add:
  
====Background image and bitmap fonts====
+
set pager=1
 +
set debug=all
  
GRUB2 comes with support for background images and bitmap fonts in pf2 format. The unifont font is included in the grub2 package under the filename {{ic|unicode.pf2}}, or, as only ascii characters under the name {{ic|ascii.pf2}}. Image formats supported include tga, png and jpeg, providing the correct modules are loaded. The maximum supported resolution depends on your hardware. There are two ways of setting a {{ic|tga}} file as background. Two sample configurations are shown below.
+
to {{ic|grub.cfg}}.
  
Edit {{ic|/etc/default/grub}} like this:
+
=== "No suitable mode found" error ===
GRUB_GFXMODE=1024x768x32
 
GRUB_GFXPAYLOAD_LINUX=keep
 
GRUB_BACKGROUND="/boot/grub/archlinux.tga"
 
#GRUB_THEME="/path/to/gfxtheme"
 
  
(archlinux.tga is a placeholder; put your file name there)
+
If you get this error when booting any menuentry:
  
To generate the changes, run:  
+
error: no suitable mode found
  grub-mkconfig -o /boot/grub/grub.cfg
+
  Booting however
  
{{Note|If this example does not work for you try to replace {{ic|1=gfxmode="1024x768x32"}} by {{ic|1=vbemode="0x105"}}.}}
+
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).
{{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.}}
 
{{Note|If you have installed Grub on a separate partition, {{ic|/boot/grub/archlinux.tga}} becomes {{ic|/grub/archlinux.tga}}.}}
 
  
====Menu colors====
+
{{Remove|''grub-install'' copies {{ic|unicode.pf2}} to {{ic|/boot/grub/fonts/}}, there is no need to do it manually.}}
  
As in Grub (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 .
+
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/}}:
Here is an example:
 
  
Edit {{ic|/etc/default/grub}}:
+
# cp /usr/share/grub/unicode.pf2 ${GRUB_PREFIX_DIR}
GRUB_COLOR_NORMAL="light-blue/black"
 
GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
 
  
Generate the changes:
+
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}}}:
grub-mkconfig -o /boot/grub/grub.cfg
 
  
====Hidden menu====
+
# grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
  
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.
+
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.
  
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:
+
After that add the following code (common to both BIOS and UEFI):
GRUB_HIDDEN_TIMEOUT=5
 
GRUB_HIDDEN_TIMEOUT_QUIET=false
 
  
and run:
+
{{bc|1=
grub-mkconfig -o /boot/grub/grub.cfg
+
loadfont "unicode"
 +
set gfxmode=auto
 +
set gfxpayload=keep
 +
insmod all_video
 +
insmod gfxterm
 +
terminal_output gfxterm
 +
}}
  
====Setting the framebuffer resolution ====
+
=== msdos-style error message ===
  
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:
+
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_GFXMODE=1024x768x32
+
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]]
GRUB_GFXPAYLOAD_LINUX=keep
 
  
To generate the changes, run:
+
=== UEFI ===
grub-mkconfig -o /boot/grub/grub.cfg
 
  
The {{ic|gfxpayload}} property will make sure the kernel keeps the resolution.
+
==== Common installation errors ====
  
If this method does not work for you, the deprecated {{ic|1=vga=}} method will still work. Just
+
* 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]].
add it next to the {{ic|1="GRUB_CMDLINE_LINUX_DEFAULT="}} line in {{ic|/etc/default/grub}}
+
* 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}}.
for eg: {{ic|1="GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"}} will give you a {{ic|1024x768}} resolution.
+
* 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}}.
  
You can choose one of these resolutions: {{ic|640×480}}, {{ic|800×600}}, {{ic|1024×768}}, {{ic|1280×1024}}, {{ic|1600×1200}}
+
==== Drop to rescue shell ====
  
=== Other Options ===
+
If GRUB loads but drops into the rescue shell with no errors, it can be due to one of these two reasons:
  
==== LVM ====
+
* 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,
 +
* It also happens if the boot partition, which is hardcoded into the {{ic|grubx64.efi}} file, has changed.
  
If you use [[LVM]] for your {{ic|/boot}}, add the following before menuentry lines:
+
==== GRUB UEFI not loaded ====
  
insmod lvm
+
An example of a working UEFI:
  
and specify your root in the menuentry as:
+
{{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\grubx64.efi)
 +
Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\shellx64.efi)
 +
Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI
 +
}}
  
set root=(''lvm_group_name''-''lvm_logical_boot_partition_name'')
+
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:
  
Example:
+
Boot0000* GRUB HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\grubx64.efi)
  
# (0) Arch Linux
+
==== Default/fallback boot path ====
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 ====
+
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:
  
Grub2 provides convenient handling of raid-volumes. You need to add:
+
# grub-install --target=x86_64-efi --efi-directory=''esp'' '''--removable'''
insmod raid
 
  
which allows you to address the volume natively. E.g. {{ic|/dev/md0}} becomes:
+
Alternatively you can move an already installed GRUB EFI executable to the default/fallback path:
set root=(md0)
 
  
whereas a partitioned raid-volume (e.g. {{ic|/dev/md0p1}}) becomes:
+
# mv ''esp''/EFI/grub ''esp''/EFI/BOOT
  set root=(md0,1)
+
  # mv ''esp''/EFI/BOOT/grubx64.efi ''esp''/EFI/BOOT/BOOTX64.EFI
  
==== Persistent block device naming ====
+
=== Invalid signature ===
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.
+
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:
  
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):
+
# mv /boot/grub/device.map /boot/grub/device.map-old
  #GRUB_DISABLE_LINUX_UUID=true
+
  # grub-mkconfig -o /boot/grub/grub.cfg
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:
+
{{ic|grub-mkconfig}} should now mention all found boot options, including Windows. If it works, remove {{ic|/boot/grub/device.map-old}}.
grub-mkconfig -o /boot/grub/grub.cfg
 
  
==== Using Labels ====
+
=== Boot freezes ===
  
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:
+
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.
# tune2fs -L a <LABEL> <PARTITION>
 
  
Then, add an entry using labels. An example of this:
+
=== Arch not found from other OS ===
  
menuentry "Arch Linux, session texte" {
+
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}}.
    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 ====
+
=== Warning when installing in chroot ===
  
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}}:
+
When installing GRUB on a LVM system in a chroot environment (e.g. during system installation), you may receive warnings like
  
  GRUB_DEFAULT=saved
+
  /run/lvm/lvmetad.socket: connect failed: No such file or directory
  
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}}:
+
or
 
 
GRUB_SAVEDEFAULT=true
 
 
 
Note that manually added menu items, eg Windows in  {{ic|/etc/grub.d/40_custom}}, will need {{ic|savedefault}} added. Remember to regenerate your configuration file.
 
  
==== Security ====
+
WARNING: failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.
  
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:
+
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.
  
{{bc|<nowiki>
+
=== GRUB loads slowly ===
Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A</nowiki>}}Then, add the following to {{ic|/etc/grub.d/00_header}}:
 
{{bc|<nowiki>cat << EOF
 
  
set superusers="username"
+
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.
password_pbkdf2 username <password>
 
  
EOF</nowiki>}}
+
=== error: unknown filesystem ===
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.
+
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.
  
=== Booting an Ubuntu ISO Image from the GRUB2 Screen ===
+
=== grub-reboot not resetting ===
  
Edit {{ic|/etc/grub.d/40_custom}} to add an entry pointing to an Ubuntu iso:
+
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}}).
  
menuentry "ubuntu-11.04-desktop-amd64.iso" {
+
=== Old BTRFS prevents installation ===
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
 
}
 
  
Be sure to adjust the "hdX,Y" in the third line to point to the correct disk/partition number of the isofile. When finished, update grub2's configuration file via:
+
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-mkconfig -o /boot/grub/grub.cfg
+
  # 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.
  
== Using the command shell ==
+
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}}
  
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.
+
=== Windows 8/10 not found ===
  
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:
+
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.
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:
+
=== VirtualBox EFI mode ===
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:
+
Install GRUB to the [[#Default/fallback boot path|default/fallback boot path]].
grub rescue> set prefix=(hdX,Y)/boot/grub
 
grub rescue> insmod (hdX,Y)/boot/grub/normal.mod
 
rescue:grub> normal
 
 
 
=== Pager support ===
 
  
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:
+
See also [[VirtualBox#Installation in EFI mode]].
sh:grub> set pager=1
 
  
== GUI configuration tools ==
+
=== Device /dev/xxx not initialized in udev database even after waiting 10000000 microseconds ===
  
Following package may be installed from [[AUR]]
+
If grub-mkconfig hangs and gives error: {{ic|WARNING: Device /dev/''xxx'' not initialized in udev database even after waiting 10000000 microseconds}}.
* [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 ==
+
You may need to provide {{ic|/run/lvm/}} access to the chroot environment using:
 
 
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:
 
parttool hd0,1 hidden+ boot-
 
parttool hd0,2 hidden+ boot-
 
parttool hd0,3 hidden- boot+
 
set root=hd0,3
 
chainloader +1
 
boot
 
 
 
== Using the rescue console ==
 
 
 
See [[#Using the command shell]] first. If unable to activate the standard shell, one possible solution is to boot using a live CD or some other rescue disk to correct configuration errors and reinstall GRUB. However, such a boot disk is not always available (nor necessary); the rescue console is surprisingly robust.
 
 
 
The available commands in GRUB rescue include "insmod", "ls", "set", and "unset". This example uses "set" and "insmod". "set" modifies variables and "insmod" inserts new modules to add functionality.
 
 
 
Before starting, the user must know the location of their {{ic|/boot}} partition (be it a separate partition, or a subdirectory under their root):
 
grub rescue> set prefix=(hdX,Y)/boot/grub
 
 
 
where X is the physical drive number and Y is the partition number.
 
 
 
To expand console capabilities, insert the "linux" module:
 
grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
 
 
 
{{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}}).}}
 
 
 
This introduces the "linux" and "initrd" commands, which should be familiar (see [[#Configuration]]).
 
 
 
An example, booting Arch Linux:
 
set root=(hd0,5)
 
linux /boot/vmlinuz-linux root=/dev/sda5
 
initrd /boot/initramfs-linux.img
 
boot
 
 
 
With a separate boot partition, again change the lines accordingly:
 
set root=(hd0,5)
 
linux /vmlinuz-linux root=/dev/sda6
 
initrd /initramfs-linux.img
 
boot
 
 
 
After successfully booting the Arch Linux installation, users can correct {{ic|grub.cfg}} as needed and then run:
 
# grub-install /dev/sda --no-floppy
 
 
 
to reinstall GRUB2 and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Bootloader installation]] for details.
 
 
 
== 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" {
 
    #Enter the UUID of your boot partition (this is where Grub and your kernel reside)
 
    set uuid_grub_boot=ece0448f-bb08-486d-9864-ac3271bd8d07
 
   
 
    #Enter the UUID of the partition containing the root partition of your Arch Linux installation.           
 
    set uuid_os_root=c55da16f-e2af-4603-9e0b-03f5f565ec4a
 
   
 
    #(Note: this may be the same as your boot partition)
 
   
 
    #Here we set the Grub "root" variable by locating the UUID of the root partition identified above 
 
    search --fs-uuid --no-floppy --set=root $uuid_os_root
 
   
 
    #Here we set a custom variable grub_boot by locating the UUID of the boot partition identified above         
 
    search --fs-uuid --no-floppy --set=grub_boot $uuid_grub_boot
 
   
 
    #Here is the magic. We test to see if the boot and root partitions have the same UUID.
 
    #If they do, we append /boot to the $grub_boot variable. For ex. (hd0,1) becomes (hd0,1)/boot.
 
    if [ $uuid_grub_boot == $uuid_os_root ] ; 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 systems and {{ic|/boot/efi/efi/grub/}} in case of UEFI systems).
 
 
 
# 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 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}/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}}. For UEFI, {{ic|grub.cfg}} must be copied into the UEFI system partition alongside grub.efi ({{ic|/boot/efi/EFI/grub}})
 
 
 
=== 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
 
Grub-mkconfig should now mention all found boot options including windows. If it works, remove /boot/grub/device.map-old.
 
  
== References ==
+
# mkdir /mnt/hostlvm
 +
# mount --bind /run/lvm /mnt/hostlvm
 +
# arch-chroot /mnt
 +
# ln -s /hostlvm /run/lvm
  
# Official GRUB2 Manual - http://www.gnu.org/software/grub/manual/grub.html
+
See {{Bug|61040}} and [https://bbs.archlinux.org/viewtopic.php?pid=1820949#p1820949 workaround].
# GRUB2 wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting - previously http://grub.enbug.org/TestingOnUEFI{{Linkrot|2011|09|05}}
 
# 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/grub2/grub2_bios.sh A Linux Bash Shell script to compile and install GRUB2 for BIOS from BZR Source]
+
* [[Wikipedia:GNU GRUB]]
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub2/grub2_uefi.sh A Linux Bash Shell script to compile and install GRUB2 for UEFI from BZR Source]
+
* [https://www.gnu.org/software/grub/manual/grub.html Official GRUB Manual]
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* [https://help.ubuntu.com/community/Grub2 Ubuntu wiki page for GRUB]
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* [https://help.ubuntu.com/community/UEFIBooting GRUB wiki page describing steps to compile for UEFI systems]
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* [[Wikipedia:BIOS Boot partition]]
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* [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]
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* [http://www.linuxjournal.com/article/4622 Boot with GRUB]

Latest revision as of 06:38, 26 January 2019

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 Partitioning#GUID Partition Table.
  • The BIOS boot partition is only needed by GRUB on a BIOS/GPT setup. On a BIOS/MBR setup, GRUB uses 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.
  • Select partition type code 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 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 if that is 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:

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) UEFI 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 in esp/EFI/ to store the EFI binary 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 the 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 places an EFI executable there, but its only purpose is to recreate the UEFI boot entry for Windows.
Note:
  • --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.

Configuration

On an installed system, GRUB loads the /boot/grub/grub.cfg configuration file each boot. You can follow #Generated grub.cfg for using a tool, or #Custom grub.cfg for a manual creation.

Generated grub.cfg

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 and/or files in /etc/grub.d/.

Generate the main configuration file

After the installation, the main configuration file /boot/grub/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/.

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 /boot/grub/grub.cfg has to be re-generated after any change to /etc/default/grub or files in /etc/grub.d/.
  • The default file path is /boot/grub/grub.cfg, not /boot/grub/i386-pc/grub.cfg.
  • If you are trying to run grub-mkconfig in a chroot or systemd-nspawn container, you might notice that it does not work, complaining that grub-probe cannot get the "canonical path of /dev/sdaX". In this case, try using arch-chroot as described in the BBS post.
  • If you are installing GRUB in chroot environment using LVM and the grub-mkconfig hangs indefinitely, see #Device /dev/xxx not initialized in udev database even after waiting 10000000 microseconds.

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

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

By default the generation scripts automatically add menu entries for all installed Arch Linux kernels to the generated configuration.

Tip:

To automatically add entries for other installed operating systems, see #Detecting other operating systems.

You can add additional custom menu entries by editing /etc/grub.d/40_custom and re-generating /boot/grub/grub.cfg. Or you can create /boot/grub/custom.cfg and add them there. Changes to /boot/grub/custom.cfg do not require re-running grub-mkconfig, since /etc/grub.d/40_custom adds the necessary source statement to the generated configuration file.

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

See #Boot menu entry examples for custom menu entry examples.

Detecting other operating systems

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 the other systems. Then re-run grub-mkconfig.

MS Windows

Often, partitions containing Windows will be automatically discovered by os-prober. However, NTFS partitions may not always be detected when mounted with the default Linux drivers. If GRUB is not detecting it, try installing ntfs-3g and remounting.

Encrypted Windows partitions may need to be decrypted before mounting. For BitLocker, this can be done with dislockerAUR. This should be sufficient for os-prober to add the correct entry.

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=UUID=uuid-of-swap-partition quiet" where uuid-of-swap-partition is the UUID of 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.

See Kernel parameters for more info.

LVM

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

Notes: grub-mkconfig is capable of detecting that it needs the lvm module, specifying it in GRUB_PRELOAD_MODULES is not required. Move warning to #Installation & #Installation_2 or create a Known issues section and document it there. (Discuss in Talk:GRUB#)
Warning: GRUB does not support thin-provisioned logical volumes.

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

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

Notes: grub-mkconfig is capable of detecting that it needs the mdraid09 and/or mdraid1x modules, specifying them in GRUB_PRELOAD_MODULES is not required. Summarize the double grub-install in a note and move it to #Installation; move set root stuff to #Custom grub.cfg. (Discuss in Talk:GRUB#)

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.

Encrypted /boot

GRUB also has special support for booting with an encrypted /boot. This is done by unlocking 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.

Note: /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; see GRUB bug #55093. Make sure to specify --type luks1 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

This option is used by grub-install to generate the grub core.img, so make sure to install grub after modifying this option.

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 implemented by the initramfs. You can use a keyfile to avoid this.

Warning:
  • If you want to generate the main configuration file, make sure that /boot is mounted.
  • 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.
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.
  • If you experience issues getting the prompt for a password to display (errors regarding cryptouuid, cryptodisk, or "device not found"), try reinstalling GRUB and appending --modules="part_gpt part_msdos" to the end of your grub-install command.
Tip: You can use pacman hooksto automount your /boot when upgrades need to access related files.

Custom grub.cfg

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Add instructions on how to write a custom /boot/grub/grub.cfg. See User:Eschwartz/Grub for a proposed draft. (Discuss in Talk:GRUB#Manually generate grub.cfg)

This section describes the manual creation of GRUB boot entries in /boot/grub/grub.cfg instead of relying on grub-mkconfig.

A basic GRUB config file uses the following options:

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

Boot menu entry examples

Tip: These boot entries can also be used when using a /boot/grub/grub.cfg generated by grub-mkconfig. Add them to /etc/grub.d/40_custom and re-generate the main configuration file or add them to /boot/grub/custom.cfg.

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

For Archiso and Archboot boot menu entries see Multiboot USB drive#Boot entries.

GRUB commands
"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)
if [ ${grub_platform} == "efi" ]; then
	menuentry "Firmware setup" {
		fwsetup
	}
fi
EFI binaries

When launched in UEFI mode, GRUB can chainload other EFI binaries.

Tip: To show these menu entries only when GRUB is launched in UEFI mode, enclose them in the following if statement:
if [ ${grub_platform} == "efi" ]; then
	place UEFI-only menu entries here
fi
UEFI Shell

You can launch UEFI Shell by using placing it in the root of the EFI system partition and adding this menu entry:

menuentry "UEFI Shell" {
	insmod fat
	insmod chain
	search --no-floppy --set=root --file /shellx64.efi
	chainloader /shellx64.efi
}
gdisk

Download the gdisk EFI application and copy gdisk_x64.efi to esp/EFI/tools/.

menuentry "gdisk" {
	insmod fat
	insmod chain
	search --no-floppy --set=root --file /EFI/tools/gdisk_x64.efi
	chainloader /EFI/tools/gdisk_x64.efi
}
Chainloading an Arch Linux .efi file

If you have an .efi file generated from following Secure Boot or other means, you can add it to the boot menu. For example:

menuentry "Arch Linux .efi" {
	insmod fat
	insmod chain
	search --no-floppy --set=root --fs-uuid FILESYSTEM_UUID
	chainloader /EFI/arch/vmlinuz.efi
}
Dual-booting
GNU/Linux

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 --no-floppy --set=root --fs-uuid 763A-9CB6

        # search by label OTHER_LINUX (make sure that partition label is unambiguous)
        #search --no-floppy --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

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 system 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 chain
		search --no-floppy --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 system 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:). The system partition's filesystem label is System Reserved or SYSTEM and the partition is only about 100 to 549 MiB in size. See Wikipedia:System partition and boot partition for more information.

Throughout this section, it is assumed your Windows partition is /dev/sda1. A different partition will change every instance of hd0,msdos1.

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 ntldr     
		search --no-floppy --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 ntldr     
		search --no-floppy --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.

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 start of a partitioned disk (MBR), at the start of a partition or a partitionless disk (VBR), or as an EFI binary in the case of UEFI.

Chainloading a partition's VBR

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

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

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

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

Similarly GRUB installed to a partition can be chainloaded.

Chainloading a disk's MBR or a partitionless disk's VBR

set root=hdX
chainloader +1
boot

Chainloading Windows/Linux installed in UEFI mode

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

insmod fat is used for loading the FAT file system module for accessing the Windows bootloader on the EFI system partition. (hd0,gpt4) or /dev/sda4 is the EFI system partition in this example. 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.

If GRUB is used with an unsupported filesystem it is not able to extract the UUID of your drive so it uses classic non-persistent /dev/sdXx names instead. In this case you might have to manually edit /boot/grub/grub.cfg and replace root=/dev/sdXx with root=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX. You can use the blkid command to get the UUID of your device, see Persistent block device naming.

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).

Tango-edit-cut.pngThis section is being considered for removal.Tango-edit-cut.png

Reason: grub-install copies unicode.pf2 to /boot/grub/fonts/, there is no need to do it manually. (Discuss in Talk:GRUB#)

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.

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

loadfont "unicode"
set gfxmode=auto
set gfxpayload=keep
insmod all_video
insmod gfxterm
terminal_output gfxterm

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 UEFI:

# 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\grubx64.efi)
Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\shellx64.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(\grubx64.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.

Device /dev/xxx not initialized in udev database even after waiting 10000000 microseconds

If grub-mkconfig hangs and gives error: WARNING: Device /dev/xxx not initialized in udev database even after waiting 10000000 microseconds.

You may need to provide /run/lvm/ access to the chroot environment using:

# mkdir /mnt/hostlvm
# mount --bind /run/lvm /mnt/hostlvm
# arch-chroot /mnt
# ln -s /hostlvm /run/lvm

See FS#61040 and workaround.

See also