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{{Related articles start}}
 
{{Related articles start}}
 
{{Related|Arch boot process}}
 
{{Related|Arch boot process}}
{{Related|Boot loaders}}
 
 
{{Related|Master Boot Record}}
 
{{Related|Master Boot Record}}
 
{{Related|GUID Partition Table}}
 
{{Related|GUID Partition Table}}
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{{Related|GRUB/EFI examples}}
 
{{Related|GRUB/EFI examples}}
 
{{Related|GRUB/Tips and tricks}}
 
{{Related|GRUB/Tips and tricks}}
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{{Related|Multiboot USB drive}}
 
{{Related articles end}}
 
{{Related articles end}}
[https://www.gnu.org/software/grub/ GRUB] — not to be confused with [[GRUB Legacy]] — is the next generation of the GRand Unified Bootloader. GRUB is derived from [http://www.nongnu.org/pupa/ PUPA] which was a research project to develop the next generation of what is now GRUB Legacy. GRUB has been rewritten from scratch to clean up everything and provide modularity and portability [https://www.gnu.org/software/grub/grub-faq.html#q1].
+
[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.
  
== Preface ==
+
{{Note|In the entire article {{ic|''esp''}} denotes the mountpoint of the [[EFI system partition]] aka ESP.}}
 
 
* A ''bootloader'' is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the Linux kernel. The kernel, in turn, initializes the rest of the operating system.
 
* The name ''GRUB'' officially refers to version ''2'' of the software, see [https://www.gnu.org/software/grub/]. If you are looking for the article on the legacy version, see [[GRUB Legacy]].
 
* GRUB supports [[Btrfs]] as root (without a separate {{ic|/boot}} file system) compressed with either zlib or LZO
 
** GRUB currently (Sep 2015) 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.
 
* GRUB does not support [[F2FS]] as root so you will need a separate {{ic|/boot}} with a supported file system.
 
  
 
== BIOS systems ==
 
== BIOS systems ==
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=== GUID Partition Table (GPT) specific instructions ===
 
=== GUID Partition Table (GPT) specific instructions ===
  
On a BIOS/[[GPT]] configuration a [http://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html BIOS boot partition] is required.  GRUB embeds its {{ic|core.img}} into this partition.
+
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|
 
{{Note|
* Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme, read more on [[GUID Partition Table#BIOS systems|GUID partition tables]].
+
* 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]].
* This additional partition is only needed on a GRUB, BIOS/GPT partitioning scheme. Previously, for a GRUB, BIOS/MBR partitioning scheme, GRUB used the Post-MBR gap for the embedding the {{ic|core.img}}). GRUB for GPT, however, does not use the Post-GPT gap to conform to GPT specifications that require 1_megabyte/2048_sector disk boundaries.
+
* 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.
* For [[UEFI]] systems this extra partition is not required as no embedding of boot sectors takes place in that case.
+
* 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 ({{ic|1=+1M}} with {{ic|fdisk}} or {{ic|gdisk}}) on the disk with no file system and type BIOS boot (''BIOS boot'' in fdisk, {{ic|ef02}} in gdisk, {{ic|bios_grub}} in {{ic|parted}}). This partition can be in any position order but has to be on the first 2 TiB of the disk.  This partition needs to be created before GRUB installation.  When the partition is ready, install the bootloader as per the instructions below.
+
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}}.
 +
 
 +
* Select partition type {{ic|BIOS boot}} for [[fdisk]].
 +
* Select partition type code {{ic|ef02}} for [[gdisk]].
 +
* For [[parted]] set/activate the flag {{ic|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 post-GPT gap can also be used as the BIOS boot partition though it will be out of GPT alignment specification.  Since the partition will not be regularly accessed performance issues can be disregarded (though some disk utilities will display a warning about it).  In {{ic|fdisk}} or {{ic|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.
+
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 ===
 
=== Master Boot Record (MBR) specific instructions ===
  
Usually the post-[[MBR]] gap (after the 512 byte MBR region and before the start of the first partition) in many MBR (or 'msdos' disklabel) partitioned systems is 31 KiB when DOS compatibility cylinder alignment issues are satisfied in the partition table. However a post-MBR gap of about 1 to 2 MiB is recommended to provide sufficient room for embedding GRUB's {{ic|core.img}} ({{bug|24103}}). It is advisable to use a partitioning tool that supports 1 MiB partition alignment to obtain this space as well as to satisfy other non-512 byte sector issues (which are unrelated to embedding of {{ic|core.img}}).
+
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}}).
  
 
=== Installation ===
 
=== Installation ===
  
[[Install]] the {{Pkg|grub}} package. It will replace {{AUR|grub-legacy}}, where already installed.
+
[[Install]] the {{Pkg|grub}} package. (It will replace {{AUR|grub-legacy}} if that is already installed.) Then do:
  
{{Note|Simply installing the package will not update the {{ic|/boot/grub/i386-pc/core.img}} file and the GRUB modules in {{ic|/boot/grub/i386-pc}}. You need to update them manually using {{ic|grub-install}} as explained below.}}
+
# grub-install --target=i386-pc /dev/sd''X''
  
==== Install boot files ====
+
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}}).
  
There are 4 ways to install GRUB boot files in BIOS booting:
+
Now you must [[#Generate the main configuration file|generate the main configuration file]].
  
* [[#Install to disk|Install to disk]] (recommended)
+
If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks.
* [[#Install to external USB stick|Install to external USB stick]] (for recovery)
 
* [[#Install to partition or partitionless disk|Install to partition or partitionless disk]] (not recommended)
 
* [[#Generate core.img alone|Generate core.img alone]] (safest method, but requires another BIOS bootloader like [[Syslinux]] to be installed to chainload {{ic|/boot/grub/i386-pc/core.img}})
 
  
{{Note|See https://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html for additional documentation.}}
+
{{Tip|See [[GRUB/Tips and tricks#Alternative installation methods]] for other ways to install GRUB, such as to a USB stick.}}
  
===== Install to disk =====
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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 {{ic|grub-install}} command.
  
{{Note|The method is specific to installing GRUB to a partitioned (MBR or GPT) disk, with GRUB files installed to {{ic|/boot/grub}} and its first stage code installed to the 440-byte MBR boot code region (not to be confused with MBR partition table). }}
+
== UEFI systems ==
  
The following commands will:
+
{{Note|
* Set up GRUB in the 440-byte Master Boot Record boot code region
+
* It is recommended to read and understand the [[Unified Extensible Firmware Interface]], [[Partitioning#GUID Partition Table]] and [[Arch boot process#Under UEFI]] pages.
* Populate the {{ic|/boot/grub}} directory
+
* 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.
* Generate the {{ic|/boot/grub/i386-pc/core.img}} file
+
* 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.
* Embed it in the 31 KiB (minimum size - varies depending on partition alignment) post-MBR gap in case of MBR partitioned disk
+
}}
* In the case of a GPT partitioned disk it will embed it in the BIOS Boot Partition , denoted by {{ic|bios_grub}} flag in parted and EF02 type code in gdisk
 
  
# grub-install --recheck /dev/sd''x''
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=== Installation ===
# grub-mkconfig -o /boot/grub/grub.cfg
 
  
{{Note|{{ic|1=--target=i386-pc}} is not needed since it is the default value, and besides GRUB will print for which platform it is installing providing an easy way to verify it.}}
+
{{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 workarounds 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 {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
 +
}}
  
If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks.
+
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.
  
===== Install to external USB stick =====
+
Then follow the below steps to install GRUB:
  
Assume your USB stick's first partition is FAT32 and its partition is /dev/sdy1
+
# [[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.
 +
# 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.
 +
# 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/}}.
  
# mkdir -p /mnt/usb ; mount /dev/sdy1 /mnt/usb
+
  # grub-install --target=x86_64-efi --efi-directory=''esp'' --bootloader-id=GRUB
  # grub-install --target=i386-pc --recheck --debug --boot-directory=/mnt/usb/boot /dev/sdy
 
# grub-mkconfig -o /mnt/usb/boot/grub/grub.cfg
 
  
# optional, backup config files of grub.cfg
+
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.
# mkdir -p /mnt/usb/etc/default
 
# cp /etc/default/grub /mnt/usb/etc/default
 
# cp -a /etc/grub.d /mnt/usb/etc
 
  
# sync; umount /mnt/usb
+
Remember to [[#Generate the main configuration file]] after finalizing the configuration.
  
===== Install to partition or partitionless disk =====
+
{{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.}}
{{Warning|GRUB '''strongly discourages''' installation to a partition boot sector or a partitionless disk as GRUB Legacy or Syslinux does. This setup is prone to breakage, especially during updates, and is '''not supported''' by the Arch developers.}}
 
 
 
To set up grub to a partition boot sector, to a partitionless disk (also called superfloppy) or to a floppy disk, run (using for example {{ic|/dev/sdaX}} as the {{ic|/boot}} partition):
 
 
 
# chattr -i /boot/grub/i386-pc/core.img
 
# grub-install --target=i386-pc --recheck --debug --force /dev/sdaX
 
# chattr +i /boot/grub/i386-pc/core.img
 
  
 
{{Note|
 
{{Note|
* {{ic|/dev/sdaX}} used for example only.
+
* {{ic|--efi-directory}} and {{ic|--bootloader-id}} are specific to GRUB UEFI, {{ic|--efi-directory}} replaces {{ic|--root-directory}} which is deprecated.
* {{ic|1=--target=i386-pc}} instructs {{ic|grub-install}} to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in ''grub-install''.
+
* 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.
 +
* Make sure to run the {{ic|grub-install}} command from the system in which GRUB will be installed as the boot looader. That means if you are booting from the live installation environment, you need to be inside the chroot when running {{ic|grub-install}}. If for some reason it is necessary to run {{ic|grub-install}} from outside of the installed system, append the {{ic|1=--boot-directory=}} option with the path to the mounted {{ic|/boot}} directory, e.g {{ic|1=--boot-directory=/mnt/boot}}.
 
}}
 
}}
  
You need to use the {{ic|--force}} option to allow usage of blocklists and should not use {{ic|1=--grub-setup=/bin/true}} (which is similar to simply generating {{ic|core.img}}).
+
See [[#UEFI|UEFI troubleshooting]] in case of problems. Additionally see [[GRUB/Tips and tricks#UEFI further reading]].
 +
 
 +
== Configuration ==
  
{{ic|grub-install}} will give out warnings like which should give you the idea of what might go wrong with this approach:
+
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.
  
/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea.
+
=== Generated grub.cfg ===
/sbin/grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.
 
                        However, blocklists are UNRELIABLE and their use is discouraged.
 
  
Without {{ic|--force}} you may get the below error and {{ic|grub-setup}} will not setup its boot code in the partition boot sector:
+
This section only covers editing the {{ic|/etc/default/grub}} configuration file. See [[GRUB/Tips and tricks]] for more information.
  
/sbin/grub-setup: error: will not proceed with blocklists
+
Remember to always [[#Generate the main configuration file]] after making changes to {{ic|/etc/default/grub}} and/or files in {{ic|/etc/grub.d/}}.
  
With {{ic|--force}} you should get:
+
==== Generate the main configuration file ====
  
Installation finished. No error reported.
+
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/}}.  
  
The reason why {{ic|grub-setup}} does not by default allow this is because in case of partition or a partitionless disk is that GRUB relies on embedded blocklists in the partition bootsector to locate the {{ic|/boot/grub/i386-pc/core.img}} file and the prefix directory {{ic|/boot/grub}}. The sector locations of {{ic|core.img}} may change whenever the file system in the partition is being altered (files copied, deleted etc.). For more info, see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915.
+
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.  
  
The workaround for this is to set the immutable flag on {{ic|/boot/grub/i386-pc/core.img}} (using {{ic|chattr}} command as mentioned above) so that the sector locations of the {{ic|core.img}} file in the disk is not altered. The immutable flag on {{ic|/boot/grub/i386-pc/core.img}} needs to be set only if GRUB is installed to a partition boot sector or a partitionless disk, not in case of installation to MBR or simple generation of {{ic|core.img}} without embedding any bootsector (mentioned above).
+
{{Note|
 +
* 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/}}.
 +
* The default file path is {{ic|/boot/grub/grub.cfg}}, not {{ic|/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 [https://bbs.archlinux.org/viewtopic.php?pid=1225067#p1225067 BBS post].
 +
* 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]].
 +
}}
  
Unfortunately, the {{ic|grub.cfg}} file that is created will not contain the proper UUID in order to boot, even if it reports no errors. see https://bbs.archlinux.org/viewtopic.php?pid=1294604#p1294604.
+
Use the ''grub-mkconfig'' tool to generate {{ic|/boot/grub/grub.cfg}}:
In order to fix this issue the following commands:
 
  
# mount /dev/sdxY /mnt        #Your root partition.
 
# mount /dev/sdxZ /mnt/boot  #Your boot partition (if you have one).
 
# arch-chroot /mnt
 
# pacman -S linux
 
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 
  # grub-mkconfig -o /boot/grub/grub.cfg
  
===== Generate core.img alone =====
+
By default the generation scripts automatically add menu entries for all installed Arch Linux [[kernel]]s to the generated configuration.
  
To populate the {{ic|/boot/grub}} directory and generate a {{ic|/boot/grub/i386-pc/core.img}} file '''without''' embedding any GRUB bootsector code in the MBR, post-MBR region, or the partition bootsector, add {{ic|1=--grub-setup=/bin/true}} to {{ic|grub-install}}:
+
{{Tip|
 +
* After installing or removing a [[kernel]], you just need to re-run the above ''grub-mkconfig'' command.
 +
* 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-install --target=i386-pc --grub-setup=/bin/true --recheck --debug /dev/sda
+
To automatically add entries for other installed operating systems, see [[#Detecting other operating systems]].
  
{{Note|
+
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/41_custom}} adds the necessary {{ic|source}} statement to the generated configuration file.
* {{ic|/dev/sda}} used for example only.
 
* {{ic|1=--target=i386-pc}} instructs {{ic|grub-install}} to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in grub-install.
 
}}
 
  
You can then chainload GRUB's {{ic|core.img}} from GRUB Legacy or syslinux as a Linux kernel or as a multiboot kernel (see also [[Syslinux#Chainloading]]).
+
{{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.}}
  
== UEFI systems ==
+
See [[#Boot menu entry examples]] for custom menu entry examples.
  
{{Note|
+
==== Detecting other operating systems ====
* It is recommended to read and understand the [[UEFI]], [[GPT]] and [[UEFI Bootloaders]] pages.
 
* When installing to use UEFI it is important to start the install with your machine in UEFI mode. The Arch Linux install media must be UEFI bootable.
 
}}
 
  
=== Check if you have GPT and an ESP ===
+
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''.
  
An EFI System Partition (ESP) is needed on every disc you want to boot using EFI. GPT is not strictly necessary, but it is highly recommended and is the only method currently supported in this article. If you are installing Arch Linux on an EFI-capable computer with an already-working operating system, like Windows 8 for example, it is very likely that you already have an ESP. To check for GPT and for an ESP, use {{ic|parted}} as root to print the partition table of the disk you want to boot from. (We are calling it {{ic|/dev/sda}}.)
+
===== MS Windows =====
  
# parted /dev/sda print
+
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.
  
For GPT, you are looking for "Partition Table: GPT". For EFI, you are looking for a small (512 MiB or less) partition with a vfat file system and the ''boot'' flag enabled. On it, there should be a directory named "EFI". If these criteria are met, this is your ESP. Make note of the partition number. You will need to know which one it is, so you can mount it later on while installing GRUB to it.
+
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.
  
=== Create an ESP ===
+
==== Additional arguments ====
  
If you do not have an ESP, you will need to create one. See [[UEFI#EFI System Partition]]
+
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.
  
=== Installation ===
+
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.
  
{{Note|UEFI firmware are not implemented consistently by hardware manufacturers. The installation examples provided are intended to work on the widest range of UEFI systems possible. Those experiencing problems despite applying these methods are encouraged to share detailed information for their hardware-specific cases, especially where solving these problems. A [[GRUB/EFI examples]] article has been provided for such cases.}}
+
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}}.
  
This section assumes you are installing GRUB for x86_64 systems (x86_64-efi). For i686 systems, replace {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
+
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}}.
  
Make sure you are in a [[bash]] shell. For example, when booting from the Arch ISO:
+
See [[Kernel parameters]] for more info.
  
# arch-chroot /mnt /bin/bash
+
==== LVM ====
  
[[Install]] the packages {{Pkg|grub}} and {{Pkg|efibootmgr}}. ''GRUB'' is the bootloader, ''efibootmgr'' creates bootable {{ic|.efi}} stub entries used by the GRUB installation script.
+
{{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.}}
  
The following steps install the GRUB UEFI application to {{ic|'''$esp'''/EFI/grub}}, install its modules to {{ic|/boot/grub/x86_64-efi}}, and place the bootable {{ic|grubx64.efi}} stub in {{ic|'''$esp'''/EFI/grub}}.
+
{{Warning|GRUB does not support thin-provisioned logical volumes.}}
  
First, tell GRUB to use UEFI, set the boot directory and set the bootloader ID. Change {{ic|$esp}} to your efi partition (usually {{ic|/boot}}):
+
If you use [[LVM]] for your {{ic|/boot}} or {{ic|/}} root partition, make sure that the {{ic|lvm}} module is preloaded:
  
# grub-install --target=x86_64-efi --efi-directory='''$esp''' --bootloader-id='''grub''' --recheck
+
{{hc|/etc/default/grub|2=
 +
GRUB_PRELOAD_MODULES="... lvm"
 +
}}
  
The {{ic|--bootloader-id}} is what appears in the boot options to identity the GRUB EFI boot option; make sure this is something you will recognize later. The install will create a directory of the same name under {{ic|$esp/EFI/}} where the EFI binary bootloader will be placed. 
+
==== RAID ====
  
After the above install finished the main GRUB directory is located at {{ic|/boot/grub/}}.  
+
{{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]].}}
  
Remember to [[#Generate the main configuration file]] after finalizing further setup dependant [[#Configuration]].  
+
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:
  
{{Note|
+
{{hc|/etc/default/grub|2=
* While some distributions require a {{ic|/boot/efi}} or {{ic|/boot/EFI}} directory, Arch does not.
+
GRUB_PRELOAD_MODULES="... mdraid09 mdraid1x"
* {{ic|--efi-directory}} and {{ic|--bootloader-id}} are specific to GRUB UEFI. {{ic|--efi-directory}} specifies the mountpoint of the ESP. It replaces {{ic|--root-directory}}, which is deprecated.
 
* 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 install script, as UEFI bootloaders do not use a MBR or partition boot sector at all.
 
 
}}
 
}}
  
See [[#UEFI|UEFI troubleshooting]] in case of problems.
+
For example, {{ic|/dev/md0}} becomes:
  
=== Further reading ===
+
set root=(md/0)
  
Below is other relevant information regarding installing Arch via UEFI
+
whereas a partitioned RAID volume (e.g. {{ic|/dev/md0p1}}) becomes:
  
==== Alternative install method ====
+
set root=(md/0,1)
  
Usually, GRUB keeps all files, including configuration files, in {{ic|/boot}}, regardless of where the EFI System Partition is mounted.
+
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:
  
If you want to keep these files inside the EFI System Partition itself, add {{ic|--boot-directory&#61;$esp}} to the grub-install command:
+
# grub-install --target=i386-pc --debug /dev/sda
 +
# grub-install --target=i386-pc --debug /dev/sdb
  
# grub-install --target=x86_64-efi --efi-directory=$esp --bootloader-id=grub --boot-directory=$esp --recheck --debug
+
Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}.
  
This puts all GRUB files in {{ic|$esp/grub}}, instead of in {{ic|/boot/grub}}. When using this method, make sure you have ''grub-mkconfig'' put the configuration file in same place:
+
{{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.}}
  
# grub-mkconfig -o $esp/grub/grub.cfg
+
==== Encrypted /boot ====
  
Configuration is otherwise the same.
+
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]].
  
==== UEFI firmware workaround ====
+
{{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.}}
  
Some UEFI firmware requires that the bootable {{ic|.efi}} stub have a specific name and be placed in a specific location: {{ic|$esp/EFI/boot/bootx64.efi}} (where {{ic|$esp}} is the UEFI partition mountpoint). Failure to do so in such instances will result in an unbootable installation. Fortunately, this will not cause any problems with other firmware that does not require this.
+
{{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 do so, first create the necessary directory, and then copy across the grub {{ic|.efi}} stub, renaming it in the process:
+
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}}:
  
# mkdir $esp/EFI/boot
+
{{hc|/etc/default/grub|output=
# cp $esp/EFI/grub_uefi/grubx64.efi  $esp/EFI/boot/bootx64.efi
+
GRUB_ENABLE_CRYPTODISK=y
 +
}}
  
==== Create a GRUB entry in the firmware boot manager ====
+
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.
{{ic|grub-install}} automatically tries to create a menu entry in the boot manager. If it does not, then see [[UEFI#efibootmgr]] for instructions to use {{ic|efibootmgr}} to create a menu entry. However, the problem is likely to be that you have not booted your CD/USB in UEFI mode, as in [[UEFI#Create UEFI bootable USB from ISO]].
 
  
==== GRUB standalone ====
+
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.
  
This section assumes you are creating a standalone GRUB for x86_64 systems (x86_64-efi). For i686 systems, replace {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
+
{{Warning|
 
+
* If you want to [[#Generate the main configuration file|generate the main configuration file]], make sure that {{ic|/boot}} is mounted.
It is possible to create a {{ic|grubx64_standalone.efi}} application which has all the modules embedded in a tar archive within the UEFI application, thus removing the need for having a separate directory populated with all of the GRUB UEFI modules and other related files. This is done using the {{ic|grub-mkstandalone}} command (included in {{Pkg|grub}}) as follows:
+
* 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]].
 
+
}}
# echo 'configfile ${cmdpath}/grub.cfg' > /tmp/grub.cfg
 
# grub-mkstandalone -d /usr/lib/grub/x86_64-efi/ -O x86_64-efi --modules="part_gpt part_msdos" --fonts="unicode" --locales="en@quot" --themes="" -o "$esp/EFI/grub/grubx64_standalone.efi"  "boot/grub/grub.cfg=/tmp/grub.cfg" -v
 
 
 
Then copy the GRUB config file to {{ic|$esp/EFI/grub/grub.cfg}} and create a UEFI Boot Manager entry for {{ic|$esp/EFI/grub/grubx64_standalone.efi}} using [[UEFI#efibootmgr|efibootmgr]].
 
  
 
{{Note|
 
{{Note|
The option {{ic|1=--modules="part_gpt part_msdos"}} (with the quotes) is necessary for the {{ic|${cmdpath} }} feature to work properly.
+
* 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.
 
}}
 
}}
  
{{Warning|You may find that the {{ic|grub.cfg}} file is not loaded due to {{ic|${cmdpath} }} missing a slash (i.e. {{ic|(hd1,msdos2)EFI/Boot}} instead of {{ic|(hd1,msdos2)/EFI/Boot}}) and so you are dropped into a GRUB shell. If this happens determine what {{ic|${cmdpath} }} is set to ({{ic|echo ${cmdpath} }}) and then load the config file manually (e.g. {{ic|configfile (hd1,msdos2)/EFI/Boot/grub.cfg}}).}}
+
{{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.}}
  
==== Technical information ====
+
=== Custom grub.cfg ===
  
The GRUB EFI file always expects its config file to be at {{ic|${prefix}/grub.cfg}}. However in the standalone GRUB EFI file, the {{ic|${prefix} }} is located inside a tar archive and embedded inside the standalone GRUB EFI file itself (inside the GRUB environment, it is denoted by {{ic|"(memdisk)"}}, without quotes). This tar archive contains all the files that would be stored normally at {{ic|/boot/grub}} in case of a normal GRUB EFI install.
+
{{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}}
  
Due to this embedding of {{ic|/boot/grub}} contents inside the standalone image itself, it does not rely on actual (external) {{ic|/boot/grub}} for anything. Thus in case of standalone GRUB EFI file {{ic|1=${prefix}==(memdisk)/boot/grub}} and the standalone GRUB EFI file reads expects the config file to be at {{ic|1=${prefix}/grub.cfg==(memdisk)/boot/grub/grub.cfg}}.
+
This section describes the manual creation of GRUB boot entries in {{ic|/boot/grub/grub.cfg}} instead of relying on ''grub-mkconfig''.
  
Hence to make sure the standalone GRUB EFI file reads the external {{ic|grub.cfg}} located in the same directory as the EFI file (inside the GRUB environment, it is denoted by {{ic|${cmdpath} }}), we create a simple {{ic|/tmp/grub.cfg}} which instructs GRUB to use {{ic|${cmdpath}/grub.cfg}} as its config ({{ic|configfile ${cmdpath}/grub.cfg}} command in {{ic|(memdisk)/boot/grub/grub.cfg}}). We then instruct grub-mkstandalone to copy this {{ic|/tmp/grub.cfg}} file to {{ic|${prefix}/grub.cfg}} (which is actually {{ic|(memdisk)/boot/grub/grub.cfg}}) using the option {{ic|1="boot/grub/grub.cfg=/tmp/grub.cfg"}}.
+
A basic GRUB config file uses the following options:
  
This way, the standalone GRUB EFI file and actual {{ic|grub.cfg}} can be stored in any directory inside the EFI System Partition (as long as they are in the same directory), thus making them portable.
+
* {{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|/}})
  
== Generate the main configuration file ==
+
==== Boot menu entry examples ====
  
After the installation, the main configuration file {{ic|grub.cfg}} needs to be generated. The generation process can be influenced by a variety of options in {{ic|/etc/default/grub}} and scripts in {{ic|/etc/grub.d/}}; see [[#Configuration]].  
+
{{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}}.}}
  
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.  
+
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]].
  
{{Note|Remember that {{ic|grub.cfg}} has to be re-generated after any change to {{ic|/etc/default/grub}} or files in {{ic|/etc/grub.d/}}.}}
+
For [[Archiso]] and [[Archboot]] boot menu entries see [[Multiboot USB drive#Boot entries]].
  
Use the ''grub-mkconfig'' tool to generate {{ic|grub.cfg}}:
+
===== GRUB commands =====
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
====== "Shutdown" menu entry ======
  
{{Note|
+
{{bc|
* The default file path is {{ic|/boot/grub/grub.cfg}}, not {{ic|/boot/grub/i386-pc/grub.cfg}}. The {{Pkg|grub}} includes a sample {{ic|/boot/grub/grub.cfg}}; ensure your intended changes were written to this file.
+
menuentry "System shutdown" {
* 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].
+
echo "System shutting down..."
 +
halt
 +
}
 
}}
 
}}
  
By default the generation scripts automatically add menu entries for Arch Linux to any generated configuration. See [[#Dual-booting]] for configuration with other systems.
+
====== "Restart" menu entry ======
  
== Configuration ==
+
{{bc|
 +
menuentry "System restart" {
 +
echo "System rebooting..."
 +
reboot
 +
}
 +
}}
  
This section only covers editing the {{ic|/etc/default/grub}} configuration file. See [[GRUB/Tips and tricks]] for more information.
+
====== "Firmware setup" menu entry (UEFI only) ======
  
Remember to always [[#Generate the main configuration file]] after making changes to {{ic|/etc/default/grub}}.
+
{{bc|1=
 +
if [ ${grub_platform} == "efi" ]; then
 +
menuentry "Firmware setup" {
 +
fwsetup
 +
}
 +
fi
 +
}}
  
=== Additional arguments ===
+
===== EFI binaries =====
  
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.
+
When launched in UEFI mode, GRUB can chainload other EFI binaries.
  
It is not necessary to use both, but can be useful. For example, you could use {{ic|<nowiki>GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sdaX</nowiki> quiet"}} where {{ic|sda'''X'''}} is your swap partition to enable resume after hibernation. This would generate a recovery boot entry without the resume and without ''quiet'' suppressing kernel messages during a boot from that menu entry. Though, the other (regular) menu entries would have them as options.
+
{{Tip|1=To show these menu entries only when GRUB is launched in UEFI mode, enclose them in the following {{ic|if}} statement:
  
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}}.
+
{{bc|1=
 +
if [ ${grub_platform} == "efi" ]; then
 +
''place UEFI-only menu entries here''
 +
fi
 +
}}
  
For generating the GRUB recovery entry you also have to comment out {{ic|<nowiki>#GRUB_DISABLE_RECOVERY=true</nowiki>}} in {{ic|/etc/default/grub}}.
+
}}
  
You can also use {{ic|<nowiki>GRUB_CMDLINE_LINUX="resume=UUID=uuid-of-swap-partition"</nowiki>}}
+
====== UEFI Shell ======
  
See [[Kernel parameters]] for more info.
+
You can launch [[Unified Extensible Firmware Interface#UEFI Shell|UEFI Shell]] by placing it in the root of the [[EFI system partition]] and adding this menu entry:
  
=== Dual-booting ===
+
{{bc|1=
 +
menuentry "UEFI Shell" {
 +
insmod fat
 +
insmod chain
 +
search --no-floppy --set=root --file /shellx64.efi
 +
chainloader /shellx64.efi
 +
}
 +
}}
  
{{Tip|To have ''grub-mkconfig'' search for other installed systems, [[install]] {{Pkg|os-prober}}.}}
+
====== gdisk ======
  
==== Automatically generating using /etc/grub.d/40_custom and grub-mkconfig ====
+
Download the [[gdisk#gdisk EFI application|gdisk EFI application]] and copy {{ic|gdisk_x64.efi}} to {{ic|''esp''/EFI/tools/}}.
  
The best way to add other entries is editing the {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}}. The entries in this file will be automatically added when running {{ic|grub-mkconfig}}.
+
{{bc|1=
After adding the new lines, run:
+
menuentry "gdisk" {
{{bc|<nowiki># grub-mkconfig -o /boot/grub/grub.cfg</nowiki>}}
 
or, for UEFI-GPT Mode (As per [[#Alternative install method]]):
 
{{bc|<nowiki># grub-mkconfig -o /boot/efi/EFI/GRUB/grub.cfg</nowiki>}}
 
to generate an updated {{ic|grub.cfg}}.
 
 
 
For example, a typical {{ic|/etc/grub.d/40_custom}} file, could appear similar to the following one, created for [http://h10025.www1.hp.com/ewfrf/wc/product?cc=us&destPage=product&lc=en&product=5402703&tmp_docname= HP Pavilion 15-e056sl Notebook PC], originally with Microsoft Windows 8 preinstalled. Each {{ic|menuentry}} should maintain a structure similar to the following ones. Note that the UEFI partition {{ic|/dev/sda2}} within GRUB is called {{ic|hd0,gpt2}} and {{ic|ahci0,gpt2}} (see [[#Windows installed in UEFI-GPT Mode menu entry|here]] for more info).
 
 
 
{{hc|/etc/grub.d/40_custom|<nowiki>#!/bin/sh
 
exec tail -n +3 $0
 
# This file provides an easy way to add custom menu entries.&nbsp; Simply type the
 
# menu entries you want to add after this comment.&nbsp; Be careful not to change
 
# the 'exec tail' line above.
 
 
 
menuentry "HP / Microsoft Windows 8.1" {
 
echo "Loading HP / Microsoft Windows 8.1..."
 
insmod part_gpt
 
 
insmod fat
 
insmod fat
insmod search_fs_uuid
 
 
insmod chain
 
insmod chain
search --fs-uuid --no-floppy --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2 763A-9CB6
+
search --no-floppy --set=root --file /EFI/tools/gdisk_x64.efi
chainloader /EFI/Microsoft/Boot/bootmgfw.efi
+
chainloader /EFI/tools/gdisk_x64.efi
 
}
 
}
 +
}}
  
menuentry "HP / Microsoft Control Center" {
+
====== Chainloading an Arch Linux .efi file ======
echo "Loading HP / Microsoft Control Center..."
+
 
insmod part_gpt
+
If you have an ''.efi'' file generated from following [[Secure Boot]] or other means, you can add it to the boot menu. For example:
 +
 
 +
{{bc|1=
 +
menuentry "Arch Linux .efi" {
 
insmod fat
 
insmod fat
insmod search_fs_uuid
 
 
insmod chain
 
insmod chain
search --fs-uuid --no-floppy --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2 763A-9CB6
+
search --no-floppy --set=root --fs-uuid ''FILESYSTEM_UUID''
chainloader /EFI/HP/boot/bootmgfw.efi
+
chainloader /EFI/arch/vmlinuz.efi
 
}
 
}
 +
}}
  
menuentry "System shutdown" {
+
===== Dual-booting =====
echo "System shutting down..."
 
halt
 
}
 
  
menuentry "System restart" {
+
====== GNU/Linux ======
echo "System rebooting..."
 
reboot
 
}</nowiki>}}
 
  
===== GNU/Linux menu entry =====
+
Assuming that the other distribution is on partition {{ic|sda2}}:
Assuming that the other distro is on partition {{ic|sda2}}:
 
  
{{bc|<nowiki>menuentry "Other Linux" {
+
{{bc|1=
 +
menuentry "Other Linux" {
 
set root=(hd0,2)
 
set root=(hd0,2)
 
linux /boot/vmlinuz (add other options here as required)
 
linux /boot/vmlinuz (add other options here as required)
 
initrd /boot/initrd.img (if the other kernel uses/needs one)
 
initrd /boot/initrd.img (if the other kernel uses/needs one)
}</nowiki>}}
+
}
 +
}}
  
Alternatively let grub search for the right partition by ''UUID'' or ''label'':
+
Alternatively let GRUB search for the right partition by ''UUID'' or ''label'':
  
{{bc|<nowiki>menuentry "Other Linux" {
+
{{bc|1=
 +
menuentry "Other Linux" {
 
         # assuming that UUID is 763A-9CB6
 
         # assuming that UUID is 763A-9CB6
search --set=root --fs-uuid 763A-9CB6
+
search --no-floppy --set=root --fs-uuid 763A-9CB6
  
 
         # search by label OTHER_LINUX (make sure that partition label is unambiguous)
 
         # search by label OTHER_LINUX (make sure that partition label is unambiguous)
         #search --set=root --label OTHER_LINUX
+
         #search --no-floppy --set=root --label OTHER_LINUX
  
 
linux /boot/vmlinuz (add other options here as required, for example: root=UUID=763A-9CB6)
 
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)
 
initrd /boot/initrd.img (if the other kernel uses/needs one)
}</nowiki>}}
 
 
===== FreeBSD menu entry =====
 
The following two method requires that FreeBSD is installed on a single partition with UFS(v2). Assuming the nested BSD partition table is on {{ic|sda4}}:
 
 
====== Loading the kernel directly ======
 
{{bc|1=
 
menuentry 'FreeBSD' {
 
insmod ufs2
 
set root='hd0,gpt4,bsd1'
 
## or 'hd0,msdos4,bsd1', if using an IBM-PC (MS-DOS) style partition table
 
kfreebsd /boot/kernel/kernel
 
kfreebsd_loadenv /boot/device.hints
 
set kFreeBSD.vfs.root.mountfrom=ufs:/dev/ada0s4a
 
set kFreeBSD.vfs.root.mountfrom.options=rw
 
 
}
 
}
 
}}
 
}}
  
====== Chainloading the embedded boot record ======
+
====== Windows installed in UEFI/GPT mode ======
{{bc|1=
 
menuentry 'FreeBSD' {
 
insmod ufs2
 
set root='hd0,gpt4,bsd1'
 
chainloader +1
 
}
 
}}
 
  
===== Windows XP menu entry=====
+
This mode determines where the Windows bootloader resides and chain-loads it after GRUB when the menu entry is selected. The main task here is finding the EFI system partition and running the bootloader from it.
This assumes that your Windows partition is {{ic|sda3}}. Remember you need to point set root and chainloader to the system reserve partition that windows made when it installed, not the actual partition windows is on. This example works if your system reserve partition is {{ic|sda3}}.
 
  
{{bc|<nowiki># (2) Windows XP
+
{{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.}}
menuentry "Windows XP" {
 
set root="(hd0,3)"
 
chainloader +1
 
}</nowiki>}}
 
  
If the Windows bootloader is on an entirely different hard drive than GRUB, it may be necessary to trick Windows into believing that it is the first hard drive. This was possible with {{ic|drivemap}}. Assuming GRUB is on {{ic|hd0}} and Windows is on {{ic|hd2}}, you need to add the following after {{ic|set root}}:
+
{{bc|1=
 
+
if [ "${grub_platform}" == "efi" ]; then
{{bc|drivemap -s hd0 hd2}}
+
menuentry "Microsoft Windows Vista/7/8/8.1 UEFI/GPT" {
 
 
===== Windows installed in UEFI-GPT Mode menu entry =====
 
 
 
{{Note|This menuentry will work only in UEFI boot mode and only if the Windows bitness matches the UEFI bitness. It '''WILL NOT WORK''' in BIOS installed GRUB. See [[Dual boot with Windows#Windows UEFI vs BIOS limitations]] and [[Dual boot with Windows#Bootloader UEFI vs BIOS limitations]] for more info.}}
 
 
 
{{bc|<nowiki>if [ "${grub_platform}" == "efi" ]; then
 
menuentry "Microsoft Windows Vista/7/8/8.1 UEFI-GPT" {
 
 
insmod part_gpt
 
insmod part_gpt
 
insmod fat
 
insmod fat
insmod search_fs_uuid
 
 
insmod chain
 
insmod chain
search --fs-uuid --set=root $hints_string $fs_uuid
+
search --no-floppy --fs-uuid --set=root $hints_string $fs_uuid
 
chainloader /EFI/Microsoft/Boot/bootmgfw.efi
 
chainloader /EFI/Microsoft/Boot/bootmgfw.efi
 
}
 
}
fi</nowiki>}}
+
fi
 +
}}
  
where {{ic|$hints_string}} and {{ic|$fs_uuid}} are obtained with the following two commands. {{ic|$fs_uuid}}'s command:
+
where {{ic|$hints_string}} and {{ic|$fs_uuid}} are obtained with the following two commands.  
  
{{hc|1=# grub-probe --target=fs_uuid $esp/EFI/Microsoft/Boot/bootmgfw.efi|2=
+
The {{ic|$fs_uuid}} command determines the UUID of the EFI system partition:
 +
 
 +
{{hc|1=# grub-probe --target=fs_uuid ''esp''/EFI/Microsoft/Boot/bootmgfw.efi|2=
 
1ce5-7f28
 
1ce5-7f28
 
}}
 
}}
  
{{ic|$hints_string}}'s command:
+
Alternatively one can run {{ic|blkid}} (as root) and read the UUID of the EFI system partition from there.
  
{{hc|1=# grub-probe --target=hints_string $esp/EFI/Microsoft/Boot/bootmgfw.efi|2=
+
The {{ic|$hints_string}} command will determine the location of the EFI system partition, in this case harddrive 0:
 +
 
 +
{{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
 
  --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
 
}}
 
}}
  
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.
+
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.
 
 
===== "Shutdown" menu entry =====
 
  
{{bc|<nowiki>menuentry "System shutdown" {
+
====== Windows installed in BIOS/MBR mode ======
echo "System shutting down..."
 
halt
 
}</nowiki>}}
 
  
===== "Restart" menu entry =====
+
{{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.}}
  
{{bc|<nowiki>menuentry "System restart" {
+
{{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.}}
echo "System rebooting..."
 
reboot
 
}</nowiki>}}
 
  
===== Windows installed in BIOS-MBR mode =====
+
Throughout this section, it is assumed your Windows partition is {{ic|/dev/sda1}}. A different partition will change every instance of {{ic|hd0,msdos1}}.
  
{{Poor writing|This section does not fit into the others, should be slimmed down a bit.}}
+
{{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]] .}}
  
{{Note|GRUB supports booting {{ic|bootmgr}} directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.}}
+
In both examples {{ic|''XXXXXXXXXXXXXXXX''}} is the filesystem UUID which can be found with command {{ic|lsblk --fs}}.
  
{{Warning|It is the '''system partition''' that has {{ic|/bootmgr}}, not your "real" Windows partition (usually C:). In {{ic|blkid}} output, the system partition is the one with {{ic|LABEL&#61;"SYSTEM RESERVED"}} or {{ic|LABEL&#61;"SYSTEM"}} and is only about 100 to 200 MB in size (much like the boot partition for Arch). See [[Wikipedia:System partition and boot partition]] for more info.}}
+
For Windows Vista/7/8/8.1/10:
  
Throughout this section, it is assumed your Windows partition is {{ic|/dev/sda1}}. A different partition will change every instance of hd0,msdos1. First, find the UUID of the NTFS file system of the Windows's SYSTEM PARTITION where the {{ic|bootmgr}} and its files reside. For example, if Windows {{ic|bootmgr}} exists at {{ic|/media/SYSTEM_RESERVED/bootmgr}}:
+
{{bc|1=
 
+
if [ "${grub_platform}" == "pc" ]; then
For Windows Vista/7/8/8.1:
+
menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS/MBR" {
 
+
insmod part_msdos
# grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr
+
insmod ntfs
69B235F6749E84CE
+
insmod ntldr     
 
+
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 ''XXXXXXXXXXXXXXXX''
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr
+
ntldr /bootmgr
--hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1
+
}
 
+
fi
{{Note|For Windows XP, replace {{ic|bootmgr}} with {{ic|NTLDR}} in the above commands. And note that there may not be a separate SYSTEM_RESERVED partition; just probe the file NTLDR on your Windows partition.}}
+
}}
 
 
Then, add the below code to {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} and regenerate {{ic|grub.cfg}} with {{ic|grub-mkconfig}} as explained above to boot Windows (XP, Vista, 7 or 8) installed in BIOS-MBR mode:
 
 
 
{{Note|These menuentries will work only in Legacy BIOS boot mode. It WILL NOT WORK in uefi installed grub(2). See [[Dual boot with Windows#Windows UEFI vs BIOS limitations]] and [[Dual boot with Windows#Bootloader UEFI vs BIOS limitations]].}}
 
 
 
For Windows Vista/7/8/8.1:
 
 
 
if [ "${grub_platform}" == "pc" ]; then
 
  menuentry "Microsoft Windows Vista/7/8/8.1 BIOS-MBR" {
 
    insmod part_msdos
 
    insmod ntfs
 
    insmod search_fs_uuid
 
    insmod ntldr     
 
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
 
    ntldr /bootmgr
 
  }
 
fi
 
  
 
For Windows XP:
 
For Windows XP:
  
if [ "${grub_platform}" == "pc" ]; then
+
{{bc|1=
  menuentry "Microsoft Windows XP" {
+
if [ "${grub_platform}" == "pc" ]; then
    insmod part_msdos
+
menuentry "Microsoft Windows XP" {
    insmod ntfs
+
insmod part_msdos
    insmod search_fs_uuid
+
insmod ntfs
    insmod ntldr     
+
insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
+
search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 ''XXXXXXXXXXXXXXXX''
    ntldr /ntldr
+
ntldr /ntldr
  }
+
}
fi
+
fi
 
 
{{Note|In some cases, mine I have installed GRUB before a clean Windows 8, you cannot boot Windows having an error with {{ic|\boot\bcd}} (error code {{ic|0xc000000f}}). You can fix it going to Windows Recovery Console (cmd from install disk) and executing:
 
x:\> "bootrec.exe /fixboot"
 
x:\> "bootrec.exe /RebuildBcd".
 
Do '''not''' use {{ic|bootrec.exe /Fixmbr}} because it will wipe GRUB out.}}
 
 
 
{{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 precendence, indicating the order the script is executed.  The order scripts are executed determine the placement in the grub boot menu.
 
 
 
{{Note|{{ic|nn}} should be greater than 06 to ensure necessary scripts are executed first.}}
 
 
 
==== With Windows via EasyBCD and NeoGRUB ====
 
 
 
{{Merge|NeoGRUB|New page has been created, so this section should be merged there.}}
 
 
 
Since EasyBCD's NeoGRUB currently does not understand the GRUB menu format, chainload to it by replacing the contents of your {{ic|C:\NST\menu.lst}} file with lines similar to the following:
 
 
 
default 0
 
timeout 1
 
 
 
title      Chainload into GRUB v2
 
root        (hd0,7)
 
kernel      /boot/grub/i386-pc/core.img
 
 
 
Finally, [[#Generate the main configuration file]].
 
 
 
==== parttool for hide/unhide ====
 
 
 
If you have a Windows 9x paradigm with hidden {{ic|C:\}} disks GRUB can hide/unhide it using {{ic|parttool}}. For example, to boot the third {{ic|C:\}} disk of three Windows 9x installations on the CLI enter the CLI and:
 
parttool hd0,1 hidden+ boot-
 
parttool hd0,2 hidden+ boot-
 
parttool hd0,3 hidden- boot+
 
set root=hd0,3
 
chainloader +1
 
boot
 
 
 
=== LVM ===
 
 
 
If you use [[LVM]] for your {{ic|/boot}}, make sure that the {{ic|lvm}} module is preloaded:
 
 
 
{{hc|/etc/default/grub|2=
 
GRUB_PRELOAD_MODULES="lvm"
 
 
}}
 
}}
  
=== RAID ===
+
{{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:
  
GRUB provides convenient handling of RAID volumes. You need to add {{ic|insmod mdraid}} which allows you to address the volume natively. For example, {{ic|/dev/md0}} becomes:
+
X:\> bootrec.exe /fixboot
  set root=(md/0)
+
  X:\> bootrec.exe /RebuildBcd
  
whereas a partitioned RAID volume (e.g. {{ic|/dev/md0p1}}) becomes:
+
Do '''not''' use {{ic|bootrec.exe /Fixmbr}} because it will wipe GRUB out.
set root=(md/0,1)
+
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.
To install grub when using RAID1 as the {{ic|/boot}} partition (or using {{ic|/boot}} housed on a RAID1 root partition), on devices with GPT ef02/'BIOS boot partition', simply run ''grub-install'' on both of the drives, such as:
 
# grub-install --target=i386-pc --recheck --debug /dev/sda
 
# grub-install --target=i386-pc --recheck --debug /dev/sdb
 
 
 
Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}.
 
 
 
=== Multiple entries ===
 
 
 
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]].
 
 
 
=== Encryption ===
 
 
 
==== Root partition ====
 
 
 
For an encrypted root filesystem, it is necessary to edit {{ic|/etc/default/grub}} with the parameters required to unlock the encrypted filesystem during boot. For example, if the [[mkinitcpio]] {{ic|encrypt}} hook is used, the {{ic|cryptdevice}} parameter must be added to {{ic|GRUB_CMDLINE_LINUX<nowiki>=</nowiki>""}} command. In the example below, the {{ic|sda2}} partition has been encrypted as {{ic|/dev/mapper/cryptroot}}:
 
 
 
{{hc|/etc/default/grub|2=
 
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:cryptroot"
 
 
}}
 
}}
 
Once {{ic|/etc/default/grub}} has been amended, it will then be necessary to [[#Generate the main configuration file]].
 
 
For further information about bootloader configuration for encrypted devices, see [[Dm-crypt/System configuration#Boot loader]].
 
 
{{Tip|If you are upgrading from a working GRUB Legacy configuration, check {{ic|/boot/grub/menu.lst.pacsave}} for the correct device/label to add. Look for them after the text {{ic|kernel /vmlinuz-linux}}.}}
 
 
==== Boot partition ====
 
 
The GRUB [https://www.gnu.org/software/grub/manual/grub.html#Simple-configuration parameter] {{ic|GRUB_ENABLE_CRYPTODISK}} can be used to enable GRUB to ask for a password to open a [[LUKS]] blockdevice in order to read its configuration and load any [[initramfs]] and [[kernel]] from it. This option tries to solve the issue of having an [[Dm-crypt/Specialties#Securing_the_unencrypted_boot_partition|unencrypted boot partition]].
 
 
The feature is enabled by adding:
 
GRUB_ENABLE_CRYPTODISK=y
 
to {{ic|/etc/default/grub}}. After this configuration a subsequent run of ''grub-mkconfig'' to [[#Generate the main configuration file]] is required while the encrypted {{ic|/boot}} is mounted.
 
{{Note|{{ic|1=GRUB_ENABLE_CRYPTODISK=1}} [https://savannah.gnu.org/bugs/?41524 will not work] as opposed to the request shown in GRUB 2.02-beta2.}}
 
 
Depending on the system's setup, note the following:
 
 
* For the feature to work it is not required that {{ic|/boot}} is kept in a separate partition, it may also stay under the system's root {{ic|/}} directory tree.
 
 
* Without further changes you will be prompted twice for a passhrase: the first for GRUB to unlock the {{ic|/boot}} mount point in early boot, the second to unlock the root filesystem itself as described in [[#Root partition]].{{Tip|See [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs]] for a workaround.}}
 
 
* In order to perform system updates involving the {{ic|/boot}} mount point, it must be ensured that the encrypted {{ic|/boot}} is unlocked to be re-mounted by the initramfs and kernel during boot. With a separate {{ic|/boot}} partition, this may be accomplished by adding an entry to {{ic|/etc/crypttab}} with a keyfile. See [[Dm-crypt/System configuration#crypttab]].
 
 
* 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 as below appending the following to the end of your installation command:
 
 
  grub-install --target=x86_64-efi --efi-directory=$esp --bootloader-id=grub --recheck '''--modules="part_gpt part_msdos"'''
 
  
 
== Using the command shell ==
 
== 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 {{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.
+
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.
  
 
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 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>
 
  grub>
  
 
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
 
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
 +
 
  grub rescue>
 
  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:
 
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> set prefix=(hdX,Y)/boot/grub
 
  grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
 
  grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
Line 631: Line 486:
  
 
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:
 
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:
 +
 
  sh:grub> set pager=1
 
  sh:grub> set pager=1
  
Line 642: Line 498:
 
''Chainloading'' means to load another boot-loader from the current one, ie, chain-loading.
 
''Chainloading'' means to load another boot-loader from the current one, ie, chain-loading.
  
The other bootloader may be embedded at the starting of the disk(MBR) or at the starting of a partition.
+
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 ====
+
==== Chainloading a partition's VBR ====
  
 
  set root=(hdX,Y)
 
  set root=(hdX,Y)
Line 653: Line 509:
 
Y=1,2,3...
 
Y=1,2,3...
  
For example to chainload Windows stored in the first partiton of the first hard disk,
+
For example to chainload Windows stored in the first partition of the first hard disk,
  
 
  set root=(hd0,1)
 
  set root=(hd0,1)
Line 661: Line 517:
 
Similarly GRUB installed to a partition can be chainloaded.
 
Similarly GRUB installed to a partition can be chainloaded.
  
==== Chainloading a disk/drive ====
+
==== Chainloading a disk's MBR or a partitionless disk's VBR ====
  
 
  set root=hdX
 
  set root=hdX
Line 669: Line 525:
 
==== Chainloading Windows/Linux installed in UEFI mode ====
 
==== Chainloading Windows/Linux installed in UEFI mode ====
  
  insmod ntfs
+
  insmod fat
 
  set root=(hd0,gpt4)
 
  set root=(hd0,gpt4)
 
  chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
 
  chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
 
  boot
 
  boot
  
''insmod ntfs'' used for loading the ntfs file system module for loading Windows.
+
{{ic|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 my EFI System Partition (ESP).
+
{{ic|(hd0,gpt4)}} or {{ic|/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.
+
The entry in the {{ic|chainloader}} line specifies the path of the ''.efi'' file to be chain-loaded.
  
 
==== Normal loading ====
 
==== Normal loading ====
Line 690: Line 546:
 
Before starting, the user must know the location of their {{ic|/boot}} partition (be it a separate partition, or a subdirectory under their root):
 
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
+
  grub rescue> set prefix=(hd''X'',''Y'')/boot/grub
 +
 
 +
where {{ic|''X''}} is the physical drive number and {{ic|''Y''}} is the partition number.
  
where X is the physical drive number and Y is the partition number.
+
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path (i.e. type {{ic|1=set prefix=(hd''X'',''Y'')/grub}}).}}
  
 
To expand console capabilities, insert the {{ic|linux}} module:
 
To expand console capabilities, insert the {{ic|linux}} module:
 +
 
  grub rescue> insmod i386-pc/linux.mod
 
  grub rescue> insmod i386-pc/linux.mod
  
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path, (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}}).}}
+
or simply
 +
 
 +
grub rescue> insmod linux
  
 
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar.
 
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar.
Line 708: Line 569:
 
  boot
 
  boot
  
With a separate boot partition, again change the lines accordingly:
+
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)
 
  set root=(hd0,5)
  linux /vmlinuz-linux root=/dev/sda6
+
  linux (hd''X'',''Y'')/vmlinuz-linux root=/dev/sda6
  initrd /initramfs-linux.img
+
  initrd (hd''X'',''Y'')/initramfs-linux.img
 
  boot
 
  boot
  
Line 720: Line 583:
  
 
To reinstall GRUB and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Installation]] for details.
 
To reinstall GRUB and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Installation]] for details.
 +
 +
== GRUB removal ==
 +
 +
{{Expansion|Migrating from BIOS booting to UEFI is not the only case where GRUB could be removed. Section needs to either cover how to remove GRUB installed for UEFI booting or it should be removed altogether as too trivial.}}
 +
 +
After migrating to GPT/UEFI one may want to remove the [[Partitioning#Master Boot Record (bootstrap code)|MBR boot code]] [[dd#Remove bootloader|using dd]]:
 +
 +
# dd if=/dev/zero of=/dev/sd''X'' bs=440 count=1
  
 
== Troubleshooting ==
 
== 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 {{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.
 +
 +
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]].
  
 
=== Intel BIOS not booting GPT ===
 
=== Intel BIOS not booting GPT ===
  
==== MBR ====
+
{{Move|Arch boot process#Troubleshooting|The issue is not limited to GRUB nor to just GPT.}}
 +
 
 +
{{Accuracy|There would be no "1007 KiB partition" in a GPT disk's protective MBR unless hybrid-MBR was used and there is no reason to assume that it would. On GPT, by default, there is only one partition in the protective MBR—{{ic|0xEE}}—which, although violates the specification, can be marked bootable using ''fdisk'' or ''parted''.}}
  
 
Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.
 
Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.
Line 735: Line 614:
 
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 cfdisk, the steps are similar, just {{ic|cfdisk /dev/sda}}, choose bootable (at the left) in the desired hard disk, and quit saving.
  
More information is available [http://www.rodsbooks.com/gdisk/bios.html here]
+
With recent version of parted, you can use {{ic|disk_toggle pmbr_boot}} option. Afterwards verify that Disk Flags show pmbr_boot.
  
==== EFI path ====
+
# parted /dev/sd''x'' disk_toggle pmbr_boot
 +
# parted /dev/sd''x'' print
  
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 place a file at one of the known locations.  Assuming the EFI partition is at {{ic|/boot/efi/}} this will work:
+
More information is available [http://www.rodsbooks.com/gdisk/bios.html here]
 
 
mkdir /boot/efi/EFI/boot
 
cp /boot/efi/EFI/grub/grubx64.efi /boot/efi/EFI/boot/bootx64.efi
 
 
 
This solution worked for an Intel DH87MC motherboard with firmware dated Jan 2014.
 
  
 
=== Enable debug messages ===
 
=== Enable debug messages ===
Line 758: Line 633:
  
 
=== "No suitable mode found" error ===
 
=== "No suitable mode found" error ===
 +
 +
{{Remove|1=This solution is probably out of date and inaccurate. This section was [[Special:Diff/160811|added to ArchWiki in 2011]], and the message was [http://git.savannah.gnu.org/cgit/grub.git/commit/grub-core/video/video.c?id=d61386e21d15b2b2c1df71d7017660d8aedcd990 edited in 2012]. Also, ''grub-install'' already installs {{ic|unicode.pf2}} to {{ic|/boot/grub/fonts/}}, there is no need to do it manually.}}
  
 
If you get this error when booting any menuentry:
 
If you get this error when booting any menuentry:
Line 766: Line 643:
 
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).
 
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).
  
Copy {{ic|/usr/share/grub/unicode.pf2}} to ${GRUB_PREFIX_DIR} ({{ic|/boot/grub/}} in case of BIOS and UEFI systems). If GRUB UEFI was installed with {{ic|1=--boot-directory=$esp/EFI}} set, then the directory is {{ic|$esp/EFI/grub/}}:
+
Copy {{ic|/usr/share/grub/unicode.pf2}} to {{ic|${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/}}:
  
 
  # cp /usr/share/grub/unicode.pf2 ${GRUB_PREFIX_DIR}
 
  # cp /usr/share/grub/unicode.pf2 ${GRUB_PREFIX_DIR}
  
If {{ic|/usr/share/grub/unicode.pf2}} does not exist, install {{Pkg|bdf-unifont}}, create the {{ic|unifont.pf2}} file and then copy it to {{ic|${GRUB_PREFIX_DIR<nowiki>}</nowiki>}}:
+
If {{ic|/usr/share/grub/unicode.pf2}} does not exist, install {{Pkg|bdf-unifont}}, create the {{ic|unifont.pf2}} file and then copy it to {{ic|1=${GRUB_PREFIX_DIR}}}:
  
 
  # grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
 
  # grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
  
 
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.
 
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.
 
BIOS systems:
 
 
insmod vbe
 
 
UEFI systems:
 
 
insmod efi_gop
 
insmod efi_uga
 
  
 
After that add the following code (common to both BIOS and UEFI):
 
After that add the following code (common to both BIOS and UEFI):
  
insmod font
+
{{bc|1=
 
+
loadfont "unicode"
if loadfont ${prefix}/fonts/unicode.pf2
+
set gfxmode=auto
then
+
set gfxpayload=keep
    insmod gfxterm
+
insmod all_video
    set gfxmode=auto
+
insmod gfxterm
    set gfxpayload=keep
+
terminal_output gfxterm
    terminal_output gfxterm
+
}}
fi
 
 
 
As you can see for gfxterm (graphical terminal) to function properly, {{ic|unicode.pf2}} font file should exist in {{ic|${GRUB_PREFIX_DIR<nowiki>}</nowiki>}}.
 
  
 
=== msdos-style error message ===
 
=== msdos-style error message ===
Line 812: Line 677:
 
==== Common installation errors ====
 
==== Common installation errors ====
  
* 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#Switch to efivarfs]].
+
* If you have a problem when running ''grub-install'' with ''sysfs'' or ''procfs'' and it says you must run {{ic|modprobe efivarfs}}, try [[Unified Extensible Firmware Interface#Mount efivarfs]].
 
* Without {{ic|--target}} or {{ic|--directory}} option, grub-install cannot determine for which firmware to install. In such cases {{ic|grub-install}} will print {{ic|source_dir does not exist. Please specify --target or --directory}}.
 
* Without {{ic|--target}} or {{ic|--directory}} option, grub-install cannot determine for which firmware to install. In such cases {{ic|grub-install}} will print {{ic|source_dir does not exist. Please specify --target or --directory}}.
 
* If after running grub-install you are told your partition does not look like an EFI partition then the partition is most likely not {{ic|Fat32}}.
 
* 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}}.
Line 818: Line 683:
 
==== Drop to rescue shell ====
 
==== Drop to rescue shell ====
  
If GRUB loads but drops you into the rescue shell with no errors, 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 OR if the partition number of the boot partition changed (which is hard-coded into the {{ic|grubx64.efi}} file).
+
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 {{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.
  
 
==== GRUB UEFI not loaded ====
 
==== GRUB UEFI not loaded ====
  
An example of a working EFI:
+
An example of a working UEFI:
  
 
{{hc|# efibootmgr -v|
 
{{hc|# efibootmgr -v|
Line 828: Line 696:
 
Timeout: 3 seconds
 
Timeout: 3 seconds
 
BootOrder: 0000,0001,0002
 
BootOrder: 0000,0001,0002
Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\efi\grub\grub.efi)
+
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(\EfiShell.efi)
+
Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\shellx64.efi)
 
Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI
 
Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI
 
}}
 
}}
Line 835: Line 703:
 
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:
 
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)
+
  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, {{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:
 +
 
 +
# 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 ===
 
=== Invalid signature ===
Line 852: Line 731:
 
=== Arch not found from other OS ===
 
=== Arch not found from other OS ===
  
Some have reported that other distributions 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}} in the [[official repositories]].
+
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}}.
  
 
=== Warning when installing in chroot ===
 
=== 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 {{ic|/run/lvm/lvmetad.socket: connect failed: No such file or directory}} or {{ic|WARNING: failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.}} 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.
+
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 {{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.
  
 
=== GRUB loads slowly ===
 
=== GRUB loads slowly ===
Line 863: Line 750:
  
 
=== error: unknown filesystem ===
 
=== error: unknown filesystem ===
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_.28GPT.29_specific_instructions|BIOS Boot Partition]] is located outside the first 2TB 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 2TB, then reinstall and reconfigure GRUB.
+
 
 +
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.
 +
 
 +
This error might also be caused by an [[ext4]] filesystem having the features {{ic|large_dir}} or {{ic|metadata_csum_seed}} set.
  
 
=== grub-reboot not resetting ===
 
=== grub-reboot not resetting ===
  
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|GRUB_DEFAULT<nowiki>=</nowiki>0}} in your {{ic|/etc/default/grub}} (don't forget {{ic|grub-mkconfig}}).
+
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}}).
 +
 
 +
=== 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 {{ic|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 {{ic|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|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: {{ic|WARNING: Device /dev/''xxx'' not initialized in udev database even after waiting 10000000 microseconds}}.
 +
 
 +
You may need to provide {{ic|/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 {{Bug|61040}} and [https://bbs.archlinux.org/viewtopic.php?pid=1820949#p1820949 workaround].
 +
 
 +
=== GRUB rescue and encrypted /boot ===
 +
 
 +
When using an [[#Encrypted /boot|encrypted /boot]], and you fail to input a correct password, you will be dropped in grub-rescue prompt.
 +
 
 +
This grub-rescue prompt has limited capabilities. Use the following commands to complete the boot:
 +
{{bc|
 +
grub rescue> cryptomount <partition>
 +
grub rescue> insmod normal
 +
grub rescue> normal
 +
}}
 +
 
 +
See [https://blog.stigok.com/2017/12/30/decrypt-and-mount-luks-disk-from-grub-rescue-mode.html this blog post] for a better description.
  
 
== See also ==
 
== See also ==
  
* Official GRUB Manual - https://www.gnu.org/software/grub/manual/grub.html
+
* [[Wikipedia:GNU GRUB]]
* Ubuntu wiki page for GRUB - https://help.ubuntu.com/community/Grub2
+
* [https://www.gnu.org/software/grub/manual/grub.html Official GRUB Manual]
* GRUB wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
+
* [https://help.ubuntu.com/community/Grub2 Ubuntu wiki page for GRUB]
* Wikipedia's page on [[Wikipedia:BIOS Boot partition|BIOS Boot partition]]
+
* [https://help.ubuntu.com/community/UEFIBooting GRUB wiki page describing steps to compile for UEFI systems]
* http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html - quite complete description of how to configure GRUB
+
* [[Wikipedia:BIOS Boot partition]]
 +
* [http://web.archive.org/web/20160424042444/http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html#Editing_etcgrub.d05_debian_theme How to configure GRUB]
 +
* [http://www.linuxjournal.com/article/4622 Boot with GRUB]
 +
* [https://forum.manjaro.org/t/detecting-efi-files-and-booting-them-from-grub/38083 Detecting efi files and booting them from grub]

Latest revision as of 19:54, 10 October 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 workarounds 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.
  • Make sure to run the grub-install command from the system in which GRUB will be installed as the boot looader. That means if you are booting from the live installation environment, you need to be inside the chroot when running grub-install. If for some reason it is necessary to run grub-install from outside of the installed system, append the --boot-directory= option with the path to the mounted /boot directory, e.g --boot-directory=/mnt/boot.

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/41_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 hooks to 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 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.

GRUB removal

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

Reason: Migrating from BIOS booting to UEFI is not the only case where GRUB could be removed. Section needs to either cover how to remove GRUB installed for UEFI booting or it should be removed altogether as too trivial. (Discuss in Talk:GRUB#)

After migrating to GPT/UEFI one may want to remove the MBR boot code using dd:

# dd if=/dev/zero of=/dev/sdX bs=440 count=1

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

Tango-go-next.pngThis article or section is a candidate for moving to Arch boot process#Troubleshooting.Tango-go-next.png

Notes: The issue is not limited to GRUB nor to just GPT. (Discuss in Talk:GRUB#)

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

Reason: There would be no "1007 KiB partition" in a GPT disk's protective MBR unless hybrid-MBR was used and there is no reason to assume that it would. On GPT, by default, there is only one partition in the protective MBR—0xEE—which, although violates the specification, can be marked bootable using fdisk or parted. (Discuss in Talk:GRUB#)

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

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

Reason: This solution is probably out of date and inaccurate. This section was added to ArchWiki in 2011, and the message was edited in 2012. Also, grub-install already installs unicode.pf2 to /boot/grub/fonts/, there is no need to do it manually. (Discuss in Talk:GRUB#)

If you get this error when booting any menuentry:

error: no suitable mode found
Booting however

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

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

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

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

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

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

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 efivarfs, 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.

This error might also be caused by an ext4 filesystem having the features large_dir or metadata_csum_seed set.

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.

GRUB rescue and encrypted /boot

When using an encrypted /boot, and you fail to input a correct password, you will be dropped in grub-rescue prompt.

This grub-rescue prompt has limited capabilities. Use the following commands to complete the boot:

grub rescue> cryptomount <partition>
grub rescue> insmod normal
grub rescue> normal

See this blog post for a better description.

See also