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[[Category:Boot loaders]]
 
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{{Article summary start}}
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[[zh-hant:GRUB]]
{{Article summary text|Covers various aspects of version 2 of the GRand Unified Bootloader (GRUB).}}
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{{Related articles start}}
{{Article summary heading|Overview}}
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{{Related|Arch boot process}}
{{Article summary text|{{Boot process overview}}}}
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{{Related|Boot loaders}}
{{Article summary heading|Related}}
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{{Related|Master Boot Record}}
{{Article summary wiki|BURG}} - BURG is a brand-new boot loader based on GRUB v2. It can be built on a wider range of OS, and has a highly configurable menu system which works in both text and graphic mode.
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{{Related|GUID Partition Table}}
{{Article summary wiki|GRUB Legacy}} - previous Version, now obsolete.
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{{Related|Unified Extensible Firmware Interface}}
{{Article summary heading|Resources}}
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{{Related|GRUB Legacy}}
{{Article summary wiki|GRUB EFI Examples}}
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{{Related|GRUB/EFI examples}}
{{Article summary link|GNU GRUB - GNU Project|https://www.gnu.org/software/grub/}}
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{{Related|GRUB/Tips and tricks}}
{{Article summary end}}
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{{Related|Multiboot USB drive}}
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{{Related articles end}}
 +
[https://www.gnu.org/software/grub/ GRUB] (GRand Unified Bootloader) is a 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.
  
[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].
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A [[boot loader]] is the first program that runs when a computer starts. It is responsible for selecting, loading and transferring control to an operating system kernel. The kernel, in turn, initializes the rest of the operating system.
  
In brief, the ''bootloader'' is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the Linux kernel. The kernel, in turn, initializes the rest of the operating system.
+
{{Note|In the entire article {{ic|''esp''}} denotes the mountpoint of the [[EFI System Partition]] aka ESP.}}
  
== Preface ==
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== BIOS systems ==
  
* 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]].
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=== GUID Partition Table (GPT) specific instructions ===
* GRUB supports [[Btrfs]] as root (without a separate {{ic|/boot}} filesystem) compressed with either zlib or LZO
 
  
=== Notes for current GRUB Legacy users ===
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On a BIOS/[[GPT]] configuration, a [https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation BIOS boot partition] is required.  GRUB embeds its {{ic|core.img}} into this partition.
 
 
* Upgrading from [[GRUB Legacy]] to GRUB is much the same as freshly installing GRUB, which is covered [[#Installation|below]]
 
* There are differences in the commands of GRUB Legacy and GRUB. Familiarize yourself with [https://www.gnu.org/software/grub/manual/grub.html#Commands GRUB commands] before proceeding (e.g. "find" has been replaced with "search")
 
* GRUB is now ''modular'' and no longer requires "stage 1.5". As a result, the bootloader itself is limited -- modules are loaded from the hard drive as needed to expand functionality (e.g. for [[LVM]] or RAID support)
 
* Device naming has changed between GRUB Legacy and GRUB. Partitions are numbered from 1 instead of 0 while drives are still numbered from 0, and prefixed with partition-table type. For example, {{ic|/dev/sda1}} would be referred to as {{ic|(hd0,msdos1)}} (for MBR) or {{ic|(hd0,gpt1)}} (for GPT)
 
* If you use systemd without systemd-sysvcompat, and have had {{ic|<nowiki>init=/usr/lib/systemd/systemd</nowiki>}} in your old grub menu.lst, the automatically generated grub.cfg file might not carry over this kernel parameter (giving you "ERROT: Root device mounted successfully, but /sbin/init does not exist" on boot). If so, edit the Arch Linux entry that grub shows you, add {{ic|<nowiki>init=/usr/lib/systemd/systemd</nowiki>}} to the kernel parameters, and then [[Grub#Additional_arguments|make it permanent]].
 
* GRUB is noticeably bigger than GRUB legacy (occupies ~13 MB in /boot). If you are booting from a separate /boot partition, and this partition is smaller than 32 MB, you will run into disk space issues, and pacman will refuse to install new kernels. If you do not want to re-partition your system, switch to [[Syslinux]] instead, which is smaller (occupies ~1.5 MB in /boot).
 
 
 
==== Backup important data ====
 
 
 
Although a GRUB installation should run smoothly, it is strongly recommended to keep the GRUB Legacy files before upgrading to GRUB v2.
 
 
 
# mv /boot/grub /boot/grub-legacy
 
 
 
Backup the MBR which contains the boot code and partition table (Replace {{ic|/dev/sd'''X'''}} with your actual disk path):
 
 
 
# dd if=/dev/sdX of=/path/to/backup/mbr_backup bs=512 count=1
 
 
 
Only 446 bytes of the MBR contain boot code, the next 64 contain the partition table. If you do not want to overwrite your partition table when restoring, it is strongly advised to backup only the MBR boot code:
 
 
 
# dd if=/dev/sdX of=/path/to/backup/bootcode_backup bs=446 count=1
 
 
 
If unable to install GRUB2 correctly, see [[#Restore GRUB Legacy]].
 
 
 
=== Preliminary requirements ===
 
 
 
==== BIOS systems ====
 
 
 
===== GUID Partition Table (GPT) specific instructions =====
 
 
 
GRUB in [[GPT|BIOS-GPT]] configuration requires a [http://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html BIOS boot partition] to embed its {{ic|core.img}} in the absence of post-MBR gap in GPT partitioned systems (which is taken over by the GPT Primary Header and Primary Partition table). This partition is used by GRUB only in BIOS-GPT setups. No such partition type exists in case of MBR partitioning (at least not for GRUB). This partition is also not required if the system is UEFI based, as no embedding of bootsectors takes place in that case.
 
 
 
For a BIOS-GPT configuration, create a 1007 KiB partition at the beginning of the disk using gdisk, cgdisk or GNU Parted with no filesystem. The size of 1007 KiB will allow for the following partition to be correctly alligned at 1024 KiB. If needed, the partition can also be located somewhere else on the disk, but it should be within the first 2 TiB region. Set the partition type to {{ic|ef02}} in (c)gdisk or {{ic|set <BOOT_PART_NUM> bios_grub on}} in GNU Parted.
 
  
 
{{Note|
 
{{Note|
* This partition should be created before {{ic|grub-install}} or {{ic|grub-setup}} is run
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* Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme. Read more on [[Partitioning#GUID_Partition_Table|GUID partition tables]].
* gdisk will only allow you to create this partition on the position which will waste the least amount of space (sector 34-2047) if you create it last, after all the other partitions. This is because gdisk will auto-align partitions to 2048-sector boundaries if possible
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* This additional partition is only needed on a GRUB, BIOS/GPT partitioning scheme.  Previously, for a GRUB, BIOS/MBR partitioning scheme, GRUB used the Post-MBR gap for the embedding the {{ic|core.img}}).  GRUB for GPT, however, does not use the Post-GPT gap to conform to GPT specifications that require 1_megabyte/2048_sector disk boundaries.
 +
* 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]].
 
}}
 
}}
  
===== Master Boot Record (MBR) specific instructions =====
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Create a mebibyte partition ({{ic|1=+1M}} with ''fdisk'' or ''gdisk'') on the disk with no file system and with partition type GUID {{ic|21686148-6449-6E6F-744E-656564454649}}.
  
Usually the post-[[MBR]] gap (after the 512 byte MBR region and before the start of the 1st partition) in many MBR (or msdos disklabel) partitioned systems is 31 KiB when DOS compatibility cylinder alignment issues are satisfied in the partition table. However a post-MBR gap of about 1 to 2 MiB is recommended to provide sufficient room for embedding GRUB's {{ic|core.img}} ({{bug|24103}}). It is advisable to use a partitioner which supports 1 MiB partition alignment to obtain this space as well as satisfy other non-512 byte sector issues (which are unrelated to embedding of {{ic|core.img}}).
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* Select partition type {{ic|BIOS boot}} for [[fdisk]], {{ic|ef02}} for [[gdisk]].
 +
* For [[parted]] set/activate the flag {{ic|bios_grub}} on the partition.
  
==== UEFI systems ====
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This partition can be in any position order but has to be on the first 2 TiB of the disk.  This partition needs to be created before GRUB installation.  When the partition is ready, install the bootloader as per the instructions below.
  
{{Note|It is recommended to read and understand the [[Unified Extensible Firmware Interface|UEFI]], [[GUID Partition Table|GPT]] and [[UEFI Bootloaders]] pages.}}
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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 ''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.
  
===== Create and Mount the UEFI System Partition =====
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=== Master Boot Record (MBR) specific instructions ===
  
Follow [[Unified Extensible Firmware Interface#EFI System Partition]] for instructions on creating an UEFI System Partition. Then mount the UEFI System Partition at {{ic|/boot/efi}}. If you have mounted the UEFI System Partition at some other mountpoint, replace {{ic|/boot/efi}} in the below instructions with that mountpoint:
+
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}}).
  
# mkdir -p /boot/efi
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=== Installation ===
# mount -t vfat <UEFI_SYSTEM_PARTITION> /boot/efi
 
  
Create a {{ic|/boot/efi/EFI}} directory:
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[[Install]] the {{Pkg|grub}} package. It will replace {{AUR|grub-legacy}}, where already installed. Then do:
  
  # mkdir /boot/efi/EFI
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  # grub-install --target=i386-pc /dev/sd'''X'''
  
== Installation ==
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where {{ic|/dev/sd'''X'''}} is the [[partition]]ed disk where grub is to be installed (for example, disk {{ic|/dev/sda}} and '''not''' partition {{ic|/dev/sda1}}).
  
=== BIOS systems ===
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Now you must [[#Generate the main configuration file]].
  
GRUB can be [[pacman|installed]] with the {{Pkg|grub}} package from the [[official repositories]]. It will replace {{Pkg|grub-legacy}} , if it is installed.
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If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks.
  
{{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.}}
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{{Tip|See [[GRUB/Tips and tricks#Alternative installation methods]] for other ways to install GRUB, such as to a USB stick.}}
  
==== Install boot files ====
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See {{man|8|grub-install}} and [https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation GRUB Manual] for more details on the ''grub-install'' command.
  
There are 3 ways to install GRUB boot files in BIOS booting:
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== UEFI systems ==
* [[#Install to GPT BIOS boot partition]] (recommended with [[GPT]])
 
* [[#Install to 440-byte MBR boot code region]] (recommended with [[MBR]])
 
* [[#Install to partition or partitionless disk]] (not recommended)
 
* [[#Generate core.img alone]] (safest method, but requires another BIOS bootloader like [[GRUB Legacy]] or [[Syslinux]] to be installed to chainload {{ic|/boot/grub/i386-pc/core.img}})
 
  
{{Note|See http://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html for additional documentation.}}
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{{Note|
 
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* It is recommended to read and understand the [[UEFI]], [[GPT]] and [[UEFI Bootloaders]] pages.
===== Install to GPT BIOS boot partition =====
+
* 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.
 
+
}}
[[GUID Partition Table]] disks do not have a reserved "boot track". Therefore you must create a BIOS Boot Partition ({{ic|ef02}}) to hold the GRUB core image.
 
 
 
Using GNU Parted, you can set this using a command such as the following:
 
 
 
# parted /dev/disk set <partition-number> bios_grub on
 
 
 
If you are using gdisk, set the partition type to {{ic|ef02}}. With partitioning programs that require setting the GUID directly, it should be {{ic|‘21686148-6449-6e6f-744e656564454649’}} (or, {{ic|[[wikipedia:BIOS_Boot_partition|Hah!IdontNeedEFI]]}}).
 
 
 
{{Warning|Be very careful which partition you select when marking it as a BIOS Boot Partition. When GRUB finds a BIOS Boot Partition during installation, it will automatically overwrite part of it. Make sure that the partition does not contain any other data.}}
 
 
 
To setup {{ic|grub}} on a GPT disk, populate the {{ic|/boot/grub}} directory, generate the {{ic|/boot/grub/i386-pc/core.img}} file, and embed it in the BIOS Boot Partition, run:
 
 
 
# modprobe dm-mod
 
# grub-install --target=i386-pc --recheck --debug /dev/sda
 
 
 
where {{ic|/dev/sda}} is the destination of the installation.
 
  
Continue with [[GRUB#Generate config file]] below.
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=== Check for an EFI System Partition ===
  
===== Install to 440-byte MBR boot code region =====
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To boot from a disk using EFI, the recommended disk partition table is GPT and this is the layout that is assumed in this article. An [[EFI System Partition]] (ESP) is required on every bootable disk.  If you are installing Arch Linux on an EFI-capable computer with an installed operating system, like Windows 10 for example, it is very likely that you already have an ESP.
  
To setup {{ic|grub}} in the 440-byte Master Boot Record boot code region, populate the {{ic|/boot/grub}} directory, generate the {{ic|/boot/grub/i386-pc/core.img}} file, embed it in the 31 KiB (minimum size - varies depending on partition alignment) post-MBR gap, and generate the configuration file, run:
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To find out the disk partition scheme and the system partition, use {{ic|parted}} as root on the disk you want to boot from:
  
  # modprobe dm-mod
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  # parted /dev/sd''x'' print
# grub-install --recheck /dev/sdX
 
  
where {{ic|/dev/sdX}} is the destination of the installation (in this case the MBR of the first SATA disk). If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks.
+
The command returns:
 +
* The disk partition layout: if the disk is GPT, it indicates {{ic|Partition Table: gpt}}.
 +
* The list of partitions on the disk: Look for the ESP in the list, it is a small (about 550 MiB) partition with a {{ic|fat32}} file system and with the flag {{ic|esp}} enabled. To confirm this is the ESP, mount it and check whether it contains a directory named {{ic|EFI}}, if it does this is definitely the ESP.
  
{{Warning|Make sure to check the {{ic|/boot}} directory if you use the latter. Sometimes the {{ic|boot-directory}} parameter creates another {{ic|/boot}} folder inside of {{ic|/boot}}. A wrong install would look like: {{ic|/boot/boot/grub/}}.}}
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Once it is found, '''take note of the ESP partition number''', it will be required for the [[#Installation_2|GRUB installation]]. If you do not have an ESP, you will need to create one. See the [[EFI System Partition]] article.
  
Continue with [[GRUB#Generate config file]] below.
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=== Installation ===
 
 
===== Install to partition or partitionless disk =====
 
 
 
{{Note|GRUB does not encourage installation to a partition boot sector or a partitionless disk like GRUB Legacy or Syslinux does. This kind of setup is prone to breakage, especially during updates, and is not supported by Arch devs.}}
 
 
 
To set up grub to a partition boot sector, to a partitionless disk (also called superfloppy) or to a floppy disk, run (using for example {{ic|/dev/sdaX}} as the {{ic|/boot}} partition):
 
 
# modprobe dm-mod
 
# 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
 
 
 
You need to use the {{ic|--force}} option to allow usage of blocklists and should not use {{ic|1=--grub-setup=/bin/true}} (which is similar to simply generating {{ic|core.img}}).
 
 
 
{{ic|grub-install}} will give out warnings like which should give you the idea of what might go wrong with this approach:
 
 
 
/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea.
 
/sbin/grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.
 
                        However, blocklists are UNRELIABLE and their use is discouraged.
 
 
 
Without {{ic|--force}} you may get the below error and {{ic|grub-setup}} will not setup its boot code in the partition boot sector:
 
 
/sbin/grub-setup: error: will not proceed with blocklists
 
 
 
With {{ic|--force}} you should get:
 
 
 
Installation finished. No error reported.
 
 
 
The reason why {{ic|grub-setup}} does not by default allow this is because in case of partition or a partitionless disk is that {{ic|grub}} relies on embedded blocklists in the partition bootsector to locate the {{ic|/boot/grub/i386-pc/core.img}} file and the prefix dir {{ic|/boot/grub}}. The sector locations of {{ic|core.img}} may change whenever the filesystem in the partition is being altered (files copied, deleted etc.). For more info see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915.
 
 
 
The workaround for this is to set the immutable flag on {{ic|/boot/grub/i386-pc/core.img}} (using chattr command as mentioned above) so that the sector locations of the {{ic|core.img}} file in the disk is not altered. The immutable flag on {{ic|/boot/grub/i386-pc/core.img}} needs to be set only if {{ic|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).
 
 
 
Continue with [[GRUB#Generate config file]] below.
 
 
 
===== Generate core.img alone =====
 
 
 
To populate the {{ic|/boot/grub}} directory and generate a {{ic|/boot/grub/i386-pc/core.img}} file '''without''' embedding any {{ic|grub}} bootsector code in the MBR, post-MBR region, or the partition bootsector, add {{ic|1=--grub-setup=/bin/true}} to {{ic|grub-install}}:
 
 
# modprobe dm-mod
 
# grub-install --target=i386-pc --grub-setup=/bin/true --recheck --debug /dev/sda
 
 
 
You can then chainload GRUB's {{ic|core.img}} from GRUB Legacy or syslinux as a Linux kernel or a multiboot kernel.
 
 
 
==== Generate config file ====
 
 
 
Finally, generate a configuration for GRUB (this is explained in greater detail in the Configuration section):
 
 
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
 
 
{{Note|The file path is {{ic|/boot/grub/grub.cfg}}, NOT {{ic|/boot/grub/i386-pc/grub.cfg}}.}}
 
 
 
If GRUB complains about "no suitable mode found" while booting, go to [[#"No suitable mode found" error]].
 
 
 
If {{ic|grub-mkconfig}} fails, convert your {{ic|/boot/grub/menu.lst}} file to {{ic|/boot/grub/grub.cfg}} using:
 
 
 
# grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
 
 
 
For example:
 
 
 
{{hc|/boot/grub/menu.lst|<nowiki>
 
default=0
 
timeout=5
 
 
 
title  Arch Linux Stock Kernel
 
root  (hd0,0)
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux.img
 
 
 
title  Arch Linux Stock Kernel Fallback
 
root  (hd0,0)
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux-fallback.img
 
</nowiki>}}
 
 
 
{{hc|/boot/grub/grub.cfg|<nowiki>
 
set default='0'; if [ x"$default" = xsaved ]; then load_env; set default="$saved_entry"; fi
 
set timeout=5
 
 
 
menuentry 'Arch Linux Stock Kernel' {
 
  set root='(hd0,1)'; set legacy_hdbias='0'
 
  legacy_kernel  '/vmlinuz-linux' '/vmlinuz-linux' 'root=/dev/sda2' 'ro'
 
  legacy_initrd '/initramfs-linux.img' '/initramfs-linux.img'
 
 
 
}
 
 
 
menuentry 'Arch Linux Stock Kernel Fallback' {
 
  set root='(hd0,1)'; set legacy_hdbias='0'
 
  legacy_kernel  '/vmlinuz-linux' '/vmlinuz-linux' 'root=/dev/sda2' 'ro'
 
  legacy_initrd '/initramfs-linux-fallback.img' '/initramfs-linux-fallback.img'
 
}
 
</nowiki>}}
 
 
 
If you forgot to create a GRUB {{ic|/boot/grub/grub.cfg}} config file and simply rebooted into GRUB Command Shell, type:
 
 
 
sh:grub> insmod legacycfg
 
sh:grub> legacy_configfile ${prefix}/menu.lst
 
 
 
Boot into Arch and re-create the proper GRUB {{ic|/boot/grub/grub.cfg}} config file.
 
 
 
{{Note|This option works only in BIOS systems, not in UEFI systems.}}
 
 
 
==== Multiboot ====
 
This should work out of the box, but an extra utility needs to be installed: os-prober. Install it, then rerun grub-mkconfig -o /boot/grub/grub.cfg. If this fails, you can try manually adding an entry by following the instructions below.
 
 
 
{{Note|If Windows is not found, try mounting its boot partition}}
 
 
 
===== Microsoft Windows installed in BIOS-MBR mode =====
 
 
 
{{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.}}
 
 
 
{{Warning|It is the '''system partition''' that has {{ic|bootmgr}}, not your "real" Windows partition (usually C:). When showing all UUIDs with blkid, the system partition is the one with {{ic|LABEL&#61;"SYSTEM RESERVED"}} and is only about 100 MB in size (much like the boot partition for Arch). See [[Wikipedia:System partition and boot partition]] for more info.}}
 
 
 
Throughout this section, it is assumed your Windows partition is /dev/sda1. A different partition will change every instance of hd0,msdos1. First, find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the {{ic|bootmgr}} and its files reside. For example, if Windows {{ic|bootmgr}} exists at {{ic|/media/SYSTEM_RESERVED/bootmgr}}:
 
 
 
For Windows Vista/7/8:
 
 
 
# grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr
 
69B235F6749E84CE
 
 
 
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr
 
--hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1
 
 
 
{{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:
 
 
 
For Windows Vista/7/8:
 
 
 
menuentry "Microsoft Windows Vista/7/8 BIOS-MBR" {
 
  insmod part_msdos
 
  insmod ntfs
 
  insmod search_fs_uuid
 
  insmod ntldr   
 
  search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
 
  ntldr /bootmgr
 
}
 
 
 
For Windows XP:
 
 
 
menuentry "Microsoft Windows XP" {
 
  insmod part_msdos
 
  insmod ntfs
 
  insmod search_fs_uuid
 
  insmod ntldr   
 
  search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
 
    ntldr /ntldr
 
}
 
 
 
{{Note| In some cases, mine I have installed GRUB before a clean Windows 8, you you cannot boot windows having an error with \boot\bcd (error code 0xc000000f). You can fix it going to Windows Recovery Console (cmd from install disk) and executing:
 
x:\> "bootrec.exe /fixboot"
 
x:\> "bootrec.exe /RebuildBcd".
 
{{Warning| Do not use "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.}}
 
 
 
=== UEFI systems ===
 
 
 
{{Note|It is well known that different motherboard manufactures implement UEFI differently.  Users experiencing problems getting Grub/EFI to work properly are encouraged to share detailed steps for hardware-specific cases where UEFI booting does not work as described below.  In an effort to keep the parent [[GRUB]] article neat and tidy, see the [[GRUB EFI Examples]] page for these special cases.}}
 
 
 
First install the {{Pkg|grub}} package and then follow the instructions below.
 
 
 
{{Note|Simply installing the package will not update the {{ic|core.efi}} file and the GRUB modules in the UEFI System Partition. You need to do this manually using {{ic|grub-install}} as explained below.}}
 
 
 
==== Install boot files ====
 
 
 
===== Install to UEFI system partition =====
 
  
 
{{Note|
 
{{Note|
* The below commands assume you are using installing GRUB for {{ic|x86_64-efi}} (for {{ic|IA32-efi}} replace {{ic|x86_64}} with {{ic|i386}} in the below commands)
+
* UEFI firmware are not implemented consistently across manufacturers. The procedure described below is intended to work on a wide range of UEFI systems but those experiencing problems despite applying this method are encouraged to share detailed information, and if possible the turnarounds found, for their hardware-specific case. A [[GRUB/EFI examples]] article has been provided for such cases.
* To do this, you need to boot using UEFI and not the BIOS. If you booted by just copying the ISO file to the USB drive, you will need to follow [[Unified Extensible Firmware Interface#Create UEFI bootable USB from ISO|this guide]] or grub-install will show errors
+
* The section assumes you are installing GRUB for x86_64 systems. For IA32 (32-bit) EFI systems (not to be confused with 32-bit CPUs), replace {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
 
}}
 
}}
  
The UEFI system partition will need to be mounted at {{ic|/boot/efi/}} for the GRUB install script to detect it:
+
First, [[install]] the packages {{Pkg|grub}} and {{Pkg|efibootmgr}}: ''GRUB'' is the bootloader while ''efibootmgr'' creates bootable ''.efi'' stub entries used by the GRUB installation script.
  
# mkdir -p /boot/efi
+
Then follow the below steps to install GRUB:
# mount -t vfat /dev/sdXY /boot/efi
 
  
Install GRUB UEFI application to {{ic|/boot/efi/EFI/arch_grub}} and its modules to {{ic|/boot/grub/x86_64-efi}} (recommended) using:
+
# [[EFI System Partition#Mount the partition|Mount the EFI System Partition]] to either {{ic|/boot}} or {{ic|/boot/efi}} and in the remainder of this section, substitute {{ic|''esp''}} with that mount point.
 +
# Choose a bootloader identifier, here named {{ic|'''''GRUB'''''}}. A directory of that name will be created to store the EFI binary bootloader in the ESP and this is the name that will appear in the EFI boot menu to identify the GRUB boot entry.
 +
# Execute the following command to install the GRUB UEFI application {{ic|grubx64.efi}} to {{ic|''esp''/EFI/'''''GRUB'''''/}} and install its modules to {{ic|/boot/grub/x86_64-efi/}}.
  
# modprobe dm-mod
+
  # grub-install --target=x86_64-efi --efi-directory=''esp'' --bootloader-id='''''GRUB'''''
  # grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=arch_grub --recheck --debug
 
  
{{Note|Without {{ic|--target}} or {{ic|--directory}} option, grub-install cannot determine for which firmware GRUB is being installed. In such cases {{ic|grub-install}} will show {{ic|source_dir does not exist. Please specify --target or --directory}} message.}}
+
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.
  
If you want to install GRUB modules and {{ic|grub.cfg}} at the directory {{ic|/boot/efi/EFI/grub}} and the {{ic|grubx64.efi}} application at {{ic|/boot/efi/EFI/arch_grub}} (ie. all the GRUB UEFI files inside the UEFISYS partition itself) use:
+
Remember to [[#Generate the main configuration file]] after finalizing [[#Configuration]].  
  
# modprobe dm-mod
+
{{Tip|If you use the option {{ic|--removable}} then GRUB will be installed to {{ic|''esp''/EFI/BOOT/BOOTX64.EFI}} and you will have the additional ability of being able to boot from the drive in case EFI variables are reset or you move the drive to another computer. Usually you can do this by selecting the drive itself similar to how you would using BIOS. If dual booting with Windows, be aware Windows usually has a {{ic|BOOT}} folder inside the {{ic|EFI}} folder of the EFI partition, but its only purpose is to recreate the EFI boot option for Windows.}}
# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=arch_grub --boot-directory=/boot/efi/EFI --recheck --debug
 
 
 
The {{ic|--efi-directory}} option mentions the mountpoint of UEFI SYSTEM PARTITION , {{ic|--bootloader-id}} mentions the name of the directory used to store the {{ic|grubx64.efi}} file and {{ic|--boot-directory}} mentions the directory wherein the actual modules will be installed (and into which {{ic|grub.cfg}} should be created).
 
 
 
The actual paths are:
 
 
 
<efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi
 
 
 
<boot-directory>/grub/x86_64-efi/<all modules, grub.efi, core.efi, grub.cfg>
 
 
 
{{Note|the {{ic|--bootloader-id}} option does not change {{ic|<boot-directory>/grub}}, i.e. you cannot install the modules to {{ic|<boot-directory>/<bootloader-id>}}, the path is hard-coded to be {{ic|<boot-directory>/grub}}.}}
 
 
 
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=grub</nowiki>}}:
 
 
 
<efi-directory>/<EFI or efi>/<bootloader-id> == <boot-directory>/grub == /boot/efi/EFI/grub
 
 
 
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=arch_grub</nowiki>}}:
 
 
 
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub
 
<boot-directory>/grub == /boot/efi/EFI/grub
 
 
 
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub</nowiki>}}:
 
 
 
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub
 
<boot-directory>/grub == /boot/grub
 
 
 
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=grub</nowiki>}}:
 
 
 
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/grub
 
<boot-directory>/grub == /boot/grub
 
 
 
The {{ic|<nowiki><efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi</nowiki>}} is an exact copy of {{ic|<nowiki><boot-directory>/grub/x86_64-efi/core.efi</nowiki>}}.
 
  
 
{{Note|
 
{{Note|
* In GRUB 2.00, the {{ic|grub-install}} option {{ic|--efi-directory}} replaces {{ic|--root-directory}} and the latter is deprecated
+
* While some distributions require a {{ic|/boot/efi}} or {{ic|/boot/EFI}} directory, Arch does not.
* The options {{ic|--efi-directory}} and {{ic|--bootloader-id}} are specific to GRUB UEFI
+
* {{ic|--efi-directory}} and {{ic|--bootloader-id}} are specific to GRUB UEFI, {{ic|--efi-directory}} 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 UEFI install script. Indeed, UEFI bootloaders do not use a MBR or partition boot sector at all.
 
}}
 
}}
 
In all the cases the UEFI SYSTEM PARTITION should be mounted for {{ic|grub-install}} to install {{ic|grubx64.efi}} in it, which will be launched by the firmware (using the {{ic|efibootmgr}} created boot entry in non-Mac systems).
 
 
If you notice carefully, there is no <device_path> option (Eg: {{ic|/dev/sda}}) at the end of the {{ic|grub-install}} command unlike the case of setting up GRUB for BIOS systems. Any <device_path> provided will be ignored by the install script as UEFI bootloaders do not use MBR or Partition boot sectors at all.
 
 
You may now be able to UEFI boot your system by creating a {{ic|grub.cfg}} file by following [[#Generate UEFI Config file]] and [[#Create GRUB entry in the firmware boot manager]].
 
 
==== Generate config file ====
 
 
Finally, generate a configuration for GRUB (this is explained in greater detail in the Configuration section):
 
 
# grub-mkconfig -o <boot-directory>/grub/grub.cfg
 
 
{{Note|The file path is {{ic|<boot-directory>/grub/grub.cfg}}, NOT {{ic|<boot-directory>/grub/x86_64-efi/grub.cfg}}.}}
 
 
If you used {{ic|<nowiki>--boot-directory=/boot</nowiki>}}:
 
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
 
If you used {{ic|<nowiki>--boot-directory=/boot/efi/EFI</nowiki>}}:
 
 
# grub-mkconfig -o /boot/efi/EFI/grub/grub.cfg
 
 
This is independent of the value of {{ic|--bootloader-id}} option.
 
 
If GRUB complains about "no suitable mode found" while booting, try [[#"No suitable mode found" error]].
 
 
==== Create GRUB entry in the firmware boot manager ====
 
 
{{ic|grub-install}} automatically tries to create a menu entry in the boot manager. If it does not, then see [[Beginners' Guide#GRUB]] for instructions to use {{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 [[Unified Extensible Firmware Interface#Create UEFI bootable USB from ISO]].
 
 
==== Create GRUB standalone UEFI application ====
 
 
It is possible to create a {{ic|grubx64_standalone.efi}} application which has all the modules embeddded in a memdisk within the UEFI application, thus removing the need for having a separate directory populated with all the GRUB UEFI modules and other related files. This is done using the {{ic|grub-mkstandalone}} command which is included in {{Pkg|grub}}.
 
  
The easiest way to do this would be with the install command already mentioned before, but specifying the modules to include. For example:
+
See [[#UEFI|UEFI troubleshooting]] in case of problems. Additionally see [[GRUB/Tips and tricks#UEFI further reading]].
  
# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \
+
== Generate the main configuration file ==
--output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" <any extra files you want to include>
 
  
The {{ic|grubx64_standalone.efi}} file expects {{ic|grub.cfg}} to be within its $prefix which is {{ic|(memdisk)/boot/grub}}. The memdisk is embedded within the EFI app. The {{ic|grub-mkstandlone}} script allow passing files to be included in the memdisk image to be as the arguments to the script (in <any extra files you want to include>).
+
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]].  
  
If you have the {{ic|grub.cfg}} at {{ic|/home/user/Desktop/grub.cfg}}, then create a temporary {{ic|/home/user/Desktop/boot/grub/}} directory, copy the {{ic|/home/user/Desktop/grub.cfg}} to {{ic|/home/user/Desktop/boot/grub/grub.cfg}}, cd into {{ic|/home/user/Desktop/boot/grub/}} and run:
+
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.  
  
# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \
+
{{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/}}.}}
--output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" "boot/grub/grub.cfg"
 
  
The reason to {{ic|cd}} into {{ic|/home/user/Desktop/boot/grub/}} and to pass the file path as {{ic|boot/grub/grub.cfg}} (notice the lack of a leading slash - {{ic|boot/}} vs. {{ic|/boot/}} ) is because {{ic|dir1/dir2/file}} is included as {{ic|(memdisk)/dir1/dir2/file}} by the {{ic|grub-mkstandalone}} script.
+
Use the ''grub-mkconfig'' tool to generate {{ic|grub.cfg}}:
 
 
If you pass {{ic|/home/user/Desktop/grub.cfg}} the file will be included as {{ic|(memdisk)/home/user/Desktop/grub.cfg}}. If you pass {{ic|/home/user/Desktop/boot/grub/grub.cfg}} the file will be included as {{ic|(memdisk)/home/user/Desktop/boot/grub/grub.cfg}}. That is the reason for {{ic|cd}}'ing into {{ic|/home/user/Desktop/boot/grub/}} and passing {{ic|boot/grub/grub.cfg}}, to include the file as {{ic|(memdisk)/boot/grub/grub.cfg}}, which is what {{ic|grub.efi}} expects the file to be.
 
 
 
You need to create an UEFI Boot Manager entry for {{ic|/boot/efi/EFI/arch_grub/grubx64_standalone.efi}} using {{ic|efibootmgr}}. Follow [[#Create GRUB entry in the Firmware Boot Manager]].
 
 
 
==== Multiboot ====
 
 
 
===== Microsoft Windows installed in UEFI-GPT mode =====
 
 
 
Find the UUID of the FAT32 filesystem in the UEFI SYSTEM PARTITION where the Windows UEFI Bootloader files reside. For example, if Windows {{ic|bootmgfw.efi}} exists at {{ic|/boot/efi/EFI/Microsoft/Boot/bootmgfw.efi}} (ignore the upper-lower case differences since that is immaterial in FAT filesystem):
 
 
 
# grub-probe --target=fs_uuid /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi
 
1ce5-7f28
 
 
 
# grub-probe --target=hints_string /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi
 
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
 
 
 
Then, add this code to {{ic|/etc/grub.d/40_custom}} to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode:
 
 
 
menuentry "Microsoft Windows Vista/7/8 x86_64 UEFI-GPT" {
 
  insmod part_gpt
 
  insmod fat
 
  insmod search_fs_uuid
 
  insmod chain
 
  search --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 1ce5-7f28
 
  chainloader /efi/Microsoft/Boot/bootmgfw.efi
 
}
 
 
 
Afterwards remake {{ic|/boot/grub/grub.cfg}}:
 
  
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 
  # grub-mkconfig -o /boot/grub/grub.cfg
  
== Configuration ==
+
By default the generation scripts automatically add menu entries for Arch Linux to any generated configuration. See [[Multiboot USB drive#Boot entries]] and [[#Dual-booting]] for custom menu entries for other systems.
  
You can also choose to automatically generate or manually edit {{ic|grub.cfg}}.
+
{{Tip|To have ''grub-mkconfig'' search for other installed systems and automatically add them to the menu, [[install]] the {{Pkg|os-prober}} package and [[mount]] the partitions that contain other systems.}}
  
 
{{Note|
 
{{Note|
* For EFI systems, if GRUB was installed with the {{ic|--boot-directory}} option set, the {{ic|grub.cfg}} file must be placed in the same directory as {{ic|grubx64.efi}}. Otherwise, the {{ic|grub.cfg}} file goes in {{ic|/boot/grub/}}, just like in GRUB BIOS
+
* The default file path is {{ic|/boot/grub/grub.cfg}}, not {{ic|/boot/grub/i386-pc/grub.cfg}}. The {{Pkg|grub}} package includes a sample {{ic|/boot/grub/grub.cfg}}; ensure your intended changes are written to this file.
* [http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html Here] is a quite complete description of how to configure GRUB
+
* 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].
 
}}
 
}}
  
=== Automatically generating using grub-mkconfig ===
+
== Configuration ==
  
The GRUB {{ic|menu.lst}} equivalent configuration files are {{ic|/etc/default/grub}} and {{ic|/etc/grub.d/*}}. {{ic|grub-mkconfig}} uses these files to generate {{ic|grub.cfg}}. By default the script outputs to stdout. To generate a {{ic|grub.cfg}} file run the command:
+
This section only covers editing the {{ic|/etc/default/grub}} configuration file. See [[GRUB/Tips and tricks]] for more information.
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
Remember to always [[#Generate the main configuration file]] after making changes to {{ic|/etc/default/grub}}.
  
{{ic|/etc/grub.d/10_linux}} is set to automatically add menu items for Arch linux that work out of the box, to any generated configuration. Other operating systems may need to be added manually to {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}}
+
=== Additional arguments ===
  
{{Note|If you're trying to do this in a chroot or systemd-nspawn container, you might notice that it doesn't work, complaining that grub-probe can't get the 'canonical path of /dev/sdaX'. In this case, try using arch-chroot as described [https://bbs.archlinux.org/viewtopic.php?pid&#61;1225067#p1225067 here].}}
+
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.
  
==== Additional arguments ====
+
It is not necessary to use both, but can be useful. For example, you could use {{ic|1=GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sdaX quiet"}} where {{ic|sda'''X'''}} is your swap partition to enable resume after hibernation. This would generate a recovery boot entry without the resume and without {{ic|quiet}} suppressing kernel messages during a boot from that menu entry. Though, the other (regular) menu entries would have them as options.
  
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 when generating {{ic|grub.cfg}} for regular boot entries. For the ''recovery'' boot entry, only {{ic|GRUB_CMDLINE_LINUX}} is used in the generation.  
+
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}}.  
  
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.  
+
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}}.
  
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|1=GRUB_CMDLINE_LINUX="resume=UUID=''uuid-of-swap-partition''"}}
 
 
You can also use {{ic|<nowiki>GRUB_CMDLINE_LINUX="resume=/dev/disk/by-uuid/${swap_uuid}"</nowiki>}}, where {{ic|${swap_uuid} }} is the [[Persistent_block_device_naming|UUID]] of your swap partition.
 
 
 
Multiple entries are separated by spaces within the double quotes.  So, for users who want both resume and systemd it would look like this:
 
{{ic|<nowiki>GRUB_CMDLINE_LINUX="resume=/dev/sdaX init=/usr/lib/systemd/systemd"</nowiki>}}
 
  
 
See [[Kernel parameters]] for more info.
 
See [[Kernel parameters]] for more info.
  
=== Manually creating grub.cfg ===
+
=== Dual-booting ===
  
{{Warning|Editing this file is strongly ''not'' recommended. The file is generated by the {{ic|grub-mkconfig}} command, and it is best to edit your {{ic|/etc/default/grub}} or one of the scripts in the {{ic|/etc/grub.d}} folder.}}
+
{{Merge|Multiboot USB drive|Same topic, substituting USB drives for SATA drives is trivial.}}
  
A basic GRUB config file uses the following options:
+
The best way to add other entries is editing {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}}. The entries in this file will be automatically added after rerunning {{ic|grub-mkconfig}}.
* {{ic|(hdX,Y)}} is the partition {{ic|Y}} on disk {{ic|X}}, partition numbers starting at 1, disk numbers starting at 0
 
* {{ic|1=set default=N}} is the default boot entry that is chosen after timeout for user action
 
* {{ic|1=set timeout=M}} is the time {{ic|M}} to wait in seconds for a user selection before default is booted
 
* {{ic|<nowiki>menuentry "title" {entry options}</nowiki>}} is a boot entry titled {{ic|title}}
 
* {{ic|1=set root=(hdX,Y)}} sets the boot partition, where the kernel and GRUB modules are stored (boot need not be a separate partition, and may simply be a directory under the "root" partition ({{ic|/}})
 
  
An example configuration:
+
==== "Shutdown" menu entry ====
  
{{hc|/boot/grub/grub.cfg|<nowiki>
+
{{bc|menuentry "System shutdown" {
# Config file for GRUB - The GNU GRand Unified Bootloader
+
echo "System shutting down..."
# /boot/grub/grub.cfg
+
halt
 +
}
 +
}}
  
# DEVICE NAME CONVERSIONS
+
==== "Restart" menu entry ====
#
 
#  Linux          Grub
 
# -------------------------
 
#  /dev/fd0        (fd0)
 
#  /dev/sda        (hd0)
 
#  /dev/sdb2      (hd1,2)
 
#  /dev/sda3      (hd0,3)
 
#
 
  
# Timeout for menu
+
{{bc|menuentry "System restart" {
set timeout=5
+
echo "System rebooting..."
 +
reboot
 +
}
 +
}}
  
# Set default boot entry as Entry 0
+
==== "Firmware setup" menu entry (UEFI only) ====
set default=0
 
  
# (0) Arch Linux
+
{{bc|menuentry "Firmware setup" {
menuentry "Arch Linux" {
+
fwsetup
  set root=(hd0,1)
 
  linux /vmlinuz-linux root=/dev/sda3 ro
 
  initrd /initramfs-linux.img
 
 
}
 
}
 +
}}
  
## (1) Windows
+
==== GNU/Linux menu entry ====
#menuentry "Windows" {
 
#  set root=(hd0,3)
 
#  chainloader +1
 
#}
 
</nowiki>}}
 
  
=== Dual-booting ===
+
Assuming that the other distribution is on partition {{ic|sda2}}:
  
{{Note|If you want GRUB to automatically search for other systems, you may wish to install {{Pkg|os-prober}}.}}
+
{{bc|1=menuentry "Other Linux" {
 +
set root=(hd0,2)
 +
linux /boot/vmlinuz (add other options here as required)
 +
initrd /boot/initrd.img (if the other kernel uses/needs one)
 +
}
 +
}}
  
==== Using grub-mkconfig ====
+
Alternatively let grub search for the right partition by ''UUID'' or ''label'':
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}}.
 
After adding the new lines, run:
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
to generate an updated {{ic|grub.cfg}}.
 
  
===== With GNU/Linux =====
+
{{bc|1=menuentry "Other Linux" {
 +
        # assuming that UUID is 763A-9CB6
 +
search --set=root --fs-uuid 763A-9CB6
  
Assuming that the other distro is on partition {{ic|sda2}}:
+
        # search by label OTHER_LINUX (make sure that partition label is unambiguous)
 +
        #search --set=root --label OTHER_LINUX
  
menuentry "Other Linux" {
+
linux /boot/vmlinuz (add other options here as required, for example: root=UUID=763A-9CB6)
  set root=(hd0,2)
+
initrd /boot/initrd.img (if the other kernel uses/needs one)
  linux /boot/vmlinuz (add other options here as required)
+
}
  initrd /boot/initrd.img (if the other kernel uses/needs one)
+
}}
}
 
  
===== With FreeBSD =====
+
==== Windows installed in UEFI/GPT Mode menu entry ====
  
Requires that FreeBSD is installed on a single partition with UFS. Assuming it is installed on {{ic|sda4}}:
+
This mode determines where the Windows bootloader resides and chain-loads it after Grub when the menu entry is selected. The main task here is finding the EFI partition and running the bootloader from it.
  
menuentry "FreeBSD" {
+
{{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.}}
  set root=(hd0,4)
 
  chainloader +1
 
}
 
  
===== With Windows =====
+
{{bc|1=if [ "${grub_platform}" == "efi" ]; then
 
+
menuentry "Microsoft Windows Vista/7/8/8.1 UEFI/GPT" {
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}}.
+
insmod part_gpt
 +
insmod fat
 +
insmod search_fs_uuid
 +
insmod chain
 +
search --fs-uuid --set=root $hints_string $fs_uuid
 +
chainloader /EFI/Microsoft/Boot/bootmgfw.efi
 +
}
 +
fi
 +
}}
  
# (2) Windows XP
+
where {{ic|$hints_string}} and {{ic|$fs_uuid}} are obtained with the following two commands.
menuentry "Windows XP" {
 
  set root="(hd0,3)"
 
  chainloader +1
 
}
 
  
If the Windows bootloader is on an entirely different hard drive than GRUB, it may be necessary to trick Windows into believing that it is the first hard drive. This was possible with {{ic|drivemap}}. Assuming GRUB is on {{ic|hd0}} and Windows is on {{ic|hd2}}, you need to add the following after {{ic|set root}}:
+
The {{ic|$fs_uuid}} command determines the UUID of the EFI partition:
  
drivemap -s hd0 hd2
+
{{hc|1=# grub-probe --target=fs_uuid ''esp''/EFI/Microsoft/Boot/bootmgfw.efi|2=
 
+
1ce5-7f28
==== With Windows via EasyBCD and NeoGRUB ====
 
 
 
Since EasyBCD's NeoGRUB currently does not understand the GRUB menu format, chainload to it by replacing the contents of your {{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
 
 
 
=== Visual configuration ===
 
 
 
In GRUB it is possible, by default, to change the look of the menu. Make sure to initialize, if not done already, GRUB graphical terminal, gfxterm, with proper video mode, gfxmode, in GRUB. This can be seen in the section [[#"No suitable mode found" error]]. This video mode is passed by GRUB to the linux kernel via 'gfxpayload' so any visual configurations need this mode in order to be in effect.
 
 
 
==== Setting the framebuffer resolution ====
 
 
 
GRUB can set the framebuffer for both GRUB itself and the kernel. The old {{ic|1=vga=}} way is deprecated. The preferred method is editing {{ic|/etc/default/grub}} as the following sample:
 
 
 
GRUB_GFXMODE=1024x768x32
 
GRUB_GFXPAYLOAD_LINUX=keep
 
 
 
To generate the changes, run:
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
 
 
The {{ic|gfxpayload}} property will make sure the kernel keeps the resolution.
 
 
 
{{Note|
 
* If this example does not work for you try to replace {{ic|1=gfxmode="1024x768x32"}} by {{ic|1=vbemode="0x105"}}. Remember to replace the specified resolution with one suitable for your screen
 
* To show all the modes you can use {{ic|1=# hwinfo --framebuffer}} (hwinfo is available in [community]), while at GRUB prompt you can use the {{ic|1=vbeinfo}} command
 
 
}}
 
}}
  
If this method does not work for you, the deprecated {{ic|1=vga=}} method will still work. Just
+
Alternatively one can run {{ic|blkid}} (as root) and read the UUID of the EFI partition from there.
add it next to the {{ic|1="GRUB_CMDLINE_LINUX_DEFAULT="}} line in {{ic|/etc/default/grub}}
 
for eg: {{ic|1="GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"}} will give you a {{ic|1024x768}} resolution.
 
  
You can choose one of these resolutions: {{ic|640×480}}, {{ic|800×600}}, {{ic|1024×768}}, {{ic|1280×1024}}, {{ic|1600×1200}}, {{ic|1920×1200}}
+
The {{ic|$hints_string}} command will determine the location of the EFI partition, in this case harddrive 0:
  
==== 915resolution hack ====
+
{{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
Some times for Intel graphic adapters neither {{ic|1=# hwinfo --framebuffer}} nor {{ic|1=vbeinfo}} will show you the desired resolution. In this case you can use {{ic|915resolution}} hack. This hack will temporarily modify video BIOS and add needed resolution. See [http://915resolution.mango-lang.org/ 915resolution's home page]
 
 
 
First you need to find a video mode which will be modified later. For that we need the GRUB command shell:
 
{{hc|sh:grub> 915resolution -l|
 
Intel 800/900 Series VBIOS Hack : version 0.5.3
 
[...]
 
'''Mode 30''' : 640x480, 8 bits/pixel
 
[...]
 
}}
 
Next, we overwrite the {{ic|Mode 30}} with {{ic|1440x900}} resolution:
 
{{hc|/etc/grub.d/00_header|
 
[...]
 
'''915resolution 30 1440 900 # Inserted line'''
 
set gfxmode&#61;${GRUB_GFXMODE}
 
[...]
 
 
}}
 
}}
Lastly we need to set {{ic|GRUB_GFXMODE}} as described earlier, regenerate GRUB configuration file and reboot to test changes:
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
# reboot
 
  
==== Background image and bitmap fonts ====
+
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.
  
GRUB comes with support for background images and bitmap fonts in {{ic|pf2}} format. The unifont font is included in the {{Pkg|grub}} package under the filename {{ic|unicode.pf2}}, or, as only ASCII characters under the name {{ic|ascii.pf2}}.
+
==== Windows installed in BIOS/MBR mode ====
  
Image formats supported include tga, png and jpeg, providing the correct modules are loaded. The maximum supported resolution depends on your hardware.
+
{{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.}}
  
Make sure you have set up the proper [[#Setting the framebuffer resolution|framebuffer resolution]].
+
{{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.}}
  
Edit {{ic|/etc/default/grub}} like this:
+
Throughout this section, it is assumed your Windows partition is {{ic|/dev/sda1}}. A different partition will change every instance of hd0,msdos1. Add the below code to {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} and regenerate {{ic|grub.cfg}} with {{ic|grub-mkconfig}} as explained above to boot Windows (XP, Vista, 7, 8 or 10) installed in BIOS/MBR mode:
GRUB_BACKGROUND="/boot/grub/myimage"
 
#GRUB_THEME="/path/to/gfxtheme"
 
GRUB_FONT="/path/to/font.pf2"
 
  
{{Note|If you have installed GRUB on a separate partition, {{ic|/boot/grub/myimage}} becomes {{ic|/grub/myimage}}.}}
+
{{Note|These menuentries will work only in Legacy 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]] .}}
  
To generate the changes and add the information into {{ic|grub.cfg}}, run:
+
In both examples {{ic|''XXXXXXXXXXXXXXXX''}} is the filesystem UUID which can be found with command {{ic|lsblk --fs}}.
# grub-mkconfig -o /boot/grub/grub.cfg
 
  
If adding the splash image was successful, the user will see {{ic|"Found background image..."}} in the terminal as the command is executed.
+
For Windows Vista/7/8/8.1/10:
If this phrase is not seen, the image information was probably not incorporated into the {{ic|grub.cfg}} file.
 
 
If the image is not displayed, check:
 
* The path and the filename in {{ic|/etc/default/grub}} are correct
 
* The image is of the proper size and format (tga, png, 8-bit jpg)
 
* The image was saved in the RGB mode, and is not indexed
 
* The console mode is not enabled in {{ic|/etc/default/grub}}
 
* The command {{ic|grub-mkconfig}} must be executed to place the background image information into the {{ic|/boot/grub/grub.cfg}} file
 
  
==== Theme ====
+
if [ "${grub_platform}" == "pc" ]; then
 +
  menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS/MBR" {
 +
    insmod part_msdos
 +
    insmod ntfs
 +
    insmod search_fs_uuid
 +
    insmod ntldr   
 +
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 ''XXXXXXXXXXXXXXXX''
 +
    ntldr /bootmgr
 +
  }
 +
fi
  
Here is an example for configuring Starfield theme which was included in GRUB package.
+
For Windows XP:
  
Edit {{ic|/etc/default/grub}}
+
if [ "${grub_platform}" == "pc" ]; then
  GRUB_THEME="/usr/share/grub/themes/starfield/theme.txt"
+
  menuentry "Microsoft Windows XP" {
 +
    insmod part_msdos
 +
    insmod ntfs
 +
    insmod search_fs_uuid
 +
    insmod ntldr   
 +
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 ''XXXXXXXXXXXXXXXX''
 +
    ntldr /ntldr
 +
  }
 +
  fi
  
Generate the changes:
+
{{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-mkconfig -o /boot/grub/grub.cfg
 
  
If configuring the theme was successful, you will see {{ic|Found theme: /usr/share/grub/themes/starfield/theme.txt}} in the terminal.
+
X:\> bootrec.exe /fixboot
Your splash image will usually not be displayed when using a theme.
+
X:\> bootrec.exe /RebuildBcd
  
==== Menu colors ====
+
Do '''not''' use {{ic|bootrec.exe /Fixmbr}} because it will wipe GRUB out.
 +
Or you can use Boot Repair function in the Troubleshooting menu - it will not wipe out GRUB but will fix most errors.
 +
Also you would better keep plugged in both the target hard drive and your bootable device '''ONLY'''. Windows usually fails to repair boot information if any other devices are connected.
 +
}}
  
You can set the menu colors in GRUB. The available colors for GRUB can be found in [https://www.gnu.org/software/grub/manual/html_node/Theme-file-format.html the GRUB Manual].
+
{{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.
Here is an example:
 
  
Edit {{ic|/etc/default/grub}}:
+
{{Note|{{ic|nn}} should be greater than 06 to ensure necessary scripts are executed first.}}
GRUB_COLOR_NORMAL="light-blue/black"
 
GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
 
 
 
Generate the changes:
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
  
==== Hidden menu ====
+
=== LVM ===
  
One of the unique features of GRUB is hiding/skipping the menu and showing it by holding {{ic|Esc}} when needed. You can also adjust whether you want to see the timeout counter.
+
If you use [[LVM]] for your {{ic|/boot}} or {{ic|/}} root partition, make sure that the {{ic|lvm}} module is preloaded:
  
Edit {{ic|/etc/default/grub}} as you wish. Here is an example where the comments from the beginning of the two lines have been removed to enable the feature, the timeout has been set to five seconds and to be shown to the user:
+
{{hc|/etc/default/grub|2=
GRUB_HIDDEN_TIMEOUT=5
+
GRUB_PRELOAD_MODULES="... lvm"
GRUB_HIDDEN_TIMEOUT_QUIET=false
+
}}
  
and run:
+
=== RAID ===
# grub-mkconfig -o /boot/grub/grub.cfg
 
  
==== Disable framebuffer ====
+
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:
  
Users who use NVIDIA proprietary driver might wish to disable GRUB's framebuffer as it can cause problems with the binary driver.
+
{{hc|/etc/default/grub|2=
 
+
GRUB_PRELOAD_MODULES="... mdraid09 mdraid1x"
To disable framebuffer, edit {{ic|/etc/default/grub}} and uncomment the following line:
+
}}
GRUB_TERMINAL_OUTPUT=console
 
 
 
and run:
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
 
 
Another option if you want to keep the framebuffer in GRUB is to revert to text mode just before starting the kernel. To do that modify the variable in {{ic|/etc/default/grub}}:
 
GRUB_GFXPAYLOAD_LINUX=text
 
 
 
and rebuild the configuration as before.
 
 
 
=== Other Options ===
 
 
 
==== LVM ====
 
 
 
If you use [[LVM]] for your {{ic|/boot}}, add the following before menuentry lines:
 
 
 
insmod lvm
 
 
 
and specify your root in the menuentry as:
 
 
 
set root=lvm/''lvm_group_name''-''lvm_logical_boot_partition_name''
 
 
 
Example:
 
 
 
# (0) Arch Linux
 
menuentry "Arch Linux" {
 
  insmod lvm
 
  set root=lvm/VolumeGroup-lv_boot
 
  # you can only set following two lines
 
  linux /vmlinuz-linux root=/dev/mapper/VolumeGroup-root ro
 
  initrd /initramfs-linux.img
 
}
 
  
==== RAID ====
+
For example, {{ic|/dev/md0}} becomes:
  
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:
+
  set root=(md/0)
  set root=(md0)
 
  
 
whereas a partitioned RAID volume (e.g. {{ic|/dev/md0p1}}) becomes:
 
whereas a partitioned RAID volume (e.g. {{ic|/dev/md0p1}}) becomes:
set root=(md0,1)
 
  
To install grub when using raid1 as the /boot partition (or using /boot housed on a raid1 root partition), on devices with GPT ef02/'BIOS boot partition', simply run grub-install on both of the drives, such as:
+
set root=(md/0,1)
grub-install --recheck --debug /dev/sda && grub-install --recheck --debug /dev/sdb
 
Where the raid1 array housing /boot is housed on /dev/sda and /dev/sdb.
 
  
==== Persistent block device naming ====
+
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:
One naming scheme for [[Persistent block device naming]] is the use of globally unique UUIDs to detect partitions instead of the "old" {{ic|/dev/sd*}}. Advantages are covered up in the above linked article.
 
  
Persistent naming via filesystem UUIDs are used by default in GRUB.
+
# grub-install --target=i386-pc --debug /dev/sda
 +
# grub-install --target=i386-pc --debug /dev/sdb
  
{{Note|The {{ic|/boot/grub.cfg}} file needs regeneration with the new UUID in {{ic|/etc/default/grub}} every time a relevant filesystem is resized or recreated. Remember this when modifying partitions & filesystems with a Live-CD.}}
+
Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}.
  
Whether to use UUIDs is controlled by an option in {{ic|/etc/default/grub}}:
+
{{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_DISABLE_LINUX_UUID=true
+
=== Multiple entries ===
  
Either way, do not forget to generate the changes:
+
For tips on managing multiple GRUB entries, for example when using both {{Pkg|linux}} and {{Pkg|linux-lts}} kernels, see [[GRUB/Tips and tricks#Multiple entries]].
# grub-mkconfig -o /boot/grub/grub.cfg
 
  
==== Using Labels ====
+
=== Encryption ===
  
It is possible to use labels, human-readable strings attached to filesystems, by using the {{ic|--label}} option to {{ic|search}}. First of all, label your existing partition:
+
==== Root partition ====
# tune2fs -L <LABEL> <PARTITION>
 
  
Then, add an entry using labels. An example of this:
+
To encrypt a root filesystem to be used with GRUB, add the {{ic|encrypt}} hook or the {{ic|sd-encrypt}} hook (if using systemd hooks) to [[mkinitcpio]]. See [[dm-crypt/System configuration#mkinitcpio]] for details, and [[Mkinitcpio#Common hooks]] for alternative encryption hooks.
  
menuentry "Arch Linux, session texte" {
+
If using the {{ic|encrypt}} hook, add the {{ic|cryptdevice}} parameter to {{ic|/etc/default/grub}}. In the example below, the {{ic|sda2}} partition has been encrypted as {{ic|/dev/mapper/cryptroot}}:
  search --label --set=root archroot
 
  linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro
 
  initrd /boot/initramfs-linux.img
 
}
 
  
==== Recall previous entry ====
+
{{hc|/etc/default/grub|2=
 
+
GRUB_CMDLINE_LINUX="cryptdevice=UUID=''device-UUID'':cryptroot"
GRUB can remember the last entry you booted from and use this as the default entry to boot from next time. This is useful if you have multiple kernels (i.e., the current Arch one and the LTS kernel as a fallback option) or operating systems. To do this, edit {{ic|/etc/default/grub}} and change the value of {{ic|GRUB_DEFAULT}}:
 
 
 
GRUB_DEFAULT=saved
 
 
 
This ensures that GRUB will default to the saved entry. To enable saving the selected entry, add the following line to {{ic|/etc/default/grub}}:
 
 
 
GRUB_SAVEDEFAULT=true
 
 
 
{{Note|Manually added menu items, e.g. Windows in {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}}, will need {{ic|savedefault}} added. Remember to regenerate([[#Generate config file]]) your configuration file.}}
 
 
 
==== Changing the default menu entry ====
 
 
 
To change the default selected entry, edit {{ic|/etc/default/grub}} and change the value of {{ic|GRUB_DEFAULT}}:
 
 
 
Using numbers :
 
GRUB_DEFAULT=0
 
Grub identifies entries in generated menu counted from zero. That means 0 for the first entry which is the default value, 1 for the second and so on.
 
 
 
Or using menu titles :
 
GRUB_DEFAULT='Arch Linux, with Linux core repo kernel'
 
 
 
{{Note|Remember to regenerate([[#Generate config file]]) your configuration file.}}
 
 
 
==== Security ====
 
 
 
If you want to secure GRUB so it is not possible for anyone to change boot parameters or use the command line, you can add a user/password combination to GRUB's configuration files. To do this, run the command {{ic|grub-mkpasswd-pbkdf2}}. Enter a password and confirm it:
 
 
 
{{hc|grub-mkpasswd-pbkdf2|
 
[...]
 
Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A
 
 
}}
 
}}
Then, add the following to {{ic|/etc/grub.d/00_header}}:
 
{{hc|/etc/grub.d/00_header|
 
cat << EOF
 
  
set superusers<nowiki>=</nowiki>"'''username'''"
+
If using the {{ic|sd-encrypt}} hook, add {{ic|rd.luks.name}}:
password_pbkdf2 '''username''' '''<password>'''
 
  
EOF
+
{{hc|/etc/default/grub|2=
 +
GRUB_CMDLINE_LINUX="rd.luks.name=''device-UUID''=cryptroot"
 
}}
 
}}
where {{ic|<password>}} is the string generated by {{ic|grub-mkpasswd_pbkdf2}}.
 
  
Regenerate your configuration file. Your GRUB command line, boot parameters and all boot entries are now protected.
+
where ''device-UUID'' is the UUID of the LUKS-encrypted device.
  
This can be relaxed and further customized with more users as described in the "Security" part of [https://www.gnu.org/software/grub/manual/grub.html#Security the GRUB manual].
+
Be sure to [[#Generate the main configuration file|generate the main configuration file]] when done.
  
==== Root encryption ====
+
For further information about bootloader configuration for encrypted devices, see [[Dm-crypt/System configuration#Boot loader]].
  
To let GRUB automatically add the kernel parameters for root encryption,
+
{{Note|If you wish to encrypt {{ic|/boot}} either as a separate partition or part of the {{ic|/}} partition, further setup is required. See [[#Boot partition]].}}
add {{ic|1=cryptdevice=/dev/yourdevice:label}} to {{ic|GRUB_CMDLINE_LINUX}} in {{ic|/etc/default/grub}}.
 
  
 
{{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}}.}}
 
{{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}}.}}
  
Example with root mapped to {{ic|/dev/mapper/root}}:
+
==== Boot partition ====
  
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:root"
+
GRUB can be set to ask for a password to open a [[LUKS]] blockdevice in order to read its configuration and load any [[initramfs]] and [[kernel]] from it. This option tries to solve the issue of having an [[Dm-crypt/Specialties#Securing_the_unencrypted_boot_partition|unencrypted boot partition]]. {{ic|/boot}} is '''not''' required to be kept in a separate partition; it may also stay under the system's root {{ic|/}} directory tree.
  
Also, disable the usage of UUIDs for the rootfs:
+
{{Warning|GRUB does not support LUKS2 headers. Make sure you do not specify {{ic|luks2}} for the type parameter when creating the encrypted partition using {{ic|cryptsetup luksFormat}}.}}
  
GRUB_DISABLE_LINUX_UUID=true
+
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}}:
  
Regenerate the configuration.
+
{{hc|/etc/default/grub|output=
 +
GRUB_ENABLE_CRYPTODISK=y
 +
}}
  
==== Boot non-default entry only once ====
+
Be sure to [[#Generate the main configuration file]] while the partition containing {{ic|/boot}} is mounted.
  
The command {{ic|grub-reboot}} is very helpful to boot another entry than the default only once. GRUB loads the entry passed in the first command line argument, when the system is rebooted the next time. Most importantly GRUB returns to loading the default entry for all future booting. Changing the configuration file or selecting an entry in the GRUB menu is not necessary.
+
Without further changes you will be prompted twice for a passhrase: the first for GRUB to unlock the {{ic|/boot}} mount point in early boot, the second to unlock the root filesystem itself as described in [[#Root partition]]. You can use a [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs|keyfile]] to avoid this.
{{Note|This requires {{ic|1=GRUB_DEFAULT=saved}} in {{ic|/etc/default/grub}} (and then regenerating {{ic|grub.cfg}}) or, in case of hand-made {{ic|grub.cfg}}, the line {{ic|1=set default="${saved_entry}"}}.}}
 
  
==== Hide GRUB unless the Shift key is held down ====
+
{{Note|
 +
* If you use a special keymap, a default GRUB installation will not know it. This is relevant for how to enter the passphrase to unlock the LUKS blockdevice.
 +
* In order to perform system updates involving the {{ic|/boot}} mount point, ensure that the encrypted {{ic|/boot}} is unlocked and mounted before performing an update. With a separate {{ic|/boot}} partition, this may be accomplished automatically on boot by using [[crypttab]] with a [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs|keyfile]].
 +
* If you experience issues getting the prompt for a password to display (errors regarding cryptouuid, cryptodisk, or "device not found"), try reinstalling grub as below appending the following to the end of your installation command:
 +
{{bc|1=# grub-install --target=x86_64-efi --efi-directory=''esp'' --bootloader-id=grub '''--modules="part_gpt part_msdos"'''}}
 +
}}
  
In order to achieve the fastest possible boot, instead of having GRUB wait for a timeout, it is possible for GRUB to hide the menu, unless the {{ic|Shift}} key is held down during GRUB's start-up.
+
=== Chainloading an Arch Linux .efi file ===
  
In order to achieve this, you should add the following line to {{ic|/etc/default/grub}}:
+
If you have an ''.efi'' file generated from following [[Secure Boot]] or other means, {{ic|/etc/grub.d/40_custom}} can be edited to add a new menu entry before regenerating {{ic|grub.cfg}} with {{ic|grub-mkconfig}}.
  
  GRUB_FORCE_HIDDEN_MENU="true"
+
{{hc|/etc/grub.d/40_custom|output=
 +
menuentry 'Arch Linux .efi' {
 +
insmod part_gpt
 +
insmod chain
 +
set root='(hdX,gptY)'
 +
chainloader /EFI/''path''/''file''.efi
 +
}
 +
}}
  
And the following file should be created:
+
== Using the command shell ==
  
{{hc|/etc/grub.d/31_hold_shift|
+
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.
<nowiki>
 
#! /bin/sh
 
set -e
 
  
# grub-mkconfig helper script.
+
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:
# Copyright (C) 2006,2007,2008,2009  Free Software Foundation, Inc.
 
#
 
# GRUB is free software: you can redistribute it and/or modify
 
# it under the terms of the GNU General Public License as published by
 
# the Free Software Foundation, either version 3 of the License, or
 
# (at your option) any later version.
 
#
 
# GRUB is distributed in the hope that it will be useful,
 
# but WITHOUT ANY WARRANTY; without even the implied warranty of
 
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 
# GNU General Public License for more details.
 
#
 
# You should have received a copy of the GNU General Public License
 
# along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
 
  
prefix="/usr"
+
grub>
exec_prefix="${prefix}"
 
datarootdir="${prefix}/share"
 
  
export TEXTDOMAIN=grub
+
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
export TEXTDOMAINDIR="${datarootdir}/locale"
 
  
. "${datarootdir}/grub/grub-mkconfig_lib"
+
grub rescue>
  
found_other_os=
+
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:
  
make_timeout () {
+
grub rescue> set prefix=(hdX,Y)/boot/grub
 +
grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
 +
rescue:grub> normal
  
  if [ "x${GRUB_FORCE_HIDDEN_MENU}" = "xtrue" ] ; then
+
=== Pager support ===
    if [ "x${1}" != "x" ] ; then
 
      if [ "x${GRUB_HIDDEN_TIMEOUT_QUIET}" = "xtrue" ] ; then
 
    verbose=
 
      else
 
    verbose=" --verbose"
 
      fi
 
  
      if [ "x${1}" = "x0" ] ; then
+
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:
    cat <<EOF
 
if [ "x\${timeout}" != "x-1" ]; then
 
  if keystatus; then
 
    if keystatus --shift; then
 
      set timeout=-1
 
    else
 
      set timeout=0
 
    fi
 
  else
 
    if sleep$verbose --interruptible 3 ; then
 
      set timeout=0
 
    fi
 
  fi
 
fi
 
EOF
 
      else
 
    cat << EOF
 
if [ "x\${timeout}" != "x-1" ]; then
 
  if sleep$verbose --interruptible ${GRUB_HIDDEN_TIMEOUT} ; then
 
    set timeout=0
 
  fi
 
fi
 
EOF
 
      fi
 
    fi
 
  fi
 
}
 
  
adjust_timeout () {
+
sh:grub> set pager=1
  if [ "x$GRUB_BUTTON_CMOS_ADDRESS" != "x" ]; then
 
    cat <<EOF
 
if cmostest $GRUB_BUTTON_CMOS_ADDRESS ; then
 
EOF
 
    make_timeout "${GRUB_HIDDEN_TIMEOUT_BUTTON}" "${GRUB_TIMEOUT_BUTTON}"
 
    echo else
 
    make_timeout "${GRUB_HIDDEN_TIMEOUT}" "${GRUB_TIMEOUT}"
 
    echo fi
 
  else
 
    make_timeout "${GRUB_HIDDEN_TIMEOUT}" "${GRUB_TIMEOUT}"
 
  fi
 
}
 
  
  adjust_timeout
+
=== Using the command shell environment to boot operating systems ===
  
    cat <<EOF
+
grub>
if [ "x\${timeout}" != "x-1" ]; then
 
  if keystatus; then
 
    if keystatus --shift; then
 
      set timeout=-1
 
    else
 
      set timeout=0
 
    fi
 
  else
 
    if sleep$verbose --interruptible 3 ; then
 
      set timeout=0
 
    fi
 
  fi
 
fi
 
EOF
 
</nowiki>
 
}}
 
  
=== Booting an ISO directly from 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'''.
  
Edit {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} to add an entry for the target ISO. When finished, update the GRUB menu as with the usual {{ic|grub-mkconfig -o /boot/grub/grub.cfg}} (as root).
+
''Chainloading'' means to load another boot-loader from the current one, ie, chain-loading.
  
==== Arch ISO ====
+
The other bootloader may be embedded at the starting of the disk(MBR) or at the starting of a partition or as an EFI file in the ESP in the case of UEFI.
  
{{Note|The following examples assume the ISO is in {{ic|/archives}} on {{ic|hd0,6}}.}}
+
==== Chainloading a partition ====
{{Tip|For thumbdrives, use something like {{ic|(hd1,$partition)}} and either {{ic|/dev/sdb'''Y'''}} for the {{ic|img_dev}} parameter or [[Persistent_block_device_naming|a persistent name]], e.g. {{ic|img_dev&#61;/dev/disk/by-label/CORSAIR}}.}}
 
  
===== x86_64 =====
+
set root=(hdX,Y)
 +
chainloader +1
 +
boot
  
menuentry "Archlinux-2013.05.01-dual.iso" --class iso {
+
X=0,1,2...
  set isofile="/archives/archlinux-2013.05.01-dual.iso"
+
Y=1,2,3...
  set partition="6"
 
  loopback loop (hd0,$partition)/$isofile
 
  linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201305 img_dev=/dev/sda$partition img_loop=$isofile earlymodules=loop
 
  initrd (loop)/arch/boot/x86_64/archiso.img
 
}
 
  
===== i686 =====
+
For example to chainload Windows stored in the first partiton of the first hard disk,
  
  menuentry "Archlinux-2013.05.01-dual.iso" --class iso {
+
  set root=(hd0,1)
  set isofile="/archives/archlinux-2013.05.01-dual.iso"
+
chainloader +1
  set partition="6"
+
boot
  loopback loop (hd0,$partition)/$isofile
 
  linux (loop)/arch/boot/i686/vmlinuz archisolabel=ARCH_201305 img_dev=/dev/sda$partition img_loop=$isofile earlymodules=loop
 
  initrd (loop)/arch/boot/i686/archiso.img
 
}
 
  
==== Ubuntu ISO ====
+
Similarly GRUB installed to a partition can be chainloaded.
  
{{Note|The example assumes that the iso is in {{ic|/archives}} on {{ic|hd0,6}}. Users must adjust the location and hdd/partition in the lines below to match their systems.}}
+
==== Chainloading a disk/drive ====
  
  menuentry "ubuntu-13.04-desktop-amd64.iso" {
+
  set root=hdX
  set isofile="/archives/ubuntu-13.04-desktop-amd64.iso"
+
chainloader +1
  loopback loop (hd0,6)/$isofile
+
boot
  linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
 
  initrd (loop)/casper/initrd.lz
 
}
 
  
menuentry "ubuntu-12.04-desktop-amd64.iso" {
+
==== Chainloading Windows/Linux installed in UEFI mode ====
  set isofile="/archives/ubuntu-12.04-desktop-amd64.iso"
 
  loopback loop (hd0,6)/$isofile
 
  linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
 
  initrd (loop)/casper/initrd.lz
 
}
 
  
==== Other ISOs ====
+
insmod ntfs
 +
set root=(hd0,gpt4)
 +
chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
 +
boot
  
Other working configurations from [http://askubuntu.com/questions/141940/how-to-boot-live-iso-images link Source].
+
{{ic|insmod ntfs}} is used for loading the ntfs file system module for loading Windows.
 +
(hd0,gpt4) or /dev/sda4 is my EFI System Partition (ESP).
 +
The entry in the ''chainloader'' line specifies the path of the ''.efi'' file to be chain-loaded.
  
== Using the command shell ==
+
==== Normal loading ====
  
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.
+
See the examples in [[#Using the rescue console]]
  
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:
+
=== Using the rescue console ===
sh:grub>
 
 
 
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
 
grub rescue>
 
 
 
The rescue shell is a restricted subset of the normal shell, offering much less functionality. If dumped to the rescue shell, first try inserting the "normal" module, then starting the "normal" shell:
 
grub rescue> set prefix=(hdX,Y)/boot/grub
 
grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
 
rescue:grub> normal
 
 
 
=== Pager support ===
 
 
 
GRUB supports pager for reading commands that provide long output (like the {{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
 
 
 
== GUI configuration tools ==
 
 
 
Following package may be installed:
 
* {{App|grub-customizer|Customize the bootloader (GRUB or BURG)|https://launchpad.net/grub-customizer|{{AUR|grub-customizer}}}}
 
* {{App|grub2-editor|KDE4 control module for configuring the GRUB bootloader|http://kde-apps.org/content/show.php?content&#61;139643|{{AUR|grub2-editor}}}}
 
* {{App|kcm-grub2|This Kcm module manages the most common settings of GRUB|http://kde-apps.org/content/show.php?content&#61;137886|{{AUR|kcm-grub2}}}}
 
* {{App|startupmanager|GUI app for changing the settings of GRUB Legacy, GRUB, Usplash and Splashy ([https://launchpad.net/startup-manager/+announcement/8300 abandonned])|http://sourceforge.net/projects/startup-manager/|{{AUR|startupmanager}}}}
 
 
 
== 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
 
 
 
== 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.
 
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.
Line 1,056: Line 490:
  
 
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=(hdX,Y)/boot/grub
  
 
where X is the physical drive number and 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=(hdX,Y)/grub}}).}}
  
 
To expand console capabilities, insert the {{ic|linux}} module:
 
To expand console capabilities, insert the {{ic|linux}} module:
grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
 
  
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path, (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}} and {{ic|insmod (hdX,Y)/grub/linux.mod}}).}}
+
grub rescue> insmod i386-pc/linux.mod
  
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar (see [[#Configuration]]).
+
or simply
 +
 
 +
grub rescue> insmod linux
 +
 
 +
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar.
  
 
An example, booting Arch Linux:
 
An example, booting Arch Linux:
 +
 
  set root=(hd0,5)
 
  set root=(hd0,5)
 
  linux /boot/vmlinuz-linux root=/dev/sda5
 
  linux /boot/vmlinuz-linux root=/dev/sda5
Line 1,073: Line 514:
 
  boot
 
  boot
  
With a separate boot partition, again change the lines accordingly:
+
With a separate boot partition (e.g. when using EFI), 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 (hdX,Y)/vmlinuz-linux root=/dev/sda6
  initrd /initramfs-linux.img
+
  initrd (hdX,Y)/initramfs-linux.img
 
  boot
 
  boot
 +
 +
{{Note|If you experienced {{ic|error: premature end of file /YOUR_KERNEL_NAME}} during execution of {{ic|linux}} command, you can try {{ic|linux16}} instead.}}
  
 
After successfully booting the Arch Linux installation, users can correct {{ic|grub.cfg}} as needed and then reinstall GRUB.
 
After successfully booting the Arch Linux installation, users can correct {{ic|grub.cfg}} as needed and then reinstall GRUB.
  
To reinstall GRUB and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Bootloader installation]] for details.
+
To reinstall GRUB and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Installation]] for details.
  
== Combining the use of UUIDs and basic scripting ==
+
== Troubleshooting ==
  
If you like the idea of using UUIDs to avoid unreliable BIOS mappings or are struggling with GRUB's syntax, here is an example boot menu item that uses UUIDs and a small script to direct GRUB to the proper disk partitions for your system. All you need to do is replace the UUIDs in the sample with the correct UUIDs for your system. The example applies to a system with a boot and root partition. You will obviously need to modify the GRUB configuration if you have additional partitions:
+
=== F2FS and other unsupported file systems ===
  
  menuentry "Arch Linux 64" {
+
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.
          # Set the UUIDs for your boot and root partition respectively
 
          set the_boot_uuid=ece0448f-bb08-486d-9864-ac3271bd8d07
 
          set the_root_uuid=c55da16f-e2af-4603-9e0b-03f5f565ec4a
 
   
 
          # (Note: This may be the same as your boot partition)
 
   
 
          # Get the boot/root devices and set them in the root and grub_boot variables
 
          search --fs-uuid $the_root_uuid --set=root
 
          search --fs-uuid $the_boot_uuid --set=grub_boot
 
   
 
          # Check to see if boot and root are equal.
 
          # If they are, then append /boot to $grub_boot (Since $grub_boot is actually the root partition)
 
          if [ $the_boot_uuid == $the_root_uuid ] ; then
 
              set grub_boot=($grub_boot)/boot
 
          else
 
              set grub_boot=($grub_boot)
 
          fi
 
   
 
          # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd
 
          linux $grub_boot/vmlinuz-linux root=/dev/disk/by-uuid/$the_root_uuid ro
 
          initrd $grub_boot/initramfs-linux.img
 
  }
 
  
== Troubleshooting ==
+
=== Intel BIOS not booting GPT ===
  
=== Intel BIOS not booting GPT ===
+
==== MBR ====
  
 
Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.
 
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 1,120: Line 544:
  
 
{{Note|The bootable-marking must be done in {{ic|fdisk}} or similar, not in GParted or others, as they will not set the bootable flag in the MBR.}}
 
{{Note|The bootable-marking must be done in {{ic|fdisk}} or similar, not in GParted or others, as they will not set the bootable flag in the MBR.}}
 +
 +
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 recent version of parted, you can use {{ic|disk_toggle pmbr_boot}} option. Afterwards verify that Disk Flags show pmbr_boot.
 +
 +
# parted /dev/sd''x'' disk_toggle pmbr_boot
 +
# parted /dev/sd''x'' print
  
 
More information is available [http://www.rodsbooks.com/gdisk/bios.html here]
 
More information is available [http://www.rodsbooks.com/gdisk/bios.html here]
 +
 +
==== 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
  
 
=== Enable debug messages ===
 
=== Enable debug messages ===
 +
 +
{{Note|This change is overwritten when [[#Generate the main configuration file]].}}
  
 
Add:
 
Add:
+
 
 
  set pager=1
 
  set pager=1
 
  set debug=all
 
  set debug=all
Line 1,141: Line 585:
 
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 ${GRUB_PREFIX_DIR} ({{ic|/boot/grub/}} in case of BIOS and UEFI systems). If GRUB UEFI was installed with {{ic|1=--boot-directory=/boot/efi/EFI}} set, then the directory is {{ic|/boot/efi/EFI/grub/}}:
+
Copy {{ic|/usr/share/grub/unicode.pf2}} to {{ic|${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
Line 1,172: Line 616:
 
  fi
 
  fi
  
As you can see for gfxterm (graphical terminal) to function properly, {{ic|unicode.pf2}} font file should exist in {{ic|${GRUB_PREFIX_DIR<nowiki>}</nowiki>}}.
+
As you can see for gfxterm (graphical terminal) to function properly, {{ic|unicode.pf2}} font file should exist in {{ic|1=${GRUB_PREFIX_DIR}}}.
  
 
=== msdos-style error message ===
 
=== msdos-style error message ===
Line 1,183: Line 627:
 
This error may occur when you try installing GRUB in a VMware container. Read more about it [https://bbs.archlinux.org/viewtopic.php?pid=581760#p581760 here]. It happens when the first partition starts just after the MBR (block 63), without the usual space of 1 MiB (2048 blocks) before the first partition. Read [[#Master Boot Record (MBR) specific instructions]]
 
This error may occur when you try installing GRUB in a VMware container. Read more about it [https://bbs.archlinux.org/viewtopic.php?pid=581760#p581760 here]. It happens when the first partition starts just after the MBR (block 63), without the usual space of 1 MiB (2048 blocks) before the first partition. Read [[#Master Boot Record (MBR) specific instructions]]
  
=== GRUB UEFI drops to shell ===
+
=== UEFI ===
  
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).
+
==== Common installation errors ====
  
=== GRUB UEFI not loaded ===
+
* If you have a problem when running ''grub-install'' with ''sysfs'' or ''procfs'' and it says you must run {{ic|modprobe efivars}}, try [[Unified Extensible Firmware Interface#Mount efivarfs]].
 +
* Without {{ic|--target}} or {{ic|--directory}} option, grub-install cannot determine for which firmware to install. In such cases {{ic|grub-install}} will print {{ic|source_dir does not exist. Please specify --target or --directory}}.
 +
* If after running grub-install you are told your partition does not look like an EFI partition then the partition is most likely not {{ic|Fat32}}.
 +
 
 +
==== 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 {{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 ====
  
 
An example of a working EFI:
 
An example of a working EFI:
 +
 
{{hc|# efibootmgr -v|
 
{{hc|# efibootmgr -v|
 
BootCurrent: 0000
 
BootCurrent: 0000
 
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\grub.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(\EfiShell.efi)
Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI
+
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 [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(\grub.efi)
  
 
=== Invalid signature ===
 
=== 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:
 
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
 
  # mv /boot/grub/device.map /boot/grub/device.map-old
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 +
 
{{ic|grub-mkconfig}} should now mention all found boot options, including Windows. If it works, remove {{ic|/boot/grub/device.map-old}}.
 
{{ic|grub-mkconfig}} should now mention all found boot options, including Windows. If it works, remove {{ic|/boot/grub/device.map-old}}.
  
Line 1,213: Line 671:
 
If booting gets stuck without any error message after GRUB loading the kernel and the initial ramdisk, try removing the {{ic|add_efi_memmap}} kernel parameter.
 
If booting gets stuck without any error message after GRUB loading the kernel and the initial ramdisk, try removing the {{ic|add_efi_memmap}} kernel parameter.
  
=== Restore GRUB Legacy ===
+
=== Arch not found from other OS ===
 +
 
 +
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}} in the [[official repositories]].
  
* Move GRUB v2 files out of the way:
+
=== Warning when installing in chroot ===
  
# mv /boot/grub /boot/grub.nonfunctional
+
When installing GRUB on a LVM system in a chroot environment (e.g. during system installation), you may receive warnings like
  
* Copy GRUB Legacy back to {{ic|/boot}}:
+
/run/lvm/lvmetad.socket: connect failed: No such file or directory
  
# cp -af /boot/grub-legacy /boot/grub
+
or
  
* Replace MBR and next 62 sectors of sda with backed up copy
+
WARNING: failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.
  
{{Warning|This command also restores the partition table, so be careful of overwriting a modified partition table with the old one. It '''will''' mess up your system.}}
+
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.
  
# dd if=/path/to/backup/first-sectors of=/dev/sdX bs=512 count=1
+
=== GRUB loads slowly ===
  
A safer way is to restore only the MBR boot code use:
+
GRUB can take a long time to load when disk space is low. Check if you have sufficient free disk space on your {{ic|/boot}} or {{ic|/}} partition when you are having problems.
  
# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=446 count=1
+
=== error: unknown filesystem ===
  
=== Arch not found from other OS ===
+
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.
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|official repositories]].
+
 
 +
=== 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|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}}
  
== References ==
+
=== Windows 8/10 not found ===
  
# Official GRUB Manual - https://www.gnu.org/software/grub/manual/grub.html
+
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.
# Ubuntu wiki page for GRUB - https://help.ubuntu.com/community/Grub2
 
# GRUB wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
 
# Wikipedia's page on [[Wikipedia:BIOS Boot partition|BIOS Boot partition]]
 
  
 
== See also ==
 
== See also ==
  
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub/grub_bios.sh A Linux Bash Shell script to compile and install GRUB for BIOS from BZR Source]
+
* [https://www.gnu.org/software/grub/manual/grub.html Official GRUB Manual]
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub/grub_uefi.sh A Linux Bash Shell script to compile and install GRUB for UEFI from BZR Source]
+
* [https://help.ubuntu.com/community/Grub2 Ubuntu wiki page for GRUB]
 +
* [https://help.ubuntu.com/community/UEFIBooting GRUB wiki page describing steps to compile for UEFI systems]
 +
* [[Wikipedia:BIOS Boot partition]]
 +
* [http://web.archive.org/web/20160424042444/http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html#Editing_etcgrub.d05_debian_theme How to configure GRUB]
 +
* [http://www.linuxjournal.com/article/4622 Boot with GRUB]

Latest revision as of 08:02, 5 May 2018

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

A boot loader is the first program that runs when a computer starts. It is responsible for selecting, loading and transferring control to an operating system kernel. The kernel, in turn, initializes the rest of the operating system.

Note: In the entire article esp denotes the mountpoint of the EFI System Partition aka ESP.

Contents

BIOS systems

GUID Partition Table (GPT) specific instructions

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

Note:
  • Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme. Read more on GUID partition tables.
  • This additional partition is only needed on a GRUB, BIOS/GPT partitioning scheme. Previously, for a GRUB, BIOS/MBR partitioning scheme, GRUB used the Post-MBR gap for the embedding the core.img). GRUB for GPT, however, does not use the Post-GPT gap to conform to GPT specifications that require 1_megabyte/2048_sector disk boundaries.
  • For UEFI systems this extra partition is not required, since no embedding of boot sectors takes place in that case. However, UEFI systems still require an EFI System Partition.

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

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

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

The 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 fdisk or gdisk create a new partition starting at sector 34 and spanning to 2047 and set the type. To have the viewable partitions begin at the base consider adding this partition last.

Master Boot Record (MBR) specific instructions

Usually the post-MBR gap (after the 512 byte MBR region and before the start of the first partition) in many MBR (or 'msdos' disklabel) partitioned systems is 31 KiB when DOS compatibility cylinder alignment issues are satisfied in the partition table. However a post-MBR gap of about 1 to 2 MiB is recommended to provide sufficient room for embedding GRUB's core.img (FS#24103). It is advisable to use a partitioning tool that supports 1 MiB partition alignment to obtain this space as well as to satisfy other non-512 byte sector issues (which are unrelated to embedding of core.img).

Installation

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

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

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

Now you must #Generate the main configuration file.

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

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

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

UEFI systems

Note:
  • It is recommended to read and understand the UEFI, GPT and 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 for an EFI System Partition

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

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

# parted /dev/sdx print

The command returns:

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

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

Installation

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

First, install the packages grub and efibootmgr: GRUB is the bootloader while efibootmgr creates bootable .efi stub entries used by the GRUB installation script.

Then follow the below steps to install GRUB:

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

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

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

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

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

Generate the main configuration file

After the installation, the main configuration file grub.cfg needs to be generated. The generation process can be influenced by a variety of options in /etc/default/grub and scripts in /etc/grub.d/; see #Configuration.

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

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

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

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

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

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

Configuration

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

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

Additional arguments

To pass custom additional arguments to the Linux image, you can set the GRUB_CMDLINE_LINUX + GRUB_CMDLINE_LINUX_DEFAULT variables in /etc/default/grub. The two are appended to each other and passed to kernel when generating regular boot entries. For the recovery boot entry, only GRUB_CMDLINE_LINUX is used in the generation.

It is not necessary to use both, but can be useful. For example, you could use GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sdaX quiet" where sdaX is your swap partition to enable resume after hibernation. This would generate a recovery boot entry without the resume and without quiet suppressing kernel messages during a boot from that menu entry. Though, the other (regular) menu entries would have them as options.

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

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

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

See Kernel parameters for more info.

Dual-booting

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

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

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

"Shutdown" menu entry

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

"Restart" menu entry

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

"Firmware setup" menu entry (UEFI only)

menuentry "Firmware setup" {
	fwsetup
}

GNU/Linux menu entry

Assuming that the other distribution is on partition sda2:

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

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

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

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

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

Windows installed in UEFI/GPT Mode menu entry

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

Note: This menuentry will work only in UEFI boot mode and only if the Windows bitness matches the UEFI bitness. It will not work in BIOS installed GRUB. See Dual boot with Windows#Windows UEFI vs BIOS limitations and Dual boot with Windows#Bootloader UEFI vs BIOS limitations for more info.
if [ "${grub_platform}" == "efi" ]; then
	menuentry "Microsoft Windows Vista/7/8/8.1 UEFI/GPT" {
		insmod part_gpt
		insmod fat
		insmod search_fs_uuid
		insmod chain
		search --fs-uuid --set=root $hints_string $fs_uuid
		chainloader /EFI/Microsoft/Boot/bootmgfw.efi
	}
fi

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

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

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

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

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

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

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

Windows installed in BIOS/MBR mode

Note: GRUB supports booting bootmgr directly and chainloading of partition boot sector is no longer required to boot Windows in a BIOS/MBR setup.
Warning: It is the system partition that has /bootmgr, not your "real" Windows partition (usually C:). In blkid output, the system partition is the one with LABEL="SYSTEM RESERVED" or LABEL="SYSTEM" and is only about 100 to 200 MB in size (much like the boot partition for Arch). See Wikipedia:System partition and boot partition for more info.

Throughout this section, it is assumed your Windows partition is /dev/sda1. A different partition will change every instance of hd0,msdos1. Add the below code to /etc/grub.d/40_custom or /boot/grub/custom.cfg and regenerate grub.cfg with grub-mkconfig as explained above to boot Windows (XP, Vista, 7, 8 or 10) installed in BIOS/MBR mode:

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

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

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

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

For Windows XP:

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

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

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

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

LVM

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

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

RAID

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

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

For example, /dev/md0 becomes:

set root=(md/0)

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

set root=(md/0,1)

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

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

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

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

Multiple entries

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

Encryption

Root partition

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

If using the encrypt hook, add the cryptdevice parameter to /etc/default/grub. In the example below, the sda2 partition has been encrypted as /dev/mapper/cryptroot:

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

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

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

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

Be sure to generate the main configuration file when done.

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

Note: If you wish to encrypt /boot either as a separate partition or part of the / partition, further setup is required. See #Boot partition.
Tip: If you are upgrading from a working GRUB Legacy configuration, check /boot/grub/menu.lst.pacsave for the correct device/label to add. Look for them after the text kernel /vmlinuz-linux.

Boot partition

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

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

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

/etc/default/grub
GRUB_ENABLE_CRYPTODISK=y

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

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

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

Chainloading an Arch Linux .efi file

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

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

Using the command shell

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

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

grub>

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

grub rescue>

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

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

Pager support

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

sh:grub> set pager=1

Using the command shell environment to boot operating systems

grub>

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

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

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

Chainloading a partition

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

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

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

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

Similarly GRUB installed to a partition can be chainloaded.

Chainloading a disk/drive

set root=hdX
chainloader +1
boot

Chainloading Windows/Linux installed in UEFI mode

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

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

Normal loading

See the examples in #Using the rescue console

Using the rescue console

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

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

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

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

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

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

To expand console capabilities, insert the linux module:

grub rescue> insmod i386-pc/linux.mod

or simply

grub rescue> insmod linux

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

An example, booting Arch Linux:

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

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

Note: Since boot is a separate partition and not part of your root partition, you must address the boot partition manually, in the same way as for the prefix variable.
set root=(hd0,5)
linux (hdX,Y)/vmlinuz-linux root=/dev/sda6
initrd (hdX,Y)/initramfs-linux.img
boot
Note: If you experienced error: premature end of file /YOUR_KERNEL_NAME during execution of linux command, you can try linux16 instead.

After successfully booting the Arch Linux installation, users can correct grub.cfg as needed and then reinstall GRUB.

To reinstall GRUB and fix the problem completely, changing /dev/sda if needed. See #Installation for details.

Troubleshooting

F2FS and other unsupported file systems

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

Intel BIOS not booting GPT

MBR

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

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

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

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

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

Enable debug messages

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

Add:

set pager=1
set debug=all

to grub.cfg.

"No suitable mode found" error

If you get this error when booting any menuentry:

error: no suitable mode found
Booting however

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

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

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

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

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

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

BIOS systems:

insmod vbe

UEFI systems:

insmod efi_gop
insmod efi_uga

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

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

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

msdos-style error message

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

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

UEFI

Common installation errors

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

Drop to rescue shell

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

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

GRUB UEFI not loaded

An example of a working EFI:

# efibootmgr -v
BootCurrent: 0000
Timeout: 3 seconds
BootOrder: 0000,0001,0002
Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\efi\grub\grub.efi)
Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\EfiShell.efi)
Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI

If the screen only goes black for a second and the next boot option is tried afterwards, according to this post, moving GRUB to the partition root can help. The boot option has to be deleted and recreated afterwards. The entry for GRUB should look like this then:

Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\grub.efi)

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 in the official repositories.

Warning when installing in chroot

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

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

or

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

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

GRUB loads slowly

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

error: unknown filesystem

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

grub-reboot not resetting

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

Old BTRFS prevents installation

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

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

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

Windows 8/10 not found

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

See also