Difference between revisions of "GRUB"

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[[Category:Boot loaders]]
 
[[Category:Boot loaders]]
 
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[[tr:GRUB2]]
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[[uk:GRUB]]
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[[zh-cn:GRUB]]
{{Article summary start}}
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[[zh-tw: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] - 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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[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].
 
+
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.
+
  
 
== Preface ==
 
== Preface ==
  
* 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]].
+
A ''bootloader'' is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the Linux kernel. The kernel, in turn, initializes the rest of the operating system. The name ''GRUB'' officially refers to version ''2'' of the software. See [https://www.gnu.org/software/grub/]. If you are looking for the article on the legacy version, see [[GRUB Legacy]].
* GRUB supports [[Btrfs]] as root (without a separate {{ic|/boot}} filesystem) compressed with either zlib or LZO
+
  
=== Notes for current GRUB Legacy users ===
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GRUB has a few root file system-specific limitations:
 +
* [[F2FS]] is not supported
  
* Upgrading from [[GRUB Legacy]] to GRUB is much the same as freshly installing GRUB, which is covered [[#Installation|below]]
+
If your root partition is on an unsupported file system, you must create a separate {{ic|/boot}} partition with a supported file system. In some cases, the development version of GRUB {{aur|grub-git}} has native support.
* 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)
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* 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]].
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* 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 ====
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== BIOS systems ==
  
Although a GRUB installation should run smoothly, it is strongly recommended to keep the GRUB Legacy files before upgrading to GRUB v2.
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=== GUID Partition Table (GPT) specific instructions ===
  
# mv /boot/grub /boot/grub-legacy
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On a BIOS/[[GPT]] configuration a [http://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html BIOS boot partition] is required.  GRUB embeds its {{ic|core.img}} into this partition.
 
+
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
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+
If unable to install GRUB2 correctly, see [[#Restore GRUB Legacy]].
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=== Preliminary requirements ===
+
 
+
==== BIOS systems ====
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===== 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.
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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.
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{{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 [[GUID Partition Table#BIOS systems|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 [[ESP]].
 
}}
 
}}
  
===== 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 BIOS boot. Select {{ic|BIOS boot}} and partition type number {{ic|4}} for ''fdisk'', {{ic|ef02}} for ''gdisk'', and {{ic|bios_grub}} for ''parted''.  This partition can be in any position order but has to be on the first 2 TiB of the disk.  This partition needs to be created before GRUB installation.  When the partition is ready, install the bootloader as per the instructions below.
  
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}}).
+
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.
  
==== UEFI systems ====
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=== Master Boot Record (MBR) specific instructions ===
  
{{Note|It is recommended to read and understand the [[Unified Extensible Firmware Interface|UEFI]], [[GUID Partition Table|GPT]] and [[UEFI Bootloaders]] pages.}}
+
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}}).
  
===== Create and Mount the UEFI System Partition =====
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=== Installation ===
  
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:
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[[Install]] the {{Pkg|grub}} package. It will replace {{AUR|grub-legacy}}, where already installed.
 
+
# mkdir -p /boot/efi
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# mount -t vfat <UEFI_SYSTEM_PARTITION> /boot/efi
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Create a {{ic|/boot/efi/EFI}} directory:
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+
# mkdir /boot/efi/EFI
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+
== Installation ==
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=== BIOS systems ===
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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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{{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.}}
 
{{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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==== Install boot files ====
 
==== Install boot files ====
  
There are 3 ways to install GRUB boot files in BIOS booting:
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There are 4 ways to install GRUB boot files in BIOS booting:
* [[#Install to GPT BIOS boot partition]] (recommended with [[GPT]])
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* [[#Install to 440-byte MBR boot code region]] (recommended with [[MBR]])
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* [[#Install to partition or partitionless disk]] (not recommended)
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* [[#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}})
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{{Note|See http://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html for additional documentation.}}
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* [[#Install to disk|Install to disk]] (recommended)
 +
* [[#Install to external USB stick|Install to external USB stick]] (for recovery)
 +
* [[#Install to partition or partitionless disk|Install to partition or partitionless disk]] (not recommended)
 +
* [[#Generate core.img alone|Generate core.img alone]] (safest method, but requires another BIOS bootloader like [[Syslinux]] to be installed to chainload {{ic|/boot/grub/i386-pc/core.img}})
  
===== Install to GPT BIOS boot partition =====
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{{Note|See https://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html for additional documentation.}}
  
[[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.
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===== Install to disk =====
  
Using GNU Parted, you can set this using a command such as the following:
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{{Note|The method is specific to installing GRUB to a partitioned (MBR or GPT) disk, with GRUB files installed to {{ic|/boot/grub}} and its first stage code installed to the 440-byte MBR boot code region (not to be confused with MBR partition table). }}
  
# parted /dev/disk set <partition-number> bios_grub on
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The following commands will:
 +
* Set up 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 in case of MBR partitioned disk
 +
* In the case of a GPT partitioned disk it will embed it in the BIOS Boot Partition , denoted by {{ic|bios_grub}} flag in parted and EF02 type code in gdisk
  
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]]}}).
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# grub-install --target=i386-pc /dev/sd''x''
 +
# grub-mkconfig -o /boot/grub/grub.cfg
  
{{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.}}
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If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks.
  
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:
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===== Install to external USB stick =====
  
# modprobe dm-mod
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Assume your USB stick's first partition is FAT32 and its partition is /dev/sdy1
# grub-install --target=i386-pc --recheck --debug /dev/sda
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where {{ic|/dev/sda}} is the destination of the installation.
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# mkdir -p /mnt/usb
 +
# mount /dev/sdy1 /mnt/usb
 +
# grub-install --target=i386-pc --debug --boot-directory=/mnt/usb/boot /dev/sdy
 +
# grub-mkconfig -o /mnt/usb/boot/grub/grub.cfg
  
Continue with [[GRUB#Generate config file]] below.
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Optionally backup configuration files of {{ic|grub.cfg}}:
 +
# mkdir -p /mnt/usb/etc/default
 +
# cp /etc/default/grub /mnt/usb/etc/default
 +
# cp -a /etc/grub.d /mnt/usb/etc
  
===== Install to 440-byte MBR boot code region =====
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  # sync; umount /mnt/usb
 
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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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+
  # modprobe dm-mod
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# grub-install --recheck /dev/sdX
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+
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.
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+
{{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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Continue with [[GRUB#Generate config file]] below.
+
  
 
===== Install to partition or partitionless disk =====
 
===== Install to partition or partitionless disk =====
 +
{{Warning|GRUB '''strongly discourages''' installation to a partition boot sector or a partitionless disk as GRUB Legacy or Syslinux does. This setup is prone to breakage, especially during updates, and is '''not supported''' by the Arch developers.}}
  
{{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.}}
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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):
  
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
 
  # chattr -i /boot/grub/i386-pc/core.img
  # grub-install --target=i386-pc --recheck --debug --force /dev/sdaX
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  # grub-install --target=i386-pc --debug --force /dev/sdaX
 
  # chattr +i /boot/grub/i386-pc/core.img
 
  # chattr +i /boot/grub/i386-pc/core.img
 +
 +
{{Note|
 +
* {{ic|/dev/sdaX}} used for example only.
 +
* {{ic|1=--target=i386-pc}} instructs {{ic|grub-install}} to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in ''grub-install''.
 +
}}
  
 
You 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}}).
 
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}}).
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  /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: 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.  
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  /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.
 
                         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:
 
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
 
  /sbin/grub-setup: error: will not proceed with blocklists
  
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  Installation finished. No error reported.
 
  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.
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The reason why {{ic|grub-setup}} does not by default allow this is because in case of partition or a partitionless disk is that GRUB relies on embedded blocklists in the partition bootsector to locate the {{ic|/boot/grub/i386-pc/core.img}} file and the prefix directory {{ic|/boot/grub}}. The sector locations of {{ic|core.img}} may change whenever the file system in the partition is being altered (files copied, deleted etc.). For more info, see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915.
  
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).
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The workaround for this is to set the immutable flag on {{ic|/boot/grub/i386-pc/core.img}} (using {{ic|chattr}} command as mentioned above) so that the sector locations of the {{ic|core.img}} file in the disk is not altered. The immutable flag on {{ic|/boot/grub/i386-pc/core.img}} needs to be set only if GRUB is installed to a partition boot sector or a partitionless disk, not in case of installation to MBR or simple generation of {{ic|core.img}} without embedding any bootsector (mentioned above).
  
Continue with [[GRUB#Generate config file]] below.
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Unfortunately, the {{ic|grub.cfg}} file that is created will not contain the proper UUID in order to boot, even if it reports no errors. see https://bbs.archlinux.org/viewtopic.php?pid=1294604#p1294604.
 
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In order to fix this issue the following commands:
===== 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 ====
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+
Finally, generate a configuration for GRUB (this is explained in greater detail in the Configuration section):
+
  
 +
# mount /dev/sdxY /mnt        #Your root partition.
 +
# mount /dev/sdxZ /mnt/boot  #Your boot partition (if you have one).
 +
# arch-chroot /mnt
 +
# pacman -S linux
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 
  # grub-mkconfig -o /boot/grub/grub.cfg
  
{{Note|The file path is {{ic|/boot/grub/grub.cfg}}, NOT {{ic|/boot/grub/i386-pc/grub.cfg}}.}}
+
===== Generate core.img alone =====
  
If GRUB complains about "no suitable mode found" while booting, go to [[#"No suitable mode found" error]].
+
To populate the {{ic|/boot/grub}} directory and generate a {{ic|/boot/grub/i386-pc/core.img}} file '''without''' embedding any GRUB bootsector code in the MBR, post-MBR region, or the partition bootsector, add {{ic|1=--grub-setup=/bin/true}} to {{ic|grub-install}}:
  
If {{ic|grub-mkconfig}} fails, convert your {{ic|/boot/grub/menu.lst}} file to {{ic|/boot/grub/grub.cfg}} using:
+
# grub-install --target=i386-pc --grub-setup=/bin/true --debug /dev/sda
  
# grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
+
{{Note|
 +
* {{ic|/dev/sda}} used for example only.
 +
* {{ic|1=--target=i386-pc}} instructs {{ic|grub-install}} to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in grub-install.
 +
}}
  
For example:
+
You can then chainload GRUB's {{ic|core.img}} from GRUB Legacy or syslinux as a Linux kernel or as a multiboot kernel (see also [[Syslinux#Chainloading]]).
  
{{hc|/boot/grub/menu.lst|<nowiki>
+
== UEFI systems ==
default=0
+
timeout=5
+
  
title  Arch Linux Stock Kernel
+
{{Note|
root  (hd0,0)
+
* It is recommended to read and understand the [[UEFI]], [[GPT]] and [[UEFI Bootloaders]] pages.
kernel /vmlinuz-linux root=/dev/sda2 ro
+
* 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.
initrd /initramfs-linux.img
+
}}
  
title  Arch Linux Stock Kernel Fallback
+
=== Check if you have GPT and an ESP ===
root  (hd0,0)
+
kernel /vmlinuz-linux root=/dev/sda2 ro
+
initrd /initramfs-linux-fallback.img
+
</nowiki>}}
+
  
{{hc|/boot/grub/grub.cfg|<nowiki>
+
An [[EFI System Partition]] (ESP) is needed on every disc you want to boot using EFI. GPT is not strictly necessary, but it is highly recommended and is the only method currently supported in this article. If you are installing Arch Linux on an EFI-capable computer with an already-working operating system, like Windows 8 for example, it is very likely that you already have an ESP. To check for GPT and for an ESP, use {{ic|parted}} as root to print the partition table of the disk you want to boot from. (We are calling it {{ic|/dev/sda}}.)
set default='0'; if [ x"$default" = xsaved ]; then load_env; set default="$saved_entry"; fi
+
set timeout=5
+
  
menuentry 'Arch Linux Stock Kernel' {
+
# parted /dev/sda print
  set root='(hd0,1)'; set legacy_hdbias='0'
+
  legacy_kernel  '/vmlinuz-linux' '/vmlinuz-linux' 'root=/dev/sda2' 'ro'
+
  legacy_initrd '/initramfs-linux.img' '/initramfs-linux.img'
+
 
+
}
+
  
menuentry 'Arch Linux Stock Kernel Fallback' {
+
For GPT, you are looking for "Partition Table: GPT". For EFI, you are looking for a small (512 MiB or less) partition with a vfat file system and the ''boot'' flag enabled. On it, there should be a directory named "EFI". If these criteria are met, this is your ESP. Make note of the partition number. You will need to know which one it is, so you can mount it later on while installing GRUB to it.
  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:
+
=== Create an ESP ===
  
sh:grub> insmod legacycfg
+
If you do not have an ESP, you will need to create one. See [[EFI System Partition]]
sh:grub> legacy_configfile ${prefix}/menu.lst
+
  
Boot into Arch and re-create the proper GRUB {{ic|/boot/grub/grub.cfg}} config file.
+
=== Installation ===
  
{{Note|This option works only in BIOS systems, not in UEFI systems.}}
+
{{Note|UEFI firmware are not implemented consistently by hardware manufacturers. The installation examples provided are intended to work on the widest range of UEFI systems possible. Those experiencing problems despite applying these methods are encouraged to share detailed information for their hardware-specific cases, especially where solving these problems. A [[GRUB/EFI examples]] article has been provided for such cases.}}
  
==== Multiboot ====
+
This section assumes you are installing GRUB for x86_64 systems (x86_64-efi). For i686 systems, replace {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
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}}
+
Make sure you are in a [[bash]] shell. For example, when booting from the Arch ISO:
  
===== Microsoft Windows installed in BIOS-MBR mode =====
+
# arch-chroot /mnt /bin/bash
  
{{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.}}
+
[[Install]] the packages {{Pkg|grub}} and {{Pkg|efibootmgr}}. ''GRUB'' is the bootloader, ''efibootmgr'' creates bootable {{ic|.efi}} stub entries used by the GRUB installation script.
  
{{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.}}
+
The following steps install the GRUB UEFI application to {{ic|''esp''/EFI/grub}}, install its modules to {{ic|/boot/grub/x86_64-efi}}, and place the bootable {{ic|grubx64.efi}} stub in {{ic|''esp''/EFI/grub}}.
  
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}}:
+
First, tell GRUB to use UEFI, set the boot directory and set the bootloader ID. Mount the ESP partition to e.g. {{ic|/boot}} or {{ic|/boot/efi}} and in the following change {{ic|''esp''}} to that mount point (usually {{ic|/boot}}):
  
For Windows Vista/7/8:
+
# grub-install --target=x86_64-efi --efi-directory=''esp'' --bootloader-id='''grub'''
  
# grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr
+
The {{ic|--bootloader-id}} is what appears in the boot options to identify the GRUB EFI boot option; make sure this is something you will recognize later. The install will create a directory of the same name under {{ic|''esp''/EFI/}} where the EFI binary bootloader will be placed.
  69B235F6749E84CE
+
{{Tip|If you use {{ic|boot}} as your bootloader-id then 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 folder called boot inside the EFI folder of the EFI partition, but the only purpose this serves is to recreate the EFI boot option for Windows.}}
  
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr
+
After the above install finished the main GRUB directory is located at {{ic|/boot/grub/}}.  
--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 =====
+
Remember to [[#Generate the main configuration file]] after finalizing further setup dependant [[#Configuration]].
  
 
{{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)
+
* While some distributions require a {{ic|/boot/efi}} or {{ic|/boot/EFI}} directory, Arch does not.
* 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
+
* {{ic|--efi-directory}} and {{ic|--bootloader-id}} are specific to GRUB UEFI. {{ic|--efi-directory}} specifies the mountpoint of the ESP. It replaces {{ic|--root-directory}}, which is deprecated.
 +
* You might note the absence of a <device_path> option (e.g.: {{ic|/dev/sda}}) in the {{ic|grub-install}} command. In fact any <device_path> provided will be ignored by the GRUB install script, as UEFI bootloaders do not use a MBR or partition boot sector at all.
 
}}
 
}}
  
The UEFI system partition will need to be mounted at {{ic|/boot/efi/}} for the GRUB install script to detect it:
+
See [[#UEFI|UEFI troubleshooting]] in case of problems.
  
# mkdir -p /boot/efi
+
=== Further reading ===
# 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:
+
Below is other relevant information regarding installing Arch via UEFI
  
# modprobe dm-mod
+
==== Alternative install method ====
# 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.}}
+
Usually, GRUB keeps all files, including configuration files, in {{ic|/boot}}, regardless of where the EFI System Partition is mounted.
  
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:
+
If you want to keep these files inside the EFI System Partition itself, add {{ic|1=--boot-directory=''esp''}} to the grub-install command:
  
# modprobe dm-mod
+
  # grub-install --target=x86_64-efi --efi-directory=''esp'' --bootloader-id=grub --boot-directory=''esp'' --debug
  # 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).
+
This puts all GRUB files in {{ic|''esp''/grub}}, instead of in {{ic|/boot/grub}}. When using this method, make sure you have ''grub-mkconfig'' put the configuration file in the same place:
  
The actual paths are:
+
# grub-mkconfig -o ''esp''/grub/grub.cfg
  
<efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi
+
Configuration is otherwise the same.
  
<boot-directory>/grub/x86_64-efi/<all modules, grub.efi, core.efi, grub.cfg>
+
==== UEFI firmware workaround ====
  
{{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}}.}}
+
Some UEFI firmware requires that the bootable {{ic|.efi}} stub have a specific name and be placed in a specific location: {{ic|''esp''/EFI/boot/bootx64.efi}} (where {{ic|''esp''}} is the UEFI partition mountpoint). Failure to do so in such instances will result in an unbootable installation. Fortunately, this will not cause any problems with other firmware that does not require this.
  
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=grub</nowiki>}}:
+
To do so, first create the necessary directory, and then copy across the grub {{ic|.efi}} stub, renaming it in the process:
  
  <efi-directory>/<EFI or efi>/<bootloader-id> == <boot-directory>/grub == /boot/efi/EFI/grub
+
  # mkdir ''esp''/EFI/boot
 +
# cp ''esp''/EFI/grub_uefi/grubx64.efi ''esp''/EFI/boot/bootx64.efi
  
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=arch_grub</nowiki>}}:
+
==== Create a 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 [[UEFI#efibootmgr]] for instructions to use {{ic|efibootmgr}} to create a menu entry. However, the problem is likely to be that you have not booted your CD/USB in UEFI mode, as in [[UEFI#Create UEFI bootable USB from ISO]].
  
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub
+
==== GRUB standalone ====
<boot-directory>/grub == /boot/efi/EFI/grub
+
  
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub</nowiki>}}:
+
This section assumes you are creating a standalone GRUB for x86_64 systems (x86_64-efi). For i686 systems, replace {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
  
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub
+
It is possible to create a {{ic|grubx64_standalone.efi}} application which has all the modules embedded in a tar archive within the UEFI application, thus removing the need for having a separate directory populated with all of the GRUB UEFI modules and other related files. This is done using the {{ic|grub-mkstandalone}} command (included in {{Pkg|grub}}) as follows:
<boot-directory>/grub == /boot/grub
+
  
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=grub</nowiki>}}:
+
# echo 'configfile ${cmdpath}/grub.cfg' > /tmp/grub.cfg
 +
# grub-mkstandalone -d /usr/lib/grub/x86_64-efi/ -O x86_64-efi --modules="part_gpt part_msdos" --fonts="unicode" --locales="en@quot" --themes="" -o "''esp''/EFI/grub/grubx64_standalone.efi"  "boot/grub/grub.cfg=/tmp/grub.cfg" -v
  
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/grub
+
Then copy the GRUB config file to {{ic|''esp''/EFI/grub/grub.cfg}} and create a UEFI Boot Manager entry for {{ic|''esp''/EFI/grub/grubx64_standalone.efi}} using [[UEFI#efibootmgr|efibootmgr]].
<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
+
The option {{ic|1=--modules="part_gpt part_msdos"}} (with the quotes) is necessary for the {{ic|${cmdpath} }} feature to work properly.
* The options {{ic|--efi-directory}} and {{ic|--bootloader-id}} are specific to GRUB UEFI
+
 
}}
 
}}
 
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.
+
{{Warning|You may find that the {{ic|grub.cfg}} file is not loaded due to {{ic|${cmdpath} }} missing a slash (i.e. {{ic|(hd1,msdos2)EFI/Boot}} instead of {{ic|(hd1,msdos2)/EFI/Boot}}) and so you are dropped into a GRUB shell. If this happens determine what {{ic|${cmdpath} }} is set to ({{ic|echo ${cmdpath} }}) and then load the config file manually (e.g. {{ic|configfile (hd1,msdos2)/EFI/Boot/grub.cfg}}).}}
  
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]].
+
==== Technical information ====
  
==== Generate config file ====
+
The GRUB EFI file always expects its config file to be at {{ic|${prefix}/grub.cfg}}. However in the standalone GRUB EFI file, the {{ic|${prefix} }} is located inside a tar archive and embedded inside the standalone GRUB EFI file itself (inside the GRUB environment, it is denoted by {{ic|"(memdisk)"}}, without quotes). This tar archive contains all the files that would be stored normally at {{ic|/boot/grub}} in case of a normal GRUB EFI install.
  
Finally, generate a configuration for GRUB (this is explained in greater detail in the Configuration section):
+
Due to this embedding of {{ic|/boot/grub}} contents inside the standalone image itself, it does not rely on actual (external) {{ic|/boot/grub}} for anything. Thus in case of standalone GRUB EFI file {{ic|1=${prefix}==(memdisk)/boot/grub}} and the standalone GRUB EFI file reads expects the config file to be at {{ic|1=${prefix}/grub.cfg==(memdisk)/boot/grub/grub.cfg}}.
  
# grub-mkconfig -o <boot-directory>/grub/grub.cfg
+
Hence to make sure the standalone GRUB EFI file reads the external {{ic|grub.cfg}} located in the same directory as the EFI file (inside the GRUB environment, it is denoted by {{ic|${cmdpath} }}), we create a simple {{ic|/tmp/grub.cfg}} which instructs GRUB to use {{ic|${cmdpath}/grub.cfg}} as its config ({{ic|configfile ${cmdpath}/grub.cfg}} command in {{ic|(memdisk)/boot/grub/grub.cfg}}). We then instruct grub-mkstandalone to copy this {{ic|/tmp/grub.cfg}} file to {{ic|${prefix}/grub.cfg}} (which is actually {{ic|(memdisk)/boot/grub/grub.cfg}}) using the option {{ic|1="boot/grub/grub.cfg=/tmp/grub.cfg"}}.
  
{{Note|The file path is {{ic|<boot-directory>/grub/grub.cfg}}, NOT {{ic|<boot-directory>/grub/x86_64-efi/grub.cfg}}.}}
+
This way, the standalone GRUB EFI file and actual {{ic|grub.cfg}} can be stored in any directory inside the EFI System Partition (as long as they are in the same directory), thus making them portable.
  
If you used {{ic|<nowiki>--boot-directory=/boot</nowiki>}}:
+
== Generate the main configuration file ==
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
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 used {{ic|<nowiki>--boot-directory=/boot/efi/EFI</nowiki>}}:
+
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-mkconfig -o /boot/efi/EFI/grub/grub.cfg
+
{{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/}}.}}
  
This is independent of the value of {{ic|--bootloader-id}} option.
+
Use the ''grub-mkconfig'' tool to generate {{ic|grub.cfg}}:
 
+
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:
+
 
+
# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \
+
--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>).
+
 
+
If you have the {{ic|grub.cfg}} at {{ic|/home/user/Desktop/grub.cfg}}, then create a temporary {{ic|/home/user/Desktop/boot/grub/}} directory, copy the {{ic|/home/user/Desktop/grub.cfg}} to {{ic|/home/user/Desktop/boot/grub/grub.cfg}}, cd into {{ic|/home/user/Desktop/boot/grub/}} and run:
+
 
+
# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \
+
--output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" "boot/grub/grub.cfg"
+
 
+
The reason to {{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.
+
 
+
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 ==
 
 
You can also choose to automatically generate or manually edit {{ic|grub.cfg}}.
 
  
 
{{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}} includes a sample {{ic|/boot/grub/grub.cfg}}; ensure your intended changes were 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 ===
+
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.
  
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:
+
{{Tip|To have ''grub-mkconfig'' search for other installed systems, [[install]] {{Pkg|os-prober}}.}}
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
== Configuration ==
  
{{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}}
+
This section only covers editing the {{ic|/etc/default/grub}} configuration file. See [[GRUB/Tips and tricks]] for more information.
  
{{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].}}
+
Remember to always [[#Generate the main configuration file]] after making changes to {{ic|/etc/default/grub}}.
  
==== Additional arguments ====
+
=== Additional arguments ===
  
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.  
+
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.
  
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.  
+
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 also have to comment out {{ic|<nowiki>#GRUB_DISABLE_RECOVERY=true</nowiki>}} in {{ic|/etc/default/grub}}.  
+
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}}.  
  
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.
+
For generating the GRUB recovery entry you also have to comment out {{ic|<nowiki>#GRUB_DISABLE_RECOVERY=true</nowiki>}} in {{ic|/etc/default/grub}}.
  
Multiple entries are separated by spaces within the double quotes.  So, for users who want both resume and systemd it would look like this:
+
You can also use {{ic|<nowiki>GRUB_CMDLINE_LINUX="resume=UUID=uuid-of-swap-partition"</nowiki>}}
{{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 ===
 
 
{{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.}}
 
 
A basic GRUB config file uses the following options:
 
* {{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:
 
 
{{hc|/boot/grub/grub.cfg|<nowiki>
 
# Config file for GRUB - The GNU GRand Unified Bootloader
 
# /boot/grub/grub.cfg
 
 
# DEVICE NAME CONVERSIONS
 
#
 
#  Linux          Grub
 
# -------------------------
 
#  /dev/fd0        (fd0)
 
#  /dev/sda        (hd0)
 
#  /dev/sdb2      (hd1,2)
 
#  /dev/sda3      (hd0,3)
 
#
 
 
# Timeout for menu
 
set timeout=5
 
 
# Set default boot entry as Entry 0
 
set default=0
 
 
# (0) Arch Linux
 
menuentry "Arch Linux" {
 
  set root=(hd0,1)
 
  linux /vmlinuz-linux root=/dev/sda3 ro
 
  initrd /initramfs-linux.img
 
}
 
 
## (1) Windows
 
#menuentry "Windows" {
 
#  set root=(hd0,3)
 
#  chainloader +1
 
#}
 
</nowiki>}}
 
  
 
=== Dual-booting ===
 
=== Dual-booting ===
  
{{Note|If you want GRUB to automatically search for other systems, you may wish to install {{Pkg|os-prober}}.}}
+
{{Merge|Multiboot USB drive|Same topic, substituting USB drives for SATA drives is trivial.}}
  
==== Using grub-mkconfig ====
+
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}}.
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:
 
After adding the new lines, run:
# grub-mkconfig -o /boot/grub/grub.cfg  
+
{{bc|<nowiki># grub-mkconfig -o /boot/grub/grub.cfg</nowiki>}}
 +
or, for UEFI-GPT Mode (As per [[#Alternative install method]]):
 +
{{bc|<nowiki># grub-mkconfig -o /boot/efi/EFI/GRUB/grub.cfg</nowiki>}}
 
to generate an updated {{ic|grub.cfg}}.
 
to generate an updated {{ic|grub.cfg}}.
  
===== With GNU/Linux =====
+
===== "Shutdown" menu entry =====
  
Assuming that the other distro is on partition {{ic|sda2}}:
+
{{bc|<nowiki>menuentry "System shutdown" {
 +
echo "System shutting down..."
 +
halt
 +
}</nowiki>}}
  
menuentry "Other Linux" {
+
===== "Restart" menu entry =====
  set root=(hd0,2)
+
  linux /boot/vmlinuz (add other options here as required)
+
  initrd /boot/initrd.img (if the other kernel uses/needs one)
+
}
+
  
===== With FreeBSD =====
+
{{bc|<nowiki>menuentry "System restart" {
 +
echo "System rebooting..."
 +
reboot
 +
}</nowiki>}}
  
Requires that FreeBSD is installed on a single partition with UFS. Assuming it is installed on {{ic|sda4}}:
+
===== GNU/Linux menu entry =====
 +
Assuming that the other distro is on partition {{ic|sda2}}:
  
menuentry "FreeBSD" {
+
{{bc|<nowiki>menuentry "Other Linux" {
  set root=(hd0,4)
+
set root=(hd0,2)
  chainloader +1
+
linux /boot/vmlinuz (add other options here as required)
}
+
initrd /boot/initrd.img (if the other kernel uses/needs one)
 +
}</nowiki>}}
  
===== With Windows =====
+
Alternatively let grub search for the right partition by ''UUID'' or ''label'':
  
This assumes that your Windows partition is {{ic|sda3}}. Remember you need to point set root and chainloader to the system reserve partition that windows made when it installed, not the actual partition windows is on. This example works if your system reserve partition is {{ic|sda3}}.
+
{{bc|<nowiki>menuentry "Other Linux" {
 +
        # assuming that UUID is 763A-9CB6
 +
search --set=root --fs-uuid 763A-9CB6
  
# (2) Windows XP
+
        # search by label OTHER_LINUX (make sure that partition label is unambiguous)
menuentry "Windows XP" {
+
        #search --set=root --label OTHER_LINUX
  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}}:
+
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)
 +
}</nowiki>}}
  
drivemap -s hd0 hd2
+
====== Encrypted GNU/Linux menuentry ======
  
==== With Windows via EasyBCD and NeoGRUB ====
+
{{bc|<nowiki>menuentry "Other Linux (Encrypted)"{
 +
      insmod luks
 +
      cryptomount (hd0,2)
 +
      set root=(crypto0)
 +
      linux /boot/vmlinuz cryptdevice=/dev/sda2:cryptroot root=/dev/mapper/cryptroot (add more options if required)
 +
      initrd /boot/initrd.img (If the other kernel uses/needs one)
 +
}</nowiki>}}
  
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:
+
===== FreeBSD menu entry =====
 +
The following three methods require that FreeBSD is installed on a single partition with UFS(v2). Assuming the nested BSD partition table is on {{ic|sda4}}:
  
default 0
+
====== Loading the kernel directly ======
timeout 1
+
{{bc|1=
 +
menuentry 'FreeBSD' {
 +
insmod ufs2
 +
set root='hd0,gpt4,bsd1'
 +
## or 'hd0,msdos4,bsd1', if using an IBM-PC (MS-DOS) style partition table
 +
kfreebsd /boot/kernel/kernel
 +
kfreebsd_loadenv /boot/device.hints
 +
set kFreeBSD.vfs.root.mountfrom=ufs:/dev/ada0s4a
 +
set kFreeBSD.vfs.root.mountfrom.options=rw
 +
}
 +
}}
  
title      Chainload into GRUB v2
+
====== Chainloading the embedded boot record ======
root       (hd0,7)
+
{{bc|1=
kernel      /boot/grub/i386-pc/core.img
+
menuentry 'FreeBSD' {
 +
insmod ufs2
 +
set root='hd0,gpt4,bsd1'
 +
chainloader +1
 +
}
 +
}}
  
=== Visual configuration ===
+
====== Running the traditional BSD 2nd stage loader ======
 +
{{bc|1=
 +
menuentry 'FreeBSD' {
 +
  insmod ufs2
 +
  set root='(hd0,4)'
 +
  kfreebsd /boot/loader
 +
}
 +
}}
  
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.
+
===== Windows installed in UEFI-GPT Mode menu entry =====
  
==== Setting the framebuffer resolution ====
+
{{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.}}
  
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:
+
{{bc|<nowiki>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</nowiki>}}
  
GRUB_GFXMODE=1024x768x32
+
where {{ic|$hints_string}} and {{ic|$fs_uuid}} are obtained with the following two commands. {{ic|$fs_uuid}}'s command:
GRUB_GFXPAYLOAD_LINUX=keep
+
  
To generate the changes, run:
+
{{hc|1=# grub-probe --target=fs_uuid $esp/EFI/Microsoft/Boot/bootmgfw.efi|2=
# grub-mkconfig -o /boot/grub/grub.cfg
+
1ce5-7f28
 
+
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
+
{{ic|$hints_string}}'s command:
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}}
+
{{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
==== 915resolution hack ====
+
 
+
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.
+
{{Poor writing|This section does not fit into the others, should be slimmed down a bit.}}
  
Make sure you have set up the proper [[#Setting the framebuffer resolution|framebuffer resolution]].
+
{{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.}}
  
Edit {{ic|/etc/default/grub}} like this:
+
{{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.}}
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}}.}}
+
Throughout this section, it is assumed your Windows partition is {{ic|/dev/sda1}}. A different partition will change every instance of hd0,msdos1. First, find the UUID of the NTFS file system of the Windows's SYSTEM PARTITION where the {{ic|bootmgr}} and its files reside. For example, if Windows {{ic|bootmgr}} exists at {{ic|/media/SYSTEM_RESERVED/bootmgr}}:
  
To generate the changes and add the information into {{ic|grub.cfg}}, run:
+
For Windows Vista/7/8/8.1:
# 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.
+
  # grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr
If this phrase is not seen, the image information was probably not incorporated into the {{ic|grub.cfg}} file.
+
69B235F6749E84CE
   
+
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 ====
+
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr
 +
--hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1
  
Here is an example for configuring Starfield theme which was included in GRUB package.
+
{{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.}}
  
Edit {{ic|/etc/default/grub}}
+
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:
GRUB_THEME="/usr/share/grub/themes/starfield/theme.txt"
+
  
Generate the changes:
+
{{Note|These menuentries will work only in Legacy BIOS boot mode. It WILL NOT WORK in uefi installed grub(2). See [[Dual boot with Windows#Windows UEFI vs BIOS limitations]] and [[Dual boot with Windows#Bootloader UEFI vs BIOS limitations]].}}
# 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.
+
For Windows Vista/7/8/8.1:
Your splash image will usually not be displayed when using a theme.
+
  
==== Menu colors ====
+
if [ "${grub_platform}" == "pc" ]; then
 +
  menuentry "Microsoft Windows Vista/7/8/8.1 BIOS-MBR" {
 +
    insmod part_msdos
 +
    insmod ntfs
 +
    insmod search_fs_uuid
 +
    insmod ntldr   
 +
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
 +
    ntldr /bootmgr
 +
  }
 +
fi
  
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].
+
For Windows XP:
Here is an example:
+
  
Edit {{ic|/etc/default/grub}}:
+
if [ "${grub_platform}" == "pc" ]; then
GRUB_COLOR_NORMAL="light-blue/black"
+
  menuentry "Microsoft Windows XP" {
GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
+
    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
 +
  }
 +
fi
  
Generate the changes:
+
{{Note|In some cases, mine I have installed GRUB before a clean Windows 8, you cannot boot Windows having an error with {{ic|\boot\bcd}} (error code {{ic|0xc000000f}}). You can fix it going to Windows Recovery Console (cmd from install disk) and executing:
  # grub-mkconfig -o /boot/grub/grub.cfg
+
  x:\> "bootrec.exe /fixboot"
 +
x:\> "bootrec.exe /RebuildBcd".
 +
Do '''not''' use {{ic|bootrec.exe /Fixmbr}} because it will wipe GRUB out.
 +
Or you can use Boot Repair function in Troubleshooting menu - it won't wipe out GRUB but will fix most error.}}
  
==== Hidden menu ====
+
{{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.
  
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.
+
{{Note|{{ic|nn}} should be greater than 06 to ensure necessary scripts are executed first.}}
  
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:
+
=== LVM ===
GRUB_HIDDEN_TIMEOUT=5
+
GRUB_HIDDEN_TIMEOUT_QUIET=false
+
  
and run:
+
If you use [[LVM]] for your {{ic|/boot}}, make sure that the {{ic|lvm}} module is preloaded:
# grub-mkconfig -o /boot/grub/grub.cfg
+
  
==== Disable framebuffer ====
+
{{hc|/etc/default/grub|2=
 +
GRUB_PRELOAD_MODULES="lvm"
 +
}}
  
Users who use NVIDIA proprietary driver might wish to disable GRUB's framebuffer as it can cause problems with the binary driver.
+
=== RAID ===
  
To disable framebuffer, edit {{ic|/etc/default/grub}} and uncomment the following line:
+
GRUB provides convenient handling of RAID volumes. You need to add {{ic|insmod mdraid09}} or {{ic|mdraid1x}} which allows you to address the volume natively. For example, {{ic|/dev/md0}} becomes:
GRUB_TERMINAL_OUTPUT=console
+
  set root=(md/0)
 
+
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 ====
+
 
+
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=(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)
+
  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 devices with GPT ef02/'BIOS boot partition', simply run grub-install on both of the drives, such as:
+
To install grub when using RAID1 as the {{ic|/boot}} partition (or using {{ic|/boot}} housed on a RAID1 root partition), on devices with GPT ef02/'BIOS boot partition', simply run ''grub-install'' on both of the drives, such as:
  grub-install --recheck --debug /dev/sda && grub-install --recheck --debug /dev/sdb
+
  # grub-install --target=i386-pc --debug /dev/sda
Where the raid1 array housing /boot is housed on /dev/sda and /dev/sdb.
+
# grub-install --target=i386-pc --debug /dev/sdb
  
==== Persistent block device naming ====
+
Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}.
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.  
+
{{Note|GRUB currently (Sep 2015) supports booting from [[Btrfs]] RAID 0/1/10, but ''not'' RAID 5/6. You may use [[mdadm]] for RAID 5/6, which is supported by GRUB.}}
  
{{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.}}
+
=== Multiple entries ===
  
Whether to use UUIDs is controlled by an option in {{ic|/etc/default/grub}}:
+
For tips on managing multiple GRUB entries, for example when using both {{Pkg|linux}} and {{Pkg|linux-lts}} kernels, see [[GRUB/Tips and tricks#Multiple entries]].
  
# GRUB_DISABLE_LINUX_UUID=true
+
=== Encryption ===
  
Either way, do not forget to generate the changes:
+
==== Root partition ====
# grub-mkconfig -o /boot/grub/grub.cfg
+
 
+
==== Using Labels ====
+
 
+
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:
+
# tune2fs -L <LABEL> <PARTITION>
+
 
+
Then, add an entry using labels. An example of this:
+
 
+
menuentry "Arch Linux, session texte" {
+
  search --label --set=root archroot
+
  linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro
+
  initrd /boot/initramfs-linux.img
+
}
+
 
+
==== Recall previous entry ====
+
 
+
GRUB can remember the last entry you booted from and use this as the default entry to boot from next time. This is useful if you have multiple kernels (i.e., the current Arch one and the LTS kernel as a fallback option) or operating systems. To do this, edit {{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 ====
+
To encrypt a root filesystem to be used with GRUB, add the {{ic|encrypt}} hook to [[mkinitcpio]]. See [[dm-crypt/System configuration#mkinitcpio]] for details, and [[Mkinitcpio#Common hooks]] for alternative encryption hooks.
  
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:
+
Then add {{ic|cryptdevice}} to {{ic|/etc/default/grub}}: In the example below, the {{ic|sda2}} partition has been encrypted as {{ic|/dev/mapper/cryptroot}}:
  
{{hc|grub-mkpasswd-pbkdf2|
+
{{hc|/etc/default/grub|2=
[...]
+
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:cryptroot"
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'''"
+
Be sure to [[#Generate the main configuration file]] when done.
password_pbkdf2 '''username''' '''<password>'''
+
  
EOF
+
For further information about bootloader configuration for encrypted devices, see [[Dm-crypt/System configuration#Boot loader]].
}}
+
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.
+
 
+
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].
+
 
+
==== Root encryption ====
+
  
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:
+
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}}:
  
GRUB_DISABLE_LINUX_UUID=true
+
{{hc|/etc/default/grub|output=
 
+
GRUB_ENABLE_CRYPTODISK=y
Regenerate the configuration.
+
 
+
==== Boot non-default entry only once ====
+
 
+
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.
+
{{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 ====
+
 
+
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.
+
 
+
In order to achieve this, you should add the following line to {{ic|/etc/default/grub}}:
+
 
+
  GRUB_FORCE_HIDDEN_MENU="true"
+
 
+
And the following file should be created:
+
 
+
{{hc|/etc/grub.d/31_hold_shift|
+
<nowiki>
+
#! /bin/sh
+
set -e
+
 
+
# grub-mkconfig helper script.
+
# Copyright (C) 2006,2007,2008,2009  Free Software Foundation, Inc.
+
#
+
# GRUB is free software: you can redistribute it and/or modify
+
# it under the terms of the GNU General Public License as published by
+
# the Free Software Foundation, either version 3 of the License, or
+
# (at your option) any later version.
+
#
+
# GRUB is distributed in the hope that it will be useful,
+
# but WITHOUT ANY WARRANTY; without even the implied warranty of
+
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+
# GNU General Public License for more details.
+
#
+
# You should have received a copy of the GNU General Public License
+
# along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+
 
+
prefix="/usr"
+
exec_prefix="${prefix}"
+
datarootdir="${prefix}/share"
+
 
+
export TEXTDOMAIN=grub
+
export TEXTDOMAINDIR="${datarootdir}/locale"
+
 
+
. "${datarootdir}/grub/grub-mkconfig_lib"
+
 
+
found_other_os=
+
 
+
make_timeout () {
+
 
+
  if [ "x${GRUB_FORCE_HIDDEN_MENU}" = "xtrue" ] ; then
+
    if [ "x${1}" != "x" ] ; then
+
      if [ "x${GRUB_HIDDEN_TIMEOUT_QUIET}" = "xtrue" ] ; then
+
    verbose=
+
      else
+
    verbose=" --verbose"
+
      fi
+
 
+
      if [ "x${1}" = "x0" ] ; then
+
    cat <<EOF
+
if [ "x\${timeout}" != "x-1" ]; then
+
  if keystatus; then
+
    if keystatus --shift; then
+
      set timeout=-1
+
    else
+
      set timeout=0
+
    fi
+
  else
+
    if sleep$verbose --interruptible 3 ; then
+
      set timeout=0
+
    fi
+
  fi
+
fi
+
EOF
+
      else
+
    cat << EOF
+
if [ "x\${timeout}" != "x-1" ]; then
+
  if sleep$verbose --interruptible ${GRUB_HIDDEN_TIMEOUT} ; then
+
    set timeout=0
+
  fi
+
fi
+
EOF
+
      fi
+
    fi
+
  fi
+
}
+
 
+
adjust_timeout () {
+
  if [ "x$GRUB_BUTTON_CMOS_ADDRESS" != "x" ]; then
+
    cat <<EOF
+
if cmostest $GRUB_BUTTON_CMOS_ADDRESS ; then
+
EOF
+
    make_timeout "${GRUB_HIDDEN_TIMEOUT_BUTTON}" "${GRUB_TIMEOUT_BUTTON}"
+
    echo else
+
    make_timeout "${GRUB_HIDDEN_TIMEOUT}" "${GRUB_TIMEOUT}"
+
    echo fi
+
  else
+
    make_timeout "${GRUB_HIDDEN_TIMEOUT}" "${GRUB_TIMEOUT}"
+
  fi
+
}
+
 
+
  adjust_timeout
+
 
+
    cat <<EOF
+
if [ "x\${timeout}" != "x-1" ]; then
+
  if keystatus; then
+
    if keystatus --shift; then
+
      set timeout=-1
+
    else
+
      set timeout=0
+
    fi
+
  else
+
    if sleep$verbose --interruptible 3 ; then
+
      set timeout=0
+
    fi
+
  fi
+
fi
+
EOF
+
</nowiki>
+
 
}}
 
}}
  
=== Booting an ISO directly from GRUB ===
+
{{Note|{{ic|1=GRUB_ENABLE_CRYPTODISK=1}} [https://savannah.gnu.org/bugs/?41524 will not work] as opposed to the request shown in GRUB 2.02-beta2.}}
  
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).
+
Be sure to [[#Generate the main configuration file]] while the partition containing {{ic|/boot}} is mounted.  
  
==== Arch ISO ====
+
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|The following examples assume the ISO is in {{ic|/archives}} on {{ic|hd0,6}}.}}
+
{{Note|
{{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}}.}}
+
* 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 [[Dm-crypt/System configuration#crypttab|crypttab]] with a [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs|keyfile]].
===== x86_64 =====
+
* 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=$esp --bootloader-id=grub '''--modules="part_gpt part_msdos"'''}}}}
menuentry "Archlinux-2013.05.01-dual.iso" --class iso {
+
  set isofile="/archives/archlinux-2013.05.01-dual.iso"
+
  set partition="6"
+
  loopback loop (hd0,$partition)/$isofile
+
  linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201305 img_dev=/dev/sda$partition img_loop=$isofile earlymodules=loop
+
  initrd (loop)/arch/boot/x86_64/archiso.img
+
}
+
 
+
===== i686 =====
+
 
+
menuentry "Archlinux-2013.05.01-dual.iso" --class iso {
+
  set isofile="/archives/archlinux-2013.05.01-dual.iso"
+
  set partition="6"
+
  loopback loop (hd0,$partition)/$isofile
+
  linux (loop)/arch/boot/i686/vmlinuz archisolabel=ARCH_201305 img_dev=/dev/sda$partition img_loop=$isofile earlymodules=loop
+
  initrd (loop)/arch/boot/i686/archiso.img
+
}
+
 
+
==== Ubuntu ISO ====
+
 
+
{{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.}}
+
 
+
menuentry "ubuntu-13.04-desktop-amd64.iso" {
+
  set isofile="/archives/ubuntu-13.04-desktop-amd64.iso"
+
  loopback loop (hd0,6)/$isofile
+
  linux (loop)/casper/vmlinuz.efi boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
+
  initrd (loop)/casper/initrd.lz
+
}
+
 
+
menuentry "ubuntu-12.04-desktop-amd64.iso" {
+
  set isofile="/archives/ubuntu-12.04-desktop-amd64.iso"
+
  loopback loop (hd0,6)/$isofile
+
  linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
+
  initrd (loop)/casper/initrd.lz
+
}
+
 
+
==== Other ISOs ====
+
 
+
Other working configurations from [http://askubuntu.com/questions/141940/how-to-boot-live-iso-images link Source].
+
  
 
== Using the command shell ==
 
== Using the command shell ==
Line 1,016: Line 569:
  
 
GRUB offers multiple shells/prompts. If there is a problem reading the menu but the bootloader is able to find the disk, you will likely be dropped to the "normal" shell:
 
GRUB offers multiple shells/prompts. If there is a problem reading the menu but the bootloader is able to find the disk, you will likely be dropped to the "normal" shell:
  sh:grub>
+
  grub>
  
 
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
 
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
Line 1,031: Line 584:
 
  sh:grub> set pager=1
 
  sh:grub> set pager=1
  
== GUI configuration tools ==
+
=== 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.
  
Following package may be installed:
+
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.
* {{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 ==
+
==== Chainloading a partition ====
  
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:
+
  set root=(hdX,Y)
parttool hd0,1 hidden+ boot-
+
parttool hd0,2 hidden+ boot-
+
parttool hd0,3 hidden- boot+
+
  set root=hd0,3
+
 
  chainloader +1
 
  chainloader +1
 
  boot
 
  boot
  
== Using the rescue console ==
+
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'' 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.
 
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 640:
  
 
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
+
  grub rescue> insmod i386-pc/linux.mod
 +
or simply
 +
grub rescue> insmod linux
  
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path, (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}} and {{ic|insmod (hdX,Y)/grub/linux.mod}}).}}
+
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar.
 
+
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar (see [[#Configuration]]).
+
  
 
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 661:
 
  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 ==
+
 
+
If you like the idea of using UUIDs to avoid unreliable BIOS mappings or are struggling with GRUB's syntax, here is an example boot menu item that uses UUIDs and a small script to direct GRUB to the proper disk partitions for your system. All you need to do is replace the UUIDs in the sample with the correct UUIDs for your system. The example applies to a system with a boot and root partition. You will obviously need to modify the GRUB configuration if you have additional partitions:
+
 
+
  menuentry "Arch Linux 64" {
+
          # Set the UUIDs for your boot and root partition respectively
+
          set the_boot_uuid=ece0448f-bb08-486d-9864-ac3271bd8d07
+
          set the_root_uuid=c55da16f-e2af-4603-9e0b-03f5f565ec4a
+
   
+
          # (Note: This may be the same as your boot partition)
+
   
+
          # Get the boot/root devices and set them in the root and grub_boot variables
+
          search --fs-uuid $the_root_uuid --set=root
+
          search --fs-uuid $the_boot_uuid --set=grub_boot
+
   
+
          # Check to see if boot and root are equal.
+
          # If they are, then append /boot to $grub_boot (Since $grub_boot is actually the root partition)
+
          if [ $the_boot_uuid == $the_root_uuid ] ; then
+
              set grub_boot=($grub_boot)/boot
+
          else
+
              set grub_boot=($grub_boot)
+
          fi
+
   
+
          # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd
+
          linux $grub_boot/vmlinuz-linux root=/dev/disk/by-uuid/$the_root_uuid ro
+
          initrd $grub_boot/initramfs-linux.img
+
  }
+
  
 
== Troubleshooting ==
 
== 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 686:
  
 
{{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.
  
 
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 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 place a file at one of the known locations.  Assuming the EFI partition is at {{ic|/boot/efi/}} this will work:
 +
 +
mkdir /boot/efi/EFI/boot
 +
cp /boot/efi/EFI/grub/grubx64.efi /boot/efi/EFI/boot/bootx64.efi
 +
 +
This solution worked for an Intel DH87MC motherboard with firmware dated Jan 2014.
  
 
=== Enable debug messages ===
 
=== Enable debug messages ===
 +
 +
{{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 720:
 
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 ${GRUB_PREFIX_DIR} ({{ic|/boot/grub/}} in case of BIOS and UEFI systems). If GRUB UEFI was installed with {{ic|1=--boot-directory=$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}
Line 1,183: Line 762:
 
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 ===
 +
 
 +
==== Common installation errors ====
 +
 
 +
* If you have a problem when running grub-install with sysfs or procfs and it says you must run {{ic|modprobe efivars}}, try [[Unified Extensible Firmware Interface#Switch to efivarfs]]{{Broken section link}}.
 +
* 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 you into the rescue shell with no errors, it may be because of a missing or misplaced {{ic|grub.cfg}}. This will happen if GRUB UEFI was installed with {{ic|--boot-directory}} and {{ic|grub.cfg}} is missing OR if the partition number of the boot partition changed (which is hard-coded into the {{ic|grubx64.efi}} file).
 
If GRUB loads but drops 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).
  
=== GRUB UEFI not loaded ===
+
==== 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 804:
 
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 ===
  
* Move GRUB v2 files out of the way:
+
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]].
  
# mv /boot/grub /boot/grub.nonfunctional
+
=== Warning when installing in chroot ===
  
* Copy GRUB Legacy back to {{ic|/boot}}:
+
When installing GRUB on a LVM system in a chroot environment (e.g. during system installation), you may receive warnings like {{ic|/run/lvm/lvmetad.socket: connect failed: No such file or directory}} or {{ic|WARNING: failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.}} This is because {{ic|/run}} is not available inside the chroot. These warnings will not prevent the system from booting, provided that everything has been done correctly, so you may continue with the installation.
  
# cp -af /boot/grub-legacy /boot/grub
+
=== GRUB loads slowly ===
  
* Replace MBR and next 62 sectors of sda with backed up copy
+
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.
  
{{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.}}
+
=== error: unknown filesystem ===
 +
GRUB may output {{ic|error: unknown filesystem}} and refuse to boot for a few reasons. If you are certain that all [[UUID]]s are correct and all filesystems are valid and supported, it may be because your [[#GUID_Partition_Table_.28GPT.29_specific_instructions|BIOS Boot Partition]] is located outside the first 2TB of the drive [https://bbs.archlinux.org/viewtopic.php?id=195948]. Use a partitioning tool of your choice to ensure this partition is located fully within the first 2TB, then reinstall and reconfigure GRUB.
  
# dd if=/path/to/backup/first-sectors of=/dev/sdX bs=512 count=1
+
=== grub-reboot not resetting ===
  
A safer way is to restore only the MBR boot code use:
+
GRUB seems to be unable to write to root BTRFS partitions [https://bbs.archlinux.org/viewtopic.php?id=166131]. If you use grub-reboot to boot into another entry it will therefore be unable to update its on-disk environment. Either run grub-reboot from the other entry (for example when switching between various distributions) or consider a different file system. You can reset a "sticky" entry by executing {{ic|grub-editenv create}} and setting {{ic|GRUB_DEFAULT<nowiki>=</nowiki>0}} in your {{ic|/etc/default/grub}} (don't forget {{ic|grub-mkconfig -o /boot/grub/grub.cfg}}).
  
# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=446 count=1
+
=== Old BTRFS prevents installation ===
  
=== Arch not found from other OS ===
+
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
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-install: warning: Attempting to install GRUB to a disk with multiple partition labels. This is not supported yet..
 +
# grub-install: error: filesystem `btrfs' doesn't 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 not found ===
  
# Official GRUB Manual - https://www.gnu.org/software/grub/manual/grub.html
+
A setting in Windows 8 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]
+
* Official GRUB Manual - https://www.gnu.org/software/grub/manual/grub.html
# [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]
+
* 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]]
 +
* http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html - quite complete description of how to configure GRUB

Latest revision as of 18:08, 11 September 2016

GRUB — not to be confused with GRUB Legacy — is the next generation of the GRand Unified Bootloader. GRUB is derived from PUPA which was a research project to develop the next generation of what is now GRUB Legacy. GRUB has been rewritten from scratch to clean up everything and provide modularity and portability [1].

Contents

Preface

A bootloader is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the Linux kernel. The kernel, in turn, initializes the rest of the operating system. The name GRUB officially refers to version 2 of the software. See [2]. If you are looking for the article on the legacy version, see GRUB Legacy.

GRUB has a few root file system-specific limitations:

  • F2FS is not supported

If your root partition is on an unsupported file system, you must create a separate /boot partition with a supported file system. In some cases, the development version of GRUB grub-gitAUR has native support.

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 ESP.

Create a mebibyte partition (+1M with fdisk or gdisk) on the disk with no file system and with partition type BIOS boot. Select BIOS boot and partition type number 4 for fdisk, ef02 for gdisk, and bios_grub for parted. This partition can be in any position order but has to be on the first 2 TiB of the disk. This partition needs to be created before GRUB installation. When the partition is ready, install the bootloader as per the instructions below.

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.

Note: Simply installing the package will not update the /boot/grub/i386-pc/core.img file and the GRUB modules in /boot/grub/i386-pc. You need to update them manually using grub-install as explained below.

Install boot files

There are 4 ways to install GRUB boot files in BIOS booting:

Install to disk
Note: The method is specific to installing GRUB to a partitioned (MBR or GPT) disk, with GRUB files installed to /boot/grub and its first stage code installed to the 440-byte MBR boot code region (not to be confused with MBR partition table).

The following commands will:

  • Set up GRUB in the 440-byte Master Boot Record boot code region
  • Populate the /boot/grub directory
  • Generate the /boot/grub/i386-pc/core.img file
  • Embed it in the 31 KiB (minimum size - varies depending on partition alignment) post-MBR gap in case of MBR partitioned disk
  • In the case of a GPT partitioned disk it will embed it in the BIOS Boot Partition , denoted by bios_grub flag in parted and EF02 type code in gdisk
# grub-install --target=i386-pc /dev/sdx
# grub-mkconfig -o /boot/grub/grub.cfg

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

Install to external USB stick

Assume your USB stick's first partition is FAT32 and its partition is /dev/sdy1

# mkdir -p /mnt/usb
# mount /dev/sdy1 /mnt/usb
# grub-install --target=i386-pc --debug --boot-directory=/mnt/usb/boot /dev/sdy
# grub-mkconfig -o /mnt/usb/boot/grub/grub.cfg

Optionally backup configuration files of grub.cfg:

# mkdir -p /mnt/usb/etc/default
# cp /etc/default/grub /mnt/usb/etc/default
# cp -a /etc/grub.d /mnt/usb/etc
# sync; umount /mnt/usb
Install to partition or partitionless disk
Warning: GRUB strongly discourages installation to a partition boot sector or a partitionless disk as GRUB Legacy or Syslinux does. This setup is prone to breakage, especially during updates, and is not supported by the Arch developers.

To set up grub to a partition boot sector, to a partitionless disk (also called superfloppy) or to a floppy disk, run (using for example /dev/sdaX as the /boot partition):

# chattr -i /boot/grub/i386-pc/core.img
# grub-install --target=i386-pc --debug --force /dev/sdaX
# chattr +i /boot/grub/i386-pc/core.img
Note:
  • /dev/sdaX used for example only.
  • --target=i386-pc instructs grub-install to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in grub-install.

You need to use the --force option to allow usage of blocklists and should not use --grub-setup=/bin/true (which is similar to simply generating core.img).

grub-install will give out warnings like which should give you the idea of what might go wrong with this approach:

/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea.
/sbin/grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.
                        However, blocklists are UNRELIABLE and their use is discouraged.

Without --force you may get the below error and grub-setup will not setup its boot code in the partition boot sector:

/sbin/grub-setup: error: will not proceed with blocklists

With --force you should get:

Installation finished. No error reported.

The reason why grub-setup does not by default allow this is because in case of partition or a partitionless disk is that GRUB relies on embedded blocklists in the partition bootsector to locate the /boot/grub/i386-pc/core.img file and the prefix directory /boot/grub. The sector locations of core.img may change whenever the file system in the partition is being altered (files copied, deleted etc.). For more info, see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915.

The workaround for this is to set the immutable flag on /boot/grub/i386-pc/core.img (using chattr command as mentioned above) so that the sector locations of the core.img file in the disk is not altered. The immutable flag on /boot/grub/i386-pc/core.img needs to be set only if GRUB is installed to a partition boot sector or a partitionless disk, not in case of installation to MBR or simple generation of core.img without embedding any bootsector (mentioned above).

Unfortunately, the grub.cfg file that is created will not contain the proper UUID in order to boot, even if it reports no errors. see https://bbs.archlinux.org/viewtopic.php?pid=1294604#p1294604. In order to fix this issue the following commands:

# mount /dev/sdxY /mnt        #Your root partition.
# mount /dev/sdxZ /mnt/boot   #Your boot partition (if you have one).
# arch-chroot /mnt
# pacman -S linux
# grub-mkconfig -o /boot/grub/grub.cfg
Generate core.img alone

To populate the /boot/grub directory and generate a /boot/grub/i386-pc/core.img file without embedding any GRUB bootsector code in the MBR, post-MBR region, or the partition bootsector, add --grub-setup=/bin/true to grub-install:

# grub-install --target=i386-pc --grub-setup=/bin/true --debug /dev/sda
Note:
  • /dev/sda used for example only.
  • --target=i386-pc instructs grub-install to install for BIOS systems only. It is recommended to always use this option to remove ambiguity in grub-install.

You can then chainload GRUB's core.img from GRUB Legacy or syslinux as a Linux kernel or as a multiboot kernel (see also Syslinux#Chainloading).

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 if you have GPT and an ESP

An EFI System Partition (ESP) is needed on every disc you want to boot using EFI. GPT is not strictly necessary, but it is highly recommended and is the only method currently supported in this article. If you are installing Arch Linux on an EFI-capable computer with an already-working operating system, like Windows 8 for example, it is very likely that you already have an ESP. To check for GPT and for an ESP, use parted as root to print the partition table of the disk you want to boot from. (We are calling it /dev/sda.)

# parted /dev/sda print

For GPT, you are looking for "Partition Table: GPT". For EFI, you are looking for a small (512 MiB or less) partition with a vfat file system and the boot flag enabled. On it, there should be a directory named "EFI". If these criteria are met, this is your ESP. Make note of the partition number. You will need to know which one it is, so you can mount it later on while installing GRUB to it.

Create an ESP

If you do not have an ESP, you will need to create one. See EFI System Partition

Installation

Note: UEFI firmware are not implemented consistently by hardware manufacturers. The installation examples provided are intended to work on the widest range of UEFI systems possible. Those experiencing problems despite applying these methods are encouraged to share detailed information for their hardware-specific cases, especially where solving these problems. A GRUB/EFI examples article has been provided for such cases.

This section assumes you are installing GRUB for x86_64 systems (x86_64-efi). For i686 systems, replace x86_64-efi with i386-efi where appropriate.

Make sure you are in a bash shell. For example, when booting from the Arch ISO:

# arch-chroot /mnt /bin/bash

Install the packages grub and efibootmgr. GRUB is the bootloader, efibootmgr creates bootable .efi stub entries used by the GRUB installation script.

The following steps install the GRUB UEFI application to esp/EFI/grub, install its modules to /boot/grub/x86_64-efi, and place the bootable grubx64.efi stub in esp/EFI/grub.

First, tell GRUB to use UEFI, set the boot directory and set the bootloader ID. Mount the ESP partition to e.g. /boot or /boot/efi and in the following change esp to that mount point (usually /boot):

# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=grub

The --bootloader-id is what appears in the boot options to identify the GRUB EFI boot option; make sure this is something you will recognize later. The install will create a directory of the same name under esp/EFI/ where the EFI binary bootloader will be placed.

Tip: If you use boot as your bootloader-id then 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 folder called boot inside the EFI folder of the EFI partition, but the only purpose this serves is to recreate the EFI boot option for Windows.

After the above install finished the main GRUB directory is located at /boot/grub/.

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

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 specifies the mountpoint of the ESP. It 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 install script, as UEFI bootloaders do not use a MBR or partition boot sector at all.

See UEFI troubleshooting in case of problems.

Further reading

Below is other relevant information regarding installing Arch via UEFI

Alternative install method

Usually, GRUB keeps all files, including configuration files, in /boot, regardless of where the EFI System Partition is mounted.

If you want to keep these files inside the EFI System Partition itself, add --boot-directory=esp to the grub-install command:

# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=grub --boot-directory=esp --debug

This puts all GRUB files in esp/grub, instead of in /boot/grub. When using this method, make sure you have grub-mkconfig put the configuration file in the same place:

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

Configuration is otherwise the same.

UEFI firmware workaround

Some UEFI firmware requires that the bootable .efi stub have a specific name and be placed in a specific location: esp/EFI/boot/bootx64.efi (where esp is the UEFI partition mountpoint). Failure to do so in such instances will result in an unbootable installation. Fortunately, this will not cause any problems with other firmware that does not require this.

To do so, first create the necessary directory, and then copy across the grub .efi stub, renaming it in the process:

# mkdir esp/EFI/boot
# cp esp/EFI/grub_uefi/grubx64.efi esp/EFI/boot/bootx64.efi

Create a GRUB entry in the firmware boot manager

grub-install automatically tries to create a menu entry in the boot manager. If it does not, then see UEFI#efibootmgr for instructions to use efibootmgr to create a menu entry. However, the problem is likely to be that you have not booted your CD/USB in UEFI mode, as in UEFI#Create UEFI bootable USB from ISO.

GRUB standalone

This section assumes you are creating a standalone GRUB for x86_64 systems (x86_64-efi). For i686 systems, replace x86_64-efi with i386-efi where appropriate.

It is possible to create a grubx64_standalone.efi application which has all the modules embedded in a tar archive within the UEFI application, thus removing the need for having a separate directory populated with all of the GRUB UEFI modules and other related files. This is done using the grub-mkstandalone command (included in grub) as follows:

# echo 'configfile ${cmdpath}/grub.cfg' > /tmp/grub.cfg
# grub-mkstandalone -d /usr/lib/grub/x86_64-efi/ -O x86_64-efi --modules="part_gpt part_msdos" --fonts="unicode" --locales="en@quot" --themes="" -o "esp/EFI/grub/grubx64_standalone.efi"  "boot/grub/grub.cfg=/tmp/grub.cfg" -v

Then copy the GRUB config file to esp/EFI/grub/grub.cfg and create a UEFI Boot Manager entry for esp/EFI/grub/grubx64_standalone.efi using efibootmgr.

Note:

The option --modules="part_gpt part_msdos" (with the quotes) is necessary for the ${cmdpath} feature to work properly.

Warning: You may find that the grub.cfg file is not loaded due to ${cmdpath} missing a slash (i.e. (hd1,msdos2)EFI/Boot instead of (hd1,msdos2)/EFI/Boot) and so you are dropped into a GRUB shell. If this happens determine what ${cmdpath} is set to (echo ${cmdpath} ) and then load the config file manually (e.g. configfile (hd1,msdos2)/EFI/Boot/grub.cfg).

Technical information

The GRUB EFI file always expects its config file to be at ${prefix}/grub.cfg. However in the standalone GRUB EFI file, the ${prefix} is located inside a tar archive and embedded inside the standalone GRUB EFI file itself (inside the GRUB environment, it is denoted by "(memdisk)", without quotes). This tar archive contains all the files that would be stored normally at /boot/grub in case of a normal GRUB EFI install.

Due to this embedding of /boot/grub contents inside the standalone image itself, it does not rely on actual (external) /boot/grub for anything. Thus in case of standalone GRUB EFI file ${prefix}==(memdisk)/boot/grub and the standalone GRUB EFI file reads expects the config file to be at ${prefix}/grub.cfg==(memdisk)/boot/grub/grub.cfg.

Hence to make sure the standalone GRUB EFI file reads the external grub.cfg located in the same directory as the EFI file (inside the GRUB environment, it is denoted by ${cmdpath} ), we create a simple /tmp/grub.cfg which instructs GRUB to use ${cmdpath}/grub.cfg as its config (configfile ${cmdpath}/grub.cfg command in (memdisk)/boot/grub/grub.cfg). We then instruct grub-mkstandalone to copy this /tmp/grub.cfg file to ${prefix}/grub.cfg (which is actually (memdisk)/boot/grub/grub.cfg) using the option "boot/grub/grub.cfg=/tmp/grub.cfg".

This way, the standalone GRUB EFI file and actual grub.cfg can be stored in any directory inside the EFI System Partition (as long as they are in the same directory), thus making them portable.

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
Note:
  • The default file path is /boot/grub/grub.cfg, not /boot/grub/i386-pc/grub.cfg. The grub includes a sample /boot/grub/grub.cfg; ensure your intended changes were 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.

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, install os-prober.

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 also have to comment out #GRUB_DISABLE_RECOVERY=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 the /etc/grub.d/40_custom or /boot/grub/custom.cfg. The entries in this file will be automatically added when running grub-mkconfig. After adding the new lines, run:

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

or, for UEFI-GPT Mode (As per #Alternative install method):

# grub-mkconfig -o /boot/efi/EFI/GRUB/grub.cfg

to generate an updated grub.cfg.

"Shutdown" menu entry
menuentry "System shutdown" {
	echo "System shutting down..."
	halt
}
"Restart" menu entry
menuentry "System restart" {
	echo "System rebooting..."
	reboot
}
GNU/Linux menu entry

Assuming that the other distro is on partition sda2:

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

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)
}
Encrypted GNU/Linux menuentry
menuentry "Other Linux (Encrypted)"{
      insmod luks
      cryptomount (hd0,2)
      set root=(crypto0)
      linux /boot/vmlinuz cryptdevice=/dev/sda2:cryptroot root=/dev/mapper/cryptroot (add more options if required)
      initrd /boot/initrd.img (If the other kernel uses/needs one)
}
FreeBSD menu entry

The following three methods require that FreeBSD is installed on a single partition with UFS(v2). Assuming the nested BSD partition table is on sda4:

Loading the kernel directly
menuentry 'FreeBSD' {
	insmod ufs2
	set root='hd0,gpt4,bsd1'
	## or 'hd0,msdos4,bsd1', if using an IBM-PC (MS-DOS) style partition table
	kfreebsd /boot/kernel/kernel
	kfreebsd_loadenv /boot/device.hints
	set kFreeBSD.vfs.root.mountfrom=ufs:/dev/ada0s4a
	set kFreeBSD.vfs.root.mountfrom.options=rw
}
Chainloading the embedded boot record
menuentry 'FreeBSD' {
	insmod ufs2
	set root='hd0,gpt4,bsd1'
	chainloader +1
}
Running the traditional BSD 2nd stage loader
menuentry 'FreeBSD' {
  insmod ufs2
  set root='(hd0,4)'
  kfreebsd /boot/loader
}
Windows installed in UEFI-GPT Mode menu entry
Note: This menuentry will work only in UEFI boot mode and only if the Windows bitness matches the UEFI bitness. It WILL NOT WORK in BIOS installed GRUB. See Dual boot with Windows#Windows UEFI vs BIOS limitations and Dual boot with Windows#Bootloader UEFI vs BIOS limitations for more info.
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. $fs_uuid's command:

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

$hints_string's command:

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

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

Windows installed in BIOS-MBR mode

Tango-edit-clear.pngThis article or section needs language, wiki syntax or style improvements.Tango-edit-clear.png

Reason: This section does not fit into the others, should be slimmed down a bit. (Discuss in Talk:GRUB#)
Note: GRUB supports booting 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 /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. First, find the UUID of the NTFS file system of the Windows's SYSTEM PARTITION where the bootmgr and its files reside. For example, if Windows bootmgr exists at /media/SYSTEM_RESERVED/bootmgr:

For Windows Vista/7/8/8.1:

# 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 bootmgr with NTLDR in the above commands. And note that there may not be a separate SYSTEM_RESERVED partition; just probe the file NTLDR on your Windows partition.

Then, add the below code to /etc/grub.d/40_custom or /boot/grub/custom.cfg and regenerate grub.cfg with grub-mkconfig as explained above to boot Windows (XP, Vista, 7 or 8) installed in BIOS-MBR mode:

Note: These menuentries will work only in Legacy BIOS boot mode. It WILL NOT WORK in uefi installed grub(2). See Dual boot with Windows#Windows UEFI vs BIOS limitations and Dual boot with Windows#Bootloader UEFI vs BIOS limitations.

For Windows Vista/7/8/8.1:

if [ "${grub_platform}" == "pc" ]; then
  menuentry "Microsoft Windows Vista/7/8/8.1 BIOS-MBR" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
    ntldr /bootmgr
  }
fi

For Windows XP:

if [ "${grub_platform}" == "pc" ]; then
  menuentry "Microsoft Windows XP" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
    ntldr /ntldr
  }
fi
Note: In some cases, mine I have installed GRUB before a clean Windows 8, 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".

Do not use bootrec.exe /Fixmbr because it will wipe GRUB out.

Or you can use Boot Repair function in Troubleshooting menu - it won't wipe out GRUB but will fix most error.

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

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

LVM

If you use LVM for your /boot, 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 add insmod mdraid09 or mdraid1x which allows you to address the volume natively. 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 devices with GPT ef02/'BIOS boot partition', 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 currently (Sep 2015) supports booting from Btrfs RAID 0/1/10, but not RAID 5/6. You may use mdadm for RAID 5/6, which is supported by GRUB.

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 to mkinitcpio. See dm-crypt/System configuration#mkinitcpio for details, and Mkinitcpio#Common hooks for alternative encryption hooks.

Then add cryptdevice 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=/dev/sda2:cryptroot"

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.

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
Note: GRUB_ENABLE_CRYPTODISK=1 will not work as opposed to the request shown in GRUB 2.02-beta2.

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"

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 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

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.

More information is available here

EFI 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 place a file at one of the known locations. Assuming the EFI partition is at /boot/efi/ this will work:

mkdir /boot/efi/EFI/boot
cp /boot/efi/EFI/grub/grubx64.efi /boot/efi/EFI/boot/bootx64.efi

This solution worked for an Intel DH87MC motherboard with firmware dated Jan 2014.

Enable debug messages

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#Switch to efivarfs[broken link: invalid section].
  • 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 you into the rescue shell with no errors, it may be because of a missing or misplaced grub.cfg. This will happen if GRUB UEFI was installed with --boot-directory and grub.cfg is missing OR if the partition number of the boot partition changed (which is hard-coded into the grubx64.efi file).

GRUB UEFI not loaded

An example of a working EFI:

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

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

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

Invalid signature

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

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

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

Boot freezes

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

Arch not found from other OS

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

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 2TB of the drive [3]. Use a partitioning tool of your choice to ensure this partition is located fully within the first 2TB, then reinstall and reconfigure GRUB.

grub-reboot not resetting

GRUB seems to be unable to write to root BTRFS partitions [4]. 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 (don't 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' doesn't 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 not found

A setting in Windows 8 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