Difference between revisions of "GRUB"

From ArchWiki
Jump to: navigation, search
m (Install to UEFI SYSTEM PARTITION)
(update interlanguage links)
(Tag: wiki-scripts)
 
Line 1: Line 1:
[[Category:Boot loaders (English)]]
+
[[Category:Boot loaders]]
{{i18n|GRUB2}}
+
[[ar:GRUB]]
[[fr:GRUB2]]
+
[[cs:GRUB]]
{{Article summary start}}
+
[[de:GRUB]]
{{Article summary text|Covers various aspects of the next generation of the GRand Unified Bootloader (GRUB2).}}
+
[[el:GRUB]]
{{Article summary heading|Overview}}
+
[[es:GRUB]]
{{Article summary text|{{Boot process overview}}}}
+
[[fa:گراب]]
{{Article summary heading|Related}}
+
[[fr:GRUB]]
{{Article summary wiki|Burg}} - Burg is a brand-new boot loader based on GRUB2. It uses a new object format which allows it to be built in a wider range of OS, including Linux/Windows/OSX/Solaris/FreeBSD, etc. It also has a highly configurable menu system which works in both text and graphic mode.
+
[[he:GRUB]]
{{Article summary heading|Resources}}
+
[[id:GRUB]]
{{Article summary link|GNU GRUB -- GNU Project|http://www.gnu.org/software/grub/}}
+
[[it:GRUB]]
{{Article summary end}}
+
[[ja:GRUB]]
 
+
[[nl:GRUB]]
[http://www.gnu.org/software/grub/ GRUB2] is the next generation of the GRand Unified Bootloader (GRUB). GRUB2 is derived from [http://www.nongnu.org/pupa/ PUPA] which was a research project to investigate the next generation of GRUB. GRUB2 has been rewritten from scratch to clean up everything and provide modularity and portability [http://www.gnu.org/software/grub/grub-faq.en.html#q1].
+
[[pt:GRUB]]
 
+
[[ru:GRUB]]
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.
+
[[zh-hans:GRUB]]
 
+
[[zh-hant:GRUB]]
{{Note|From 1.99-6 onwards GRUB2 supports Btrfs as root (without a separate {{ic|/boot}} filesystem) compressed with either zlib or LZO.}}
+
{{Related articles start}}
 
+
{{Related|Arch boot process}}
{{Note|[[Archboot]] iso is required for {{Pkg|grub2-bios}} and {{Pkg|grub2-efi-x86_64}} installation. The official installer AIF (Arch Installation Framework) based [[Archiso]] does not support it.}}
+
{{Related|Boot loaders}}
 +
{{Related|Master Boot Record}}
 +
{{Related|GUID Partition Table}}
 +
{{Related|Unified Extensible Firmware Interface}}
 +
{{Related|GRUB Legacy}}
 +
{{Related|GRUB/EFI examples}}
 +
{{Related|GRUB/Tips and tricks}}
 +
{{Related|Multiboot USB drive}}
 +
{{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].
  
 
== Preface ==
 
== Preface ==
  
Although, [[GRUB]] (i.e. version 0.9x) is the standard bootloader of Arch Linux, it is considered 'legacy' by upstream. It is being replaced by GRUB2 and [[Syslinux]] in many distributions. Upstream recommends GRUB2 >=1.99 over GRUB Legacy, even for current GRUB Legacy users.
+
A [[boot loader]] is the first software program that runs when a computer starts. It is responsible for selecting, loading and transferring control to an operating system kernel. The kernel, in turn, initializes the rest of the operating system. The name ''GRUB'' officially refers to version ''2'' of the software. If you are looking for the article on the legacy version, see [[GRUB Legacy]].
  
=== Notes for current GRUB Legacy users ===
+
GRUB has a few root file system-specific limitations:
 +
* [[F2FS]] is not supported
  
* There are differences in the commands of GRUB and GRUB2. Familiarize yourself with [http://www.gnu.org/software/grub/manual/grub.html#Commands GRUB2 commands] before proceeding (e.g. "find" has been replaced with "search").
+
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.
  
* GRUB2 is now ''modular'' and no longer requires "stage 1.5". As a result, the bootloader itself is limited -- modules are loaded from the hard drive as needed to expand functionality (e.g. for [[LVM]] or RAID support).
+
== BIOS systems ==
  
* Device naming has changed between GRUB and GRUB2. Partitions are numbered from 1 instead of 0 while drives are still numbered from 0, and prefixed with partition-table type. For example, {{ic|/dev/sda1}} would be referred to as {{ic|(hd0,msdos1)}} (for MBR) or {{ic|(hd0,gpt1)}} (for GPT) using GRUB2.
+
=== GUID Partition Table (GPT) specific instructions ===
  
=== Preliminary Requirements for GRUB2 ===
+
On a BIOS/[[GPT]] configuration, a [https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation BIOS boot partition] is required.  GRUB embeds its {{ic|core.img}} into this partition.
  
==== BIOS systems ====
+
{{Note|
 +
* Before attempting this method keep in mind that not all systems will be able to support this partitioning scheme. Read more on [[Partitioning#GUID_Partition_Table|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 {{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]].
 +
}}
  
===== [[GPT]] specific instructions =====
+
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.
  
GRUB2 in BIOS-GPT configuration requires a BIOS Boot Partition to embed its {{ic|core.img}} in the absence of post-MBR gap in GPT partitioned systems (which is taken over by the GPT Primary Header and Primary Partition table). This partition is used by GRUB2 only in BIOS-GPT setups. No such partition type exists in case of MBR partitioning (at least not for GRUB2). This partition is also not required if the system is UEFI based, as no embedding of bootsectors takes place in that case. Syslinux does not require this partition.
+
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.
  
For a BIOS-GPT configuration, create a 2 MiB partition using cgdisk or GNU Parted with no filesystem. The location of the partition in the partition table does not matter but it should be within the first 2 TiB region of the disk. It is advisable to put it somewhere in the beginning of the disk before the /boot partition. Set the partition type to "EF02" in cgdisk or {{ic|set <BOOT_PART_NUM> bios_grub on}} in GNU Parted.
+
=== Master Boot Record (MBR) specific instructions ===
  
{{Note|This partition should be created before {{ic|grub-install}} or {{ic|grub-setup}} is run or before the '''Install Bootloader''' step of the Archlinux installer (if GRUB2 BIOS is selected as bootloader).}}
+
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}}).
  
===== [[MBR]] aka msdos partitioning specific instructions =====
+
=== Installation ===
  
Usually the post-MBR gap (after the 512 byte MBR region and before the start of the 1st partition) in many MBR (or msdos disklabel) partitioned systems is 32 KiB when DOS compatibility cylinder alignment issues are satisfied in the partition table. However a post-MBR gap of about 1 to 2 MiB is recommended to provide sufficient room for embedding GRUB2's {{ic|core.img}} ([https://bugs.archlinux.org/task/24103]). It is advisable to use a partitioner which supports 1 MiB partition alignment to obtain this space as well as satisfy other non-512 byte sector issues (which are unrelated to embedding of {{ic|core.img}}).
+
[[Install]] the {{Pkg|grub}} package. It will replace {{AUR|grub-legacy}}, where already installed. Then do:
  
If you do not dual-boot with MS Windows (any version) in BIOS systems, it is advisable to switch to GPT partitioning - [[GUID_Partition_Table#Convert_from_MBR_to_GPT_without_data_loss]]
+
# grub-install --target=i386-pc /dev/sd''x''
  
{{Note|Create the 2MiB partition mentioned above BEFORE you convert to GPT. If you do not, gparted will not resize your boot partition to allow its creation, and when you reboot GRUB2 will not know where to look.}}
+
where {{ic|/dev/sd''x''}} is the [[partition]]ed disk where grub is to be installed.
  
==== UEFI systems ====
+
Now you must [[#Generate the main configuration file]].
  
===== Create and Mount the UEFI SYSTEM PARTITION =====
+
If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB on multiple physical disks.
  
Follow [[Unified_Extensible_Firmware_Interface#Create_an_UEFI_SYSTEM_PARTITION_in_Linux]] for instructions on creating a UEFI SYSTEM PARTITION. Then mount the UEFI SYSTEM PARTITION at {{ic|/boot/efi}}. It should be FAT32 formatted and should be >=200 MiB in size. If you have mounted the UEFISYS partition in some other mountpoint, replace {{ic|/boot/efi}} in the below instructions with that mountpoint:
+
{{Tip|See [[GRUB/Tips and tricks#Alternative installation methods]] for other ways to install GRUB, such as to a USB stick.}}
  
# mkdir -p /boot/efi
+
See {{man|8|grub-install}} and [https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation] for more details on the ''grub-install'' command.
# mount -t vfat <UEFISYS_PART_DEVICE> /boot/efi
 
  
Create a <UEFI_SYSTEM_PARTITION>{{ic|/efi}} directory, if it does not exist:
+
== UEFI systems ==
  
# mkdir -p /boot/efi/efi
+
{{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.
 +
}}
  
== Installation ==
+
=== Check if you have GPT and an ESP ===
  
=== During Arch Linux installation ===
+
An [[EFI System Partition]] (ESP) is needed on every disk 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.
  
* Skip the '''Install Bootloader''' step and exit the installer.
+
  # parted /dev/sd''x'' print
* Configure the network:
 
  # aif -p partial-configure-network
 
This will bring up a prompt; put in the network interface to use, (e.g., {{ic|eth0}}) and use DHCP for easy configuration.
 
* If you did not configure the installed system's {{ic|/etc/resolv.conf}} file during installation (for instance, if you plan to let DHCP generate it later), you will need to copy the one generated by AIF when it configured the network:
 
# cp /etc/resolv.conf /mnt/etc/resolv.conf
 
* If you run into network issues in the pacman update step below, you may have needed to install the {{Pkg|net-tools}} package.
 
* Check and see if the dm_mod module is loaded. If it is not, load it manually (you might need {{Pkg|grub2-bios}}).:
 
# lsmod | grep dm_mod
 
# modprobe dm-mod
 
{{Note|This is necessary at this point, and cannot be postponed after the chroot. If you try to use modprobe in a chroot environment that has a later kernel version from that of the installing device (at the time of writing, 2.6.33), modprobe will fail. This happens routinely using the Arch "net" installations.}}
 
* From the installer's live shell, chroot to the installed system:
 
# mount -o bind /dev /mnt/dev
 
# mount -t proc /proc /mnt/proc/
 
# mount -t sysfs /sys /mnt/sys/
 
# chroot /mnt bash
 
* Update pacman's database:
 
# pacman-db-upgrade
 
* Refresh the package list (with an extra {{ic|-y}} flag to force a refresh of all package lists even if they appear to be up to date):
 
# pacman -Syy
 
* Install the GRUB2 package as mentioned in the section [[#From a running Arch Linux]] (Note that the {{ic|dm-mod}} module has already been loaded, no need to do that again).
 
  
=== From a running Arch Linux ===
+
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/fat32 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. In the following of this section {{ic|''esp''}} must be substituted by it in commands.
  
==== BIOS systems ====
+
If you do not have an ESP, you will need to create one. See [[EFI System Partition]].
  
===== Backup Important Data =====
+
=== Installation ===
  
Though a GRUB2 installation should run smoothly, it is strongly recommended to make a backup before installing {{Pkg|grub2-bios}}.
+
{{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.}}
  
* copy GRUB modules and configuration
+
This section assumes you are installing GRUB for x86_64 systems (x86_64-efi). For 32-bit EFI systems (not to be confused with 32-bit CPUs), replace {{ic|x86_64-efi}} with {{ic|i386-efi}} where appropriate.
  
# cp -a /boot/grub /path/to/backup/
+
Make sure you are in a [[bash]] shell.
  
* backup the MBR and GRUB Legacy stage 1.5
+
[[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.
  
# dd if=/dev/sdX of=/path/to/backup/first-sectors bs=512 count=63
+
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}}.
  
Replace /dev/sdaX with your actual disk path.
+
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_mount''}} to that mount point (usually {{ic|/boot}}):
  
{{Note|This command backs up the partition table too. Be careful while restoring if you've changed your partition setup in the meantime}}
+
# grub-install --target=x86_64-efi --efi-directory=''esp_mount'' --bootloader-id='''grub'''
  
To backup only the MBR boot code use:
+
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.
 +
{{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.}}
  
# dd if=/dev/sdX of=/path/to/backup/mbr-boot-code bs=440 count=1
+
After the above install finished the main GRUB directory is located at {{ic|/boot/grub/}}.
  
You may now lightly remove {{ic|/boot/grub}} with:
+
Remember to [[#Generate the main configuration file]] after finalizing [[#Configuration]].
  
# rm -rf /boot/grub
+
{{Note|
 +
* While some distributions require a {{ic|/boot/efi}} or {{ic|/boot/EFI}} directory, Arch does not.
 +
* {{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.
 +
}}
  
and follow the instructions below. You know that if things get nasty, you could reboot your system thanks to an installation media and:
+
See [[#UEFI|UEFI troubleshooting]] in case of problems. Additionally see [[GRUB/Tips and tricks#UEFI further reading]].
  
* move old GRUB Legacy or GRUB2 files out of the way
+
== Generate the main configuration file ==
  
# mv /boot/grub /boot/grub.nonfunctional
+
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]].
  
* copy GRUB Legacy back to {{ic|/boot}}
+
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.
  
# cp -a /path/to/backup/grub /boot/
+
{{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/}}.}}
  
* replace MBR and next 62 sectors of sda with backed up copy (DANGEROUS!)
+
Use the ''grub-mkconfig'' tool to generate {{ic|grub.cfg}}:
  
  # dd if=/path/to/backup/first-sectors of=/dev/sdX bs=512 count=63
+
  # grub-mkconfig -o /boot/grub/grub.cfg
  
{{Note|This command also restores the partition table so be careful.}}
+
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.
  
To restore only the MBR boot code use:
+
{{Tip|To have ''grub-mkconfig'' search for other installed systems and automatically add them to the menu, [[install]] the {{Pkg|os-prober}} package and [[mount]] the partitions that contain other systems.}}
  
# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=440 count=1
+
{{Note|
 +
* The default file path is {{ic|/boot/grub/grub.cfg}}, not {{ic|/boot/grub/i386-pc/grub.cfg}}. The {{Pkg|grub}} package includes a sample {{ic|/boot/grub/grub.cfg}}; ensure your intended changes are written to this file.
 +
* If you are trying to run ''grub-mkconfig'' in a chroot or ''systemd-nspawn'' container, you might notice that it does not work, complaining that ''grub-probe'' cannot get the "canonical path of /dev/sdaX". In this case, try using ''arch-chroot'' as described in the [https://bbs.archlinux.org/viewtopic.php?pid&#61;1225067#p1225067 BBS post].
 +
}}
  
===== Install grub2-bios package =====
+
== Configuration ==
  
The GRUB2 package can be installed with pacman (and will replace {{Pkg|grub}}, if it is installed).
+
This section only covers editing the {{ic|/etc/default/grub}} configuration file. See [[GRUB/Tips and tricks]] for more information.
 
# pacman -S grub2-bios
 
  
{{Note|Simply installing the package won't update the {{ic|/boot/grub/i386-pc/core.img}} file and the GRUB2 modules in {{ic|/boot/grub/i386-pc}}. You need to update them manually using {{ic|grub-install}} as explained below.}}
+
Remember to always [[#Generate the main configuration file]] after making changes to {{ic|/etc/default/grub}}.
  
Also load the device-mapper kernel module without which {{ic|grub-probe}} does not reliably detect disks and partitions:
+
=== Additional arguments ===
  
# modprobe dm-mod
+
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.
  
===== Install grub2-bios boot files =====
+
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.
  
There are 3 ways to install GRUB2 boot files in BIOS booting:
+
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}}.  
*[[#Install_to_440-byte_MBR_boot_code_region]] (recommended) ,
 
*[[#Install_to_Partition_or_Partitionless_Disk]] (not recommended),
 
*[[#Generate_core.img_alone]] (safest method, but requires another BIOS bootloader like [[grub-legacy]] or [[syslinux]] to be installed to chainload {{ic|/boot/grub/i386-pc/core.img}} ).  
 
  
====== Install to 440-byte MBR boot code region ======
+
For generating the GRUB recovery entry you have to ensure that {{ic|GRUB_DISABLE_RECOVERY}} is not set to {{ic|true}} in {{ic|/etc/default/grub}}.
  
To setup {{ic|grub2-bios}} in the 440-byte Master Boot Record boot code region, populate the {{ic|/boot/grub}} directory, generate the {{ic|/boot/grub/i386-pc/core.img}} file, and embed it in the 32 KiB (minimum size - varies depending on partition alignment) post-MBR gap (MBR disks) or in BIOS Boot Partition (GPT disks), run:
+
You can also use {{ic|<nowiki>GRUB_CMDLINE_LINUX="resume=UUID=uuid-of-swap-partition"</nowiki>}}
  
# grub-install --directory=/usr/lib/grub/i386-pc --target=i386-pc --boot-directory=/boot --recheck --debug /dev/sda
+
See [[Kernel parameters]] for more info.
  
where {{ic|/dev/sda}} is the destination of the installation (in this case the MBR of the first SATA disk). If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB2 on multiple physical disks.
+
=== Dual-booting ===
  
The {{ic|--no-floppy}} tells {{ic|grub2-bios}} utilities not to search for any floppy devices which reduces the overall execution time of {{ic|grub-install}} on many systems (it will also prevent the issue below from occurring). Otherwise you get an error that looks like this:
+
{{Merge|Multiboot USB drive|Same topic, substituting USB drives for SATA drives is trivial.}}
  
grub-probe: error: Cannot get the real path of '/dev/fd0'
+
The best way to add other entries is editing {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}}. The entries in this file will be automatically added after rerunning {{ic|grub-mkconfig}}.
Auto-detection of a filesystem module failed.
 
Please specify the module with the option '--modules' explicitly.
 
  
{{Note|{{ic|--no-floppy}} has been removed from {{ic|grub-install}} in 2.00~beta2 upstream release, and replaced with {{ic|--allow-floppy}}.}}
+
==== "Shutdown" menu entry ====
  
{{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/}}.}}
+
{{bc|<nowiki>menuentry "System shutdown" {
 +
echo "System shutting down..."
 +
halt
 +
}</nowiki>}}
  
====== Install to Partition or Partitionless Disk ======
+
==== "Restart" menu entry ====
  
{{Note|{{ic|grub2-bios}} (any version - including upstream Bazaar repo) does not encourage installation to a partition boot sector or a partitionless disk like GRUB Legacy or syslinux does. Neither do the Arch devs.}}
+
{{bc|<nowiki>menuentry "System restart" {
 +
echo "System rebooting..."
 +
reboot
 +
}</nowiki>}}
  
To setup {{ic|grub2-bios}} to a partition boot sector, to a partitionless disk (also called superfloppy) or to a floppy disk, run (using for example /dev/sda1 as the /boot partition)
+
==== "Firmware setup" menu entry (UEFI only) ====
 
# chattr -i /boot/grub/i386-pc/core.img
 
# grub-install --directory=/usr/lib/grub/i386-pc --target=i386-pc --boot-directory=/boot --recheck --force --debug /dev/sda1
 
# chattr +i /boot/grub/i386-pc/core.img
 
  
You need to use the {{ic|--force}} option to allow usage of blocklists and should not use {{ic|1=--grub-setup=/bin/true}} (which is similar to simply generating {{ic|core.img}}).
+
{{bc|<nowiki>menuentry "Firmware setup" {
 +
fwsetup
 +
}</nowiki>}}
  
{{ic|grub-install}} will give out warnings like which should give you the idea of what might go wrong with this approach.
+
==== GNU/Linux menu entry ====
 +
Assuming that the other distro is on partition {{ic|sda2}}:
  
/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea.
+
{{bc|<nowiki>menuentry "Other Linux" {
/sbin/grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.  
+
set root=(hd0,2)
                        However, blocklists are UNRELIABLE and their use is discouraged.
+
linux /boot/vmlinuz (add other options here as required)
 +
initrd /boot/initrd.img (if the other kernel uses/needs one)
 +
}</nowiki>}}
  
Without {{ic|--force}} you may get the below error and {{ic|grub-setup}} will not setup its boot code in the partition boot sector.
+
Alternatively let grub search for the right partition by ''UUID'' or ''label'':
 
/sbin/grub-setup: error: will not proceed with blocklists
 
  
With {{ic|--force}} you should get
+
{{bc|<nowiki>menuentry "Other Linux" {
 +
        # assuming that UUID is 763A-9CB6
 +
search --set=root --fs-uuid 763A-9CB6
  
Installation finished. No error reported.
+
        # search by label OTHER_LINUX (make sure that partition label is unambiguous)
 +
        #search --set=root --label OTHER_LINUX
  
The reason why {{ic|grub-setup}} does not by default allow this is because in case of partition or a partitionless disk is that {{ic|grub2-bios}} relies on embedded blocklists in the partition bootsector to locate the {{ic|/boot/grub/i386-pc/core.img}} file and the prefix dir {{ic|/boot/grub}}. The sector locations of {{ic|core.img}} may change whenever the filesystem in the partition is being altered (files copied, deleted etc.). For more info see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915.
+
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>}}
  
The workaround for this is to set the immutable flag on {{ic|/boot/grub/i386-pc/core.img}} (using chattr command as mentioned above) so that the sector locations of the {{ic|core.img}} file in the disk is not altered. The immutable flag on {{ic|/boot/grub/i386-pc/core.img}} needs to be set only if {{ic|grub2-bios}} is installed to a partition boot sector or a partitionless disk, not in case of installtion to MBR or simple generation of {{ic|core.img}} without embedding any bootsector (mentioned above).
+
==== Windows installed in UEFI-GPT Mode menu entry ====
  
====== Generate core.img alone ======
+
This mode determines where the Windows bootloader resides and chain-loads it after Grub when the menu entry is selected. The main task here is finding the EFI partition and running the bootloader from it.
  
To populate the {{ic|/boot/grub}} directory and generate a {{ic|/boot/grub/i386-pc/core.img}} file '''without''' embedding any {{ic|grub2-bios}} bootsector code in the MBR, post-MBR region, or the partition bootsector, add {{ic|1=--grub-setup=/bin/true}} to {{ic|grub-install}}:
+
{{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-install --directory=/usr/lib/grub/i386-pc --target=i386-pc --grub-setup=/bin/true --boot-directory=/boot --recheck --debug /dev/sda
 
  
You can then chainload GRUB2's {{{ic|core.img}} from GRUB Legacy or syslinux as a Linux kernel or a multiboot kernel.
+
{{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>}}
  
===== Generate GRUB2 BIOS Config file =====
+
where {{ic|$hints_string}} and {{ic|$fs_uuid}} are obtained with the following two commands.
  
Finally, generate a configuration for GRUB2 (this is explained in greater detail in the Configuration section):
+
The {{ic|$fs_uuid}} command determines the UUID of the EFI partition:
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
{{hc|1=# grub-probe --target=fs_uuid $esp/EFI/Microsoft/Boot/bootmgfw.efi|2=
 +
1ce5-7f28
 +
}}
  
{{Note|The file path is {{ic|/boot/grub/grub.cfg}}, NOT {{ic|/boot/grub/i386-pc/grub.cfg}}.}}
+
Alternatively one can run {{ic|blkid}} (as root) and read the UUID of the EFI partition from there.
  
If grub2 complains about "no suitable mode found" while booting, go to [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]].
+
The {{ic|$hints_string}} command will determine the location of the EFI partition, in this case harddrive 0:
  
If {{ic|grub-mkconfig}} fails, convert your {{ic|/boot/grub/menu.lst}} file to {{ic|/boot/grub/grub.cfg}} using:
+
{{hc|1=# grub-probe --target=hints_string $esp/EFI/Microsoft/Boot/bootmgfw.efi|2=
 
+
  --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
# grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
+
}}
 
 
For example:
 
 
 
{{hc|/boot/grub/menu.lst|<nowiki>
 
default=0
 
timeout=5
 
 
 
title Arch Linux Stock Kernel
 
root  (hd0,0)
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux.img
 
 
 
title  Arch Linux Stock Kernel Fallback
 
root  (hd0,0)
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux-fallback.img
 
</nowiki>}}
 
 
 
{{hc|/boot/grub/grub.cfg|<nowiki>
 
set default='0'; if [ x"$default" = xsaved ]; then load_env; set default="$saved_entry"; fi
 
set timeout=5
 
 
 
menuentry 'Arch Linux Stock Kernel' {
 
  set root='(hd0,1)'; set legacy_hdbias='0'
 
  legacy_kernel  '/vmlinuz-linux' '/vmlinuz-linux' 'root=/dev/sda2' 'ro'
 
  legacy_initrd '/initramfs-linux.img' '/initramfs-linux.img'
 
 
 
}
 
 
 
menuentry 'Arch Linux Stock Kernel Fallback' {
 
  set root='(hd0,1)'; set legacy_hdbias='0'
 
  legacy_kernel  '/vmlinuz-linux' '/vmlinuz-linux' 'root=/dev/sda2' 'ro'
 
  legacy_initrd '/initramfs-linux-fallback.img' '/initramfs-linux-fallback.img'
 
}
 
</nowiki>}}
 
 
 
If you forgot to create a GRUB2 {{ic|/boot/grub/grub.cfg}} config file and simply rebooted into GRUB2 Command Shell, type:
 
 
 
sh:grub> insmod legacycfg
 
sh:grub> legacy_configfile ${prefix}/menu.lst
 
  
Boot into Arch and re-create the proper GRUB2 {{ic|/boot/grub/grub.cfg}} config file.
+
These two commands assume the ESP Windows uses is mounted at {{ic|$esp}}. There might be case differences in the path to Windows's EFI file, what with being Windows, and all.
  
{{Note|This option works only in BIOS systems, not in UEFI systems.}}
+
==== Windows installed in BIOS-MBR mode ====
  
===== Multiboot in BIOS =====
+
{{Note|GRUB supports booting {{ic|bootmgr}} directly and [https://www.gnu.org/software/grub/manual/grub.html#Chain_002dloading chainloading] of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.}}
  
====== Boot Microsoft Windows installed in BIOS-MBR mode ======
+
{{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.}}
  
{{Note|GRUB2 supports booting {{ic|bootmgr}} directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.}}
+
Throughout this section, it is assumed your Windows partition is {{ic|/dev/sda1}}. A different partition will change every instance of hd0,msdos1. Add the below code to {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} and regenerate {{ic|grub.cfg}} with {{ic|grub-mkconfig}} as explained above to boot Windows (XP, Vista, 7, 8 or 10) installed in BIOS-MBR mode:
  
Find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the {{ic|bootmgr}} and its files reside. For example, if Windows {{ic|bootmgr}} exists at {{ic|/media/Windows/bootmgr}}:
+
{{Note|These menuentries will work only in Legacy BIOS boot mode. It will not work in UEFI installed GRUB. See [[Dual boot with Windows#Windows UEFI vs BIOS limitations]] and [[Dual boot with Windows#Bootloader UEFI vs BIOS limitations]] .}}
  
# grub-probe --target=fs_uuid /media/Windows/bootmgr
+
''In both examples ''69B235F6749E84CE'' is the partition UUID which can be found with command ''lsblk --fs''.''
69B235F6749E84CE
 
  
Then, add the below code to {{ic|/etc/grub.d/40_custom}} and regenerate {{ic|grub.cfg}} with {{ic|grub-mkconfig}} as explained above to chainload Windows (Vista, 7 or 8) installed in BIOS-MBR mode:
+
For Windows Vista/7/8/8.1/10:
  
  menuentry "Microsoft Windows 7 BIOS-MBR" {
+
  if [ "${grub_platform}" == "pc" ]; then
 +
  menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS-MBR" {
 
     insmod part_msdos
 
     insmod part_msdos
 
     insmod ntfs
 
     insmod ntfs
 
     insmod search_fs_uuid
 
     insmod search_fs_uuid
 
     insmod ntldr     
 
     insmod ntldr     
     search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
+
     search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
 
     ntldr /bootmgr
 
     ntldr /bootmgr
  }
+
  }
 +
  fi
  
For Windows XP
+
For Windows XP:
  
  menuentry "Microsoft Windows XP" {
+
  if [ "${grub_platform}" == "pc" ]; then
 +
  menuentry "Microsoft Windows XP" {
 
     insmod part_msdos
 
     insmod part_msdos
 
     insmod ntfs
 
     insmod ntfs
 
     insmod search_fs_uuid
 
     insmod search_fs_uuid
 
     insmod ntldr     
 
     insmod ntldr     
     search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
+
     search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
 
     ntldr /ntldr
 
     ntldr /ntldr
  }
+
  }
 +
  fi
  
==== [[UEFI]] systems ====
+
{{Note|In some cases, GRUB may be installed without a clean Windows 8, in which case you cannot boot Windows without having an error with {{ic|\boot\bcd}} (error code {{ic|0xc000000f}}). You can fix it by going to Windows Recovery Console (cmd from install disk) and executing:
 +
x:\> "bootrec.exe /fixboot"
 +
x:\> "bootrec.exe /RebuildBcd".
 +
Do '''not''' use {{ic|bootrec.exe /Fixmbr}} because it will wipe GRUB out.
 +
Or you can use Boot Repair function in the Troubleshooting menu - it will not wipe out GRUB but will fix most errors.
 +
Also you would better keep plugged in both the target hard drive and your bootable device '''ONLY'''. Windows usually fails to repair boot information if any other devices are connected.}}
  
===== Install grub2-uefi package =====
+
{{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|Unless specified as EFI 1.x , EFI and UEFI terms are used interchangeably to denote UEFI 2.x firmware. Also unless stated explicitely, the instructions are general and not Mac specific. Some of them may not work or may be different in Macs. Apple's EFI implementation is neither a EFI 1.x version nor UEFI 2.x version but mixes up both. This kind of firmware does not fall under any one UEFI Specification version and is therefore not a standard UEFI firmware.}}
+
{{Note|{{ic|nn}} should be greater than 06 to ensure necessary scripts are executed first.}}
  
GRUB2 UEFI bootloader is available in Arch Linux only from version 1.99~rc1. To install, first [https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interface#Detecting_UEFI_Firmware_Arch Detect which UEFI firmware arch] you have (either x86_64 or i386).
+
=== LVM ===
  
Depending on that, install the appropriate package
+
If you use [[LVM]] for your {{ic|/boot}}, make sure that the {{ic|lvm}} module is preloaded:
  
For 64-bit aka x86_64 UEFI firmware:
+
{{hc|/etc/default/grub|2=
# pacman -S grub2-efi-x86_64
+
GRUB_PRELOAD_MODULES="lvm"
 +
}}
  
For 32-bit aka i386 UEFI firmware:
+
=== RAID ===
# pacman -S grub2-efi-i386
 
  
{{Note|Simply installing the package won't update the {{ic|grub.efi}} file and the GRUB2 modules in the UEFI System Partition. You need to do this manually using {{ic|grub-install}} as explained below.}}
+
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:
 +
set root=(md/0)
  
Also load the device-mapper kernel module without which {{ic|grub-probe}} does not reliably detect disks and partitions:
+
whereas a partitioned RAID volume (e.g. {{ic|/dev/md0p1}}) becomes:
 +
set root=(md/0,1)
  
  # modprobe dm-mod
+
To install grub when using RAID1 as the {{ic|/boot}} partition (or using {{ic|/boot}} housed on a RAID1 root partition), on devices with GPT ef02/'BIOS boot partition', simply run ''grub-install'' on both of the drives, such as:
 +
# grub-install --target=i386-pc --debug /dev/sda
 +
  # grub-install --target=i386-pc --debug /dev/sdb
  
===== Install grub2-uefi boot files =====
+
Where the RAID 1 array housing {{ic|/boot}} is housed on {{ic|/dev/sda}} and {{ic|/dev/sdb}}.
  
====== Install to UEFI SYSTEM PARTITION ======
+
{{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 below commands assume you are using {{ic|grub2-efi-x86_64}} (for {{ic|grub2-efi-i386}} replace {{ic|x86_64}} with {{ic|i386}} in the below commands).}}
+
=== Multiple entries ===
  
The UEFI system partition will need to be mounted at {{ic|/boot/efi/}} for the GRUB2 install script to detect it.
+
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]].
  
# mkdir -p /boot/efi
+
=== Encryption ===
# 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
+
==== Root partition ====
  
# grub-install --directory=/usr/lib/grub/x86_64-efi --target=x86_64-efi --root-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub --recheck --debug
+
To encrypt a root filesystem to be used with GRUB, add the {{ic|encrypt}} hook or the {{ic|sd-encrypt}} hook (if using systemd hooks) to [[mkinitcpio]]. See [[dm-crypt/System configuration#mkinitcpio]] for details, and [[Mkinitcpio#Common hooks]] for alternative encryption hooks.
  
If you want to install grub2 modules and {{ic|grub.cfg}} at the directory {{ic|/boot/efi/efi/grub}} and the {{ic|grubx64.efi}} application at {{ic|/boot/efi/efi/arch_grub}} use
+
If using the {{ic|encrypt}} hook, add the {{ic|cryptdevice}} parameter to {{ic|/etc/default/grub}}. In the example below, the {{ic|sda2}} partition has been encrypted as {{ic|/dev/mapper/cryptroot}}:
  
# grub-install --directory=/usr/lib/grub/x86_64-efi --target=x86_64-efi --root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=arch_grub --recheck --debug
+
{{hc|/etc/default/grub|2=
 +
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:cryptroot"
 +
}}
  
In this case {{ic|grub2-efi-x86_64}} will be installed into {{ic|/boot/grub}}, making the behavior consistent with the BIOS verion of GRUB2, but this is not recommended if you use both {{ic|grub2-bios}} and {{ic|grub2-efi-x86_64}} in your system, as this will overwrite {{ic|grub2-bios }}modules in {{ic|/boot/grub}}.
+
If using the {{ic|sd-encrypt}} hook, add {{ic|luks.uuid}}:
  
The {{ic|--root-directory}} option mentions the mountpoint of UEFI SYSTEM PARTITION , {{ic|--bootloader-id}} mentions the name of the directory used to store the {{ic|grubx64.efi}} file and {{ic|--boot-directory}} mentions the directory wherein the actual modules will be installed (and into which {{ic|grub.cfg}} should be created).
+
{{hc|/etc/default/grub|2=
 +
GRUB_CMDLINE_LINUX="luks.uuid=''UUID''"
 +
}}
  
The actual paths are:
+
where ''UUID'' is the UUID of the LUKS-encrypted device.
  
<root-directory>/<efi or EFI>/<bootloader-id>/grubx64.efi
+
Be sure to [[#Generate the main configuration file]] when done.
  
<boot-directory>/grub/x86_64-efi/<all modules, grub.efi, core.efi, grub.cfg>
+
For further information about bootloader configuration for encrypted devices, see [[Dm-crypt/System configuration#Boot loader]].
  
{{Note|the {{ic|--bootloader-id}} option does not change {{ic|<boot-directory>/grub}}, i.e. you cannot install the modules to {{ic|<boot-directory>/<bootloader-id>}}, the path is hard-coded to {{ic|<boot-directory>/grub}}.}}
+
{{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]].}}
  
In {{ic|<nowiki>--root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=grub</nowiki>}}
+
{{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}}.}}
  
<root-directory>/<efi or EFI>/<bootloader-id> == <boot-directory>/grub == /boot/efi/efi/grub
+
==== Boot partition ====
  
In {{ic|<nowiki>--root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=arch_grub</nowiki>}}
+
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.
  
<root-directory>/<efi or EFI>/<bootloader-id> == /boot/efi/efi/arch_grub
+
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}}:
<boot-directory>/grub == /boot/efi/efi/grub
 
  
In {{ic|<nowiki>--root-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub</nowiki>}}
+
{{hc|/etc/default/grub|output=
 +
GRUB_ENABLE_CRYPTODISK=y
 +
}}
  
<root-directory>/<efi or EFI>/<bootloader-id> == /boot/efi/efi/arch_grub
+
Be sure to [[#Generate the main configuration file]] while the partition containing {{ic|/boot}} is mounted.
<boot-directory>/grub == /boot/grub
 
  
In {{ic|<nowiki>--root-directory=/boot/efi --boot-directory=/boot --bootloader-id=grub</nowiki>}}
+
Without further changes you will be prompted twice for a passhrase: the first for GRUB to unlock the {{ic|/boot}} mount point in early boot, the second to unlock the root filesystem itself as described in [[#Root partition]]. You can use a [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs|keyfile]] to avoid this.
  
<root-directory>/<efi or EFI>/<bootloader-id> == /boot/efi/efi/grub
+
{{Note|
<boot-directory>/grub == /boot/grub
+
* If you use a special keymap, a default GRUB installation will not know it. This is relevant for how to enter the passphrase to unlock the LUKS blockdevice.
 +
* In order to perform system updates involving the {{ic|/boot}} mount point, ensure that the encrypted {{ic|/boot}} is unlocked and mounted before performing an update. With a separate {{ic|/boot}} partition, this may be accomplished automatically on boot by using [[crypttab]] with a [[Dm-crypt/Device encryption#With a keyfile embedded in the initramfs|keyfile]].
 +
* If you experience issues getting the prompt for a password to display (errors regarding cryptouuid, cryptodisk, or "device not found"), try reinstalling grub as below appending the following to the end of your installation command:
 +
{{bc|1=# grub-install --target=x86_64-efi --efi-directory=$esp --bootloader-id=grub '''--modules="part_gpt part_msdos"'''}}}}
  
The {{ic|<nowiki><root-directory>/<efi or EFI>/<bootloader-id>/grubx64.efi</nowiki>}} is an exact copy of {{ic|<nowiki><boot-directory>/grub/x86_64-efi/core.efi</nowiki>}}.
+
== Using the command shell ==
  
{{Note|This behavior of {{ic|--root-directory}}, {{ic|--boot-directory}}, and {{ic|--bootloader-id}} options are specific to UEFI systems and does not occur is BIOS mode. In {{ic|grub-install}}, {{ic|--root-directory}} is deprecated and {{ic|--bootloader-id}} does not exist.}}
+
Since the MBR is too small to store all GRUB modules, only the menu and a few basic commands reside there. The majority of GRUB functionality remains in modules in {{ic|/boot/grub}}, which are inserted as needed. In error conditions (e.g. if the partition layout changes) GRUB may fail to boot. When this happens, a command shell may appear.
 
In all the cases the UEFI SYSTEM PARTITION should be mounted for {{ic|grub-install}} to install {{ic|grubx64.efi}} in it, which will be launched by the firmware (using the efibootmgr created boot entry in non-Mac systems).
 
  
If you notice carefully, there is no <device_path> option (Eg: {{ic|/dev/sda}}) at the end of the {{ic|grub-install}} command unlike the case of setting up GRUB2 for BIOS systems. Any <device_path> provided will be ignored by the install script as UEFI bootloaders do not use MBR or Partition boot sectors at all.
+
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>
  
You may now be able to UEFI boot your system by creating a {{ic|grub.cfg}} file by following [[#Generate_GRUB2_UEFI_Config_file]] and [[#Create_GRUB2_entry_in_the_Firmware_Boot_Manager]].
+
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>
  
===== Create GRUB2 entry in the Firmware Boot Manager =====
+
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
  
====== Non-Mac UEFI systems ======
+
=== Pager support ===
  
{{ic|grub-install}} will ensure that {{ic|/boot/efi/efi/arch_grub/grubx64.efi}} is launched by default if it detects {{ic|efibootmgr}} and if it is able to access UEFI Runtime Services. Follow [[Unified_Extensible_Firmware_Interface#efibootmgr]] for more info.
+
GRUB supports pager for reading commands that provide long output (like the {{ic|help}} command). This works only in normal shell mode and not in rescue mode. To enable pager, in GRUB command shell type:
 +
sh:grub> set pager=1
  
If you have problems running GRUB2 in UEFI mode you can try the following (worked on an ASUS Z68 mainboard):
+
=== Using the command shell environment to boot operating systems ===
 
# cp /boot/efi/efi/arch_grub/grubx64.efi /boot/efi/shellx64.efi
 
  
or
+
  grub>
   
 
# cp /boot/efi/efi/arch_grub/grubx64.efi /boot/efi/efi/shellx64.efi
 
  
or
+
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'''.
  
# cp /boot/efi/efi/arch_grub/grubx64.efi /boot/efi/efi/shell/shellx64.efi
+
''Chainloading'' means to load another boot-loader from the current one, ie, chain-loading.
  
After this launch the UEFI Shell from the UEFI setup/menu (in ASUS UEFI BIOS, switch to advanced mode, press Exit in the top right corner and choose "Launch EFI shell from filesystem device"). The GRUB2 menu will show up and you can boot into your system. Afterwards you can use efibootmgr to setup a menu entry (see above).
+
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.
  
====== Apple Mac EFI systems ======
+
==== Chainloading a partition ====
  
{{Note|TODO: GRUB upstream Bazaar mactel branch http://bzr.savannah.gnu.org/lh/grub/branches/mactel/changes}}
+
set root=(hdX,Y)
{{Note|TODO: Fedora's mactel-boot ( https://bugzilla.redhat.com/show_bug.cgi?id&#61;755093 )}}
+
chainloader +1
 +
boot
  
Use bless command from within Mac OS X to set {{ic|grubx64.efi}} as the default boot option. You can also boot from the Mac OS X install disc and launch a Terminal there if you only have Linux installed. In the Terminal, create a directory and mount the EFI System Partition:
+
X=0,1,2...
 +
Y=1,2,3...
  
# cd /Volumes
+
For example to chainload Windows stored in the first partiton of the first hard disk,
# mkdir efi
 
# mount -t msdos /dev/disk0s1 /Volumes/efi
 
  
Then run bless on {{ic|grub.efi}} and on the EFI partition to set them as the default boot options.
+
set root=(hd0,1)
 +
chainloader +1
 +
boot
  
# bless --folder=/Volumes/efi --file=/Volumes/efi/efi/arch_grub/grubx64.efi --setBoot
+
Similarly GRUB installed to a partition can be chainloaded.
# bless --mount=/Volumes/efi --file=/Volumes/efi/efi/arch_grub/grubx64.efi --setBoot
 
  
More info at https://help.ubuntu.com/community/UEFIBooting#Apple_Mac_EFI_systems_.28both_EFI_architecture.29.
+
==== Chainloading a disk/drive ====
  
===== Generate GRUB2 UEFI Config file =====
+
set root=hdX
 +
chainloader +1
 +
boot
  
Finally, generate a configuration for GRUB2 (this is explained in greater detail in the Configuration section):
+
==== Chainloading Windows/Linux installed in UEFI mode ====
  
  # grub-mkconfig -o <boot-directory>/grub/grub.cfg
+
  insmod ntfs
 +
set root=(hd0,gpt4)
 +
chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi
 +
boot
  
{{Note|The file path is {{ic|<boot-directory>/grub/grub.cfg}}, NOT {{ic|<boot-directory>/grub/x86_64-efi/grub.cfg}}.}}
+
''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.
  
If you used {{ic|<nowiki>--boot-directory=/boot</nowiki>}} :
+
==== Normal loading ====
  
# grub-mkconfig -o /boot/grub/grub.cfg
+
See the examples in [[#Using the rescue console]]
  
If you used {{ic|<nowiki>--boot-directory=/boot/efi/efi</nowiki>}} :
+
=== Using the rescue console ===
  
# grub-mkconfig -o /boot/efi/efi/grub/grub.cfg
+
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.
  
This is independent of the value of {{ic|--bootloader-id}} option.
+
The available commands in GRUB rescue include {{ic|insmod}}, {{ic|ls}}, {{ic|set}}, and {{ic|unset}}. This example uses {{ic|set}} and {{ic|insmod}}. {{ic|set}} modifies variables and {{ic|insmod}} inserts new modules to add functionality.
  
If grub2-uefi complains about "no suitable mode found" while booting, try [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]].
+
Before starting, the user must know the location of their {{ic|/boot}} partition (be it a separate partition, or a subdirectory under their root):
  
===== Create GRUB2 Standalone UEFI Application =====
+
grub rescue> set prefix=(hdX,Y)/boot/grub
  
It is possible to create a {{ic|grubx64_standalone.efi}} application which has all the modules embeddded in a memdisk within the uefi application, thus removing the need for having a separate directory populated with all the GRUB2 uefi modules and other related files. This is done using the {{ic|grub-mkstandalone}} command which is included in {{Pkg|grub2-common}} >= 1:1.99-6 package.
+
where X is the physical drive number and Y is the partition number.
  
The easiest way to do this would be with the install command already mentioned before, but specifying the modules to include. For example:
+
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}}).}}
  
  # grub-mkstandlone --directory="/usr/lib/grub-x86_64-efi" --format="x86_64-efi" --compression="xz" \
+
To expand console capabilities, insert the {{ic|linux}} module:
  --output="/boot/efi/efi/arch_grub/grubx64_standalone.efi" <any extra files you want to include>
+
  grub rescue> insmod i386-pc/linux.mod
 +
or simply
 +
  grub rescue> insmod linux
  
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>).
+
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar.
  
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
+
An example, booting Arch Linux:
  
  # grub-mkstandlone --directory="/usr/lib/grub-x86_64-efi" --format="x86_64-efi" --compression="xz" \
+
  set root=(hd0,5)
  --output="/boot/efi/efi/arch_grub/grubx64_standalone.efi" "boot/grub/grub.cfg"
+
linux /boot/vmlinuz-linux root=/dev/sda5
 +
  initrd /boot/initramfs-linux.img
 +
boot
  
The reason to cd into {{ic|/home/user/Desktop/boot/grub/}} and to pass the file path as {{ic|boot/grub/grub.cfg}} (notice the lack of a leading slash - boot/ vs /boot/ ) is because {{ic|dir1/dir2/file}} is included as {{ic|(memdisk)/dir1/dir2/file}} by the {{ic|grub-mkstandalone}} script.
+
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.}}
  
If you pass {{ic|/home/user/Desktop/grub.cfg}} the file will be included as {{ic|(memdisk)/home/user/Desktop/grub.cfg}}. If you pass {{ic|/home/user/Desktop/boot/grub/grub.cfg}} the file will be included as {{ic|(memdisk)/home/user/Desktop/boot/grub/grub.cfg}}. That is the reason for cd'ing into {{ic|/home/user/Desktop/boot/grub/}} and passing {{ic|boot/grub/grub.cfg}}, to includ the file as {{ic|(memdisk)/boot/grub/grub.cfg}}, which is what {{ic|grub.efi}} expects the file to be.
+
set root=(hd0,5)
 +
linux (hdX,Y)/vmlinuz-linux root=/dev/sda6
 +
initrd (hdX,Y)/initramfs-linux.img
 +
boot
  
You need to create an UEFI Boot Manager entry for {{ic|/boot/efi/efi/arch_grub/grubx64_standalone.efi}} using {{ic|efibootmgr}}. Follow [[#Create GRUB2 entry in the Firmware Boot Manager]].
+
{{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.}}
  
===== Multiboot in UEFI =====
+
After successfully booting the Arch Linux installation, users can correct {{ic|grub.cfg}} as needed and then reinstall GRUB.
  
====== Chainload Microsoft Windows x86_64 UEFI-GPT ======
+
To reinstall GRUB and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Installation]] for details.
  
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):
+
== Troubleshooting ==
  
# grub-probe --target=fs_uuid /boot/efi/efi/Microsoft/Boot/bootmgfw.efi
+
=== Intel BIOS not booting GPT ===
1ce5-7f28
 
  
# grub-probe --target=hints_string /boot/efi/efi/Microsoft/Boot/bootmgfw.efi
+
==== MBR ====
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
 
  
Then, add this code to {{ic|/boot/grub/grub.cfg}} OR {{ic|/boot/efi/efi/grub/grub.cfg}} to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode:
+
Some Intel BIOS's require at least one bootable MBR partition to be present at boot, causing GPT-partitioned boot setups to be unbootable.
  
menuentry "Microsoft Windows x86_64 UEFI-GPT" {
+
This can be circumvented by using (for instance) fdisk to mark one of the GPT partitions (preferably the 1007 KiB partition you have created for GRUB already) bootable in the MBR. This can be achieved, using fdisk, by the following commands: Start fdisk against the disk you are installing, for instance {{ic|fdisk /dev/sda}}, then press {{ic|a}} and select the partition you wish to mark as bootable (probably #1) by pressing the corresponding number, finally press {{ic|w}} to write the changes to the MBR.
    insmod part_gpt
 
    insmod fat
 
    insmod search_fs_uuid
 
    insmod chain
 
    search --fs-uuid --no-floppy --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 1ce5-7f28
 
    chainloader /efi/Microsoft/Boot/bootmgfw.efi
 
}
 
  
== Configuration ==
+
{{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.}}
  
You can also choose to automatically generate or manually edit {{ic|grub.cfg}}.
+
With cfdisk, the steps are similar, just {{ic|cfdisk /dev/sda}}, choose bootable (at the left) in the desired hard disk, and quit saving.
  
{{Note|If GRUB2 was installed with the {{ic|--boot-directory}} option set, the {{ic|grub.cfg}} file must be placed in the same directory as {{ic|grubx64.efi}}. Otherwise, the {{ic|grub.cfg}} file goes in {{ic|/boot/grub/}}, just like in the BIOS version of GRUB2.}}
+
With recent version of parted, you can use {{ic|disk_toggle pmbr_boot}} option. Afterwards verify that Disk Flags show pmbr_boot.
 +
# parted /dev/sd''x'' disk_toggle pmbr_boot
 +
# parted /dev/sd''x'' print
  
=== Automatically generating using grub-mkconfig (Recommended) ===
+
More information is available [http://www.rodsbooks.com/gdisk/bios.html here]
  
The GRUB2 {{ic|menu.lst}} equivalent configuration files are {{ic|/etc/default/grub}} and {{ic|/etc/grub.d/*}}. {{ic|grub-mkconfig}} uses these files to generate {{ic|grub.cfg}}. By default the script outputs to stdout. To generate a {{ic|grub.cfg}} file run the command:
+
==== EFI path ====
  
  # grub-mkconfig -o /boot/grub/grub.cfg
+
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:
  
{{ic|/etc/grub.d/10_linux}} is set to automatically add menu items for Arch linux that work out of the box, to any generated configuration. Other operating systems may need to be added manually by editing {{ic|/etc/grub.d/40_custom}}
+
mkdir /boot/efi/EFI/boot
 +
cp /boot/efi/EFI/grub/grubx64.efi /boot/efi/EFI/boot/bootx64.efi
  
=== Manually creating grub.cfg ===
+
This solution worked for an Intel DH87MC motherboard with firmware dated Jan 2014.
  
A basic GRUB config file uses the following options
+
=== Enable debug messages ===
* {{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:
+
{{Note|This change is overwritten when [[#Generate the main configuration file]].}}
  
{{hc
+
Add:
|/boot/grub/grub.cfg
 
|<nowiki>
 
# Config file for GRUB2 - The GNU GRand Unified Bootloader
 
# /boot/grub/grub.cfg
 
  
# DEVICE NAME CONVERSIONS
+
  set pager=1
#
+
  set debug=all
#  Linux          Grub
 
# -------------------------
 
#  /dev/fd0        (fd0)
 
# /dev/sda        (hd0)
 
# /dev/sdb2      (hd1,2)
 
#  /dev/sda3      (hd0,3)
 
#
 
  
# Timeout for menu
+
to {{ic|grub.cfg}}.
set timeout=5
 
  
# Set default boot entry as Entry 0
+
=== "No suitable mode found" error ===
set default=0
 
  
# (0) Arch Linux
+
If you get this error when booting any menuentry:
menuentry "Arch Linux" {
 
    set root=(hd0,1)
 
    linux /vmlinuz-linux root=/dev/sda3 ro
 
    initrd /initramfs-linux.img
 
}
 
  
## (1) Windows
+
error: no suitable mode found
#menuentry "Windows" {
+
Booting however
#set root=(hd0,3)
 
#chainloader +1
 
#}
 
</nowiki>}}
 
  
=== Dual-booting ===
+
Then you need to initialize GRUB graphical terminal ({{ic|gfxterm}}) with proper video mode ({{ic|gfxmode}}) in GRUB. This video mode is passed by GRUB to the linux kernel via 'gfxpayload'. In case of UEFI systems, if the GRUB video mode is not initialized, no kernel boot messages will be shown in the terminal (atleast until KMS kicks in).
  
{{Note|If you want GRUB2 to automatically search for other systems, you may wish to install {{Pkg|os-prober}}.}}
+
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/}}:
  
==== Using grub-mkconfig ====
+
  # cp /usr/share/grub/unicode.pf2 ${GRUB_PREFIX_DIR}
The best way to add other entries is editing the {{ic|/etc/grub.d/40_custom}}. The entries in this file will be automatically added when running {{ic|grub-mkconfig}}.
 
After adding the new lines, run:
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 
to generate an updated {{ic|grub.cfg}}.
 
  
===== With GNU/Linux =====
+
If {{ic|/usr/share/grub/unicode.pf2}} does not exist, install {{Pkg|bdf-unifont}}, create the {{ic|unifont.pf2}} file and then copy it to {{ic|${GRUB_PREFIX_DIR<nowiki>}</nowiki>}}:
  
Assuming that the other distro is on partition {{ic|sda2}}:
+
# grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
  
menuentry "Other Linux" {
+
Then, in the {{ic|grub.cfg}} file, add the following lines to enable GRUB to pass the video mode correctly to the kernel, without of which you will only get a black screen (no output) but booting (actually) proceeds successfully without any system hang.
set root=(hd0,2)
 
linux /boot/vmlinuz (add other options here as required)
 
initrd /boot/initrd.img (if the other kernel uses/needs one)
 
}
 
  
===== With FreeBSD =====
+
BIOS systems:
  
Requires that FreeBSD is installed on a single partition with UFS. Assuming it is installed on {{ic|sda4}}:
+
insmod vbe
  
menuentry "FreeBSD" {
+
UEFI systems:
set root=(hd0,4)
 
chainloader +1
 
}
 
  
===== With Windows =====
+
insmod efi_gop
 +
insmod efi_uga
  
This assumes that your Windows partition is {{ic|sda3}}.
+
After that add the following code (common to both BIOS and UEFI):
  
  # (2) Windows XP
+
  insmod font
menuentry "Windows XP" {
 
    set root=(hd0,3)
 
    chainloader (hd0,3)+1
 
}
 
  
If the Windows Bootloader is on an entirely different harddrive than GRUB, it may be necessary to trick Windows into believing that it is in fact the first harddrive. This was possible in the old GRUB with {{ic|map}} and is now done with {{ic|drivemap}}. Assume GRUB is on {{ic|hd0}} and windows on {{ic|hd2}}, you need to add the following after {{ic|set root}}:
+
if loadfont ${prefix}/fonts/unicode.pf2
 +
then
 +
    insmod gfxterm
 +
    set gfxmode=auto
 +
    set gfxpayload=keep
 +
    terminal_output gfxterm
 +
fi
  
drivemap -s hd0 hd2
+
As you can see for gfxterm (graphical terminal) to function properly, {{ic|unicode.pf2}} font file should exist in {{ic|${GRUB_PREFIX_DIR<nowiki>}</nowiki>}}.
  
==== With Windows via EasyBCD and NeoGRUB ====
+
=== msdos-style error message ===
  
Since EasyBCD's NeoGRUB currently does not understand the GRUB2 menu format, chainload to it by replacing the contents of your {{ic|C:\NST\menu.lst}} file with lines similar to the following:
+
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.
  
default 0
+
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]]
timeout 1
 
  
title      Chainload into GRUB v2
+
=== UEFI ===
root        (hd0,7)
 
kernel      /boot/grub/i386-pc/core.img
 
  
===Visual Configuration===
+
==== Common installation errors ====
  
In GRUB2 it is possible, by default, to change the look of the menu. Make sure to initialize, if not done already, GRUB2 graphical terminal, gfxterm, with proper video mode, gfxmode, in GRUB2. This can be seen in the section [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]]. This video mode is passed by GRUB2 to the linux kernel via 'gfxpayload' so any visual configurations need this mode in order to be in effect.
+
* If you have a problem when running grub-install with sysfs or procfs and it says you must run {{ic|modprobe efivars}}, try [[Unified Extensible Firmware Interface#Mount efivarfs]].
 +
* Without {{ic|--target}} or {{ic|--directory}} option, grub-install cannot determine for which firmware to install. In such cases {{ic|grub-install}} will print {{ic|source_dir does not exist. Please specify --target or --directory}}.
 +
* If after running grub-install you are told your partition does not look like an EFI partition then the partition is most likely not {{ic|Fat32}}.
  
====Setting the framebuffer resolution ====
+
==== Drop to rescue shell ====
  
GRUB2 can set the framebuffer for both GRUB2 itself and the kernel. The old ''vga='' way is deprecated. The preferred method is editing {{ic|/etc/default/grub}} as the following sample:
+
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_GFXMODE=1024x768x32
+
==== GRUB UEFI not loaded ====
GRUB_GFXPAYLOAD_LINUX=keep
 
  
To generate the changes, run:  
+
An example of a working EFI:
grub-mkconfig -o /boot/grub/grub.cfg
 
  
The {{ic|gfxpayload}} property will make sure the kernel keeps the resolution.
+
{{hc|# efibootmgr -v|
 +
BootCurrent: 0000
 +
Timeout: 3 seconds
 +
BootOrder: 0000,0001,0002
 +
Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\efi\grub\grub.efi)
 +
Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\EfiShell.efi)
 +
Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI
 +
}}
  
{{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.}}
+
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:
{{Note|To show all the modes you can use {{ic|1=# hwinfo --framebuffer}} (hwinfo is available in [community]), while at GRUB2 prompt you can use the {{ic|1=vbeinfo}} command.}}
 
  
If this method does not work for you, the deprecated {{ic|1=vga=}} method will still work. Just
+
Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\grub.efi)
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}}
+
=== Invalid signature ===
  
====915resolution hack ====
+
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:
  
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]
+
# mv /boot/grub/device.map /boot/grub/device.map-old
 
 
In the following I will proceed with the example for my system. Please adjust the recipe for your needs. First you need to find a video mode which will be modified later. For that, run {{ic|915resolution}} in GRUB2 command shell.
 
915resolution -l
 
The output will be something like:
 
Intel 800/900 Series VBIOS Hack : version 0.5.3
 
...
 
Mode 30 : 640x480, 8 bits/pixel
 
...
 
Next, our purpose is to overwrite mode 30. (You can choose what ever mode you want.) In the file {{ic|/etc/grub.d/00_header}} just before the {{ic|set gfxmode&#61;${GRUB_GFXMODE} }} line insert
 
915resolution 30 1440 900
 
Here we are overwriting the mode {{ic|30}} with {{ic|1440x900}} resolution. Lastly we need to set {{ic|GRUB_GFXMODE}} as described earlier, regenerate GRUB2 configuration file and reboot to test changes.
 
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 
  # grub-mkconfig -o /boot/grub/grub.cfg
# reboot
 
  
====Background image and bitmap fonts====
+
{{ic|grub-mkconfig}} should now mention all found boot options, including Windows. If it works, remove {{ic|/boot/grub/device.map-old}}.
  
GRUB2 comes with support for background images and bitmap fonts in {{ic|pf2}} format. The unifont font is included in the {{Pkg|grub2-common}} package under the filename {{ic|unicode.pf2}}, or, as only ASCII characters under the name {{ic|ascii.pf2}}.
+
=== Boot freezes ===
  
Image formats supported include tga, png and jpeg, providing the correct modules are loaded. The maximum supported resolution depends on your hardware.
+
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.
  
Make sure you have set up the proper [https://wiki.archlinux.org/index.php/GRUB2#Setting_the_framebuffer_resolution framebuffer resolution].
+
=== Arch not found from other OS ===
  
Edit {{ic|/etc/default/grub}} like this:
+
Some have reported that other distributions may have trouble finding Arch Linux automatically with {{ic|os-prober}}. If this problem arises, it has been reported that detection can be improved with the presence of {{ic|/etc/lsb-release}}. This file and updating tool is available with the package {{Pkg|lsb-release}} in the [[official repositories]].
GRUB_BACKGROUND="/boot/grub/archlinux.tga"
 
#GRUB_THEME="/path/to/gfxtheme"
 
  
(archlinux.tga is a placeholder; put your file name there)
+
=== Warning when installing in chroot ===
  
{{Note|If you have installed GRUB on a separate partition, {{ic|/boot/grub/archlinux.tga}} becomes {{ic|/grub/archlinux.tga}}.}}
+
When installing GRUB on a LVM system in a chroot environment (e.g. during system installation), you may receive warnings like
  
To generate the changes and add the information into {{ic|grub.cfg}}, run:
+
  /run/lvm/lvmetad.socket: connect failed: No such file or directory
  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.
+
or
If this phrase is not seen, the image information was probably not incorporated into the {{ic|grub.cfg}} file.
 
 
If the image is not displayed, check:
 
* The path and the filename in {{ic|/etc/default/grub}} are correct.
 
* The image is of the proper size and format (tga, png, 8-bit jpg).
 
* The image was saved in the RGB mode, and is not indexed.
 
* The console mode is not enabled in {{ic|/etc/default/grub}}.
 
* The command {{ic|grub-mkconfig}} must be executed to place the background image information into the {{ic|/boot/grub/grub.cfg}} file.
 
  
====Theme====
+
WARNING: failed to connect to lvmetad: No such file or directory. Falling back to internal scanning.
  
Here is an example for configuring Starfield theme which was included in GRUB2 package.
+
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.
  
Edit {{ic|/etc/default/grub}}
+
=== GRUB loads slowly ===
GRUB_THEME="/boot/grub/themes/starfield/theme.txt"
 
  
Generate the changes:
+
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.
grub-mkconfig -o /boot/grub/grub.cfg
 
  
If configuring the theme was successful, you'll see {{ic|Found theme: /boot/grub/themes/starfield/theme.txt}} in the terminal.
+
=== 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.
  
====Menu colors====
+
=== grub-reboot not resetting ===
  
As in GRUB Legacy (0.9x), you can change the menu colors in GRUB2. The available colors for GRUB2 are at http://www.gnu.org/software/grub/manual/html_node/Theme-file-format.html#Theme-file-format.
+
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}} (do not forget {{ic|grub-mkconfig -o /boot/grub/grub.cfg}}).
Here is an example:
 
  
Edit {{ic|/etc/default/grub}}:
+
=== Old BTRFS prevents installation ===
GRUB_COLOR_NORMAL="light-blue/black"
 
GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
 
  
Generate the changes:
+
If a drive is formatted with BTRFS without creating a partition table (eg. /dev/sdx), then later has partition table written to, there are parts of the BTRFS format that persist. Most utilities and OS's do not see this, but GRUB will refuse to install, even with --force
grub-mkconfig -o /boot/grub/grub.cfg
 
  
====Hidden menu====
+
# grub-install: warning: Attempting to install GRUB to a disk with multiple partition labels. This is not supported yet..
 +
# grub-install: error: filesystem `btrfs' does not support blocklists.
  
One of the unique features of GRUB2 is hiding/skipping the menu and showing it by holding "Shift" when needed. You can also adjust whether you want to see the timeout counter.
+
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}}
 
 
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:
 
GRUB_HIDDEN_TIMEOUT=5
 
GRUB_HIDDEN_TIMEOUT_QUIET=false
 
 
 
and run:
 
grub-mkconfig -o /boot/grub/grub.cfg
 
 
 
=== 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_group_name''-''lvm_logical_boot_partition_name'')
 
 
 
Example:
 
 
 
# (0) Arch Linux
 
menuentry "Arch Linux" {
 
insmod lvm
 
set root=(VolumeGroup-lv_boot)
 
# you can only set following two lines
 
linux /vmlinuz-linux root=/dev/mapper/VolumeGroup-root ro
 
initrd /initramfs-linux.img
 
}
 
 
 
==== Raid ====
 
 
 
GRUB2 provides convenient handling of raid-volumes. You need to add:
 
insmod raid
 
 
 
which allows you to address the volume natively. E.g. {{ic|/dev/md0}} becomes:
 
set root=(md0)
 
 
 
whereas a partitioned raid-volume (e.g. {{ic|/dev/md0p1}}) becomes:
 
set root=(md0,1)
 
 
 
==== Persistent block device naming ====
 
You can use UUIDs to detect partitions instead of the "old" {{ic|/dev/sd*}} and {{ic|/dev/hd*}} scheming. It has the advantage of detecting partitions by their unique UUIDs, which is needed by some people booting with complicated partition setups.
 
 
 
UUIDs are used by default in the recent versions of GRUB2 - there is no downside in it anyway except that you need to re-generate the {{ic|grub.cfg}} file every time you resize or reformat your partitions. Remember this when modifying partitions with Live-CD.
 
 
 
The recent versions of GRUB2 use UUIDs by default. You can re-enable the use of UUIDS by simply commenting the UUID line (this is also what it looks like by default):
 
#GRUB_DISABLE_LINUX_UUID=true
 
you can also just set the value as {{ic|false}} as shown here:
 
GRUB_DISABLE_LINUX_UUID=false
 
 
 
Either way, do not forget to generate the changes:
 
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 a <LABEL> <PARTITION>
 
 
 
Then, add an entry using labels. An example of this:
 
 
 
menuentry "Arch Linux, session texte" {
 
    search --label --no-floppy --set=root archroot
 
    linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro
 
    initrd /boot/initramfs-linux.img
 
}
 
 
 
==== Recall previous entry ====
 
 
 
GRUB2 can remember the last entry you booted from and use this as the default entry to boot from next time. This is useful if you have multiple kernels (i.e., the current Arch one and the LTS kernel as a fallback option) or operating systems. To do this, edit {{ic|/etc/default/grub}} and change the setting of {{ic|GRUB_DEFAULT}}:
 
 
 
GRUB_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, eg Windows in {{ic|/etc/grub.d/40_custom}}, will need {{ic|savedefault}} added. Remember to regenerate your configuration file.}}
 
 
 
==== Security ====
 
 
 
If you want to secure GRUB2 so it is not possible for anyone to change boot parameters or use the command line, you can add a user/password combination to GRUB2's configuration files. To do this, run the command {{ic|grub-mkpasswd_pbkdf2}}. Enter a password and confirm it. The output will look like this:
 
 
 
{{bc|<nowiki>
 
Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A</nowiki>}}Then, add the following to {{ic|/etc/grub.d/00_header}}:
 
{{bc|<nowiki>cat << EOF
 
 
 
set superusers="username"
 
password_pbkdf2 username <password>
 
 
 
EOF</nowiki>}}
 
where <password> is the string generated by {{ic|grub-mkpasswd_pbkdf2}}.
 
 
 
Regenerate your configuration file. Your GRUB2 command line and boot parameters are now protected.
 
 
 
==== Root Encryption ====
 
 
 
To let GRUB2 automatically add the kernel parameters for root encryption,
 
add {{ic|1=cryptdevice=/dev/yourdevice:label}} to {{ic|GRUB_CMDLINE_LINUX}} in {{ic|/etc/defaults/grub}}.
 
 
 
Example with root mapped to {{ic|/dev/mapper/root}}:
 
 
 
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:root"
 
 
 
Also, disable the usage of UUIDs for the rootfs:
 
 
 
GRUB_DISABLE_LINUX_UUID=true
 
 
 
Regenerate the configuration.
 
 
 
=== Booting an ISO Directly From GRUB2 ===
 
Edit {{ic|/etc/grub.d/40_custom}} to add an entry for the target ISO. When finished, update the GRUB menu as with the usual {{ic|grub-mkconfig -o /boot/grub/grub.cfg}} (as root).
 
 
 
==== Arch ISO ====
 
{{Note|Be sure to adjust the "hdX,Y" in the third line to point to the correct disk/partition number of the isofile. Also adjust the img_dev line to match this same location.}}
 
 
 
menuentry "Archlinux-2011.08.19-netinstall-x86_64.iso" {
 
    set isofile="/archives/archlinux-2011.08.19-netinstall-x86_64.iso"
 
    loopback loop (hd0,7)$isofile
 
    linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201108 img_dev=/dev/sda7 img_loop=$isofile earlymodules=loop
 
    initrd (loop)/arch/boot/x86_64/archiso.img
 
}
 
 
 
==== Ubuntu ISO ====
 
{{Note|Be sure to adjust the "hdX,Y" in the third line to point to the correct disk/partition number of the isofile. }}
 
 
 
menuentry "ubuntu-11.04-desktop-amd64.iso" {
 
    set isofile="/path/to/ubuntu-11.04-desktop-amd64.iso"
 
    loopback loop (hdX,Y)$isofile
 
    linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
 
    initrd (loop)/casper/initrd.lz
 
}
 
 
 
== Using the command shell ==
 
 
 
Since the MBR is too small to store all GRUB2 modules, only the menu and a few basic commands reside there. The majority of GRUB2 functionality remains in modules in {{ic|/boot/grub}}, which are inserted as needed. In error conditions (e.g. if the partition layout changes) GRUB2 may fail to boot. When this happens, a command shell may appear.
 
 
 
GRUB2 offers multiple shells/prompts. If there is a problem reading the menu but the bootloader is able to find the disk, you will likely be dropped to the "normal" shell:
 
sh:grub>
 
 
 
If there is a more serious problem (e.g. GRUB cannot find required files), you may instead be dropped to the "rescue" shell:
 
grub rescue>
 
 
 
The rescue shell is a restricted subset of the normal shell, offering much less functionality. If dumped to the rescue shell, first try inserting the "normal" module, then starting the "normal" shell:
 
grub rescue> set prefix=(hdX,Y)/boot/grub
 
grub rescue> insmod (hdX,Y)/boot/grub/normal.mod
 
rescue:grub> normal
 
 
 
=== Pager support ===
 
 
 
GRUB2 supports pager for reading commands that provide long output (like the help command). This works only in normal shell mode and not in rescue mode. To enable pager, in GRUB2 command shell type:
 
sh:grub> set pager=1
 
 
 
== GUI configuration tools ==
 
 
 
Following package may be installed from [[AUR]]
 
* [https://aur.archlinux.org/packages.php?ID=44020 grub-customizer] (requires gettext gksu gtkmm hicolor-icon-theme openssl)
 
*:Customize the bootloader (GRUB2 or BURG)
 
* [http://kde-apps.org/content/show.php?content=139643 grub2-editor] (requires kdelibs)
 
*:A KDE4 control module for configuring the GRUB2 bootloader
 
* [http://kde-apps.org/content/show.php?content=137886 kcm-grub2] (requires kdelibs python2-qt kdebindings-python)
 
*:This Kcm module manages the most common settings of Grub2.
 
* [http://sourceforge.net/projects/startup-manager/ startupmanager] (requires gnome-python imagemagick yelp python2 xorg-xrandr)
 
*:GUI app for changing the settings of GRUB, GRUB2, Usplash and Splashy
 
 
 
== parttool or legacy hide/unhide ==
 
 
 
If you have a win9x paradigm with hidden C disks GRUB Legacy had the hide/unhide feature. In GRUB2 this has been replaced by parttool. For example, to boot the third C disk of three win9x installations on the CLI enter the CLI and:
 
parttool hd0,1 hidden+ boot-
 
parttool hd0,2 hidden+ boot-
 
parttool hd0,3 hidden- boot+
 
set root=hd0,3
 
chainloader +1
 
boot
 
 
 
== Using the rescue console ==
 
 
 
See [[#Using the command shell]] first. If unable to activate the standard shell, one possible solution is to boot using a live CD or some other rescue disk to correct configuration errors and reinstall GRUB. However, such a boot disk is not always available (nor necessary); the rescue console is surprisingly robust.
 
 
 
The available commands in GRUB rescue include {{ic|insmod}}, {{ic|ls}}, {{ic|set}}, and {{ic|unset}}. This example uses {{ic|set}} and {{ic|insmod}}. {{ic|set}} modifies variables and {{ic|insmod}} inserts new modules to add functionality.
 
 
 
Before starting, the user must know the location of their {{ic|/boot}} partition (be it a separate partition, or a subdirectory under their root):
 
grub rescue> set prefix=(hdX,Y)/boot/grub
 
 
 
where X is the physical drive number and Y is the partition number.
 
 
 
To expand console capabilities, insert the {{ic|linux}} module:
 
grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
 
 
 
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path, (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}} and {{ic|insmod (hdX,Y)/grub/linux.mod}}).}}
 
 
 
This introduces the "linux" and "initrd" commands, which should be familiar (see [[#Configuration]]).
 
 
 
An example, booting Arch Linux:
 
set root=(hd0,5)
 
linux /boot/vmlinuz-linux root=/dev/sda5
 
initrd /boot/initramfs-linux.img
 
boot
 
 
 
With a separate boot partition, again change the lines accordingly:
 
set root=(hd0,5)
 
linux /vmlinuz-linux root=/dev/sda6
 
initrd /initramfs-linux.img
 
boot
 
 
 
After successfully booting the Arch Linux installation, users can correct {{ic|grub.cfg}} as needed and then reinstall GRUB2.
 
 
 
to reinstall GRUB2 and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Bootloader installation]] for details.
 
 
 
== Combining the use of UUID's and basic scripting  ==
 
 
 
If you like the idea of using UUID's to avoid unreliable BIOS mappings or are struggling with GRUB's syntax, here is an example boot menu item that uses UUID's and a small script to direct GRUB to the proper disk partitions for your system. All you need to do is replace the UUID's in the sample with the correct UUID's for your system. (The example applies to a system with a boot and root partition. You will obviously need to modify the GRUB configuration if you have additional partitions.)
 
 
 
  menuentry "Arch Linux 64" {
 
      # Set the UUIDs for your boot and root partition respectively
 
      set the_boot_uuid=ece0448f-bb08-486d-9864-ac3271bd8d07 
 
      set the_root_uuid=c55da16f-e2af-4603-9e0b-03f5f565ec4a
 
   
 
      # (Note: This may be the same as your boot partition)
 
   
 
      # Get the boot/root devices and set them in the root and grub_boot variables 
 
      search --fs-uuid --no-floppy --set=root $the_root_uuid     
 
      search --fs-uuid --no-floppy --set=grub_boot $the_boot_uuid
 
   
 
      # Check to see if boot and root are equal.
 
      # If they are, then append /boot to $grub_boot (Since $grub_boot is actually the root partition)
 
      if [ $the_boot_uuid == $the_root_uuid] ; then
 
          set grub_boot=$grub_boot/boot
 
      fi
 
   
 
      # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd
 
      linux ($grub_boot)/vmlinuz-linux root=/dev/disk/by-uuid/$uuid_os_root ro
 
      initrd ($grub_boot)/initramfs-linux.img
 
  }
 
 
 
== Troubleshooting ==
 
 
 
Any troubleshooting should be added here.
 
 
 
=== Enable GRUB2 debug messages ===
 
 
 
Add
 
 
set pager=1
 
set debug=all
 
 
 
to {{ic|grub.cfg}}.
 
 
 
=== Correct GRUB2 No Suitable Mode Found Error ===
 
 
 
If you get this error when booting any menuentry
 
 
 
error: no suitable mode found
 
Booting however
 
 
 
Then you need to initialize GRUB2 graphical terminal (gfxterm) with proper video mode (gfxmode) in GRUB2. This video mode is passed by GRUB2 to the linux kernel via 'gfxpayload'. In case of UEFI systems, if the GRUB2 video mode is not initialized, no kernel boot messages will be shown in the terminal (atleast until KMS kicks in)
 
 
 
Copy {{ic|/usr/share/grub/unicode.pf2}} to ${GRUB2_PREFIX_DIR} ({{ic|/boot/grub/}} in case of BIOS and UEFI systems. If GRUB2 UEFI was installed with {{ic|1=--boot-directory=/boot/efi/efi}} set, then the directory is {{ic|/boot/efi/efi/grub/}}.
 
 
 
# cp /usr/share/grub/unicode.pf2 ${GRUB2_PREFIX_DIR}
 
 
 
If {{ic|/usr/share/grub/unicode.pf2}} does not exist, install {{Pkg|bdf-unifont}}, create the {{ic|unifont.pf2}} file and then copy it to ${GRUB2_PREFIX_DIR}.
 
 
 
# grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
 
 
 
Then, in the {{ic|grub.cfg}} file, add the following lines to enable GRUB2 to pass the video mode correctly to the kernel, without of which you will only get a black screen (no output) but booting (actually) proceeds successfully without any system hang:
 
 
 
BIOS systems
 
 
 
insmod vbe
 
 
 
UEFI systems
 
 
 
insmod efi_gop
 
insmod efi_uga
 
 
 
After that add the following code (common to both BIOS and UEFI)
 
 
 
insmod font
 
 
 
if loadfont ${prefix}/fonts/unicode.pf2
 
then
 
    insmod gfxterm
 
    set gfxmode=auto
 
    set gfxpayload=keep
 
    terminal_output gfxterm
 
fi
 
 
 
As you can see for gfxterm (graphical terminal) to function properly, {{ic|unicode.pf2}} font file should exist in ${GRUB2_PREFIX_DIR}.
 
 
 
=== msdos-style error message ===
 
 
 
grub-setup: warn: This msdos-style partition label has no post-MBR gap; embedding won't be possible!
 
grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.
 
            However, blocklists are UNRELIABLE and its use is discouraged.
 
grub-setup: error: If you really want blocklists, use --force.
 
 
 
This error may occur when you try installing GRUB2 in a VMware container. Read more about it [http://bbs.archlinux.org/viewtopic.php?pid=581760#p581760 here]. It happens when the first partition starts just after the MBR (block 63), without the usual space of 1 MiB (2048 blocks) before the first partition. Read [[#MBR_aka_msdos_partitioning_specific_instructions]]
 
 
 
=== UEFI GRUB2 drops to shell ===
 
 
 
If grub loads but drop you into the rescue shell with no errors, it may be because of a missing or misplaced {{ic|grub.cfg}}. This will happen if GRUB2 UEFI was installed with {{ic|--boot-directory}} and {{ic|grub.cfg}} is missing OR if the partition number of the boot partition changed (which is hard-coded into the {{ic|grubx64.efi}} file).
 
 
 
=== UEFI GRUB2 not loaded ===
 
In some cases the EFI may fail to load GRUB correctly. Provided everything is set up correctly, the output of
 
efibootmgr -v
 
might look something like this:
 
BootCurrent: 0000
 
Timeout: 3 seconds
 
BootOrder: 0000,0001,0002
 
Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\efi\grub\grub.efi)
 
Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\EfiShell.efi)
 
Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI
 
If everything works correctly, the EFI would now automatically load grub.<br>
 
If the screen only goes black for a second and the next boot option is tried afterwards, according to [https://bbs.archlinux.org/viewtopic.php?pid=981560#p981560 this post], moving grub to the partition root can help. The boot option has to be deleted and recreated afterwards. The entry for grub should look like this then:
 
Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\grub.efi)
 
 
 
=== Invalid signature ===
 
If trying to boot windows results in an "invalid signature" error, e.g. after reconfiguring partitions or adding additional hard drives, (re)move grub's device configuration and let it reconfigure.
 
# mv /boot/grub/device.map /boot/grub/device.map-old
 
# grub-mkconfig -o /boot/grub/grub.cfg
 
{{ic|grub-mkconfig}} should now mention all found boot options including windows. If it works, remove {{ic|/boot/grub/device.map-old}}.
 
  
== References ==
+
=== Windows 8/10 not found ===
  
# Official GRUB2 Manual - http://www.gnu.org/software/grub/manual/grub.html
+
A setting in Windows 8/10 called "Hiberboot", "Hybrid Boot" or "Fast Boot" can prevent the Windows partition from being mounted, so {{ic|grub-mkconfig}} will not find a Windows install. Disabling Hiberboot in Windows will allow it to be added to the GRUB menu.
# Ubuntu wiki page for Grub2 - https://help.ubuntu.com/community/Grub2
 
# GRUB2 wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
 
# Wikipedia's page on [http://en.wikipedia.org/wiki/BIOS_Boot_partition BIOS Boot Partition]
 
  
== External Links ==
+
== See also ==
  
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub/grub_bios.sh A Linux Bash Shell script to compile and install GRUB2 for BIOS from BZR Source]
+
* [https://www.gnu.org/software/grub/manual/grub.html Official GRUB Manual]
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub/grub_uefi.sh A Linux Bash Shell script to compile and install GRUB2 for UEFI from BZR Source]
+
* [https://help.ubuntu.com/community/Grub2 Ubuntu wiki page for GRUB]
 +
* [https://help.ubuntu.com/community/UEFIBooting GRUB wiki page describing steps to compile for UEFI systems]
 +
* [[Wikipedia:BIOS Boot partition]]
 +
* [http://web.archive.org/web/20160424042444/http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html#Editing_etcgrub.d05_debian_theme How to configure GRUB]
 +
* [http://www.linuxjournal.com/article/4622 Boot with GRUB]

Latest revision as of 17:27, 13 December 2017

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].

Preface

A boot loader is the first software program that runs when a computer starts. It is responsible for selecting, loading and transferring control to an operating system kernel. The kernel, in turn, initializes the rest of the operating system. The name GRUB officially refers to version 2 of the software. 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. Then do:

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

where /dev/sdx is the partitioned disk where grub is to be installed.

Now you must #Generate the main configuration file.

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

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

See grub-install(8) and [2] for more details on the grub-install command.

UEFI systems

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

Check if you have GPT and an ESP

An EFI System Partition (ESP) is needed on every disk 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.

# parted /dev/sdx 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/fat32 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. In the following of this section esp must be substituted by it in commands.

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 32-bit EFI systems (not to be confused with 32-bit CPUs), replace x86_64-efi with i386-efi where appropriate.

Make sure you are in a bash shell.

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_mount to that mount point (usually /boot):

# grub-install --target=x86_64-efi --efi-directory=esp_mount --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 #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. Additionally see GRUB/Tips and tricks#UEFI further reading.

Generate the main configuration file

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

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

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

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

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

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

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

Configuration

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

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

Additional arguments

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

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

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

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

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

See Kernel parameters for more info.

Dual-booting

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

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

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

"Shutdown" menu entry

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

"Restart" menu entry

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

"Firmware setup" menu entry (UEFI only)

menuentry "Firmware setup" {
	fwsetup
}

GNU/Linux menu entry

Assuming that the other 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)
}

Windows installed in UEFI-GPT Mode menu entry

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

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

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

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

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

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

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

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

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

Windows installed in BIOS-MBR mode

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

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

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

In both examples 69B235F6749E84CE is the partition UUID which can be found with command lsblk --fs.

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

if [ "${grub_platform}" == "pc" ]; then
  menuentry "Microsoft Windows Vista/7/8/8.1/10 BIOS-MBR" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 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, GRUB may be installed without a clean Windows 8, in which case you cannot boot Windows without having an error with \boot\bcd (error code 0xc000000f). You can fix it by going to Windows Recovery Console (cmd from install disk) and executing:
x:\> "bootrec.exe /fixboot" 
x:\> "bootrec.exe /RebuildBcd".

Do not use bootrec.exe /Fixmbr because it will wipe GRUB out. Or you can use Boot Repair function in the Troubleshooting menu - it will not wipe out GRUB but will fix most errors.

Also you would better keep plugged in both the target hard drive and your bootable device ONLY. Windows usually fails to repair boot information if any other devices are connected.

/etc/grub.d/40_custom can be used as a template to create /etc/grub.d/nn_custom. Where nn defines the 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 or the sd-encrypt hook (if using systemd hooks) to mkinitcpio. See dm-crypt/System configuration#mkinitcpio for details, and Mkinitcpio#Common hooks for alternative encryption hooks.

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

/etc/default/grub
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:cryptroot"

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

/etc/default/grub
GRUB_CMDLINE_LINUX="luks.uuid=UUID"

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

Be sure to #Generate the main configuration file when done.

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

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

Boot partition

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

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

/etc/default/grub
GRUB_ENABLE_CRYPTODISK=y

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

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

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

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.

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

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

More information is available here

EFI 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#Mount efivarfs.
  • Without --target or --directory option, grub-install cannot determine for which firmware to install. In such cases grub-install will print source_dir does not exist. Please specify --target or --directory.
  • If after running grub-install you are told your partition does not look like an EFI partition then the partition is most likely not Fat32.

Drop to rescue shell

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

Warning when installing in chroot

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

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

or

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

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

GRUB loads slowly

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

error: unknown filesystem

GRUB may output error: unknown filesystem and refuse to boot for a few reasons. If you are certain that all UUIDs are correct and all filesystems are valid and supported, it may be because your BIOS Boot Partition is located outside the first 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 (do not forget grub-mkconfig -o /boot/grub/grub.cfg).

Old BTRFS prevents installation

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

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

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

Windows 8/10 not found

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

See also