Difference between revisions of "GRUB"

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*copy grub modules and configuration
 
*copy grub modules and configuration
# cp -a /boot/grub /path/to/backup/
+
# cp -a /boot/grub /path/to/backup/
 
*backup the MBR and GRUB stage 1.5
 
*backup the MBR and GRUB stage 1.5
# dd if=/dev/sda of=/path/to/backup/first-sectors count=63
+
# dd if=/dev/sda of=/path/to/backup/first-sectors count=63
  
 
You could now lightly remove /boot/grub and follow the instructions below.You know that if things get nasty, you could reboot your system thanks to an installation media and :
 
You could now lightly remove /boot/grub and follow the instructions below.You know that if things get nasty, you could reboot your system thanks to an installation media and :
  
 
*move old grub2 files out of the way
 
*move old grub2 files out of the way
# mv /boot/grub /boot/grub.nonfunctional
+
# mv /boot/grub /boot/grub.nonfunctional
 
*copy grub back to /boot
 
*copy grub back to /boot
# cp -a /path/to/backup/grub /boot/
+
# cp -a /path/to/backup/grub /boot/
 
*replace MBR and next 62 sectors of sda with backed up copy (DANGEROUS!)
 
*replace MBR and next 62 sectors of sda with backed up copy (DANGEROUS!)
# dd if=/path/to/backup/first-sectors of=/dev/sda count=63
+
# dd if=/path/to/backup/first-sectors of=/dev/sda count=63
  
 
==== BIOS systems ====
 
==== BIOS systems ====

Revision as of 17:32, 29 October 2011

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Summary help replacing me
Covers various aspects of the next generation of the GRand Unified Bootloader (GRUB2).
Overview
Template:Boot process overview
Related
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.
Resources
GNU GRUB -- GNU Project
GNU GRUB WikiTemplate:Linkrot

GRUB2 is the next generation of the GRand Unified Bootloader (GRUB). GRUB2 is derived from PUPA which was a research project to investigate the next generation of GRUB. GRUB 2 has been rewritten from scratch to clean up everything and provide modularity and portability [1].

Briefly, the bootloader is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the Linux kernel. The kernel, in turn, initializes the rest of the operating system.

Contents

Preface

Although, GRUB (i.e. version 0.9x) is the de facto standard bootloader of Linux, it is considered 'legacy' by upstream. It is being replaced by GRUB2 in many distributions. Upstream recommends GRUB2 >=1.99~rc2 over grub-legacy, even for current grub-legacy users.

Note: grub2 from 1.99~rc2 and later supports btrfs as root (without a separate /boot filesystem).

Notes for current GRUB users

  • There are differences in the commands of GRUB and GRUB2. Familiarize yourself with GRUB2 commands before proceeding (e.g. "find" has been replaced with "search").
  • 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).
  • 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, Template:Filename would be referred to as Template:Codeline (for MBR) or Template:Codeline (for GPT) using GRUB2.

Installation

During Arch Linux installation

  • Skip the Install Bootloader step and exit the installer.
  • Configure the network:
# aif -p partial-configure-network

This will bring up a prompt; put in the network interface to use, (e.g., eth0) and use DHCP for easy configuration.

  • If you did not configure the installed system's Template:Filename 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
  • Load the dm-mod module (you might need grub2-bios; install the package if needed):
# modprobe dm-mod
Note: This is necessary at this point, and cannot be postponed after the chroot. If you try to use modprobe in a chroot environment that has a later kernel version from that of the installing device (at the time of writing, 2.6.33), modprobe will fail. This happens routinely using the Arch "net" installations.
  • From the installer's live shell, chroot to the installed system:
# mount -o bind /dev /mnt/dev
# chroot /mnt bash
  • Update pacman's database:
# pacman-db-upgrade
  • Refresh the package list (with an extra -y flag to force a refresh of all package lists even if they appear to be up to date):
# pacman -Syy
  • Install the GRUB2 package as mentioned in the section #From a running Arch Linux. Note that the dm-mod module has already been loaded, no need to do that again.

From a running Arch Linux

Make a backup of your precious data

In general, a grub installation ran smoothly and you got no problems at all. And sometimes it could simply messed up your system. You're strongly advised to make a backup before even think of grub2.

  • copy grub modules and configuration
# cp -a /boot/grub /path/to/backup/
  • backup the MBR and GRUB stage 1.5
# dd if=/dev/sda of=/path/to/backup/first-sectors count=63

You could now lightly remove /boot/grub and follow the instructions below.You know that if things get nasty, you could reboot your system thanks to an installation media and :

  • move old grub2 files out of the way
# mv /boot/grub /boot/grub.nonfunctional
  • copy grub back to /boot
# cp -a /path/to/backup/grub /boot/
  • replace MBR and next 62 sectors of sda with backed up copy (DANGEROUS!)
# dd if=/path/to/backup/first-sectors of=/dev/sda count=63

BIOS systems

Preliminary Considerations for GRUB2 BIOS
GPT specific instructions

GRUB2 in BIOS-GPT configuration requires a BIOS Boot Partition to embed its core.img in the absence of post-MBR gap in GPT partitioned systems (which is taken over by the GPT Primary Header and Primary Partition table). This partition is used by GRUB2 only in BIOS-GPT setups. No such partition type exists in case of MBR partitioning (at least not for GRUB2). This partition is also not required if the system is UEFI based, as no embedding of bootsectors takes place in that case. Syslinux does not require this partition.

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 Template:Codeline in GNU Parted.

Note: This partition should be created before grub_bios-install or grub-setup is run or before the Install Bootloader step of the Archlinux installer (if GRUB2 is selected as bootloader).
MBR aka msdos partitioning specific instructions

Usually the post-MBR gap (after the 512 byte MBR region and before the start of the 1st partition) in many MBR (or msdos disklabel) partitioned systems is 32 KiB when DOS compatibility cylinder alignment issues are satisfied in the partition table. However a post-MBR gap of about 1 to 2 MiB is recommended to provide sufficient room for embedding grub2's core.img ( https://bugs.archlinux.org/task/24103 ). It is advisable to use a partitioner which supports 1 MiB partition alignment to obtain this space as well as satisfy other non-512 byte sector issues (which are unrelated to embedding of core.img).

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

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.
Before grub_bios-install

The GRUB2 package can be installed with pacman (and will replace Template:Package Official, if it is installed):

# pacman -S grub2-bios
Note: Installing grub2-common (a dependency of grub2-bios) 1.99~rc1 or later, may take forever in some systems since the post_install script runs grub-mkconfig and this script does not provide the option --no-floppy. For more details search this option in the article.
Note: Simply installing the package won't update the /boot/grub/core.img file and the grub2 modules in /boot/grub . You need to update the core.img file and the grub2 modules manually using grub_bios-install as explained below.

Also load the device-mapper kernel module without which grub-probe does not reliably detect disks and partitions

# modprobe dm-mod


Run grub_bios-install

There are 3 ways to install grub2 in BIOS booting - #Install_to_440-byte_MBR_boot_code_region (recommended) , #Install_to_Partition_or_Partitionless_Disk (not recommended) or #Generate_core.img_alone (safest method, but requires another BIOS bootloader like grub-legacy or syslinux to be installed to chainload Template:Filename ). For all the ways #Before_grub_bios-install step is needed.

Install to 440-byte MBR boot code region

To setup grub2-bios in the 440-byte Master Boot Record boot code region, populate the Template:Filename directory, generate the Template:Filename 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

# grub_bios-install --boot-directory=/boot --no-floppy --recheck /dev/sda

where Template:Filename is the destination of the installation (in this case the MBR of the first SATA disk). If you use LVM for your Template:Filename, you can install GRUB2 on multiple physical disks.

The Template:Codeline tells grub2-bios utilities not to search for any floppy devices which reduces the overall execution time of grub_bios-install on many systems (it will also prevent the issue below from occuring). Otherwise you get an error like this

grub-probe: error: Cannot get the real path of '/dev/fd0'
Auto-detection of a filesystem module failed.
Please specify the module with the option '--modules' explicitly.

Then:

# grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg

For example:

Template:File

Template:File


  • If you forgot to create a GRUB2 Template:Filename configfile 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 Template:Filename configfile.

Note: This option works only in BIOS systems, not in UEFI systems.
Install to Partition or Partitionless Disk
Note: grub2-bios (any version - including upstream bzr repo) does not encourage installation to a partition boot sector or a partitionless disk like grub-legacy or syslinux does. Neither do the Arch devs.

To setup grub2-bios to a partition boot sector, to a partitionless disk (also called superfloppy) or to a floppy disk, run (using for example /dev/sda1 as the /boot partition)

# chattr -i /boot/grub/core.img
# grub_bios-install --boot-directory=/boot --no-floppy --recheck --force /dev/sda1
# chattr +i /boot/grub/core.img

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

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

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

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

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

With Template:Codeline you should get

Installation finished. No error reported.

The reason why grub-setup does not by default allow this is because in case of partition or a partitionless disk is that grub2-bios relies on embedded blocklists in the partition bootsector to locate the Template:Filename file and the prefix dir Template:Filename . The sector locations of Template:Filename may change whenever the filesystem in the partition is being altered (files copied, deleted etc.). For more info see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915 .

The workaround for this is to set the immutable flag on Template:Filename (using chattr command as mentioned above) so that the sector locations of the Template:Filename file in the disk is not altered. The immutable flag on Template:Filename needs to be set only if grub2-bios is installed to a partition boot sector or a partitionless disk, not in case of installtion to MBR or simple generation of Template:Filename without embedding any bootsector (mentioned above).

Generate core.img alone

To populate the Template:Filename directory and generate a Template:Filename file WITHOUT embedding any grub2-bios bootsector code in the MBR, post-MBR region, or the partition bootsector, add --grub-setup=/bin/true to grub_bios-install:

# grub_bios-install --grub-setup=/bin/true --boot-directory=/boot --no-floppy --recheck /dev/sda

You can then chainload grub2's core.img from grub-legacy or syslinux as a Linux kernel or a multiboot kernel.

After grub_bios-install
Generate GRUB2 BIOS Config file

Finally, generate a configuration for grub2 (this is explained in greater detail in the Configuration section):

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

If grub2 complains about "no suitable mode found" while booting, go to #Correct_GRUB2_No_Suitable_Mode_Found_Error .

Multiboot in BIOS
Boot Microsoft Windows installed in BIOS-MBR mode
Note: GRUB2 supports booting Template:Filename directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.

Find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the bootmgr and its files reside. For example, if Windows Template:Filename exists at Template:Filename:

# grub-probe --target=fs_uuid /media/Windows/bootmgr
69B235F6749E84CE

Then, add the below code to Template:Filename to chainload Windows (Vista, 7 or 8) installed in BIOS-MBR mode :

menuentry "Microsoft Windows 7 BIOS-MBR" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
    ntldr (${root})/bootmgr
}

For Windows XP

menuentry "Microsoft Windows XP" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
    ntldr (${root})/ntldr
}

UEFI systems

Before grub_efi_${UEFI_ARCH}-install
Note: Unless specified as EFI 1.x , EFI and UEFI terms are used interchangeably to denote UEFI 2.x firmware. Also unless stated explicitely, the instructions are general and not Mac specific. Some of them may not work or may be different in Macs. Apple's EFI implementation is neither a EFI 1.x version nor UEFI 2.x version but mixes up both. This kind of firmware does not fall under any one UEFI Specification version and is therefore not a standard UEFI firmware.

GRUB2 UEFI bootloader is available in Arch Linux only from version 1.99~rc1 . To install, first Detect which UEFI firmware arch you have (either x86_64 or i386).

Depending on that, install the appropriate package

For 64-bit aka x86_64 UEFI firmware:

# pacman -S grub2-efi-x86_64

For 32-bit aka i386 UEFI firmware:

# pacman -S grub2-efi-i386
Note: Installing grub2-common (a dependency of grub2-bios) 1.99~rc1 or later, may take forever in some systems since the post_install script runs grub-mkconfig and this script does not provide the option --no-floppy. For more details search this option in the article.
Note: Simply installing the package won't update the grub.efi file and the grub2 modules in the UEFI System Partition . You need to update the grub.efi file and the grub2 modules in the UEFI System Partition manually using grub_efi_${UEFI_ARCH}-install as explained below.

Also load the device-mapper kernel module without which grub-probe does not reliably detect disks and partitions

# modprobe dm-mod
Install to UEFI SYSTEM PARTITION
Mount UEFI SYSTEM PARTITION

Mount the UEFI SYSTEM PARTITION in your system at Template:Filename. It should be FAT32 formatted and should be at least 200 MiB in size. If you have mounted the UEFISYS partition in some other mountpoint, replace Template:Filename in the below commands with that mountpoint:

# mkdir -p /boot/efi
# mount -t vfat <UEFISYS_PART_DEVICE> /boot/efi
# mkdir -p /boot/efi/efi
Run grub_efi_${UEFI_ARCH}-install
Note: The below commands assume you are using Template:Codeline (for Template:Codeline replace Template:Codeline with Template:Codeline in the below commands).
# grub_efi_x86_64-install --root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=grub --no-floppy --recheck

The Template:Codeline automatically generates a Template:Filename while setting up the Template:Filename directory.

If you notice carefully, there is no <device_path> option (Eg: Template:Filename) at the end of the Template:Codeline 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.

You may now be able to UEFI boot your system by creating a grub.cfg file using grub-mkconfig and copying /boot/efi/efi/grub/grub.efi to /boot/efi/efi/boot/bootx64.efi.

After grub_efi_${UEFI_ARCH}-install
Launch GRUB2 as default in non-Mac UEFI systems
Note: The below steps will not work if the system has been booted in BIOS mode and will not work if the UEFI processor architecture does not match the kernel one, i.e. x86_64 UEFI + ix86 32-bit Kernel and vice-versa config will not work.

grub_efi_${UEFI_ARCH}-install will ensure Template:Filename is launched by default if it detects Template:Codeline and if it is able to access UEFI Runtime Services. Template:Codeline command will work only if you have booted the system in UEFI mode itself, since it requires access to UEFI Runtime Variables which are available only in UEFI boot mode (with "noefi" kernel parameter NOT being used). Initially the user is required to manually launch Template:Filename from the firmware itself (using maybe the UEFI Shell) if grub2-efi was installed in BIOS mode. Then Template:Codeline should be run to make grub2 as the default entry in the UEFI Boot Manager

First boot into UEFI mode manually either using the firmware boot menu, UEFI shell, or using any UEFI capable bootable iso (Archboot or Ubuntu non-Mac iso). Use grub probe to determine the device path of your EFI System Partition:

# grub-probe --target=device /boot/efi/efi/grub/grub.efi

It should give something like Template:Filename (used as example in the remaining steps). Load 'efivars' kernel module:

# modprobe efivars

If you get no such device found error for this command, that means you have not booted in UEFI mode or due to some reason the kernel is unable to access UEFI Runtime Variables.

Verify whether there are files in /sys/firmware/efi/vars/ directory. This directory and its contents are created by "efivars" kernel module and it will exist only if you have booted in UEFI mode without the "noefi" kernel parameter.

# ls -1 /sys/firmware/efi/vars/

Sample output (x86_64-UEFI 2.3.1 in x86_64 Kernel:

# ls -1 /sys/firmware/efi/vars/
Boot0000-8be4df61-93ca-11d2-aa0d-00e098032b8c/
BootCurrent-8be4df61-93ca-11d2-aa0d-00e098032b8c/
BootOptionSupport-8be4df61-93ca-11d2-aa0d-00e098032b8c/
BootOrder-8be4df61-93ca-11d2-aa0d-00e098032b8c/
ConIn-8be4df61-93ca-11d2-aa0d-00e098032b8c/
ConInDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
ConOut-8be4df61-93ca-11d2-aa0d-00e098032b8c/
ConOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
ErrOutDev-8be4df61-93ca-11d2-aa0d-00e098032b8c/
Lang-8be4df61-93ca-11d2-aa0d-00e098032b8c/
LangCodes-8be4df61-93ca-11d2-aa0d-00e098032b8c/
MTC-eb704011-1402-11d3-8e77-00a0c969723b/
MemoryTypeInformation-4c19049f-4137-4dd3-9c10-8b97a83ffdfa/
PlatformLang-8be4df61-93ca-11d2-aa0d-00e098032b8c/
PlatformLangCodes-8be4df61-93ca-11d2-aa0d-00e098032b8c/
RTC-378d7b65-8da9-4773-b6e4-a47826a833e1/
del_var
new_var

If /sys/firmware/efi/vars/ directory is empty or does not exist, then Template:Codeline command will not work. If you are unable to make the ISO/CD/DVD/USB boot in UEFI mode try https://gitorious.org/tianocore_uefi_duet_builds/pages/Linux_Windows_BIOS_UEFI_boot_USB .

If /sys/firmware/efi/vars/ directory (along with the exists then run Template:Codeline and reboot:

# efibootmgr --create --gpt --disk /dev/sda --part 1 --write-signature --label "GRUB2" --loader "\\EFI\\grub\\grub.efi"

In the above command, Template:Filename can be split up as Template:Filename and Template:Filename, which translates to Template:Filename -> partition 1 -> Template:Filename.

FAT32 filesystem is case-insensitive since it does not use UTF-8 encoding by default. In that case the firmware uses capital 'EFI' instead of small 'efi', therefore using Template:Filename or Template:Filename does not matter (this will change if the filesystem encoding is UTF-8). UEFI uses backward slash as path separatoir (similar to Windows paths). In the above command "double" backward slashes are used instead of single ones, since a backward slash is used as a escape character by sh shells, the first backward slash escapes the second one so that the path Template:Filename is passed to Template:Codeline.

The 'label' is the name of the menu entry shown in the UEFI boot menu. This name is user's choice and does not affect the booting of the system. More info can be obtained from efibootmgr GIT README

If you have problems running GRUB2 in UEFI mode you can try the following (worked on an ASUS Z68 mainboard):

# cp /boot/efi/efi/grub/grub.efi /boot/efi/shellx64.efi

or

# cp /boot/efi/efi/grub/grub.efi /boot/efi/efi/shellx64.efi

or

# cp /boot/efi/efi/grub/grub.efi /boot/efi/efi/shell/shellx64.efi

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).

Launch GRUB2 as default in Apple Mac EFI systems
Note: Using Template:Filename in Apple Macs will brick the firmware and may need reflash of the motherboard ROM. There have been bug reports regarding this in Ubuntu/Launchpad bug tracker. Use bless command alone in case of Macs

Use bless command from within Mac OS X to setup Template:Filename as the default boot option. More info at https://help.ubuntu.com/community/UEFIBooting#Apple_Mac_EFI_systems_.28both_EFI_architecture.29 .

Generate GRUB2 UEFI Config file

Finally, generate a configuration for grub2 (this is explained in greater detail in the Configuration section):

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

If grub2-uefi complains about "no suitable mode found" while booting, go to #Correct_GRUB2_No_Suitable_Mode_Found_Error .

Generate a custom GRUB2 UEFI Application

If you want, you can create a custom Template:Filename app using:

# grub-mkimage -d /usr/lib/grub/x86_64-efi -O x86_64-efi -p "" -o /boot/efi/efi/grub/grub_custom.efi <GRUB2_Modules_to_be_included>
Note: The -p option is important for creating a portable Template:Filename app.

There is no file-size restriction on Template:Filename either due to GRUB2 or due to the UEFI firmware. Therefore you can include any number of modules you want.

A "Template:Filename" created for BIOS based GRUB2 will be sufficient for the UEFI GRUB2 as long as all the paths in the config are absolute paths. The Template:Filename file should exist in the same directory as Template:Filename or Template:Filename.

The Template:Filename UEFI application can be launched using the firmware's "Boot Manager", "Boot from file" option or using the UEFI Shell.

Alternatively, you can also setup Template:Filename directory by copying all the files in Template:Filename to Template:Filename and using the above grub-mkimage command to create a Template:Filename application. Just make sure you have the required modules embedded in Template:Filename to enable it to access the EFI SYSTEM PARTITION.

A basic Template:Filename can be generated using the following command:

# sudo grub-mkimage -d /usr/lib/grub/x86_64-efi -O x86_64-efi -p "" -o /boot/efi/efi/grub/grub_custom.efi part_gpt fat iso9660 udf normal chain linux \
ls search search_fs_file search_fs_uuid search_label help boot configfile echo efi_gop
Multiboot in UEFI
Chainload Microsoft Windows x86_64 UEFI-GPT

Find the UUID of the FAT32 filesystem in the UEFI SYSTEM PARTITION where the Windows UEFI Bootloader files reside. For example, if Windows Template:Filename exists at Template:Filename (ignore the upper-lower case differences since that is immaterial in FAT filesystem):

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

Then, add this code to Template:Filename to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode :

menuentry "Microsoft Windows x86_64 UEFI-GPT" {
    insmod part_gpt
    insmod fat
    insmod search_fs_uuid
    insmod chain
    search --fs-uuid --no-floppy --set=root 1ce5-7f28
    chainloader (${root})/efi/Microsoft/Boot/bootmgfw.efi
}

Manual Compilation

For BIOS Systems

GRUB2 for BIOS systems should be compiled as follows:

./autogen.sh

./configure --with-platform=pc --prefix=/usr

make

make install

The --with-platform=pc generates grub2 for bios alone irrespective of the firmware of the build system.

For UEFI Systems

First Detect which UEFI Firmware arch you have and then follow the compile instructions below:

./autogen.sh

./configure --with-platform=efi --target=TARGET_UEFI_ARCH --prefix=/usr

make

make install

The "--target" option denotes the UEFI firmware arch. for which grub2 should be compiled, not the architecture of the linux kernel grub2 may boot.

It is possible to use UEFI 64-bit firmware + GRUB2 as x86_64-EFI app loading a i686 linux kernel, as long as the kernel does not try to access UEFI Runtime Services. Vice-versa situation is also possible. But a x86_64 UEFI firmware cannot launch GRUB2 i386-efi app (unlike x86_64 Operating Systems), and a i386 UEFI firmware will not launch GRUB2 Template:Codeline app. It is important to compile GRUB2 to match the architecture of the UEFI firmware.

Configuration

The configuration files are Template:Filename and Template:Filename. These files are used to generate the Template:Filename file. You can also choose to manually edit Template:Filename.

grub-mkconfig

The grub-mkconfig script can be used to generate a Template:Filename file. By default the script outputs to stdout. Note that gettext ― an optional dependency of the GRUB2 package ― is required by the grub-mkconfig script. To generate a Template:Filename file run the command:

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

Note that grub-mkconfig probably has your grub directory hardcoded to /boot/grub, which is probably wrong if you're using UEFI. Either mount your efi grub directory at /boot/grub or edit the script.

grub.cfg

A basic grub file uses the following options

An example configuration:

Template:File

Dual-booting

NOTE: If you want GRUB2 to automatically search for other systems, for example as in Ubuntu. Then you may need to download Template:Package AUR from the AUR.

Using grub-mkconfig

The best way to add other entries is editing the Template:Filename. The entries in this file will be automatically added when running grub-mkconfig. After adding the new lines, run:

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

to generate an updated Template:Filename.

With GNU/Linux

Assuming that the other distro is on partition Template:Filename:

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)
}
With Windows

This assumes that your Windows partition is Template:Filename.

# (2) Windows XP
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 Template:Codeline and is now done with Template:Codeline. Assume grub is on Template:Filename and windows on Template:Filename, you need to add the following after Template:Codeline:

drivemap -s hd0 hd2

With Windows via EasyBCD and NeoGRUB

Since EasyBCD's NeoGRUB currently does not understand the GRUB2 menu format, chainload to it by replacing the contents of your Template:Filename file with lines similar to the following:

default 0
timeout 1
title       Chainload into GRUB v2
root        (hd0,7)
kernel      /boot/grub/core.img

Visual Configuration

In GRUB2 it is possible, by default, to change the look of the menu.

Background image and bitmap fonts

GRUB2 comes with support for background images and bitmap fonts in pf2 format. The unifont font is included in the grub2 package under the filename Template:Filename, or, as only ascii characters under the name Template:Filename. Image formats supported include tga, png and jpeg, providing the correct modules are loaded. The maximum supported resolution depends on your hardware. There are two ways of setting a Template:Filename file as background. Two sample configurations are shown below.

Edit Template:Filename like this:

GRUB_GFXMODE=1024x768x32
GRUB_GFXPAYLOAD_LINUX=keep
GRUB_BACKGROUND="/boot/grub/archlinux.tga"
#GRUB_THEME="/path/to/gfxtheme"

(archlinux.tga is a placeholder; put your file name there)

To generate the changes, run:

grub-mkconfig -o /boot/grub/grub.cfg
Note: If this example does not work for you try to replace Template:Codeline by Template:Codeline.
Note: To show all the modes you can use Template:Codeline (hwinfo is available in [community]), while at grub2 prompt you can use the Template:Codeline command.
Note: If you have installed Grub on a separate partition, Template:Filename becomes Template:Filename.

Menu colors

As in Grub (0.9x), you can change the menu colors in Grub2. The available colors for GRUB2 are at http://www.gnu.org/software/grub/manual/html_node/Theme-file-format.html#Theme-file-format . Here is an example:

Edit Template:Filename:

GRUB_COLOR_NORMAL="light-blue/black"
GRUB_COLOR_HIGHLIGHT="light-cyan/blue"

Generate the changes:

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

Hidden menu

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.

Edit Template:Filename 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

Setting the framebuffer resolution

Grub2 can set the framebuffer for both grub2 itself and the kernel. The old vga= way is deprecated. The preferred method is editing Template:Filename as the following sample:

GRUB_GFXMODE=1024x768x32
GRUB_GFXPAYLOAD_LINUX=keep

To generate the changes, run:

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

The Template:Codeline property will make sure the kernel keeps the resolution.

If this method does not work for you, the deprecated vga= method will still work. Just add it next to the "GRUB_CMDLINE_LINUX_DEFAULT=" line in Template:Filename for eg: "GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792" will give you a Template:Codeline resolution.

You can choose one of these resolutions: Template:Codeline, Template:Codeline, Template:Codeline, Template:Codeline, Template:Codeline

Other Options

LVM

If you use LVM for your Template:Filename, 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. Template:Filename becomes:

set root=(md0)

whereas a partitioned raid-volume (e.g. Template:Filename) becomes:

set root=(md0,1)

Persistent block device naming

You can use UUIDs to detect partitions instead of the "old" Template:Filename and Template:Filename 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 Template:Filename 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 Template:Codeline 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 Template:Codeline option to Template:Codeline. 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 Template:Filename and change the setting of Template:Codeline:

GRUB_DEFAULT=saved

This ensures that grub will default to the saved entry. To enable saving the selected entry, add the following line to Template:Filename:

GRUB_SAVEDEFAULT=true

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 Template:Codeline. Enter a password and confirm it. The output will look like this:

Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A
Then, add the following to Template:Filename:
cat << EOF

set superusers="username"
password_pbkdf2 username <password>

EOF

where <password> is the string generated by Template:Codeline.

Regenerate your configuration file. Your GRUB2 command line and boot parameters are now protected.

Booting an Ubuntu ISO Image from the GRUB2 Screen

Edit Template:Filename to add an entry pointing to an Ubuntu iso:

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
}

Be sure to adjust the "hdX,Y" in the third line to point to the correct disk/partition number of the isofile. When finished, update grub2's configuration file via:

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

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 Template:Filename, 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

  • grub2-editor (requires kdelibs)
    A KDE4 control module for configuring the GRUB2 bootloader
  • kcm-grub2 (requires kdelibs python2-qt kdebindings-python)
    This Kcm module manages the most common settings of Grub2.
  • 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 "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 Template:Filename partition (be it a separate partition, or a subdirectory under their root):

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

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

To expand console capabilities, insert the "linux" module:

grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
Note: With a separate boot partition, omit Template:Filename from the path, (i.e. type Template:Codeline and Template:Codeline).

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 Template:Filename as needed and then run:

# grub-install /dev/sda --no-floppy

to reinstall GRUB2 and fix the problem completely, changing Template:Filename if needed. See #Bootloader installation for details.

Combining the use of UUID's and basic scripting

If you like the idea of using UUID's to avoid unreliable BIOS mappings or are struggling with Grub's syntax, here is an example boot menu item that uses UUID's and a small script to direct Grub to the proper disk partitions for your system. All you need to do is replace the UUID's in the sample with the correct UUID's for your system. (The example applies to a system with a boot and root partition. You will obviously need to modify the Grub configuration if you have additional partitions.)

 menuentry "Arch Linux 64" {
   #Enter the UUID of your boot partition (this is where Grub and your kernel reside)
   set uuid_grub_boot=ece0448f-bb08-486d-9864-ac3271bd8d07
   
   #Enter the UUID of the partition containing the root partition of your Arch Linux installation.            
   set uuid_os_root=c55da16f-e2af-4603-9e0b-03f5f565ec4a
   
   #(Note: this may be the same as your boot partition)
   
   #Here we set the Grub "root" variable by locating the UUID of the root partition identified above   
   search --fs-uuid --no-floppy --set=root $uuid_os_root
   
   #Here we set a custom variable grub_boot by locating the UUID of the boot partition identified above          
   search --fs-uuid --no-floppy --set=grub_boot $uuid_grub_boot
   
   #Here is the magic. We test to see if the boot and root partitions have the same UUID.
   #If they do, we append /boot to the $grub_boot variable. For ex. (hd0,1) becomes (hd0,1)/boot.
   if [ $uuid_grub_boot == $uuid_os_root ] ; then
      set grub_boot=$grub_boot/boot
   fi
   
   # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd
   linux ($grub_boot)/vmlinuz-linux root=/dev/disk/by-uuid/$uuid_os_root ro
   initrd ($grub_boot)/initramfs-linux.img
 }

Troubleshooting

Any troubleshooting should be added here.

Enable GRUB2 debug messages

Add

set pager=1
set debug=all

to Template:Filename.

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 Template:Filename to ${GRUB2_PREFIX_DIR} (Template:Filename in case of BIOS systems and Template:Filename in case of UEFI systems).

# cp /usr/share/grub/unicode.pf2 ${GRUB2_PREFIX_DIR}

If Template:Filename does not exist, install Template:Package Official, create the unifont.pf2 file and then copy it to ${GRUB2_PREFIX_DIR} .

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

Then, in the Template:Filename file, add the following lines to enable grub2 to pass the video mode correctly to the kernel, without of which you will only get a black screen (no output) but booting (actually) proceeds successfully without any system hang:

BIOS systems

insmod vbe

UEFI systems

insmod efi_gop
insmod efi_uga

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

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

As you can see for gfxterm (graphical terminal) to function properly, Template:Filename 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 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 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.
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.

References

  1. Official GRUB2 Manual - http://www.gnu.org/software/grub/manual/grub.html
  2. GRUB2 wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting - previously http://grub.enbug.org/TestingOnUEFITemplate:Linkrot
  3. Wikipedia's page on BIOS Boot Partition

External Links

  1. A Linux Bash Shell script to compile and install GRUB2 for BIOS from BZR Source
  2. A Linux Bash Shell script to compile and install GRUB2 for UEFI from BZR Source