Difference between revisions of "GRUB"
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{{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|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 [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). | + | 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). |
Depending on that, install the appropriate package | Depending on that, install the appropriate package |
Revision as of 00:01, 27 December 2011
Template:Article summary text Template:Article summary heading Template:Article summary text Template:Article summary heading Template:Article summary wiki - 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. Template:Article summary heading Template:Article summary link Template:Article summary end
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].
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.
Contents
- 1 Preface
- 2 Installation
- 2.1 During Arch Linux installation
- 2.2 From a running Arch Linux
- 2.2.1 BIOS systems
- 2.2.2 UEFI systems
- 3 Configuration
- 4 Using the command shell
- 5 GUI configuration tools
- 6 parttool or legacy hide/unhide
- 7 Using the rescue console
- 8 Combining the use of UUID's and basic scripting
- 9 Troubleshooting
- 10 References
- 11 External Links
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.
Notes for current GRUB Legacy 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,
/dev/sda1
would be referred to as(hd0,msdos1)
(for MBR) or(hd0,gpt1)
(for GPT) using GRUB2.
Preliminary Requirements for GRUB2
BIOS systems
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 set <BOOT_PART_NUM> bios_grub on
in GNU Parted.
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
UEFI systems
Create and Mount the UEFI SYSTEM PARTITION
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 /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 /boot/efi
in the below instructions with that mountpoint:
# mkdir -p /boot/efi # mount -t vfat <UEFISYS_PART_DEVICE> /boot/efi
Create a <UEFI_SYSTEM_PARTITION>/efi directory if it does not exist:
# mkdir -p /boot/efi/efi
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
/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 /tmp/install/etc/resolv.conf
- If you run into network issues in the pacman update step below, you may have needed to install the net-tools package.
- Load the dm-mod module (you might need grub2-bios; install the package if needed):
# modprobe dm-mod
- 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 -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
BIOS systems
Backup Important Data
In general, a grub installation should run smoothly. Sometimes it could mess up your system. You're strongly advised to make a backup before installing grub2-bios.
- copy grub modules and configuration
# cp -a /boot/grub /path/to/backup/
- backup the MBR and GRUB-Legacy stage 1.5
# dd if=/dev/sdX of=/path/to/backup/first-sectors bs=512 count=63
Replace /dev/sdaX with you disk path (mostly /dev/sda).
To backup only the MBR boot code use:
# dd if=/dev/sdX of=/path/to/backup/mbr-boot-code bs=440 count=1
You could now lightly remove /boot/grub
with:
# rm -rf /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 grub-legacy or 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/sdX bs=512 count=63
To restore only the MBR boot code use:
# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=440 count=1
Install grub2-bios package
The GRUB2 package can be installed with pacman (and will replace grub, if it is installed). Simply installing the package won't update the /boot/grub/core.img
file and the grub2 modules in /boot/grub
. You need to update them manually using grub_bios-install as explained below.
# pacman -S grub2-bios
--no-floppy
. For more details search this option in the article.Also load the device-mapper kernel module without which grub-probe does not reliably detect disks and partitions:
# modprobe dm-mod
Install grub2-bios boot files
There are 3 ways to install grub2 boot files in BIOS booting:
- #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
/boot/grub/core.img
).
Install to 440-byte MBR boot code region
To setup grub2-bios in the 440-byte Master Boot Record boot code region, populate the /boot/grub
directory, generate the /boot/grub/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:
# grub_bios-install --boot-directory=/boot --no-floppy --recheck --debug /dev/sda
where /dev/sda
is the destination of the installation (in this case the MBR of the first SATA disk). If you use LVM for your /boot
, you can install GRUB2 on multiple physical disks.
The --no-floppy
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 occurring). 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.
Install to Partition or Partitionless Disk
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 --debug /dev/sda1 # chattr +i /boot/grub/core.img
You need to use the --force
option to allow usage of blocklists and should not use --grub-setup=/bin/true
(which is similar to simply generating core.img).
grub_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 --force
you may get the below error and grub-setup will not setup its boot code in the partition boot sector.
/sbin/grub-setup: error: will not proceed with blocklists
With --force
you should get
Installation finished. No error reported.
The reason why grub-setup does not by default allow this is because in case of partition or a partitionless disk is that grub2-bios relies on embedded blocklists in the partition bootsector to locate the /boot/grub/core.img
file and the prefix dir /boot/grub
. The sector locations of core.img
may change whenever the filesystem in the partition is being altered (files copied, deleted etc.). For more info see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915 .
The workaround for this is to set the immutable flag on /boot/grub/core.img
(using chattr command as mentioned above) so that the sector locations of the core.img
file in the disk is not altered. The immutable flag on /boot/grub/core.img
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 core.img
without embedding any bootsector (mentioned above).
Generate core.img alone
To populate the /boot/grub
directory and generate a /boot/grub/core.img
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 --debug /dev/sda
You can then chainload grub2's core.img from grub-legacy or syslinux as a Linux kernel or a multiboot kernel.
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 .
If grub-mkconfig
fails, convert your /boot/grub/menu.lst
file to /boot/grub/grub.cfg
using:
# grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
For example:
/boot/grub/menu.lst
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
/boot/grub/grub.cfg
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' }
If you forgot to create a GRUB2 /boot/grub/grub.cfg
configfile and simply rebooted into GRUB2 Command Shell, type:
sh:grub> insmod legacycfg sh:grub> legacy_configfile ${prefix}/menu.lst
Boot into Arch and re-create the proper GRUB2 /boot/grub/grub.cfg
configfile.
Multiboot in BIOS
Boot Microsoft Windows installed in BIOS-MBR mode
bootmgr
directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.Find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the bootmgr and its files reside. For example, if Windows bootmgr
exists at /media/Windows/bootmgr
:
# grub-probe --target=fs_uuid /media/Windows/bootmgr 69B235F6749E84CE
Then, add the below code to /etc/grub.d/40_custom
and regenerate grub.cfg with grub-mkconfig as explained above to chainload Windows (Vista, 7 or 8) installed in BIOS-MBR mode:
menuentry "Microsoft Windows 7 BIOS-MBR" { insmod part_msdos insmod ntfs insmod search_fs_uuid insmod ntldr search --fs-uuid --no-floppy --set=root 69B235F6749E84CE ntldr (${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 (${root})/ntldr }
UEFI systems
Install grub2-uefi package
GRUB2 UEFI bootloader is available in Arch Linux only from version 1.99~rc1. To install, first Detect which UEFI firmware arch you have (either x86_64 or i386).
Depending on that, install the appropriate package
For 64-bit aka x86_64 UEFI firmware:
# pacman -S grub2-efi-x86_64
For 32-bit aka i386 UEFI firmware:
# pacman -S grub2-efi-i386
--no-floppy
. For more details search this option in the article.Also load the device-mapper kernel module without which grub-probe does not reliably detect disks and partitions
# modprobe dm-mod
Install grub2-uefi boot files
Install to UEFI SYSTEM PARTITION
grub2-efi-x86_64
(for grub2-efi-i386
replace x86_64
with i386
in the below commands).# grub_efi_x86_64-install --root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=grub --no-floppy --recheck --debug
The grub_efi_x86_64-install
automatically generates a grub.efi
while setting up the /boot/efi/efi/grub/
directory.
If you notice carefully, there is no <device_path> option (Eg: /dev/sda
) at the end of the grub_efi_x86_64-install
command unlike the case of setting up grub2 for BIOS systems. Any <device_path> provided will be ignored by the install script as UEFI bootloaders do not use MBR or Partition boot sectors at all.
You may now be able to UEFI boot your system by creating a grub.cfg file by following #Generate_GRUB2_UEFI_Config_file and copying /boot/efi/efi/grub/grubx64.efi to /boot/efi/efi/boot/bootx64.efi.
Create GRUB2 entry in the Firmware Boot Manager
Non-Mac UEFI systems
efibootmgr
in Apple Macs will brick the firmware and may need reflash of the motherboard ROM. There have been bug reports regarding this in Ubuntu/Launchpad bug tracker. Use bless command alone in case of Macs (see chapter regarding Apple systems
grub_efi_${UEFI_ARCH}-install will ensure /boot/efi/efi/grub/grub.efi
is launched by default if it detects efibootmgr
and if it is able to access UEFI Runtime Services. efibootmgr
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 /boot/efi/efi/grub/grub.efi
from the firmware itself (using maybe the UEFI Shell) if grub2-efi was installed in BIOS mode. Then efibootmgr
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 /dev/sda1
(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 efibootmgr
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 efibootmgr
and reboot:
# efibootmgr --create --gpt --disk /dev/sda --part 1 --write-signature --label "GRUB2" --loader "\\EFI\\grub\\grub.efi"
In the above command, /boot/efi/efi/grub/grub.efi
can be split up as /boot/efi
and /efi/grub/grub.efi
, which translates to (/dev/sda)
-> partition 1 -> \\EFI\\grub\\grub.efi
.
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 \\EFI\\grub\\grub.efi
or \\efi\\grub\\grub.efi
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 \EFI\grub\grub.efi
is passed to efibootmgr
.
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/grubx64.efi /boot/efi/shellx64.efi
or
# cp /boot/efi/efi/grub/grubx64.efi /boot/efi/efi/shellx64.efi
or
# cp /boot/efi/efi/grub/grubx64.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).
Apple Mac EFI systems
Use bless command from within Mac OS X to set grub.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:
# cd /Volumes # mkdir efi # mount -t msdos /dev/disk0s1 /Volumes/efi
Then run bless on grub.efi
and on the EFI partition to set them as the default boot options.
# bless --folder=/Volumes/efi --file=/Volumes/efi/efi/grub/grub.efi --setBoot # bless --mount=/Volumes/efi --file=/Volumes/efi/efi/grub/grub.efi --setBoot
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 .
Create GRUB2 Standalone UEFI Application
It is possible to create a grub_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.
The easiest way to do this would be with the install command already mentioned before, but specifying the modules to include. For example:
# grub_efi_x86_64-install --root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=grub --no-floppy --recheck --debug \ --modules="normal help ext2 video efi_gop gfxterm gzio"
However, you might want to embed certain configuration as well, for which you might want to use a script like this:
grub_image_helper
#!/bin/bash ARCH=${1:-x86_64-efi} cat << EOF > "grub.cfg" search --no-floppy --fs-uuid --set=grub_root 5EF2-55E6 set prefix=(\$grub_root)/efi/grub EOF grub-mkimage --format=$ARCH --compression=xz --output=/boot/efi/efi/grub/grub_standalone.efi --config grub.cfg '--prefix=(,gpt1)/efi/grub' fat part_gpt search
You would need to create an entry with efibootmgr
for grub_standalone.efi, just use grub.efi instead to replace the original, or you can use the UEFI shell to try it out first. See #Create GRUB2 entry in the Firmware Boot Manager.
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 bootmgfw.efi
exists at /boot/efi/efi/Microsoft/Boot/bootmgfw.efi
(ignore the upper-lower case differences since that is immaterial in FAT filesystem):
# grub-probe --target=fs_uuid /boot/efi/efi/Microsoft/Boot/bootmgfw.efi 1ce5-7f28
Then, add this code to /boot/efi/efi/grub/grub.cfg
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 }
Configuration
You can also choose to automatically generate or manually edit grub.cfg
.
grub.cfg
must be placed alongside grub.efl
on the UEFI system partition. The easiest way is to copy the configuration file created below from /boot/grub/grub.cfg
to /boot/efi/EFI/grub
where /boot/efi
is the mounted UEFI partition. Automatically generating using grub-mkconfig (Recommended)
The GRUB2 menu.1st
equivalent configuration files are /etc/default/grub
and /etc/grub.d/*
. grub-mkconfig uses these files to generate grub.cfg
. By default the script outputs to stdout. To generate a grub.cfg
file run the command:
# grub-mkconfig -o /boot/grub/grub.cfg
/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 /etc/grub.d/40_custom
Manually creating grub.cfg
A basic grub file uses the following options
-
(hdX,Y)
is the partitionY
on diskX
, partition numbers starting at 1, disk numbers starting at 0 -
set default=N
is the default boot entry that is chosen after timeout for user action -
set timeout=M
is the timeM
to wait in seconds for a user selection before default is booted -
menuentry "title" {entry options}
is a boot entry titledtitle
-
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 (/
)
An example configuration:
/boot/grub/grub.cfg
# Config file for GRUB2 - The GNU GRand Unified Bootloader # /boot/grub/grub.cfg # DEVICE NAME CONVERSIONS # # Linux Grub # ------------------------- # /dev/fd0 (fd0) # /dev/sda (hd0) # /dev/sdb2 (hd1,2) # /dev/sda3 (hd0,3) # # Timeout for menu set timeout=5 # Set default boot entry as Entry 0 set default=0 # (0) Arch Linux menuentry "Arch Linux" { set root=(hd0,1) linux /vmlinuz-linux root=/dev/sda3 ro initrd /initramfs-linux.img } ## (1) Windows #menuentry "Windows" { #set root=(hd0,3) #chainloader +1 #}
Dual-booting
NOTE: If you want GRUB2 to automatically search for other systems, for example as in Ubuntu. Then you may need to download os-proberAUR from the AUR.
Using grub-mkconfig
The best way to add other entries is editing the /etc/grub.d/40_custom
. 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 grub.cfg
.
With GNU/Linux
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) }
With FreeBSD
Requires that FreeBSD is installed on a single partition with UFS. Assuming it is installed on sda4
:
menuentry "FreeBSD" { set root=(hd0,4) chainloader +1 }
With Windows
This assumes that your Windows partition is sda3
.
# (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 map
and is now done with drivemap
. Assume grub is on hd0
and windows on hd2
, you need to add the following after set root
:
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 C:\NST\menu.lst
file with lines similar to the following:
default 0 timeout 1
title Chainload into GRUB v2 root (hd0,7) kernel /boot/grub/core.img
Visual Configuration
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.
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 /etc/default/grub
as the following sample:
GRUB_GFXMODE=1024x768x32 GRUB_GFXPAYLOAD_LINUX=keep
To generate the changes, run:
grub-mkconfig -o /boot/grub/grub.cfg
The gfxpayload
property will make sure the kernel keeps the resolution.
gfxmode="1024x768x32"
by vbemode="0x105"
. Remember to replace the specified resolution with one suitable for your screen.# hwinfo --framebuffer
(hwinfo is available in [community]), while at grub2 prompt you can use the vbeinfo
command.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 /etc/default/grub
for eg: "GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"
will give you a 1024x768
resolution.
You can choose one of these resolutions: 640×480
, 800×600
, 1024×768
, 1280×1024
, 1600×1200
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 unicode.pf2
, or, as only ascii characters under the name ascii.pf2
.
Image formats supported include tga, png and jpeg, providing the correct modules are loaded. The maximum supported resolution depends on your hardware.
Make sure you have set up the proper framebuffer resolution.
Edit /etc/default/grub
like this:
GRUB_BACKGROUND="/boot/grub/archlinux.tga" #GRUB_THEME="/path/to/gfxtheme"
(archlinux.tga is a placeholder; put your file name there)
/boot/grub/archlinux.tga
becomes /grub/archlinux.tga
.To generate the changes and add the information into grub.cfg, run:
grub-mkconfig -o /boot/grub/grub.cfg
If adding the splash image was successful, the user will see "Found background image..." in the terminal as the command is executed. If this phrase is not seen, the image information was probably not incorporated into the grub.cfg file.
If the image is not displayed, check:
- The path and the filename in /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 /etc/default/grub.
- The command grub-mkconfig must be executed to place the background image information into the /boot/grub/grub.cfg file.
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 /etc/default/grub
:
GRUB_COLOR_NORMAL="light-blue/black" GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
Generate the changes:
grub-mkconfig -o /boot/grub/grub.cfg
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 /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 /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. /dev/md0
becomes:
set root=(md0)
whereas a partitioned raid-volume (e.g. /dev/md0p1
) becomes:
set root=(md0,1)
Persistent block device naming
You can use UUIDs to detect partitions instead of the "old" /dev/sd*
and /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 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 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 --label
option to 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 /etc/default/grub
and change the setting of 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 /etc/default/grub
:
GRUB_SAVEDEFAULT=true
Note that manually added menu items, eg Windows in /etc/grub.d/40_custom
, will need 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 grub-mkpasswd_pbkdf2
. Enter a password and confirm it. The output will look like this:
Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269AThen, add the following to
/etc/grub.d/00_header
:
cat << EOF set superusers="username" password_pbkdf2 username <password> EOF
where <password> is the string generated by grub-mkpasswd_pbkdf2
.
Regenerate your configuration file. Your GRUB2 command line and boot parameters are now protected.
Booting an Ubuntu ISO Image from the GRUB2 Screen
Edit /etc/grub.d/40_custom
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 /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
- 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 /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 "linux" module:
grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
/boot
from the path, (i.e. type set prefix=(hdX,Y)/grub
and 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 grub.cfg
as needed and then run:
# grub-install /dev/sda --no-floppy
to reinstall GRUB2 and fix the problem completely, changing /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" { #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 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 /usr/share/grub/unicode.pf2
to ${GRUB2_PREFIX_DIR} (/boot/grub/
in case of BIOS systems and /boot/efi/efi/grub/
in case of UEFI systems).
# cp /usr/share/grub/unicode.pf2 ${GRUB2_PREFIX_DIR}
If /usr/share/grub/unicode.pf2
does not exist, install bdf-unifont, 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 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}/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 ${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 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 grub.cfg
. For UEFI, grub.cfg
must be copied into the UEFI system partition alongside grub.efi (/boot/efi/EFI/grub
)
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
- Official GRUB2 Manual - http://www.gnu.org/software/grub/manual/grub.html
- 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 BIOS Boot Partition