Difference between revisions of "GRUB"

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[[Category:Boot loaders (English)]]
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[[Category:Boot loaders]]
{{i18n|GRUB2}}
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[[cs:GRUB2]]
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[[de:GRUB]]
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[[es:GRUB2]]
 
[[fr:GRUB2]]
 
[[fr:GRUB2]]
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[[id:GRUB2]]
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[[it:GRUB2]]
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[[ru:GRUB2]]
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[[tr:GRUB2]]
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[[zh-CN:GRUB2]]
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[[zh-TW:GRUB2]]
 
{{Article summary start}}
 
{{Article summary start}}
 
{{Article summary text|Covers various aspects of the next generation of the GRand Unified Bootloader (GRUB2).}}
 
{{Article summary text|Covers various aspects of the next generation of the GRand Unified Bootloader (GRUB2).}}
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{{Article summary text|{{Boot process overview}}}}
 
{{Article summary text|{{Boot process overview}}}}
 
{{Article summary heading|Related}}
 
{{Article summary heading|Related}}
{{Article summary wiki|Burg}} - Burg is a brand-new boot loader based on GRUB2. It uses a new object format which allows it to be built in a wider range of OS, including Linux/Windows/OSX/Solaris/FreeBSD, etc. It also has a highly configurable menu system which works in both text and graphic mode.  
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{{Article summary wiki|BURG}} - BURG is a brand-new boot loader based on GRUB2. It can be built on a wider range of OS, and has a highly configurable menu system which works in both text and graphic mode.
 +
{{Article summary wiki|GRUB Legacy}} - previous Version, now obsolete.
 
{{Article summary heading|Resources}}
 
{{Article summary heading|Resources}}
{{Article summary link|GNU GRUB -- GNU Project|http://www.gnu.org/software/grub/}}
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{{Article summary wiki|GRUB EFI Examples}}
{{Article summary link|GNU GRUB Wiki|http://grub.enbug.org/}}{{Linkrot|2011|09|05}}
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{{Article summary link|GNU GRUB - GNU Project|https://www.gnu.org/software/grub/}}
 
{{Article summary end}}
 
{{Article summary end}}
 +
[https://www.gnu.org/software/grub/ GRUB2] is the next generation of the GRand Unified Bootloader (GRUB). GRUB2 is derived from [http://www.nongnu.org/pupa/ PUPA] which was a research project to investigate the next generation of GRUB. GRUB2 has been rewritten from scratch to clean up everything and provide modularity and portability [https://www.gnu.org/software/grub/grub-faq.html#q1].
  
[http://www.gnu.org/software/grub/ GRUB2] is the next generation of the GRand Unified Bootloader (GRUB). GRUB2 is derived from [http://www.nongnu.org/pupa/ PUPA] which was a research project to investigate the next generation of GRUB. GRUB 2 has been rewritten from scratch to clean up everything and provide modularity and portability [http://www.gnu.org/software/grub/grub-faq.en.html#q1].
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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.
 
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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.
+
  
 
== Preface ==
 
== Preface ==
 +
Here is some information that needs to be clarified:
 +
* The name ''GRUB'' officially refers to version ''2'' of the software, see [https://www.gnu.org/software/grub/]. If you are looking for the article on the legacy version, see [[GRUB Legacy]].
  
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.
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* From 1.99-6 onwards, GRUB2 supports [[Btrfs]] as root (without a separate {{ic|/boot}} filesystem) compressed with either zlib or LZO.
  
{{Note|grub2 from 1.99~rc2 and later supports btrfs as root (without a separate /boot filesystem).}}
+
* For GRUB2 UEFI info, it is recommended to read the [[Unified Extensible Firmware Interface|UEFI]], [[GUID Partition Table|GPT]] and [[UEFI Bootloaders]] pages before reading this page.
  
=== Notes for current GRUB users ===
+
=== Notes for current GRUB Legacy users ===
 +
* Upgrade from [[GRUB Legacy]] to GRUB2 is the much same as fresh installing GRUB2 which is covered [[#Installation|below]].
  
* There are differences in the commands of GRUB and GRUB2. Familiarize yourself with [http://www.gnu.org/software/grub/manual/grub.html#Commands GRUB2 commands] before proceeding (e.g. "find" has been replaced with "search").
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* There are differences in the commands of GRUB and GRUB2. Familiarize yourself with [https://www.gnu.org/software/grub/manual/grub.html#Commands 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).
 
* 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, {{Filename|/dev/sda1}} would be referred to as {{Codeline|(hd0,msdos1)}} (for MBR) or {{Codeline|(hd0,gpt1)}} (for GPT) using GRUB2.
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* Device naming has changed between GRUB and GRUB2. Partitions are numbered from 1 instead of 0 while drives are still numbered from 0, and prefixed with partition-table type. For example, {{ic|/dev/sda1}} would be referred to as {{ic|(hd0,msdos1)}} (for MBR) or {{ic|(hd0,gpt1)}} (for GPT) using GRUB2.
  
===== Preliminary Considerations for GRUB2 BIOS =====
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=== Preliminary Requirements for GRUB2 ===
  
====== [[GPT]] specific instructions ======
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==== BIOS systems ====
  
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.
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===== [[GUID Partition Table]] (GPT) specific instructions =====
 +
GRUB2 in BIOS-GPT configuration requires a [http://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html BIOS Boot Partition] to embed its {{ic|core.img}} in the absence of post-MBR gap in GPT partitioned systems (which is taken over by the GPT Primary Header and Primary Partition table). This partition is used by 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 {{Codeline|set <BOOT_PART_NUM> bios_grub on}} in GNU Parted.
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For a BIOS-GPT configuration, create a 1007 KiB partition at the beginning of the disk using cgdisk or GNU Parted with no filesystem. The size of 1007 KiB will allow for the following partition to be correctly alligned at 1024 KiB. If needed, the partition can also be located somewhere else on the disk, but it should be within the first 2 TiB region. Set the partition type to {{ic|0xEF02}} in gdisk, {{ic|EF02}} in cgdisk or {{ic|set <BOOT_PART_NUM> bios_grub on}} 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).}}
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{{Note|This partition should be created before {{ic|grub-install}} or {{ic|grub-setup}} is run.}}
 +
{{Note|gdisk will only allow you to create this partition on the position which will waste the least amount of space (sector 34-2047) if you create it last, after all the other partitions. This is because gdisk will auto-align partitions to 2048-sector boundaries if possible.}}
  
====== [[MBR]] aka msdos partitioning specific instructions ======
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===== [[Master Boot Record]] (MBR) 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 31 KiB when DOS compatibility cylinder alignment issues are satisfied in the partition table. However a post-MBR gap of about 1 to 2 MiB is recommended to provide sufficient room for embedding GRUB2's {{ic|core.img}} ({{bug|24103}}). It is advisable to use a partitioner which supports 1 MiB partition alignment to obtain this space as well as satisfy other non-512 byte sector issues (which are unrelated to embedding of {{ic|core.img}}).
  
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).
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MBR partitioning has better support in other operating systems, such as Microsoft Windows (up to Windows 7) and Haiku, than GPT partitioning. If you dual boot another operating system, consider using MBR partitioning.
  
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]]
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A MBR disk may be convertible to GPT if there is a small amount of extra space available. See [[GUID Partition Table#Convert from MBR to GPT]]
{{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.}}
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 +
==== UEFI systems ====
 +
{{Note|It is recommended to read and understand the [[Unified Extensible Firmware Interface|UEFI]], [[GUID Partition Table|GPT]] and [[UEFI Bootloaders]] pages.}}
 +
 
 +
===== Create and Mount the UEFI System Partition =====
 +
Follow [[Unified Extensible Firmware Interface#EFI System Partition]] for instructions on creating a UEFI SYSTEM PARTITION. Then mount the UEFI SYSTEM PARTITION at {{ic|/boot/efi}}. If you have mounted the UEFISYS partition in some other mountpoint, replace {{ic|/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>{{ic|/EFI}} directory, if it does not exist:
 +
 
 +
# mkdir -p /boot/efi/EFI
  
 
== Installation ==
 
== Installation ==
  
=== During Arch Linux installation ===
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=== BIOS systems ===
  
* Skip the '''Install Bootloader''' step and exit the installer.
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==== Backup Important Data ====
* Configure the network:
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# aif -p partial-configure-network
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This will bring up a prompt; put in the network interface to use, (e.g., eth0) and use DHCP for easy configuration.
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* If you did not configure the installed system's {{Filename|/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:
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# cp /etc/resolv.conf /mnt/etc/resolv.conf
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* Load the dm-mod module (you might need grub2-bios; install the package if needed):
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# modprobe dm-mod
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{{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.}}
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* From the installer's live shell, chroot to the installed system:
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# mount -o bind /dev /mnt/dev
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# chroot /mnt bash
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* Update pacman's database:
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# pacman-db-upgrade
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* 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):
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# pacman -Syy
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* 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 ===
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Although a GRUB(2) installation should run smoothly, it is strongly recommended to keep the GRUB Legacy files before installing {{Pkg|grub-bios}}.
  
====Make a backup of your precious data====
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# mv /boot/grub /boot/grub-legacy
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
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Backup the MBR which contains the boot code and partition table (Replace {{ic|/dev/sd'''X'''}} with your actual disk path)
# cp -a /boot/grub /path/to/backup/
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*backup the MBR and GRUB stage 1.5
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# dd if=/dev/sda of=/path/to/backup/first-sectors count=63
+
  
You could now lightly remove {{Filename|/boot/grub}} with:
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  # dd if=/dev/sdX of=/path/to/backup/mbr_backup bs=512 count=1
  # 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 :
+
Only 446 bytes of the MBR contain boot code, the next 64 contain the partition table. If you do not want to overwrite your partition table when restoring, it is strongly advised to backup only the MBR boot code:
  
*move old grub2 files out of the way
+
  # dd if=/dev/sdX of=/path/to/backup/bootcode_backup bs=446 count=1
  # mv /boot/grub /boot/grub.nonfunctional
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*copy grub back to /boot
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# cp -a /path/to/backup/grub /boot/
+
*replace MBR and next 62 sectors of sda with backed up copy (DANGEROUS!)
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# dd if=/path/to/backup/first-sectors of=/dev/sda count=63
+
  
 +
If unable to install GRUB2 correctly, see [[#Restore GRUB Legacy]].
  
===== grub2-bios-install =====
+
==== Install grub-bios package ====
  
The GRUB2 package can be installed with pacman (and will replace {{Package Official|grub}}, if it is installed):
+
The GRUB(2) packages can be installed with pacman (and will replace {{Pkg|grub-legacy}} or {{Pkg|grub}}, if it is installed):
 
   
 
   
  # pacman -S grub2-bios
+
  # pacman -S grub-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 <code>--no-floppy</code>. For more details search this option in the article.}}
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{{Note|Simply installing the package won't update the {{ic|/boot/grub/i386-pc/core.img}} file and the GRUB(2) modules in {{ic|/boot/grub/i386-pc}}. You need to update them manually using {{ic|grub-install}} as explained below.}}
  
{{Note|Simply installing the package 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.}}
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==== Install grub-bios boot files ====
  
Also load the device-mapper kernel module without which grub-probe does not reliably detect disks and partitions
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There are 3 ways to install GRUB(2) boot files in BIOS booting:
 +
*[[#Install to GPT BIOS Boot Partition]] (recommended with [[GPT]])
 +
*[[#Install to 440-byte MBR boot code region]] (recommended with [[MBR]])
 +
*[[#Install to Partition or Partitionless Disk]] (not recommended)
 +
*[[#Generate core.img alone]] (safest method, but requires another BIOS bootloader like [[grub-legacy]] or [[syslinux]] to be installed to chainload {{ic|/boot/grub/i386-pc/core.img}})
 +
 
 +
{{Note|See http://www.gnu.org/software/grub/manual/html_node/BIOS-installation.html for additional documentation.}}
 +
 
 +
===== Install to 440-byte MBR boot code region =====
 +
 
 +
To setup {{ic|grub-bios}} in the 440-byte Master Boot Record boot code region, populate the {{ic|/boot/grub}} directory, generate the {{ic|/boot/grub/i386-pc/core.img}} file, embed it in the 31 KiB (minimum size - varies depending on partition alignment) post-MBR gap, and generate the configuration file, run:
  
 
  # modprobe dm-mod
 
  # modprobe dm-mod
 +
# grub-install --recheck /dev/sda
 +
# grub-mkconfig -o /boot/grub/grub.cfg
  
 +
where {{ic|/dev/sda}} is the destination of the installation (in this case the MBR of the first SATA disk). If you use [[LVM]] for your {{ic|/boot}}, you can install GRUB2 on multiple physical disks.
  
===== Run grub_bios-install =====
+
{{Note|{{ic|--no-floppy}} has been removed from {{ic|grub-install}} in 2.00~beta2 upstream release, and replaced with {{ic|--allow-floppy}}.}}
  
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 {{Filename|/boot/grub/core.img}} ). For all the ways [[#Before_grub_bios-install]] step is needed.
+
{{Warning|Make sure to check the {{ic|/boot}} directory if you use the latter. Sometimes the {{ic| boot-directory}} parameter creates another {{ic|/boot}} folder inside of {{ic|/boot}}. A wrong install would look like: {{ic|/boot/boot/grub/}}.}}
  
====== Install to 440-byte MBR boot code region ======
+
===== Install to GPT BIOS Boot Partition =====
  
To setup grub2-bios in the 440-byte Master Boot Record boot code region, populate the {{Filename|/boot/grub}} directory, generate the {{Filename|/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
+
[[GUID Partition Table]] disks do not have a reserved "boot track". Therefore you must create a BIOS Boot Partition (0xEF02) to hold the GRUB core image.
  
# grub_bios-install --boot-directory=/boot --no-floppy --recheck /dev/sda
+
Using GNU Parted, you can set this using a command such as the following:
  
where {{Filename|/dev/sda}} is the destination of the installation (in this case the MBR of the first SATA disk). If you use [[LVM]] for your {{Filename|/boot}}, you can install GRUB2 on multiple physical disks.
+
# parted /dev/disk set <partition-number> bios_grub on
  
The {{Codeline|--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 occuring). Otherwise you get an error like this
+
If you are using gdisk, set the partition type to {{Keypress|0xEF02}}. With partitioning programs that require setting the GUID directly, it should be {{ic|‘21686148-6449-6e6f-744e656564454649’}} (stored on disk as {{ic|"Hah!IdontNeedEFI"}} if interpreted as ASCII).
  
grub-probe: error: Cannot get the real path of '/dev/fd0'
+
{{Warning|Be very careful which partition you select when marking it as a BIOS Boot Partition. When GRUB finds a BIOS Boot Partition during installation, it will automatically overwrite part of it. Make sure that the partition does not contain any other data.}}
Auto-detection of a filesystem module failed.
+
Please specify the module with the option '--modules' explicitly.
+
  
Follow [[#Generate_GRUB2_BIOS_Config_file]] or if that fails, convert your {{Filename|/boot/grub/menu.lst}} file to {{Filename|/boot/grub/grub.cfg}} using:
+
To setup {{ic|grub-bios}} on a GPT disk, populate the {{ic|/boot/grub}} directory, generate the {{ic|/boot/grub/i386-pc/core.img}} file, and embed it in the BIOS Boot Partition, run:
 +
 
 +
# modprobe dm-mod
 +
# grub-install --target=i386-pc --recheck --debug /dev/sda
 +
# mkdir -p /boot/grub/locale
 +
# cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
 +
 
 +
where {{ic|/dev/sda}} is the destination of the installation.
 +
 
 +
===== Install to Partition or Partitionless Disk =====
 +
 
 +
{{Note|{{ic|grub-bios}} (any version - including upstream Bazaar repo) does not encourage installation to a partition boot sector or a partitionless disk like GRUB Legacy or Syslinux does. This kind of setup is prone to breakage, especially during updates, and is not supported by Arch devs.}}
 +
 
 +
To set up {{ic|grub-bios}} to a partition boot sector, to a partitionless disk (also called superfloppy) or to a floppy disk, run (using for example {{ic|/dev/sdaX}} as the {{ic|/boot}} partition):
 +
 +
# modprobe dm-mod
 +
# grub-install --target=i386-pc --recheck --debug --force /dev/sdaX
 +
# chattr -i /boot/grub/i386-pc/core.img
 +
# mkdir -p /boot/grub/locale
 +
# cp /usr/share/locale/en@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
 +
# chattr +i /boot/grub/i386-pc/core.img
 +
 
 +
You need to use the {{ic|--force}} option to allow usage of blocklists and should not use {{ic|1=--grub-setup=/bin/true}} (which is similar to simply generating {{ic|core.img}}).
 +
 
 +
{{ic|grub-install}} will give out warnings like which should give you the idea of what might go wrong with this approach:
 +
 
 +
/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea.
 +
/sbin/grub-setup: warn: Embedding is not possible. GRUB can only be installed in this setup by using blocklists.
 +
                        However, blocklists are UNRELIABLE and their use is discouraged.
 +
 
 +
Without {{ic|--force}} you may get the below error and {{ic|grub-setup}} will not setup its boot code in the partition boot sector:
 +
 +
/sbin/grub-setup: error: will not proceed with blocklists
 +
 
 +
With {{ic|--force}} you should get:
 +
 
 +
Installation finished. No error reported.
 +
 
 +
The reason why {{ic|grub-setup}} does not by default allow this is because in case of partition or a partitionless disk is that {{ic|grub-bios}} relies on embedded blocklists in the partition bootsector to locate the {{ic|/boot/grub/i386-pc/core.img}} file and the prefix dir {{ic|/boot/grub}}. The sector locations of {{ic|core.img}} may change whenever the filesystem in the partition is being altered (files copied, deleted etc.). For more info see https://bugzilla.redhat.com/show_bug.cgi?id=728742 and https://bugzilla.redhat.com/show_bug.cgi?id=730915.
 +
 
 +
The workaround for this is to set the immutable flag on {{ic|/boot/grub/i386-pc/core.img}} (using chattr command as mentioned above) so that the sector locations of the {{ic|core.img}} file in the disk is not altered. The immutable flag on {{ic|/boot/grub/i386-pc/core.img}} needs to be set only if {{ic|grub-bios}} is installed to a partition boot sector or a partitionless disk, not in case of installation to MBR or simple generation of {{ic|core.img}} without embedding any bootsector (mentioned above).
 +
 
 +
===== Generate core.img alone =====
 +
 
 +
To populate the {{ic|/boot/grub}} directory and generate a {{ic|/boot/grub/i386-pc/core.img}} file '''without''' embedding any {{ic|grub-bios}} bootsector code in the MBR, post-MBR region, or the partition bootsector, add {{ic|1=--grub-setup=/bin/true}} to {{ic|grub-install}}:
 +
 +
# modprobe dm-mod
 +
# grub-install --target=i386-pc --grub-setup=/bin/true --recheck --debug /dev/sda
 +
# mkdir -p /boot/grub/locale
 +
# cp /usr/share/locale/en@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
 +
 
 +
You can then chainload GRUB2's {{ic|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
 +
 
 +
{{Note|The file path is {{ic|/boot/grub/grub.cfg}}, NOT {{ic|/boot/grub/i386-pc/grub.cfg}}.}}
 +
 
 +
If grub(2) complains about "no suitable mode found" while booting, go to [[#Correct GRUB2 No Suitable Mode Found Error]].
 +
 
 +
If {{ic|grub-mkconfig}} fails, convert your {{ic|/boot/grub/menu.lst}} file to {{ic|/boot/grub/grub.cfg}} using:
  
 
  # grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
 
  # grub-menulst2cfg /boot/grub/menu.lst /boot/grub/grub.cfg
Line 132: Line 207:
 
For example:
 
For example:
  
{{File|name=/boot/grub/menu.lst|content=
+
{{hc|/boot/grub/menu.lst|<nowiki>
 
default=0
 
default=0
 
timeout=5
 
timeout=5
Line 145: Line 220:
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
kernel /vmlinuz-linux root=/dev/sda2 ro
 
initrd /initramfs-linux-fallback.img
 
initrd /initramfs-linux-fallback.img
}}
+
</nowiki>}}
  
{{File|name=/boot/grub/grub.cfg|content=
+
{{hc|/boot/grub/grub.cfg|<nowiki>
 
set default='0'; if [ x"$default" = xsaved ]; then load_env; set default="$saved_entry"; fi
 
set default='0'; if [ x"$default" = xsaved ]; then load_env; set default="$saved_entry"; fi
 
set timeout=5
 
set timeout=5
Line 163: Line 238:
 
   legacy_initrd '/initramfs-linux-fallback.img' '/initramfs-linux-fallback.img'
 
   legacy_initrd '/initramfs-linux-fallback.img' '/initramfs-linux-fallback.img'
 
}
 
}
}}
+
</nowiki>}}
 
+
  
If you forgot to create a GRUB2 {{Filename|/boot/grub/grub.cfg}} configfile and simply rebooted into GRUB2 Command Shell, type:
+
If you forgot to create a GRUB2 {{ic|/boot/grub/grub.cfg}} config file and simply rebooted into GRUB2 Command Shell, type:
  
 
  sh:grub> insmod legacycfg
 
  sh:grub> insmod legacycfg
 
  sh:grub> legacy_configfile ${prefix}/menu.lst
 
  sh:grub> legacy_configfile ${prefix}/menu.lst
  
Boot into Arch and re-create the proper GRUB2 {{Filename|/boot/grub/grub.cfg}} configfile.
+
Boot into Arch and re-create the proper GRUB2 {{ic|/boot/grub/grub.cfg}} config file.
  
 
{{Note|This option works only in BIOS systems, not in UEFI systems.}}
 
{{Note|This option works only in BIOS systems, not in UEFI systems.}}
  
====== Install to Partition or Partitionless Disk ======
+
==== Multiboot in BIOS ====
  
{{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.}}
+
===== Boot Microsoft Windows installed in BIOS-MBR mode =====
  
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)
+
{{Note|GRUB(2) supports booting {{ic|bootmgr}} directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.}}
+
# 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 {{Codeline|--force}} option to allow usage of blocklists and should not use <code>--grub-setup=/bin/true</code> (which is similar to simply generating core.img).
+
{{Warning|Take note that it is the '''system partition''' that has {{ic|bootmgr}}, not your "real" Windows partition (usually C:). When showing all UUIDs with blkid, the system partition is the one with {{ic|LABEL&#61;"SYSTEM RESERVED"}} and is only about 100 MB in size (much like the boot partition for Arch). See http://en.wikipedia.org/wiki/System_partition_and_boot_partition for more info.}}
  
grub_bios-install will give out warnings like which should give you the idea of what might go wrong with this approach.
+
Find the UUID of the NTFS filesystem of the Windows's SYSTEM PARTITION where the {{ic|bootmgr}} and its files reside. For example, if Windows {{ic|bootmgr}} exists at {{ic|/media/SYSTEM_RESERVED/bootmgr}}:
  
/sbin/grub-setup: warn: Attempting to install GRUB to a partitionless disk or to a partition.  This is a BAD idea.
+
For Windows Vista/7/8:
/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 {{Codeline|--force}} you may get the below error and grub-setup will not setup its boot code in the partition boot sector.
+
# grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr
   
+
  69B235F6749E84CE
/sbin/grub-setup: error: will not proceed with blocklists
+
  
With {{Codeline|--force}} you should get
+
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr
 +
--hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1
  
Installation finished. No error reported.
+
{{Note|{{ic|grub-probe}} should be run as root.}}
  
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 {{Filename|/boot/grub/core.img}} file and the prefix dir {{Filename|/boot/grub}} . The sector locations of {{Filename|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 .
+
{{Note|For Windows XP, replace {{ic|bootmgr}} with {{ic|ntldr}} in the above commands.}}
  
The workaround for this is to set the immutable flag on {{Filename|/boot/grub/core.img}} (using chattr command as mentioned above) so that the sector locations of the {{Filename|core.img}} file in the disk is not altered. The immutable flag on {{Filename|/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 {{Filename|core.img}} without embedding any bootsector (mentioned above).
+
Then, add the below code to {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} and regenerate {{ic|grub.cfg}} with {{ic|grub-mkconfig}} as explained above to boot Windows (XP, Vista, 7 or 8) installed in BIOS-MBR mode:
  
====== Generate core.img alone ======
+
For Windows Vista/7/8:
  
To populate the {{Filename|/boot/grub}} directory and generate a {{Filename|/boot/grub/core.img}} file WITHOUT embedding any grub2-bios bootsector code in the MBR, post-MBR region, or the partition bootsector, add <code>--grub-setup=/bin/true</code> to grub_bios-install:
+
<pre>
+
menuentry "Microsoft Windows Vista/7/8 BIOS-MBR" {
# grub_bios-install --grub-setup=/bin/true --boot-directory=/boot --no-floppy --recheck /dev/sda
+
    insmod part_msdos
 +
    insmod ntfs
 +
    insmod search_fs_uuid
 +
    insmod ntldr   
 +
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
 +
    ntldr /bootmgr
 +
}</pre>
  
You can then chainload grub2's core.img from grub-legacy or syslinux as a Linux kernel or a multiboot kernel.
+
For Windows XP:
  
===== After grub_bios-install =====
+
  menuentry "Microsoft Windows XP" {
 
+
====== 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 {{Filename|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 {{Filename|bootmgr}} exists at {{Filename|/media/Windows/bootmgr}}:
+
 
+
# grub-probe --target=fs_uuid /media/Windows/bootmgr
+
69B235F6749E84CE
+
 
+
Then, add the below code to {{Filename|/boot/grub/grub.cfg}} to chainload Windows (Vista, 7 or 8) installed in BIOS-MBR mode :
+
 
+
  menuentry "Microsoft Windows 7 BIOS-MBR" {
+
 
     insmod part_msdos
 
     insmod part_msdos
 
     insmod ntfs
 
     insmod ntfs
 
     insmod search_fs_uuid
 
     insmod search_fs_uuid
 
     insmod ntldr     
 
     insmod ntldr     
     search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
+
     search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
     ntldr (${root})/bootmgr
+
     ntldr /ntldr
 
  }
 
  }
  
For Windows XP
+
{{ic|/etc/grub.d/40_custom}} can be used as a template to create {{ic|/etc/grub.d/nn_custom}}.  Where nn defines the precendence, indicating the order the script is executed.  The order scripts are executed determine the placement in the grub boot menu.
  
menuentry "Microsoft Windows XP" {
+
{{Note| nn should be greater than 06 to ensure necessary scripts are executed first.}}
    insmod part_msdos
+
    insmod ntfs
+
    insmod search_fs_uuid
+
    insmod ntldr   
+
    search --fs-uuid --no-floppy --set=root 69B235F6749E84CE
+
    ntldr (${root})/ntldr
+
}
+
  
==== [[UEFI]] systems ====
+
=== UEFI systems ===
  
===== Before grub_efi_${UEFI_ARCH}-install =====
+
{{Note|It is recommended to read the [[Unified Extensible Firmware Interface|UEFI]], [[GUID Partition Table|GPT]] and [[UEFI Bootloaders]] pages before reading this part.}}
  
{{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.}}
+
==== Hardware-Specific UEFI Examples ====
  
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).
+
It is well know that different motherboard manufactures implement UEFI differently.  Users experiencing problems getting Grub/EFI to work properly are encouraged to share detailed steps for hardware-specific cases where UEFI booting does not work as described below.  In an effort to keep the parent [[GRUB]] article neat and tidy, see the [[GRUB EFI Examples]] page for these special cases.
 +
 
 +
==== Install grub-uefi package ====
 +
 
 +
{{Note|Unless specified as EFI 1.x , EFI and UEFI terms are used interchangeably to denote UEFI 2.x firmware. Also unless stated explicitly, 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.}}
 +
 
 +
GRUB(2) UEFI bootloader is available in Arch Linux only from version 1.99~rc1. To install, first [[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
  
 
For 64-bit aka x86_64 UEFI firmware:
 
For 64-bit aka x86_64 UEFI firmware:
  # pacman -S grub2-efi-x86_64
+
  # pacman -S grub-efi-x86_64
  
 
For 32-bit aka i386 UEFI firmware:
 
For 32-bit aka i386 UEFI firmware:
  # pacman -S grub2-efi-i386
+
  # pacman -S grub-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 <code>--no-floppy</code>. For more details search this option in the article.}}
+
{{Note|Simply installing the package will not update the {{ic|core.efi}} file and the GRUB(2) modules in the UEFI System Partition. You need to do this manually using {{ic|grub-install}} as explained below.}}
  
{{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.}}
+
==== Install grub-uefi boot files ====
  
Also load the device-mapper kernel module without which grub-probe does not reliably detect disks and partitions
+
===== Install to UEFI System Partition =====
 +
 
 +
{{Note|The below commands assume you are using {{ic|grub-efi-x86_64}} (for {{ic|grub-efi-i386}} replace {{ic|x86_64}} with {{ic|i386}} in the below commands).}}
 +
 
 +
{{Note|To do this, you need to boot using UEFI and not the BIOS. If you booted by just copying the ISO file to the USB drive, you will need to follow [[Unified Extensible Firmware Interface#Create UEFI bootable USB from ISO|this guide]] or grub-install will show errors.}}
 +
 
 +
The UEFI system partition will need to be mounted at {{ic|/boot/efi/}} for the GRUB(2) install script to detect it:
 +
 
 +
# mkdir -p /boot/efi
 +
# mount -t vfat /dev/sdXY /boot/efi
 +
 
 +
Install GRUB UEFI application to {{ic|/boot/efi/EFI/arch_grub}} and its modules to {{ic|/boot/grub/x86_64-efi}} (recommended) using:
  
 
  # modprobe dm-mod
 
  # modprobe dm-mod
 +
# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=arch_grub --recheck --debug
 +
# mkdir -p /boot/grub/locale
 +
# cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
  
===== Install to UEFI SYSTEM PARTITION =====
+
{{Note|Without {{ic|--target}} or {{ic|--directory}} option, grub-install cannot determine for which firmware grub(2) is being installed. In such cases grub-install will show {{ic|source_dir doesn't exist. Please specify --target or --directory}} message.}}
  
====== Mount UEFI SYSTEM PARTITION ======
+
If you want to install grub(2) modules and {{ic|grub.cfg}} at the directory {{ic|/boot/efi/EFI/grub}} and the {{ic|grubx64.efi}} application at {{ic|/boot/efi/EFI/arch_grub}} (ie. all the grub(2) uefi files inside the UEFISYS partition itself) use:
  
Mount the [https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interface#Creating_a_UEFI_SYSTEM_PARTITION_in_Linux UEFI SYSTEM PARTITION] in your system at {{Filename|/boot/efi}}. 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 {{Filename|/boot/efi}} in the below commands with that mountpoint:
+
# modprobe dm-mod
 +
# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=arch_grub --boot-directory=/boot/efi/EFI --recheck --debug
 +
# mkdir -p /boot/efi/EFI/grub/locale
 +
# cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/efi/EFI/grub/locale/en.mo
  
# mkdir -p /boot/efi
+
The {{ic|--efi-directory}} option mentions the mountpoint of UEFI SYSTEM PARTITION , {{ic|--bootloader-id}} mentions the name of the directory used to store the {{ic|grubx64.efi}} file and {{ic|--boot-directory}} mentions the directory wherein the actual modules will be installed (and into which {{ic|grub.cfg}} should be created).
# mount -t vfat <UEFISYS_PART_DEVICE> /boot/efi
+
# mkdir -p /boot/efi/efi
+
  
====== Run grub_efi_${UEFI_ARCH}-install ======
+
The actual paths are:
  
{{Note|The below commands assume you are using {{Codeline|grub2-efi-x86_64}} (for {{Codeline|grub2-efi-i386}} replace {{Codeline|x86_64}} with {{Codeline|i386}} in the below commands).}}
+
<efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi
  
  # grub_efi_x86_64-install --root-directory=/boot/efi --boot-directory=/boot/efi/efi --bootloader-id=grub --no-floppy --recheck
+
  <boot-directory>/grub/x86_64-efi/<all modules, grub.efi, core.efi, grub.cfg>
  
The {{Codeline|grub_efi_x86_64-install}} automatically generates a {{Filename|grub.efi}} while setting up the {{Filename|/boot/efi/efi/grub/}} directory.
+
{{Note|the {{ic|--bootloader-id}} option does not change {{ic|<boot-directory>/grub}}, i.e. you cannot install the modules to {{ic|<boot-directory>/<bootloader-id>}}, the path is hard-coded to be {{ic|<boot-directory>/grub}}.}}
  
If you notice carefully, there is no <device_path> option (Eg: {{Filename|/dev/sda}}) at the end of the {{Codeline|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.
+
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=grub</nowiki>}}:
  
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.
+
<efi-directory>/<EFI or efi>/<bootloader-id> == <boot-directory>/grub == /boot/efi/EFI/grub
  
===== After grub_efi_${UEFI_ARCH}-install =====
+
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=arch_grub</nowiki>}}:
  
====== Launch GRUB2 as default in non-Mac UEFI systems ======
+
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub
 +
<boot-directory>/grub == /boot/efi/EFI/grub
  
{{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.}}
+
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub</nowiki>}}:
  
grub_efi_${UEFI_ARCH}-install will ensure {{Filename|/boot/efi/efi/grub/grub.efi}} is launched by default if it detects {{Codeline|efibootmgr}} and if it is able to access UEFI Runtime Services. {{Codeline|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 {{Filename|/boot/efi/efi/grub/grub.efi}} from the firmware itself (using maybe the UEFI Shell) if grub2-efi was installed in BIOS mode. Then {{Codeline|efibootmgr}} should be run to make grub2 as the default entry in the UEFI Boot Manager
+
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub
 +
<boot-directory>/grub == /boot/grub
  
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:
+
In {{ic|<nowiki>--efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=grub</nowiki>}}:
# grub-probe --target=device /boot/efi/efi/grub/grub.efi
+
  
It should give something like {{Filename|/dev/sda1}} (used as example in the remaining steps). Load 'efivars' kernel module:
+
<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/grub
  # modprobe efivars
+
  <boot-directory>/grub == /boot/grub
  
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.
+
The {{ic|<nowiki><efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi</nowiki>}} is an exact copy of {{ic|<nowiki><boot-directory>/grub/x86_64-efi/core.efi</nowiki>}}.
  
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.
+
{{Note|In GRUB 2.00, the {{ic|grub-install}} option {{ic|--efi-directory}} replaces {{ic|--root-directory}} and the latter is deprecated.}}
+
# ls -1 /sys/firmware/efi/vars/
+
  
Sample output (x86_64-UEFI 2.3.1 in x86_64 Kernel:
+
{{Note|The options {{ic|--efi-directory}} and {{ic|--bootloader-id}} are specific to GRUB(2) UEFI.}}
 
   
 
   
# ls -1 /sys/firmware/efi/vars/
+
In all the cases the UEFI SYSTEM PARTITION should be mounted for {{ic|grub-install}} to install {{ic|grubx64.efi}} in it, which will be launched by the firmware (using the {{ic|efibootmgr}} created boot entry in non-Mac systems).
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 {{Codeline|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 you notice carefully, there is no <device_path> option (Eg: {{ic|/dev/sda}}) at the end of the {{ic|grub-install}} command unlike the case of setting up GRUB(2) 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.
  
If ''/sys/firmware/efi/vars/'' directory (along with the exists then run {{Codeline|efibootmgr}} and reboot:
+
You may now be able to UEFI boot your system by creating a {{ic|grub.cfg}} file by following [[#Generate GRUB2 UEFI Config file]] and [[#Create GRUB2 entry in the Firmware Boot Manager]].
+
# efibootmgr --create --gpt --disk /dev/sda --part 1 --write-signature --label "GRUB2" --loader "\\EFI\\grub\\grub.efi"
+
  
In the above command, {{Filename|/boot/efi/efi/grub/grub/efi}} can be split up as {{Filename|/boot/efi}} and {{Filename|/efi/grub/grub.efi}}, which translates to {{Filename|(/dev/sda)}} -> partition 1 -> {{Filename|\\EFI\\grub\\grub.efi}}.
+
==== Generate GRUB2 UEFI Config file ====
  
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 {{Filename|\\EFI\\grub\\grub.efi}} or {{Filename|\\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 {{Filename|\EFI\grub\grub.efi}} is passed to {{Codeline|efibootmgr}}.
+
Finally, generate a configuration for GRUB(2) (this is explained in greater detail in the Configuration section):
  
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 [http://linux.dell.com/cgi-bin/gitweb/gitweb.cgi?p=efibootmgr.git;a=blob_plain;f=README;hb=HEAD efibootmgr GIT README]
+
# grub-mkconfig -o <boot-directory>/grub/grub.cfg
  
If you have problems running GRUB2 in UEFI mode you can try the following (worked on an ASUS Z68 mainboard):
+
{{Note|The file path is {{ic|<boot-directory>/grub/grub.cfg}}, NOT {{ic|<boot-directory>/grub/x86_64-efi/grub.cfg}}.}}
+
# cp /boot/efi/efi/grub/grub.efi /boot/efi/shellx64.efi
+
  
or
+
If you used {{ic|<nowiki>--boot-directory=/boot</nowiki>}}:
+
# 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
+
  # grub-mkconfig -o /boot/grub/grub.cfg
  
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).
+
If you used {{ic|<nowiki>--boot-directory=/boot/efi/EFI</nowiki>}}:
  
====== Launch GRUB2 as default in Apple Mac EFI systems ======
+
# grub-mkconfig -o /boot/efi/EFI/grub/grub.cfg
  
{{Note|Using {{Filename|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}}
+
This is independent of the value of {{ic|--bootloader-id}} option.
  
Use bless command from within Mac OS X to setup {{Filename|grub.efi}} as the default boot option. More info at https://help.ubuntu.com/community/UEFIBooting#Apple_Mac_EFI_systems_.28both_EFI_architecture.29 .
+
If GRUB2 complains about "no suitable mode found" while booting, try [[#Correct GRUB2 No Suitable Mode Found Error]].
  
====== Generate GRUB2 UEFI Config file ======
+
==== Create GRUB2 entry in the Firmware Boot Manager ====
  
Finally, generate a configuration for grub2 (this is explained in greater detail in the Configuration section):
+
As of grub-efi-x86_64 version 2.00, {{ic|grub-install}} automatically tries to create a menu entry in the boot manager. If it doesn't, then see [[Beginners' Guide#GRUB]] for instructions to use {{ic|efibootmgr}} to create a menu entry. However, the problem is likely to be that you haven't booted your CD/USB in UEFI mode, as in [[Unified Extensible Firmware Interface#Create UEFI bootable USB from ISO]].
  
# grub-mkconfig -o /boot/efi/efi/grub/grub.cfg
+
==== Create GRUB2 Standalone UEFI Application ====
  
If grub2-uefi complains about "no suitable mode found" while booting, go to [[#Correct_GRUB2_No_Suitable_Mode_Found_Error]] .
+
It is possible to create a {{ic|grubx64_standalone.efi}} application which has all the modules embeddded in a memdisk within the uefi application, thus removing the need for having a separate directory populated with all the GRUB2 uefi modules and other related files. This is done using the {{ic|grub-mkstandalone}} command which is included in {{Pkg|grub-common}} >= 1:1.99-6 package.
  
===== Generate a custom GRUB2 UEFI Application =====
+
The easiest way to do this would be with the install command already mentioned before, but specifying the modules to include. For example:
  
If you want, you can create a custom {{Filename|grub_custom.efi}} app using:
+
  # grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \
  # 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>
+
--output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" <any extra files you want to include>
  
{{Note|The '''-p''' option is important for creating a portable {{Filename|grub_custom.efi}} app.}}
+
The {{ic|grubx64_standalone.efi}} file expects {{ic|grub.cfg}} to be within its $prefix which is {{ic|(memdisk)/boot/grub}}. The memdisk is embedded within the efi app. The {{ic|grub-mkstandlone}} script allow passing files to be included in the memdisk image to be as the arguments to the script (in <any extra files you want to include>).
  
There is no file-size restriction on {{Filename|grub_custom.efi}} either due to GRUB2 or due to the UEFI firmware. Therefore you can include any number of modules you want.
+
If you have the {{ic|grub.cfg}} at {{ic|/home/user/Desktop/grub.cfg}}, then create a temporary {{ic|/home/user/Desktop/boot/grub/}} directory, copy the {{ic|/home/user/Desktop/grub.cfg}} to {{ic|/home/user/Desktop/boot/grub/grub.cfg}}, cd into {{ic|/home/user/Desktop/boot/grub/}} and run:
  
A "{{Filename|grub.cfg}}" 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 {{Filename|grub.cfg}} file should exist in the same directory as {{Filename|grub.efi}} or {{Filename|grub_custom.efi}}.
+
# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \
 +
--output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" "boot/grub/grub.cfg"
  
The {{Filename|grub.efi}} UEFI application can be launched using the firmware's "Boot Manager", "Boot from file" option or using the [https://wiki.archlinux.org/index.php/UEFI#UEFI_Shell UEFI Shell].
+
The reason to cd into {{ic|/home/user/Desktop/boot/grub/}} and to pass the file path as {{ic|boot/grub/grub.cfg}} (notice the lack of a leading slash - boot/ vs /boot/ ) is because {{ic|dir1/dir2/file}} is included as {{ic|(memdisk)/dir1/dir2/file}} by the {{ic|grub-mkstandalone}} script.  
  
Alternatively, you can also setup {{Filename|/boot/efi/efi/grub}} directory by copying all the files in {{Filename|/usr/lib/grub/x86_64-efi}} to {{Filename|/boot/efi/efi/grub}} and using the above grub-mkimage command to create a {{Filename|grub_custom.efi}} application. Just make sure you have the required modules embedded in {{Filename|grub_custom.efi}} to enable it to access the EFI SYSTEM PARTITION.
+
If you pass {{ic|/home/user/Desktop/grub.cfg}} the file will be included as {{ic|(memdisk)/home/user/Desktop/grub.cfg}}. If you pass {{ic|/home/user/Desktop/boot/grub/grub.cfg}} the file will be included as {{ic|(memdisk)/home/user/Desktop/boot/grub/grub.cfg}}. That is the reason for cd'ing into {{ic|/home/user/Desktop/boot/grub/}} and passing {{ic|boot/grub/grub.cfg}}, to include the file as {{ic|(memdisk)/boot/grub/grub.cfg}}, which is what {{ic|grub.efi}} expects the file to be.
  
A basic {{Filename|grub_custom.efi}} can be generated using the following command:
+
You need to create an UEFI Boot Manager entry for {{ic|/boot/efi/EFI/arch_grub/grubx64_standalone.efi}} using {{ic|efibootmgr}}. Follow [[#Create GRUB2 entry in the Firmware Boot Manager]].
# 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 =====
+
==== Multiboot in UEFI ====
  
====== Chainload Microsoft Windows x86_64 UEFI-GPT ======
+
===== 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 {{Filename|bootmgfw.efi}} exists at {{Filename|/boot/efi/efi/Microsoft/Boot/bootmgfw.efi}} (ignore the upper-lower case differences since that is immaterial in FAT filesystem):
+
Find the UUID of the FAT32 filesystem in the UEFI SYSTEM PARTITION where the Windows UEFI Bootloader files reside. For example, if Windows {{ic|bootmgfw.efi}} exists at {{ic|/boot/efi/EFI/Microsoft/Boot/bootmgfw.efi}} (ignore the upper-lower case differences since that is immaterial in FAT filesystem):
  
  # grub-probe --target=fs_uuid /boot/efi/efi/Microsoft/Boot/bootmgfw.efi
+
  # grub-probe --target=fs_uuid /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi
 
  1ce5-7f28
 
  1ce5-7f28
  
Then, add this code to {{Filename|/boot/efi/efi/grub/grub.cfg}} to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode :
+
# grub-probe --target=hints_string /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi
 +
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
 +
 
 +
{{Note|{{ic|grub-probe}} should be run as root.}}
 +
 
 +
Then, add this code to {{ic|/etc/grub.d/40_custom}} to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode:
  
  menuentry "Microsoft Windows x86_64 UEFI-GPT" {
+
  menuentry "Microsoft Windows Vista/7/8 x86_64 UEFI-GPT" {
 
     insmod part_gpt
 
     insmod part_gpt
 
     insmod fat
 
     insmod fat
 
     insmod search_fs_uuid
 
     insmod search_fs_uuid
 
     insmod chain
 
     insmod chain
     search --fs-uuid --no-floppy --set=root 1ce5-7f28
+
     search --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 1ce5-7f28
     chainloader (${root})/efi/Microsoft/Boot/bootmgfw.efi
+
     chainloader /efi/Microsoft/Boot/bootmgfw.efi
 
  }
 
  }
  
== Manual Compilation ==
+
Afterwards remake {{ic|/boot/grub/grub.cfg}}
  
=== For BIOS Systems ===
+
# grub-mkconfig -o /boot/grub/grub.cfg
  
GRUB2 for BIOS systems should be compiled as follows:
+
== Configuration ==
<pre>
+
./autogen.sh
+
  
./configure --with-platform=pc --prefix=/usr
+
You can also choose to automatically generate or manually edit {{ic|grub.cfg}}.
  
make
+
{{Note|For EFI systems, if GRUB2 was installed with the {{ic|--boot-directory}} option set, the {{ic|grub.cfg}} file must be placed in the same directory as {{ic|grubx64.efi}}. Otherwise, the {{ic|grub.cfg}} file goes in {{ic|/boot/grub/}}, just like in the BIOS version of GRUB2.}}
  
make install
+
{{Note|Here is a quite complete description of how to configure GRUB2: http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html }}
</pre>
+
  
The <code>--with-platform=pc</code> generates grub2 for bios alone irrespective of the firmware of the build system.
+
=== Automatically generating using grub-mkconfig (Recommended) ===
  
=== For UEFI Systems ===
+
The GRUB2 {{ic|menu.lst}} equivalent configuration files are {{ic|/etc/default/grub}} and {{ic|/etc/grub.d/*}}. {{ic|grub-mkconfig}} uses these files to generate {{ic|grub.cfg}}. By default the script outputs to stdout. To generate a {{ic|grub.cfg}} file run the command:
  
First [https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interface#Detecting_UEFI_Firmware_Arch Detect which UEFI Firmware arch] you have and then follow the compile instructions below:
+
# grub-mkconfig -o /boot/grub/grub.cfg
<pre>
+
./autogen.sh
+
  
./configure --with-platform=efi --target=TARGET_UEFI_ARCH --prefix=/usr
+
{{ic|/etc/grub.d/10_linux}} is set to automatically add menu items for Arch linux that work out of the box, to any generated configuration. Other operating systems may need to be added manually to {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}}
  
make
+
==== Additional arguments ====
  
make install
+
To pass custom additional arguments to the Linux image, you can set the {{ic|GRUB_CMDLINE_LINUX}} variable in {{ic|/etc/default/grub}}.
</pre>
+
  
The "--target" option denotes the UEFI firmware arch. for which grub2 should be compiled, not the architecture of the linux kernel grub2 may boot.  
+
For example, use {{ic|<nowiki>GRUB_CMDLINE_LINUX="resume=/dev/sdaX"</nowiki>}} where {{ic|sda'''X'''}} is your swap partition to enable resume after hibernation.
  
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 {{Codeline|x86_64-efi}} app. It is important to compile GRUB2 to match the architecture of the UEFI firmware.
+
You can also use {{ic|<nowiki>GRUB_CMDLINE_LINUX="resume=/dev/disk/by-uuid/${swap_uuid}"</nowiki>}}, where {{ic|${swap_uuid} }} is the [[Persistent_block_device_naming|UUID]] of your swap partition.
  
== Configuration ==
+
Multiple entries are separated by spaces within the double quotes.  So, for users who want both resume and systemd it would look like this:
 +
{{ic|<nowiki>GRUB_CMDLINE_LINUX="resume=/dev/sdaX init=/usr/lib/systemd/systemd"</nowiki>}}
  
The configuration files are {{Filename|/etc/default/grub}} and {{Filename|/etc/grub.d/*}}. These files are used to generate the {{Filename|/boot/grub/grub.cfg}} file. You can also choose to manually edit {{Filename|grub.cfg}}.
+
See [[Kernel parameters]] for more info.
  
=== grub-mkconfig ===
+
=== Manually creating grub.cfg ===
  
The grub-mkconfig script can be used to generate a {{Filename|grub.cfg}} 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 {{Filename|grub.cfg}} file run the command:
+
{{Warning|Editing this file is strongly ''not'' recommended. The file is generated by the {{ic|grub-mkconfig}} command, and it is best to edit your {{ic|/etc/default/grub}} or one of the scripts in the {{ic|/etc/grub.d}} folder.}}
# 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
+
A basic GRUB config file uses the following options
* {{Codeline|(hdX,Y)}} is the partition {{Codeline|Y}} on disk {{Codeline|X}}, partition numbers starting at 1, disk numbers starting at 0
+
* {{ic|(hdX,Y)}} is the partition {{ic|Y}} on disk {{ic|X}}, partition numbers starting at 1, disk numbers starting at 0
* {{Codeline|1=set default=N}} is the default boot entry that is chosen after timeout for user action
+
* {{ic|1=set default=N}} is the default boot entry that is chosen after timeout for user action
* {{Codeline|1=set timeout=M}} is the time {{Codeline|M}} to wait in seconds for a user selection before default is booted
+
* {{ic|1=set timeout=M}} is the time {{ic|M}} to wait in seconds for a user selection before default is booted
* {{Codeline|<nowiki>menuentry "title" {entry options}</nowiki>}} is a boot entry titled {{Codeline|title}}
+
* {{ic|<nowiki>menuentry "title" {entry options}</nowiki>}} is a boot entry titled {{ic|title}}
* {{Codeline|1=set root=(hdX,Y)}} sets the boot partition, where the kernel and GRUB modules are stored (boot need not be a separate partition, and may simply be a directory under the "root" partition ({{Filename|/}})
+
* {{ic|1=set root=(hdX,Y)}} sets the boot partition, where the kernel and GRUB modules are stored (boot need not be a separate partition, and may simply be a directory under the "root" partition ({{ic|/}})
  
 
An example configuration:
 
An example configuration:
  
{{File
+
{{hc
|name=/boot/grub/grub.cfg
+
|/boot/grub/grub.cfg
|content=<nowiki>
+
|<nowiki>
 
# Config file for GRUB2 - The GNU GRand Unified Bootloader
 
# Config file for GRUB2 - The GNU GRand Unified Bootloader
 
# /boot/grub/grub.cfg
 
# /boot/grub/grub.cfg
Line 501: Line 535:
 
# (0) Arch Linux
 
# (0) Arch Linux
 
menuentry "Arch Linux" {
 
menuentry "Arch Linux" {
set root=(hd0,1)
+
    set root=(hd0,1)
linux /vmlinuz-linux root=/dev/sda3 ro
+
    linux /vmlinuz-linux root=/dev/sda3 ro
initrd /initramfs-linux.img
+
    initrd /initramfs-linux.img
 
}
 
}
  
Line 515: Line 549:
 
=== Dual-booting ===
 
=== Dual-booting ===
  
''NOTE: If you want GRUB2 to automatically search for other systems, for example as in Ubuntu. Then you may need to download {{Package AUR|os-prober}} from the [[AUR]].''
+
{{Note|If you want GRUB2 to automatically search for other systems, you may wish to install {{Pkg|os-prober}}.}}
  
 
==== Using grub-mkconfig ====
 
==== Using grub-mkconfig ====
The best way to add other entries is editing the {{Filename|/etc/grub.d/40_custom}}. The entries in this file will be automatically added when running '''grub-mkconfig'''.
+
The best way to add other entries is editing the {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} . The entries in this file will be automatically added when running {{ic|grub-mkconfig}}.
 
After adding the new lines, run:
 
After adding the new lines, run:
 
  # grub-mkconfig -o /boot/grub/grub.cfg  
 
  # grub-mkconfig -o /boot/grub/grub.cfg  
to generate an updated {{Filename|grub.cfg}}.
+
to generate an updated {{ic|grub.cfg}}.
  
 
===== With GNU/Linux =====
 
===== With GNU/Linux =====
  
Assuming that the other distro is on partition {{Filename|sda2}}:
+
Assuming that the other distro is on partition {{ic|sda2}}:
  
 
  menuentry "Other Linux" {
 
  menuentry "Other Linux" {
Line 531: Line 565:
 
  linux /boot/vmlinuz (add other options here as required)
 
  linux /boot/vmlinuz (add other options here as required)
 
  initrd /boot/initrd.img (if the other kernel uses/needs one)
 
  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 {{ic|sda4}}:
 +
 +
menuentry "FreeBSD" {
 +
set root=(hd0,4)
 +
chainloader +1
 
  }
 
  }
  
 
===== With Windows =====
 
===== With Windows =====
  
This assumes that your Windows partition is {{Filename|sda3}}.
+
This assumes that your Windows partition is {{ic|sda3}}. Remember you need to point set root and chainloader to the system reserve partition that windows made when it installed, not the actual partition windows is on. This example works if your system reserve partition is {{ic|sda3}}.
  
 
  # (2) Windows XP
 
  # (2) Windows XP
Line 543: Line 586:
 
  }
 
  }
  
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 {{Codeline|map}} and is now done with {{Codeline|drivemap}}. Assume grub is on {{Filename|hd0}} and windows on {{Filename|hd2}}, you need to add the following after {{Codeline|set root}}:
+
If the Windows bootloader is on an entirely different hard drive than GRUB, it may be necessary to trick Windows into believing that it is the first hard drive. This was possible with {{ic|drivemap}}. Assuming GRUB is on {{ic|hd0}} and Windows is on {{ic|hd2}}, you need to add the following after {{ic|set root}}:
  
 
  drivemap -s hd0 hd2
 
  drivemap -s hd0 hd2
Line 549: Line 592:
 
==== With Windows via EasyBCD and NeoGRUB ====
 
==== 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 {{Filename|C:\NST\menu.lst}} file with lines similar to the following:
+
Since EasyBCD's NeoGRUB currently does not understand the GRUB2 menu format, chainload to it by replacing the contents of your {{ic|C:\NST\menu.lst}} file with lines similar to the following:
  
 
  default 0
 
  default 0
Line 556: Line 599:
 
  title      Chainload into GRUB v2
 
  title      Chainload into GRUB v2
 
  root        (hd0,7)
 
  root        (hd0,7)
  kernel      /boot/grub/core.img
+
  kernel      /boot/grub/i386-pc/core.img
  
 
===Visual Configuration===
 
===Visual Configuration===
  
In GRUB2 it is possible, by default, to change the look of the menu.
+
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.
  
====Background image and bitmap fonts====
+
====Setting the framebuffer resolution ====
  
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 {{Filename|unicode.pf2}}, or, as only ascii characters under the name {{Filename|ascii.pf2}}. 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 {{Filename|tga}} file as background. Two sample configurations are shown below.
+
GRUB2 can set the framebuffer for both GRUB2 itself and the kernel. The old {{ic|1=vga=}} way is deprecated. The preferred method is editing {{ic|/etc/default/grub}} as the following sample:
  
Edit {{Filename|/etc/default/grub}} like this:
 
 
  GRUB_GFXMODE=1024x768x32
 
  GRUB_GFXMODE=1024x768x32
 
  GRUB_GFXPAYLOAD_LINUX=keep
 
  GRUB_GFXPAYLOAD_LINUX=keep
  GRUB_BACKGROUND="/boot/grub/archlinux.tga"
+
 
 +
To generate the changes, run:
 +
  # grub-mkconfig -o /boot/grub/grub.cfg
 +
 
 +
The {{ic|gfxpayload}} property will make sure the kernel keeps the resolution.
 +
 
 +
{{Note|If this example does not work for you try to replace {{ic|1=gfxmode="1024x768x32"}} by {{ic|1=vbemode="0x105"}}. Remember to replace the specified resolution with one suitable for your screen.}}
 +
{{Note|To show all the modes you can use {{ic|1=# hwinfo --framebuffer}} (hwinfo is available in [community]), while at GRUB2 prompt you can use the {{ic|1=vbeinfo}} command.}}
 +
 
 +
If this method does not work for you, the deprecated {{ic|1=vga=}} method will still work. Just
 +
add it next to the {{ic|1="GRUB_CMDLINE_LINUX_DEFAULT="}} line in {{ic|/etc/default/grub}}
 +
for eg: {{ic|1="GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"}} will give you a {{ic|1024x768}} resolution.
 +
 
 +
You can choose one of these resolutions: {{ic|640×480}}, {{ic|800×600}}, {{ic|1024×768}}, {{ic|1280×1024}}, {{ic|1600×1200}}, {{ic|1920×1200}}
 +
 
 +
====915resolution hack ====
 +
 
 +
Some times for Intel graphic adapters neither {{ic|1=# hwinfo --framebuffer}} nor {{ic|1=vbeinfo}} will show you the desired resolution. In this case you can use {{ic|915resolution}} hack. This hack will temporarily modify video BIOS and add needed resolution. See [http://915resolution.mango-lang.org/ 915resolution's home page]
 +
 
 +
In the following I will proceed with the example for my system. Please adjust the recipe for your needs. First you need to find a video mode which will be modified later. For that, run {{ic|915resolution}} in GRUB2 command shell:
 +
915resolution -l
 +
The output will be something like:
 +
Intel 800/900 Series VBIOS Hack : version 0.5.3
 +
...
 +
Mode 30 : 640x480, 8 bits/pixel
 +
...
 +
Next, our purpose is to overwrite mode 30. (You can choose what ever mode you want.) In the file {{ic|/etc/grub.d/00_header}} just before the {{ic|set gfxmode&#61;${GRUB_GFXMODE}}} line insert:
 +
915resolution 30 1440 900
 +
Here we are overwriting the mode {{ic|30}} with {{ic|1440x900}} resolution. Lastly we need to set {{ic|GRUB_GFXMODE}} as described earlier, regenerate GRUB2 configuration file and reboot to test changes:
 +
# grub-mkconfig -o /boot/grub/grub.cfg
 +
# reboot
 +
 
 +
====Background image and bitmap fonts====
 +
 
 +
GRUB2 comes with support for background images and bitmap fonts in {{ic|pf2}} format. The unifont font is included in the {{Pkg|grub-common}} package under the filename {{ic|unicode.pf2}}, or, as only ASCII characters under the name {{ic|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 [[#Setting the framebuffer resolution|framebuffer resolution]].
 +
 
 +
Edit {{ic|/etc/default/grub}} like this:
 +
GRUB_BACKGROUND="/boot/grub/myimage"
 
  #GRUB_THEME="/path/to/gfxtheme"
 
  #GRUB_THEME="/path/to/gfxtheme"
 +
GRUB_FONT="/path/to/font.pf2"
  
(archlinux.tga is a placeholder; put your file name there)
+
{{Note|If you have installed GRUB on a separate partition, {{ic|/boot/grub/myimage}} becomes {{ic|/grub/myimage}}.}}
  
To generate the changes, run:  
+
To generate the changes and add the information into {{ic|grub.cfg}}, run:
 +
grub-mkconfig -o /boot/grub/grub.cfg
 +
 
 +
If adding the splash image was successful, the user will see {{ic|"Found background image..."}} in the terminal as the command is executed.
 +
If this phrase is not seen, the image information was probably not incorporated into the {{ic|grub.cfg}} file.
 +
 +
If the image is not displayed, check:
 +
* The path and the filename in {{ic|/etc/default/grub}} are correct.
 +
* The image is of the proper size and format (tga, png, 8-bit jpg).
 +
* The image was saved in the RGB mode, and is not indexed.
 +
* The console mode is not enabled in {{ic|/etc/default/grub}}.
 +
* The command {{ic|grub-mkconfig}} must be executed to place the background image information into the {{ic|/boot/grub/grub.cfg}} file.
 +
 
 +
====Theme====
 +
 
 +
Here is an example for configuring Starfield theme which was included in GRUB2 package.
 +
 
 +
Edit {{ic|/etc/default/grub}}
 +
GRUB_THEME="/usr/share/grub/themes/starfield/theme.txt"
 +
 
 +
Generate the changes:
 
  grub-mkconfig -o /boot/grub/grub.cfg
 
  grub-mkconfig -o /boot/grub/grub.cfg
  
{{Note|If this example does not work for you try to replace {{Codeline|1=gfxmode="1024x768x32"}} by {{Codeline|1=vbemode="0x105"}}.}}
+
If configuring the theme was successful, you'll see {{ic|Found theme: /usr/share/grub/themes/starfield/theme.txt}} in the terminal.
{{Note|To show all the modes you can use {{Codeline|1=# hwinfo --framebuffer}} (hwinfo is available in [community]), while at grub2 prompt you can use the {{Codeline|1=vbeinfo}} command.}}
+
Your splash image will usually not be displayed when using a theme.
{{Note|If you have installed Grub on a separate partition, {{Filename|/boot/grub/archlinux.tga}} becomes {{Filename|/grub/archlinux.tga}}.}}
+
  
 
====Menu colors====
 
====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 .  
+
You can set the menu colors in GRUB2. The available colors for GRUB2 can be found in [https://www.gnu.org/software/grub/manual/html_node/Theme-file-format.html the GRUB Manual].
 
Here is an example:
 
Here is an example:
  
Edit {{Filename|/etc/default/grub}}:
+
Edit {{ic|/etc/default/grub}}:
 
  GRUB_COLOR_NORMAL="light-blue/black"
 
  GRUB_COLOR_NORMAL="light-blue/black"
 
  GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
 
  GRUB_COLOR_HIGHLIGHT="light-cyan/blue"
Line 595: Line 698:
 
====Hidden menu====
 
====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.
+
One of the unique features of GRUB2 is hiding/skipping the menu and showing it by holding {{keypress|Esc}} when needed. You can also adjust whether you want to see the timeout counter.
  
Edit {{Filename|/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:
+
Edit {{ic|/etc/default/grub}} as you wish. Here is an example where the comments from the beginning of the two lines have been removed to enable the feature, the timeout has been set to five seconds and to be shown to the user:
 
  GRUB_HIDDEN_TIMEOUT=5
 
  GRUB_HIDDEN_TIMEOUT=5
 
  GRUB_HIDDEN_TIMEOUT_QUIET=false
 
  GRUB_HIDDEN_TIMEOUT_QUIET=false
  
 
and run:
 
and run:
  grub-mkconfig -o /boot/grub/grub.cfg
+
  # grub-mkconfig -o /boot/grub/grub.cfg
  
====Setting the framebuffer resolution ====
+
====Disable framebuffer====
  
Grub2 can set the framebuffer for both grub2 itself and the kernel. The old ''vga='' way is deprecated. The preferred method is editing {{Filename|/etc/default/grub}} as the following sample:
+
Users who use NVIDIA proprietary driver might wish to disable GRUB2's framebuffer as it can cause problems with the binary driver.
  
GRUB_GFXMODE=1024x768x32
+
To disable framebuffer, edit {{ic|/etc/default/grub}} and uncomment the following line:
  GRUB_GFXPAYLOAD_LINUX=keep
+
  GRUB_TERMINAL_OUTPUT=console
  
To generate the changes, run:  
+
and run:
 
  grub-mkconfig -o /boot/grub/grub.cfg
 
  grub-mkconfig -o /boot/grub/grub.cfg
 
The {{Codeline|gfxpayload}} property will make sure the kernel keeps the resolution.
 
 
If this method does not work for you, the deprecated <code>vga=</code> method will still work. Just
 
add it next to the <code>"GRUB_CMDLINE_LINUX_DEFAULT="</code> line in {{Filename|/etc/default/grub}}
 
for eg: <code>"GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=792"</code> will give you a {{Codeline|1024x768}} resolution.
 
 
You can choose one of these resolutions: {{Codeline|640×480}}, {{Codeline|800×600}}, {{Codeline|1024×768}}, {{Codeline|1280×1024}}, {{Codeline|1600×1200}}
 
  
 
=== Other Options ===
 
=== Other Options ===
Line 626: Line 721:
 
==== LVM ====
 
==== LVM ====
  
If you use [[LVM]] for your {{Filename|/boot}}, add the following before menuentry lines:
+
If you use [[LVM]] for your {{ic|/boot}}, add the following before menuentry lines:
  
 
  insmod lvm
 
  insmod lvm
Line 632: Line 727:
 
and specify your root in the menuentry as:
 
and specify your root in the menuentry as:
  
  set root=(''lvm_group_name''-''lvm_logical_boot_partition_name'')
+
  set root=lvm/''lvm_group_name''-''lvm_logical_boot_partition_name''
  
 
Example:
 
Example:
Line 639: Line 734:
 
  menuentry "Arch Linux" {
 
  menuentry "Arch Linux" {
 
  insmod lvm
 
  insmod lvm
  set root=(VolumeGroup-lv_boot)
+
  set root=lvm/VolumeGroup-lv_boot
 
  # you can only set following two lines
 
  # you can only set following two lines
 
  linux /vmlinuz-linux root=/dev/mapper/VolumeGroup-root ro
 
  linux /vmlinuz-linux root=/dev/mapper/VolumeGroup-root ro
Line 645: Line 740:
 
  }
 
  }
  
==== Raid ====
+
==== RAID ====
  
Grub2 provides convenient handling of raid-volumes. You need to add:
+
GRUB2 provides convenient handling of RAID volumes. You need to add {{ic|insmod mdraid}} which allows you to address the volume natively. For example, {{ic|/dev/md0}} becomes:
insmod raid
+
 
+
which allows you to address the volume natively. E.g. {{Filename|/dev/md0}} becomes:
+
 
  set root=(md0)
 
  set root=(md0)
  
whereas a partitioned raid-volume (e.g. {{Filename|/dev/md0p1}}) becomes:
+
whereas a partitioned RAID volume (e.g. {{ic|/dev/md0p1}}) becomes:
 
  set root=(md0,1)
 
  set root=(md0,1)
  
 
==== Persistent block device naming ====
 
==== Persistent block device naming ====
You can use UUIDs to detect partitions instead of the "old" {{Filename|/dev/sd*}} and {{Filename|/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.
+
One naming scheme for [[Persistent block device naming]] is the use of globally unique UUIDs to detect partitions instead of the "old" {{ic|/dev/sd*}}. Advantages are covered up in the above linked article.  
  
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 {{Filename|grub.cfg}} file every time you resize or reformat your partitions. Remember this when modifying partitions with Live-CD.
+
Persistent naming via filesystem UUIDs are used by default in GRUB2.  
  
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):
+
{{Note|The {{ic|/boot/grub.cfg}} file needs regeneration with the new UUID in {{ic|/etc/default/grub}} every time a relevant filesystem is resized or recreated. Remember this when modifying partitions & filesystems with a Live-CD.}}
#GRUB_DISABLE_LINUX_UUID=true
+
 
you can also just set the value as {{Codeline|false}} as shown here:
+
Whether to use UUIDs is controlled by an option in /etc/default/grub:
GRUB_DISABLE_LINUX_UUID=false
+
 
 +
{{bc|1=# GRUB_DISABLE_LINUX_UUID=true}}
  
 
Either way, do not forget to generate the changes:
 
Either way, do not forget to generate the changes:
grub-mkconfig -o /boot/grub/grub.cfg
+
{{bc|# grub-mkconfig -o /boot/grub/grub.cfg}}
  
 
==== Using Labels ====
 
==== Using Labels ====
  
It is possible to use labels, human-readable strings attached to filesystems, by using the {{Codeline|--label}} option to {{Codeline|search}}. First of all, label your existing partition:
+
It is possible to use labels, human-readable strings attached to filesystems, by using the {{ic|--label}} option to {{ic|search}}. First of all, label your existing partition:
  # tune2fs -L a <LABEL> <PARTITION>
+
  # tune2fs -L <LABEL> <PARTITION>
  
 
Then, add an entry using labels. An example of this:
 
Then, add an entry using labels. An example of this:
  
 
  menuentry "Arch Linux, session texte" {
 
  menuentry "Arch Linux, session texte" {
     search --label --no-floppy --set=root archroot
+
     search --label --set=root archroot
 
     linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro
 
     linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro
 
     initrd /boot/initramfs-linux.img
 
     initrd /boot/initramfs-linux.img
Line 684: Line 777:
 
==== Recall previous entry ====
 
==== 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 {{Filename|/etc/default/grub}} and change the setting of {{Codeline|GRUB_DEFAULT}}:
+
GRUB2 can remember the last entry you booted from and use this as the default entry to boot from next time. This is useful if you have multiple kernels (i.e., the current Arch one and the LTS kernel as a fallback option) or operating systems. To do this, edit {{ic|/etc/default/grub}} and change the setting of {{ic|GRUB_DEFAULT}}:
  
 
  GRUB_DEFAULT=saved
 
  GRUB_DEFAULT=saved
  
This ensures that grub will default to the saved entry. To enable saving the selected entry, add the following line to {{Filename|/etc/default/grub}}:
+
This ensures that GRUB will default to the saved entry. To enable saving the selected entry, add the following line to {{ic|/etc/default/grub}}:
  
 
  GRUB_SAVEDEFAULT=true
 
  GRUB_SAVEDEFAULT=true
  
Remember to regenerate your configuration file.
+
{{Note|Manually added menu items, eg Windows in {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} , will need {{ic|savedefault}} added. Remember to regenerate your configuration file.}}
  
 
==== Security ====
 
==== 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 {{Codeline|grub-mkpasswd_pbkdf2}}. Enter a password and confirm it. The output will look like this:
+
If you want to secure GRUB2 so it is not possible for anyone to change boot parameters or use the command line, you can add a user/password combination to GRUB2's configuration files. To do this, run the command {{ic|grub-mkpasswd-pbkdf2}}. Enter a password and confirm it. The output will look like this:
  
<pre style='overflow:auto'>
+
{{bc|<nowiki>
Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A</pre>Then, add the following to {{Filename|/etc/grub.d/00_header}}:
+
Your PBKDF2 is grub.pbkdf2.sha512.10000.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A</nowiki>}}Then, add the following to {{ic|/etc/grub.d/00_header}}:
<pre>cat << EOF
+
{{bc|<nowiki>cat << EOF
  
 
set superusers="username"
 
set superusers="username"
 
password_pbkdf2 username <password>
 
password_pbkdf2 username <password>
  
EOF</pre>
+
EOF</nowiki>}}
where <password> is the string generated by {{Codeline|grub-mkpasswd_pbkdf2}}.
+
where {{ic|<password>}} is the string generated by {{ic|grub-mkpasswd_pbkdf2}}.
 +
 
 +
Regenerate your configuration file. Your GRUB2 command line, boot parameters and all boot entries are now protected.
 +
 
 +
This can be relaxed and further customized with more users as described in the "Security" part of [https://www.gnu.org/software/grub/manual/grub.html#Security the GRUB manual].
 +
 
 +
==== Root Encryption ====
 +
 
 +
To let GRUB2 automatically add the kernel parameters for root encryption,
 +
add {{ic|1=cryptdevice=/dev/yourdevice:label}} to {{ic|GRUB_CMDLINE_LINUX}} in {{ic|/etc/default/grub}}.
 +
 
 +
Example with root mapped to {{ic|/dev/mapper/root}}:
 +
 
 +
GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:root"
 +
 
 +
Also, disable the usage of UUIDs for the rootfs:
 +
 
 +
GRUB_DISABLE_LINUX_UUID=true
 +
 
 +
Regenerate the configuration.
 +
 
 +
==== Boot non-default entry only once ====
  
Regenerate your configuration file. Your GRUB2 command line and boot parameters are now protected.
+
The command {{ic|grub-reboot}} is very helpful to boot another entry than the default only once. GRUB2 loads the entry passed in the first command line argument, when the system is rebooted the next time. Most importantly GRUB2 returns to loading the default entry for all future booting. Changing the configuration file or selecting an entry in the GRUB2 menu is not necessary.
  
=== Booting an Ubuntu ISO Image from the GRUB2 Screen ===
+
=== Booting an ISO Directly From GRUB2 ===
 +
Edit {{ic|/etc/grub.d/40_custom}} or {{ic|/boot/grub/custom.cfg}} to add an entry for the target ISO. When finished, update the GRUB menu as with the usual {{ic|grub-mkconfig -o /boot/grub/grub.cfg}} (as root).
  
Edit {{Filename|/etc/grub.d/40_custom}} to add an entry pointing to an Ubuntu iso:
+
==== Arch ISO ====
 +
{{Note|The example assumes that the iso is in {{ic|/archives}} on {{ic|hd0,6}}. Users must adjust the location and hdd/partition in ALL of the lines below to match their systems. However, if booting the ISO from USB on a computer which also has one internal HDD, then it needs to be {{ic|hd0,Y}} with {{ic|sdbY}}, instead of {{ic|sdaY}}.}}
  
  menuentry "ubuntu-11.04-desktop-amd64.iso" {
+
'''Example using x86_64'''
set isofile="/path/to/ubuntu-11.04-desktop-amd64.iso"
+
  menuentry "Archlinux-2013.01.04-dual.iso" --class iso {
loopback loop (hdX,Y)$isofile
+
  set isofile="/archives/archlinux-2013.01.04-dual.iso"
linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
+
  loopback loop (hd0,6)$isofile
initrd (loop)/casper/initrd.lz
+
  linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201301 img_dev=/dev/sda6 img_loop=$isofile earlymodules=loop
 +
  initrd (loop)/arch/boot/x86_64/archiso.img
 
  }
 
  }
  
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:
+
'''Example using i686'''
 +
menuentry "Archlinux-2013.01.04-dual.iso" --class iso {
 +
  set isofile="/archives/archlinux-2013.01.04-dual.iso"
 +
  loopback loop (hd0,6)$isofile
 +
  linux (loop)/arch/boot/i686/vmlinuz archisolabel=ARCH_201301 img_dev=/dev/sda6 img_loop=$isofile earlymodules=loop
 +
  initrd (loop)/arch/boot/i686/archiso.img
 +
  }
  
  grub-mkconfig -o /boot/grub/grub.cfg
+
{{Tip|For thumbdrives, use [[Persistent_block_device_naming|Persistent block device names]] for the "img_dev" kernel parameter. '''Ex:''' img_dev&#61;/dev/disk/by-label/CORSAIR}}
 +
 
 +
==== Ubuntu ISO ====
 +
{{Note|The example assumes that the iso is in {{ic|/archives}} on {{ic|hd0,6}}. Users must adjust the location and hdd/partition in the lines below to match their systems.}}
 +
 
 +
  menuentry "ubuntu-12.04-desktop-amd64.iso" {
 +
    set isofile="/archives/ubuntu-12.04-desktop-amd64.iso"
 +
    loopback loop (hd0,6)$isofile
 +
    linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
 +
    initrd (loop)/casper/initrd.lz
 +
}
 +
 
 +
==== Other ISOs ====
 +
 
 +
Other working configurations from [http://askubuntu.com/questions/141940/how-to-boot-live-iso-images link Source].
  
 
== Using the command shell ==
 
== Using the command shell ==
  
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 {{Filename|/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.
+
Since the MBR is too small to store all GRUB2 modules, only the menu and a few basic commands reside there. The majority of GRUB2 functionality remains in modules in {{ic|/boot/grub}}, which are inserted as needed. In error conditions (e.g. if the partition layout changes) GRUB2 may fail to boot. When this happens, a command shell may appear.
  
 
GRUB2 offers multiple shells/prompts. If there is a problem reading the menu but the bootloader is able to find the disk, you will likely be dropped to the "normal" shell:
 
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:
Line 737: Line 874:
 
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:
 
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> set prefix=(hdX,Y)/boot/grub
  grub rescue> insmod (hdX,Y)/boot/grub/normal.mod
+
  grub rescue> insmod (hdX,Y)/boot/grub/i386-pc/normal.mod
 
  rescue:grub> normal
 
  rescue:grub> normal
  
Line 748: Line 885:
  
 
Following package may be installed from [[AUR]]
 
Following package may be installed from [[AUR]]
* [http://kde-apps.org/content/show.php?content=139643 grub2-editor] (requires kdelibs)
+
* {{aur|grub-customizer}} (requires gettext gksu gtkmm hicolor-icon-theme openssl)
 +
*:Customize the bootloader (GRUB2 or BURG)
 +
* {{aur|grub2-editor}} (requires kdelibs)
 
*:A KDE4 control module for configuring the GRUB2 bootloader
 
*:A KDE4 control module for configuring the GRUB2 bootloader
* [http://kde-apps.org/content/show.php?content=137886 kcm-grub2] (requires kdelibs python2-qt kdebindings-python)
+
* {{aur|kcm-grub2}} (requires kdelibs python2-qt kdebindings-python)
 
*:This Kcm module manages the most common settings of Grub2.
 
*:This Kcm module manages the most common settings of Grub2.
* [http://sourceforge.net/projects/startup-manager/ startupmanager] (requires gnome-python imagemagick yelp python2 xorg-xrandr)
+
* {{aur|startupmanager}} (requires gnome-python imagemagick yelp python2 xorg-xrandr)
 
*:GUI app for changing the settings of GRUB, GRUB2, Usplash and Splashy
 
*:GUI app for changing the settings of GRUB, GRUB2, Usplash and Splashy
  
== parttool or legacy hide/unhide ==
+
== parttool for 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:
+
If you have a Windows 9x paradigm with hidden C:\ disks GRUB can hide/unhide it using {{ic|parttool}}. For example, to boot the third C:\ disk of three Windows 9x installations on the CLI enter the CLI and:
 
  parttool hd0,1 hidden+ boot-
 
  parttool hd0,1 hidden+ boot-
 
  parttool hd0,2 hidden+ boot-
 
  parttool hd0,2 hidden+ boot-
Line 769: Line 908:
 
See [[#Using the command shell]] first. If unable to activate the standard shell, one possible solution is to boot using a live CD or some other rescue disk to correct configuration errors and reinstall GRUB. However, such a boot disk is not always available (nor necessary); the rescue console is surprisingly robust.
 
See [[#Using the command shell]] first. If unable to activate the standard shell, one possible solution is to boot using a live CD or some other rescue disk to correct configuration errors and reinstall GRUB. However, such a boot disk is not always available (nor necessary); the rescue console is surprisingly robust.
  
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.
+
The available commands in GRUB rescue include {{ic|insmod}}, {{ic|ls}}, {{ic|set}}, and {{ic|unset}}. This example uses {{ic|set}} and {{ic|insmod}}. {{ic|set}} modifies variables and {{ic|insmod}} inserts new modules to add functionality.
  
Before starting, the user must know the location of their {{Filename|/boot}} partition (be it a separate partition, or a subdirectory under their root):
+
Before starting, the user must know the location of their {{ic|/boot}} partition (be it a separate partition, or a subdirectory under their root):
 
  grub rescue> set prefix=(hdX,Y)/boot/grub
 
  grub rescue> set prefix=(hdX,Y)/boot/grub
  
 
where X is the physical drive number and Y is the partition number.
 
where X is the physical drive number and Y is the partition number.
  
To expand console capabilities, insert the "linux" module:
+
To expand console capabilities, insert the {{ic|linux}} module:
 
  grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
 
  grub rescue> insmod (hdX,Y)/boot/grub/linux.mod
  
{{Note|With a separate boot partition, omit {{Filename|/boot}} from the path, (i.e. type {{Codeline|1=set prefix=(hdX,Y)/grub}} and {{Codeline|insmod (hdX,Y)/grub/linux.mod}}).}}
+
{{Note|With a separate boot partition, omit {{ic|/boot}} from the path, (i.e. type {{ic|1=set prefix=(hdX,Y)/grub}} and {{ic|insmod (hdX,Y)/grub/linux.mod}}).}}
  
This introduces the "linux" and "initrd" commands, which should be familiar (see [[#Configuration]]).
+
This introduces the {{ic|linux}} and {{ic|initrd}} commands, which should be familiar (see [[#Configuration]]).
  
 
An example, booting Arch Linux:
 
An example, booting Arch Linux:
Line 795: Line 934:
 
  boot
 
  boot
  
After successfully booting the Arch Linux installation, users can correct {{Filename|grub.cfg}} as needed and then run:
+
After successfully booting the Arch Linux installation, users can correct {{ic|grub.cfg}} as needed and then reinstall GRUB2.
# grub-install /dev/sda --no-floppy
+
  
to reinstall GRUB2 and fix the problem completely, changing {{Filename|/dev/sda}} if needed. See [[#Bootloader installation]] for details.
+
to reinstall GRUB2 and fix the problem completely, changing {{ic|/dev/sda}} if needed. See [[#Bootloader installation]] for details.
  
== Combining the use of UUID's and basic scripting ==
+
== Combining the use of UUIDs 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.)
+
If you like the idea of using UUIDs to avoid unreliable BIOS mappings or are struggling with GRUB's syntax, here is an example boot menu item that uses UUIDs and a small script to direct GRUB to the proper disk partitions for your system. All you need to do is replace the UUIDs in the sample with the correct UUIDs for your system. The example applies to a system with a boot and root partition. You will obviously need to modify the GRUB configuration if you have additional partitions:
  
 
   menuentry "Arch Linux 64" {
 
   menuentry "Arch Linux 64" {
    #Enter the UUID of your boot partition (this is where Grub and your kernel reside)
+
      # Set the UUIDs for your boot and root partition respectively
    set uuid_grub_boot=ece0448f-bb08-486d-9864-ac3271bd8d07
+
      set the_boot_uuid=ece0448f-bb08-486d-9864-ac3271bd8d07
 +
      set the_root_uuid=c55da16f-e2af-4603-9e0b-03f5f565ec4a
 
      
 
      
    #Enter the UUID of the partition containing the root partition of your Arch Linux installation.           
+
      # (Note: This may be the same as your boot partition)
    set uuid_os_root=c55da16f-e2af-4603-9e0b-03f5f565ec4a
+
 
      
 
      
    #(Note: this may be the same as your boot partition)
+
      # Get the boot/root devices and set them in the root and grub_boot variables
 +
      search --fs-uuid --set=root $the_root_uuid
 +
      search --fs-uuid --set=grub_boot $the_boot_uuid
 
      
 
      
    #Here we set the Grub "root" variable by locating the UUID of the root partition identified above 
+
      # Check to see if boot and root are equal.
    search --fs-uuid --no-floppy --set=root $uuid_os_root
+
      # If they are, then append /boot to $grub_boot (Since $grub_boot is actually the root partition)
 +
      if [ $the_boot_uuid == $the_root_uuid] ; then
 +
          set grub_boot=$grub_boot/boot
 +
      fi
 
      
 
      
    #Here we set a custom variable grub_boot by locating the UUID of the boot partition identified above         
+
      # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd
    search --fs-uuid --no-floppy --set=grub_boot $uuid_grub_boot
+
      linux ($grub_boot)/vmlinuz-linux root=/dev/disk/by-uuid/$uuid_os_root ro
   
+
      initrd ($grub_boot)/initramfs-linux.img
    #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
+
 
   }
 
   }
  
Line 836: Line 970:
 
=== Enable GRUB2 debug messages ===
 
=== Enable GRUB2 debug messages ===
  
Add
+
Add:
 
   
 
   
 
  set pager=1
 
  set pager=1
 
  set debug=all
 
  set debug=all
  
to {{Filename|grub.cfg}}.
+
to {{ic|grub.cfg}}.
  
 
=== Correct GRUB2 No Suitable Mode Found Error ===
 
=== Correct GRUB2 No Suitable Mode Found Error ===
  
If you get this error when booting any menuentry
+
If you get this error when booting any menuentry:
  
 
  error: no suitable mode found
 
  error: no suitable mode found
 
  Booting however
 
  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)
+
Then you need to initialize GRUB2 graphical terminal ({{ic|gfxterm}}) with proper video mode ({{ic|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 {{Filename|/usr/share/grub/unicode.pf2}} to ${GRUB2_PREFIX_DIR} ({{Filename|/boot/grub/}} in case of BIOS systems and {{Filename|/boot/efi/efi/grub/}} in case of UEFI systems).
+
Copy {{ic|/usr/share/grub/unicode.pf2}} to ${GRUB2_PREFIX_DIR} ({{ic|/boot/grub/}} in case of BIOS and UEFI systems). If GRUB2 UEFI was installed with {{ic|1=--boot-directory=/boot/efi/EFI}} set, then the directory is {{ic|/boot/efi/EFI/grub/}}:
  
 
  # cp /usr/share/grub/unicode.pf2 ${GRUB2_PREFIX_DIR}
 
  # cp /usr/share/grub/unicode.pf2 ${GRUB2_PREFIX_DIR}
  
If {{Filename|/usr/share/grub/unicode.pf2}} does not exist, install {{Package Official|bdf-unifont}}, create the unifont.pf2 file and then copy it to ${GRUB2_PREFIX_DIR} .
+
If {{ic|/usr/share/grub/unicode.pf2}} does not exist, install {{Pkg|bdf-unifont}}, create the {{ic|unifont.pf2}} file and then copy it to {{ic|${GRUB2_PREFIX_DIR<nowiki>}</nowiki>}}:
  
 
  # grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
 
  # grub-mkfont -o unicode.pf2 /usr/share/fonts/misc/unifont.bdf
  
Then, in the {{Filename|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:
+
Then, in the {{ic|grub.cfg}} file, add the following lines to enable GRUB2 to pass the video mode correctly to the kernel, without of which you will only get a black screen (no output) but booting (actually) proceeds successfully without any system hang.
  
BIOS systems
+
BIOS systems:
  
 
  insmod vbe
 
  insmod vbe
  
UEFI systems
+
UEFI systems:
  
 
  insmod efi_gop
 
  insmod efi_gop
 
  insmod efi_uga
 
  insmod efi_uga
  
After that add the following code (common to both BIOS and UEFI)
+
After that add the following code (common to both BIOS and UEFI):
  
 
  insmod font
 
  insmod font
  
  if loadfont ${prefix}/unicode.pf2
+
  if loadfont ${prefix}/fonts/unicode.pf2
 
  then
 
  then
 
     insmod gfxterm
 
     insmod gfxterm
Line 883: Line 1,017:
 
  fi
 
  fi
  
As you can see for gfxterm (graphical terminal) to function properly, {{Filename|unicode.pf2}} font file should exist in ${GRUB2_PREFIX_DIR}.
+
As you can see for gfxterm (graphical terminal) to function properly, {{ic|unicode.pf2}} font file should exist in {{ic|${GRUB2_PREFIX_DIR<nowiki>}</nowiki>}}.
  
 
=== msdos-style error message ===
 
=== msdos-style error message ===
Line 892: Line 1,026:
 
  grub-setup: error: If you really want blocklists, use --force.
 
  grub-setup: error: If you really want blocklists, use --force.
  
This error may occur when you try installing GRUB2 in a VMware container. Read more about it [http://bbs.archlinux.org/viewtopic.php?pid=581760#p581760 here]. It happens when the first partition starts just after the MBR (block 63), without the usual space of 1 MiB (2048 blocks) before the first partition. Read [[#MBR_aka_msdos_partitioning_specific_instructions]]
+
This error may occur when you try installing GRUB2 in a VMware container. Read more about it [https://bbs.archlinux.org/viewtopic.php?pid=581760#p581760 here]. It happens when the first partition starts just after the MBR (block 63), without the usual space of 1 MiB (2048 blocks) before the first partition. Read [[#Master Boot Record (MBR) specific instructions]]
 +
 
 +
=== UEFI GRUB2 drops to shell ===
 +
 
 +
If GRUB loads but drops you into the rescue shell with no errors, it may be because of a missing or misplaced {{ic|grub.cfg}}. This will happen if GRUB2 UEFI was installed with {{ic|--boot-directory}} and {{ic|grub.cfg}} is missing OR if the partition number of the boot partition changed (which is hard-coded into the {{ic|grubx64.efi}} file).
  
 
=== UEFI GRUB2 not loaded ===
 
=== UEFI GRUB2 not loaded ===
In some cases the EFI may fail to load grub correctly. Provided everything is set up correctly, the output of
+
In some cases the EFI may fail to load GRUB correctly. Provided everything is set up correctly, the output of:
 
  efibootmgr -v
 
  efibootmgr -v
 
might look something like this:
 
might look something like this:
Line 903: Line 1,041:
 
  Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\efi\grub\grub.efi)
 
  Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\efi\grub\grub.efi)
 
  Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\EfiShell.efi)
 
  Boot0001* Shell HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\EfiShell.efi)
  Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI           .
+
  Boot0002* Festplatte BIOS(2,0,00)P0: SAMSUNG HD204UI
If everything works correctly, the EFI would now automatically load grub.<br>
+
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 [https://bbs.archlinux.org/viewtopic.php?pid=981560#p981560 this post], moving grub to the partition root can help. The boot option has to be deleted and recreated afterwards. The entry for grub should look like this then:
+
 
 +
If the screen only goes black for a second and the next boot option is tried afterwards, according to [https://bbs.archlinux.org/viewtopic.php?pid=981560#p981560 this post], moving GRUB to the partition root can help. The boot option has to be deleted and recreated afterwards. The entry for GRUB should look like this then:
 
  Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\grub.efi)
 
  Boot0000* Grub HD(1,800,32000,23532fbb-1bfa-4e46-851a-b494bfe9478c)File(\grub.efi)
  
 
=== Invalid signature ===
 
=== Invalid signature ===
If trying to boot windows results in an "invalid signature" error, e.g. after reconfiguring partitions or adding additional hard drives, (re)move grub's device configuration and let it reconfigure.
+
If trying to boot Windows results in an "invalid signature" error, e.g. after reconfiguring partitions or adding additional hard drives, (re)move GRUB's device configuration and let it reconfigure:
 
  # mv /boot/grub/device.map /boot/grub/device.map-old
 
  # mv /boot/grub/device.map /boot/grub/device.map-old
 
  # grub-mkconfig -o /boot/grub/grub.cfg
 
  # grub-mkconfig -o /boot/grub/grub.cfg
Grub-mkconfig should now mention all found boot options including windows. If it works, remove /boot/grub/device.map-old.
+
{{ic|grub-mkconfig}} should now mention all found boot options, including Windows. If it works, remove {{ic|/boot/grub/device.map-old}}.
 +
 
 +
=== Boot freezes ===
 +
If booting gets stuck without any error message after grub2 loading the kernel and the initial ramdisk, try removing the {{ic|add_efi_memmap}} kernel parameter.
 +
 
 +
=== Restore GRUB Legacy ===
 +
 
 +
* Move GRUB2 files out of the way:
 +
 
 +
# mv /boot/grub /boot/grub.nonfunctional
 +
 
 +
* Copy GRUB Legacy back to {{ic|/boot}}:
 +
 
 +
# cp -af /boot/grub-legacy /boot/grub
 +
 
 +
* Replace MBR and next 62 sectors of sda with backed up copy
 +
 
 +
{{Warning|This command also restores the partition table, so be careful of overwriting a modified partition table with the old one. It '''will''' mess up your system.}}
 +
 
 +
# dd if=/path/to/backup/first-sectors of=/dev/sdX bs=512 count=1
 +
 
 +
A safer way is to restore only the MBR boot code use:
 +
 
 +
# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=446 count=1
  
 
== References ==
 
== References ==
  
# Official GRUB2 Manual - http://www.gnu.org/software/grub/manual/grub.html
+
# Official GRUB2 Manual - https://www.gnu.org/software/grub/manual/grub.html
# GRUB2 wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting - previously http://grub.enbug.org/TestingOnUEFI{{Linkrot|2011|09|05}}
+
# Ubuntu wiki page for GRUB2 - https://help.ubuntu.com/community/Grub2
# Wikipedia's page on [http://en.wikipedia.org/wiki/BIOS_Boot_partition BIOS Boot Partition]
+
# GRUB2 wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
 +
# Wikipedia's page on [[Wikipedia:BIOS Boot partition|BIOS Boot partition]]
  
 
== External Links ==
 
== External Links ==
  
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub2/grub2_bios.sh A Linux Bash Shell script to compile and install GRUB2 for BIOS from BZR Source]
+
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub/grub_bios.sh A Linux Bash Shell script to compile and install GRUB(2) for BIOS from BZR Source]
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub2/grub2_uefi.sh A Linux Bash Shell script to compile and install GRUB2 for UEFI from BZR Source]
+
# [https://github.com/the-ridikulus-rat/My_Shell_Scripts/blob/master/grub/grub_uefi.sh A Linux Bash Shell script to compile and install GRUB(2) for UEFI from BZR Source]

Revision as of 16:03, 10 April 2013

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 can be built on a wider range of OS, and has a highly configurable menu system which works in both text and graphic mode.
GRUB Legacy - previous Version, now obsolete.
Resources
GRUB EFI Examples
GNU GRUB - GNU Project

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. GRUB2 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

Preface

Here is some information that needs to be clarified:

  • The name GRUB officially refers to version 2 of the software, see [2]. If you are looking for the article on the legacy version, see GRUB Legacy.
  • From 1.99-6 onwards, GRUB2 supports Btrfs as root (without a separate /boot filesystem) compressed with either zlib or LZO.

Notes for current GRUB Legacy users

  • Upgrade from GRUB Legacy to GRUB2 is the much same as fresh installing GRUB2 which is covered below.
  • 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

GUID Partition Table (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 1007 KiB partition at the beginning of the disk using cgdisk or GNU Parted with no filesystem. The size of 1007 KiB will allow for the following partition to be correctly alligned at 1024 KiB. If needed, the partition can also be located somewhere else on the disk, but it should be within the first 2 TiB region. Set the partition type to 0xEF02 in gdisk, EF02 in cgdisk or set <BOOT_PART_NUM> bios_grub on in GNU Parted.

Note: This partition should be created before grub-install or grub-setup is run.
Note: gdisk will only allow you to create this partition on the position which will waste the least amount of space (sector 34-2047) if you create it last, after all the other partitions. This is because gdisk will auto-align partitions to 2048-sector boundaries if possible.
Master Boot Record (MBR) 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 31 KiB when DOS compatibility cylinder alignment issues are satisfied in the partition table. However a post-MBR gap of about 1 to 2 MiB is recommended to provide sufficient room for embedding GRUB2's core.img (FS#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).

MBR partitioning has better support in other operating systems, such as Microsoft Windows (up to Windows 7) and Haiku, than GPT partitioning. If you dual boot another operating system, consider using MBR partitioning.

A MBR disk may be convertible to GPT if there is a small amount of extra space available. See GUID Partition Table#Convert from MBR to GPT

UEFI systems

Note: It is recommended to read and understand the UEFI, GPT and UEFI Bootloaders pages.
Create and Mount the UEFI System Partition

Follow Unified Extensible Firmware Interface#EFI System Partition for instructions on creating a UEFI SYSTEM PARTITION. Then mount the UEFI SYSTEM PARTITION at /boot/efi. 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

BIOS systems

Backup Important Data

Although a GRUB(2) installation should run smoothly, it is strongly recommended to keep the GRUB Legacy files before installing grub-bios.

# mv /boot/grub /boot/grub-legacy

Backup the MBR which contains the boot code and partition table (Replace /dev/sdX with your actual disk path)

# dd if=/dev/sdX of=/path/to/backup/mbr_backup bs=512 count=1

Only 446 bytes of the MBR contain boot code, the next 64 contain the partition table. If you do not want to overwrite your partition table when restoring, it is strongly advised to backup only the MBR boot code:

# dd if=/dev/sdX of=/path/to/backup/bootcode_backup bs=446 count=1

If unable to install GRUB2 correctly, see #Restore GRUB Legacy.

Install grub-bios package

The GRUB(2) packages can be installed with pacman (and will replace grub-legacy or grub, if it is installed):

# pacman -S grub-bios
Note: Simply installing the package won't update the /boot/grub/i386-pc/core.img file and the GRUB(2) modules in /boot/grub/i386-pc. You need to update them manually using grub-install as explained below.

Install grub-bios boot files

There are 3 ways to install GRUB(2) boot files in BIOS booting:

Install to 440-byte MBR boot code region

To setup grub-bios in the 440-byte Master Boot Record boot code region, populate the /boot/grub directory, generate the /boot/grub/i386-pc/core.img file, embed it in the 31 KiB (minimum size - varies depending on partition alignment) post-MBR gap, and generate the configuration file, run:

# modprobe dm-mod
# grub-install --recheck /dev/sda
# grub-mkconfig -o /boot/grub/grub.cfg

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.

Note: --no-floppy has been removed from grub-install in 2.00~beta2 upstream release, and replaced with --allow-floppy.
Warning: Make sure to check the /boot directory if you use the latter. Sometimes the boot-directory parameter creates another /boot folder inside of /boot. A wrong install would look like: /boot/boot/grub/.
Install to GPT BIOS Boot Partition

GUID Partition Table disks do not have a reserved "boot track". Therefore you must create a BIOS Boot Partition (0xEF02) to hold the GRUB core image.

Using GNU Parted, you can set this using a command such as the following:

# parted /dev/disk set <partition-number> bios_grub on

If you are using gdisk, set the partition type to Template:Keypress. With partitioning programs that require setting the GUID directly, it should be ‘21686148-6449-6e6f-744e656564454649’ (stored on disk as "Hah!IdontNeedEFI" if interpreted as ASCII).

Warning: Be very careful which partition you select when marking it as a BIOS Boot Partition. When GRUB finds a BIOS Boot Partition during installation, it will automatically overwrite part of it. Make sure that the partition does not contain any other data.

To setup grub-bios on a GPT disk, populate the /boot/grub directory, generate the /boot/grub/i386-pc/core.img file, and embed it in the BIOS Boot Partition, run:

# modprobe dm-mod
# grub-install --target=i386-pc --recheck --debug /dev/sda
# mkdir -p /boot/grub/locale
# cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo

where /dev/sda is the destination of the installation.

Install to Partition or Partitionless Disk
Note: grub-bios (any version - including upstream Bazaar repo) does not encourage installation to a partition boot sector or a partitionless disk like GRUB Legacy or Syslinux does. This kind of setup is prone to breakage, especially during updates, and is not supported by Arch devs.

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

# modprobe dm-mod 
# grub-install --target=i386-pc --recheck --debug --force /dev/sdaX
# chattr -i /boot/grub/i386-pc/core.img
# mkdir -p /boot/grub/locale
# cp /usr/share/locale/en@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
# chattr +i /boot/grub/i386-pc/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-install will give out warnings like which should give you the idea of what might go wrong with this approach:

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

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

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

With --force you should get:

Installation finished. No error reported.

The reason why grub-setup does not by default allow this is because in case of partition or a partitionless disk is that grub-bios relies on embedded blocklists in the partition bootsector to locate the /boot/grub/i386-pc/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/i386-pc/core.img (using chattr command as mentioned above) so that the sector locations of the core.img file in the disk is not altered. The immutable flag on /boot/grub/i386-pc/core.img needs to be set only if grub-bios is installed to a partition boot sector or a partitionless disk, not in case of installation to MBR or simple generation of core.img without embedding any bootsector (mentioned above).

Generate core.img alone

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

# modprobe dm-mod
# grub-install --target=i386-pc --grub-setup=/bin/true --recheck --debug /dev/sda
# mkdir -p /boot/grub/locale
# cp /usr/share/locale/en@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo

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
Note: The file path is /boot/grub/grub.cfg, NOT /boot/grub/i386-pc/grub.cfg.

If grub(2) 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 config file and simply rebooted into GRUB2 Command Shell, type:

sh:grub> insmod legacycfg
sh:grub> legacy_configfile ${prefix}/menu.lst

Boot into Arch and re-create the proper GRUB2 /boot/grub/grub.cfg config file.

Note: This option works only in BIOS systems, not in UEFI systems.

Multiboot in BIOS

Boot Microsoft Windows installed in BIOS-MBR mode
Note: GRUB(2) supports booting bootmgr directly and chainload of partition boot sector is no longer required to boot Windows in a BIOS-MBR setup.
Warning: Take note that it is the system partition that has bootmgr, not your "real" Windows partition (usually C:). When showing all UUIDs with blkid, the system partition is the one with LABEL="SYSTEM RESERVED" and is only about 100 MB in size (much like the boot partition for Arch). See http://en.wikipedia.org/wiki/System_partition_and_boot_partition for more info.

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/SYSTEM_RESERVED/bootmgr:

For Windows Vista/7/8:

# grub-probe --target=fs_uuid /media/SYSTEM_RESERVED/bootmgr
69B235F6749E84CE
# grub-probe --target=hints_string /media/SYSTEM_RESERVED/bootmgr
--hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1
Note: grub-probe should be run as root.
Note: For Windows XP, replace bootmgr with ntldr in the above commands.

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

For Windows Vista/7/8:

menuentry "Microsoft Windows Vista/7/8 BIOS-MBR" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
    ntldr /bootmgr
}

For Windows XP:

menuentry "Microsoft Windows XP" {
    insmod part_msdos
    insmod ntfs
    insmod search_fs_uuid
    insmod ntldr     
    search --fs-uuid --set=root --hint-bios=hd0,msdos1 --hint-efi=hd0,msdos1 --hint-baremetal=ahci0,msdos1 69B235F6749E84CE
    ntldr /ntldr
}

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

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

UEFI systems

Note: It is recommended to read the UEFI, GPT and UEFI Bootloaders pages before reading this part.

Hardware-Specific UEFI Examples

It is well know that different motherboard manufactures implement UEFI differently. Users experiencing problems getting Grub/EFI to work properly are encouraged to share detailed steps for hardware-specific cases where UEFI booting does not work as described below. In an effort to keep the parent GRUB article neat and tidy, see the GRUB EFI Examples page for these special cases.

Install grub-uefi package

Note: Unless specified as EFI 1.x , EFI and UEFI terms are used interchangeably to denote UEFI 2.x firmware. Also unless stated explicitly, 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.

GRUB(2) 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 grub-efi-x86_64

For 32-bit aka i386 UEFI firmware:

# pacman -S grub-efi-i386
Note: Simply installing the package will not update the core.efi file and the GRUB(2) modules in the UEFI System Partition. You need to do this manually using grub-install as explained below.

Install grub-uefi boot files

Install to UEFI System Partition
Note: The below commands assume you are using grub-efi-x86_64 (for grub-efi-i386 replace x86_64 with i386 in the below commands).
Note: To do this, you need to boot using UEFI and not the BIOS. If you booted by just copying the ISO file to the USB drive, you will need to follow this guide or grub-install will show errors.

The UEFI system partition will need to be mounted at /boot/efi/ for the GRUB(2) install script to detect it:

# mkdir -p /boot/efi
# mount -t vfat /dev/sdXY /boot/efi

Install GRUB UEFI application to /boot/efi/EFI/arch_grub and its modules to /boot/grub/x86_64-efi (recommended) using:

# modprobe dm-mod
# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=arch_grub --recheck --debug
# mkdir -p /boot/grub/locale
# cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/grub/locale/en.mo
Note: Without --target or --directory option, grub-install cannot determine for which firmware grub(2) is being installed. In such cases grub-install will show source_dir doesn't exist. Please specify --target or --directory message.

If you want to install grub(2) modules and grub.cfg at the directory /boot/efi/EFI/grub and the grubx64.efi application at /boot/efi/EFI/arch_grub (ie. all the grub(2) uefi files inside the UEFISYS partition itself) use:

# modprobe dm-mod 
# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=arch_grub --boot-directory=/boot/efi/EFI --recheck --debug
# mkdir -p /boot/efi/EFI/grub/locale
# cp /usr/share/locale/en\@quot/LC_MESSAGES/grub.mo /boot/efi/EFI/grub/locale/en.mo

The --efi-directory option mentions the mountpoint of UEFI SYSTEM PARTITION , --bootloader-id mentions the name of the directory used to store the grubx64.efi file and --boot-directory mentions the directory wherein the actual modules will be installed (and into which grub.cfg should be created).

The actual paths are:

<efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi
<boot-directory>/grub/x86_64-efi/<all modules, grub.efi, core.efi, grub.cfg>
Note: the --bootloader-id option does not change <boot-directory>/grub, i.e. you cannot install the modules to <boot-directory>/<bootloader-id>, the path is hard-coded to be <boot-directory>/grub.

In --efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=grub:

<efi-directory>/<EFI or efi>/<bootloader-id> == <boot-directory>/grub == /boot/efi/EFI/grub

In --efi-directory=/boot/efi --boot-directory=/boot/efi/EFI --bootloader-id=arch_grub:

<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub
<boot-directory>/grub == /boot/efi/EFI/grub

In --efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=arch_grub:

<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/arch_grub
<boot-directory>/grub == /boot/grub

In --efi-directory=/boot/efi --boot-directory=/boot --bootloader-id=grub:

<efi-directory>/<EFI or efi>/<bootloader-id> == /boot/efi/EFI/grub
<boot-directory>/grub == /boot/grub

The <efi-directory>/<EFI or efi>/<bootloader-id>/grubx64.efi is an exact copy of <boot-directory>/grub/x86_64-efi/core.efi.

Note: In GRUB 2.00, the grub-install option --efi-directory replaces --root-directory and the latter is deprecated.
Note: The options --efi-directory and --bootloader-id are specific to GRUB(2) UEFI.

In all the cases the UEFI SYSTEM PARTITION should be mounted for grub-install to install grubx64.efi in it, which will be launched by the firmware (using the efibootmgr created boot entry in non-Mac systems).

If you notice carefully, there is no <device_path> option (Eg: /dev/sda) at the end of the grub-install command unlike the case of setting up GRUB(2) 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 #Create GRUB2 entry in the Firmware Boot Manager.

Generate GRUB2 UEFI Config file

Finally, generate a configuration for GRUB(2) (this is explained in greater detail in the Configuration section):

# grub-mkconfig -o <boot-directory>/grub/grub.cfg
Note: The file path is <boot-directory>/grub/grub.cfg, NOT <boot-directory>/grub/x86_64-efi/grub.cfg.

If you used --boot-directory=/boot:

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

If you used --boot-directory=/boot/efi/EFI:

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

This is independent of the value of --bootloader-id option.

If GRUB2 complains about "no suitable mode found" while booting, try #Correct GRUB2 No Suitable Mode Found Error.

Create GRUB2 entry in the Firmware Boot Manager

As of grub-efi-x86_64 version 2.00, grub-install automatically tries to create a menu entry in the boot manager. If it doesn't, then see Beginners' Guide#GRUB for instructions to use efibootmgr to create a menu entry. However, the problem is likely to be that you haven't booted your CD/USB in UEFI mode, as in Unified Extensible Firmware Interface#Create UEFI bootable USB from ISO.

Create GRUB2 Standalone UEFI Application

It is possible to create a grubx64_standalone.efi application which has all the modules embeddded in a memdisk within the uefi application, thus removing the need for having a separate directory populated with all the GRUB2 uefi modules and other related files. This is done using the grub-mkstandalone command which is included in grub-common >= 1:1.99-6 package.

The easiest way to do this would be with the install command already mentioned before, but specifying the modules to include. For example:

# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \
--output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" <any extra files you want to include>

The grubx64_standalone.efi file expects grub.cfg to be within its $prefix which is (memdisk)/boot/grub. The memdisk is embedded within the efi app. The grub-mkstandlone script allow passing files to be included in the memdisk image to be as the arguments to the script (in <any extra files you want to include>).

If you have the grub.cfg at /home/user/Desktop/grub.cfg, then create a temporary /home/user/Desktop/boot/grub/ directory, copy the /home/user/Desktop/grub.cfg to /home/user/Desktop/boot/grub/grub.cfg, cd into /home/user/Desktop/boot/grub/ and run:

# grub-mkstandalone --directory="/usr/lib/grub/x86_64-efi/" --format="x86_64-efi" --compression="xz" \
--output="/boot/efi/EFI/arch_grub/grubx64_standalone.efi" "boot/grub/grub.cfg"

The reason to cd into /home/user/Desktop/boot/grub/ and to pass the file path as boot/grub/grub.cfg (notice the lack of a leading slash - boot/ vs /boot/ ) is because dir1/dir2/file is included as (memdisk)/dir1/dir2/file by the grub-mkstandalone script.

If you pass /home/user/Desktop/grub.cfg the file will be included as (memdisk)/home/user/Desktop/grub.cfg. If you pass /home/user/Desktop/boot/grub/grub.cfg the file will be included as (memdisk)/home/user/Desktop/boot/grub/grub.cfg. That is the reason for cd'ing into /home/user/Desktop/boot/grub/ and passing boot/grub/grub.cfg, to include the file as (memdisk)/boot/grub/grub.cfg, which is what grub.efi expects the file to be.

You need to create an UEFI Boot Manager entry for /boot/efi/EFI/arch_grub/grubx64_standalone.efi using efibootmgr. Follow #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
# grub-probe --target=hints_string /boot/efi/EFI/Microsoft/Boot/bootmgfw.efi
--hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1
Note: grub-probe should be run as root.

Then, add this code to /etc/grub.d/40_custom to chainload Windows x86_64 (Vista SP1+, 7 or 8) installed in UEFI-GPT mode:

menuentry "Microsoft Windows Vista/7/8 x86_64 UEFI-GPT" {
    insmod part_gpt
    insmod fat
    insmod search_fs_uuid
    insmod chain
    search --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 1ce5-7f28
    chainloader /efi/Microsoft/Boot/bootmgfw.efi
}

Afterwards remake /boot/grub/grub.cfg

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

Configuration

You can also choose to automatically generate or manually edit grub.cfg.

Note: For EFI systems, if GRUB2 was installed with the --boot-directory option set, the grub.cfg file must be placed in the same directory as grubx64.efi. Otherwise, the grub.cfg file goes in /boot/grub/, just like in the BIOS version of GRUB2.
Note: Here is a quite complete description of how to configure GRUB2: http://members.iinet.net/~herman546/p20/GRUB2%20Configuration%20File%20Commands.html

Automatically generating using grub-mkconfig (Recommended)

The GRUB2 menu.lst 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 to /etc/grub.d/40_custom or /boot/grub/custom.cfg

Additional arguments

To pass custom additional arguments to the Linux image, you can set the GRUB_CMDLINE_LINUX variable in /etc/default/grub.

For example, use GRUB_CMDLINE_LINUX="resume=/dev/sdaX" where sdaX is your swap partition to enable resume after hibernation.

You can also use GRUB_CMDLINE_LINUX="resume=/dev/disk/by-uuid/${swap_uuid}", where ${swap_uuid} is the UUID of your swap partition.

Multiple entries are separated by spaces within the double quotes. So, for users who want both resume and systemd it would look like this: GRUB_CMDLINE_LINUX="resume=/dev/sdaX init=/usr/lib/systemd/systemd"

See Kernel parameters for more info.

Manually creating grub.cfg

Warning: Editing this file is strongly not recommended. The file is generated by the grub-mkconfig command, and it is best to edit your /etc/default/grub or one of the scripts in the /etc/grub.d folder.

A basic GRUB config file uses the following options

  • (hdX,Y) is the partition Y on disk X, 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 time M to wait in seconds for a user selection before default is booted
  • menuentry "title" {entry options} is a boot entry titled title
  • 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, you may wish to install os-prober.

Using grub-mkconfig

The best way to add other entries is editing the /etc/grub.d/40_custom or /boot/grub/custom.cfg . The entries in this file will be automatically added when running grub-mkconfig. After adding the new lines, run:

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

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. Remember you need to point set root and chainloader to the system reserve partition that windows made when it installed, not the actual partition windows is on. This example works if your system reserve partition is sda3.

# (2) Windows XP
menuentry "Windows XP" {
    set root=(hd0,3)
    chainloader (hd0,3)+1
}

If the Windows bootloader is on an entirely different hard drive than GRUB, it may be necessary to trick Windows into believing that it is the first hard drive. This was possible with drivemap. Assuming GRUB is on hd0 and Windows is 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/i386-pc/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.

Note: If this example does not work for you try to replace gfxmode="1024x768x32" by vbemode="0x105". Remember to replace the specified resolution with one suitable for your screen.
Note: To show all the modes you can use # 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, 1920×1200

915resolution hack

Some times for Intel graphic adapters neither # hwinfo --framebuffer nor vbeinfo will show you the desired resolution. In this case you can use 915resolution hack. This hack will temporarily modify video BIOS and add needed resolution. See 915resolution's home page

In the following I will proceed with the example for my system. Please adjust the recipe for your needs. First you need to find a video mode which will be modified later. For that, run 915resolution in GRUB2 command shell:

915resolution -l

The output will be something like:

Intel 800/900 Series VBIOS Hack : version 0.5.3
...
Mode 30 : 640x480, 8 bits/pixel
...

Next, our purpose is to overwrite mode 30. (You can choose what ever mode you want.) In the file /etc/grub.d/00_header just before the set gfxmode=${GRUB_GFXMODE} line insert:

915resolution 30 1440 900

Here we are overwriting the mode 30 with 1440x900 resolution. Lastly we need to set GRUB_GFXMODE as described earlier, regenerate GRUB2 configuration file and reboot to test changes:

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

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 grub-common 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/myimage"
#GRUB_THEME="/path/to/gfxtheme"
GRUB_FONT="/path/to/font.pf2"
Note: If you have installed GRUB on a separate partition, /boot/grub/myimage becomes /grub/myimage.

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.

Theme

Here is an example for configuring Starfield theme which was included in GRUB2 package.

Edit /etc/default/grub

GRUB_THEME="/usr/share/grub/themes/starfield/theme.txt"

Generate the changes:

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

If configuring the theme was successful, you'll see Found theme: /usr/share/grub/themes/starfield/theme.txt in the terminal. Your splash image will usually not be displayed when using a theme.

Menu colors

You can set the menu colors in GRUB2. The available colors for GRUB2 can be found in the GRUB Manual. 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

Hidden menu

One of the unique features of GRUB2 is hiding/skipping the menu and showing it by holding Template:Keypress 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

Disable framebuffer

Users who use NVIDIA proprietary driver might wish to disable GRUB2's framebuffer as it can cause problems with the binary driver.

To disable framebuffer, edit /etc/default/grub and uncomment the following line:

GRUB_TERMINAL_OUTPUT=console

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/lvm_group_name-lvm_logical_boot_partition_name

Example:

# (0) Arch Linux
menuentry "Arch Linux" {
insmod lvm
set root=lvm/VolumeGroup-lv_boot
# you can only set following two lines
linux /vmlinuz-linux root=/dev/mapper/VolumeGroup-root ro
initrd /initramfs-linux.img
}

RAID

GRUB2 provides convenient handling of RAID volumes. You need to add insmod mdraid which allows you to address the volume natively. For example, /dev/md0 becomes:

set root=(md0)

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

set root=(md0,1)

Persistent block device naming

One naming scheme for Persistent block device naming is the use of globally unique UUIDs to detect partitions instead of the "old" /dev/sd*. Advantages are covered up in the above linked article.

Persistent naming via filesystem UUIDs are used by default in GRUB2.

Note: The /boot/grub.cfg file needs regeneration with the new UUID in /etc/default/grub every time a relevant filesystem is resized or recreated. Remember this when modifying partitions & filesystems with a Live-CD.

Whether to use UUIDs is controlled by an option in /etc/default/grub:

# GRUB_DISABLE_LINUX_UUID=true

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 <LABEL> <PARTITION>

Then, add an entry using labels. An example of this:

menuentry "Arch Linux, session texte" {
    search --label --set=root archroot
    linux /boot/vmlinuz-linux root=/dev/disk/by-label/archroot ro
    initrd /boot/initramfs-linux.img
}

Recall previous entry

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: Manually added menu items, eg Windows in /etc/grub.d/40_custom or /boot/grub/custom.cfg , 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.C8ABD3E93C4DFC83138B0C7A3D719BC650E6234310DA069E6FDB0DD4156313DA3D0D9BFFC2846C21D5A2DDA515114CF6378F8A064C94198D0618E70D23717E82.509BFA8A4217EAD0B33C87432524C0B6B64B34FBAD22D3E6E6874D9B101996C5F98AB1746FE7C7199147ECF4ABD8661C222EEEDB7D14A843261FFF2C07B1269A
Then, 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, boot parameters and all boot entries are now protected.

This can be relaxed and further customized with more users as described in the "Security" part of the GRUB manual.

Root Encryption

To let GRUB2 automatically add the kernel parameters for root encryption, add cryptdevice=/dev/yourdevice:label to GRUB_CMDLINE_LINUX in /etc/default/grub.

Example with root mapped to /dev/mapper/root:

GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda2:root"

Also, disable the usage of UUIDs for the rootfs:

GRUB_DISABLE_LINUX_UUID=true

Regenerate the configuration.

Boot non-default entry only once

The command grub-reboot is very helpful to boot another entry than the default only once. GRUB2 loads the entry passed in the first command line argument, when the system is rebooted the next time. Most importantly GRUB2 returns to loading the default entry for all future booting. Changing the configuration file or selecting an entry in the GRUB2 menu is not necessary.

Booting an ISO Directly From GRUB2

Edit /etc/grub.d/40_custom or /boot/grub/custom.cfg to add an entry for the target ISO. When finished, update the GRUB menu as with the usual grub-mkconfig -o /boot/grub/grub.cfg (as root).

Arch ISO

Note: The example assumes that the iso is in /archives on hd0,6. Users must adjust the location and hdd/partition in ALL of the lines below to match their systems. However, if booting the ISO from USB on a computer which also has one internal HDD, then it needs to be hd0,Y with sdbY, instead of sdaY.

Example using x86_64

menuentry "Archlinux-2013.01.04-dual.iso" --class iso {
  set isofile="/archives/archlinux-2013.01.04-dual.iso"
  loopback loop (hd0,6)$isofile
  linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201301 img_dev=/dev/sda6 img_loop=$isofile earlymodules=loop
  initrd (loop)/arch/boot/x86_64/archiso.img
}

Example using i686

menuentry "Archlinux-2013.01.04-dual.iso" --class iso {
  set isofile="/archives/archlinux-2013.01.04-dual.iso"
  loopback loop (hd0,6)$isofile
  linux (loop)/arch/boot/i686/vmlinuz archisolabel=ARCH_201301 img_dev=/dev/sda6 img_loop=$isofile earlymodules=loop
  initrd (loop)/arch/boot/i686/archiso.img
}
Tip: For thumbdrives, use Persistent block device names for the "img_dev" kernel parameter. Ex: img_dev=/dev/disk/by-label/CORSAIR

Ubuntu ISO

Note: The example assumes that the iso is in /archives on hd0,6. Users must adjust the location and hdd/partition in the lines below to match their systems.
menuentry "ubuntu-12.04-desktop-amd64.iso" {
    set isofile="/archives/ubuntu-12.04-desktop-amd64.iso"
    loopback loop (hd0,6)$isofile
    linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile quiet noeject noprompt splash --
    initrd (loop)/casper/initrd.lz
}

Other ISOs

Other working configurations from link Source.

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/i386-pc/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

  • grub-customizerAUR (requires gettext gksu gtkmm hicolor-icon-theme openssl)
    Customize the bootloader (GRUB2 or BURG)
  • grub2-editorAUR (requires kdelibs)
    A KDE4 control module for configuring the GRUB2 bootloader
  • kcm-grub2AUR (requires kdelibs python2-qt kdebindings-python)
    This Kcm module manages the most common settings of Grub2.
  • startupmanagerAUR (requires gnome-python imagemagick yelp python2 xorg-xrandr)
    GUI app for changing the settings of GRUB, GRUB2, Usplash and Splashy

parttool for hide/unhide

If you have a Windows 9x paradigm with hidden C:\ disks GRUB can hide/unhide it using parttool. For example, to boot the third C:\ disk of three Windows 9x installations on the CLI enter the CLI and:

parttool hd0,1 hidden+ boot-
parttool hd0,2 hidden+ boot-
parttool hd0,3 hidden- boot+
set root=hd0,3
chainloader +1
boot

Using the rescue console

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

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
Note: With a separate boot partition, omit /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 reinstall GRUB2.

to reinstall GRUB2 and fix the problem completely, changing /dev/sda if needed. See #Bootloader installation for details.

Combining the use of UUIDs and basic scripting

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

 menuentry "Arch Linux 64" {
     # Set the UUIDs for your boot and root partition respectively
     set the_boot_uuid=ece0448f-bb08-486d-9864-ac3271bd8d07
     set the_root_uuid=c55da16f-e2af-4603-9e0b-03f5f565ec4a
   
     # (Note: This may be the same as your boot partition)
   
     # Get the boot/root devices and set them in the root and grub_boot variables
     search --fs-uuid --set=root $the_root_uuid
     search --fs-uuid --set=grub_boot $the_boot_uuid
   
     # Check to see if boot and root are equal.
     # If they are, then append /boot to $grub_boot (Since $grub_boot is actually the root partition)
     if [ $the_boot_uuid == $the_root_uuid] ; then
         set grub_boot=$grub_boot/boot
     fi
   
     # $grub_boot now points to the correct location, so the following will properly find the kernel and initrd
     linux ($grub_boot)/vmlinuz-linux root=/dev/disk/by-uuid/$uuid_os_root ro
     initrd ($grub_boot)/initramfs-linux.img
 }

Troubleshooting

Any troubleshooting should be added here.

Enable GRUB2 debug messages

Add:

set pager=1
set debug=all

to 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 and UEFI systems). If GRUB2 UEFI was installed with --boot-directory=/boot/efi/EFI set, then the directory is /boot/efi/EFI/grub/:

# 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}/fonts/unicode.pf2
then
    insmod gfxterm
    set gfxmode=auto
    set gfxpayload=keep
    terminal_output gfxterm
fi

As you can see for gfxterm (graphical terminal) to function properly, unicode.pf2 font file should exist in ${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 #Master Boot Record (MBR) specific instructions

UEFI GRUB2 drops to shell

If GRUB loads but drops you into the rescue shell with no errors, it may be because of a missing or misplaced grub.cfg. This will happen if GRUB2 UEFI was installed with --boot-directory and grub.cfg is missing OR if the partition number of the boot partition changed (which is hard-coded into the grubx64.efi file).

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.

Boot freezes

If booting gets stuck without any error message after grub2 loading the kernel and the initial ramdisk, try removing the add_efi_memmap kernel parameter.

Restore GRUB Legacy

  • Move GRUB2 files out of the way:
# mv /boot/grub /boot/grub.nonfunctional
  • Copy GRUB Legacy back to /boot:
# cp -af /boot/grub-legacy /boot/grub
  • Replace MBR and next 62 sectors of sda with backed up copy
Warning: This command also restores the partition table, so be careful of overwriting a modified partition table with the old one. It will mess up your system.
# dd if=/path/to/backup/first-sectors of=/dev/sdX bs=512 count=1

A safer way is to restore only the MBR boot code use:

# dd if=/path/to/backup/mbr-boot-code of=/dev/sdX bs=446 count=1

References

  1. Official GRUB2 Manual - https://www.gnu.org/software/grub/manual/grub.html
  2. Ubuntu wiki page for GRUB2 - https://help.ubuntu.com/community/Grub2
  3. GRUB2 wiki page describing steps to compile for UEFI systems - https://help.ubuntu.com/community/UEFIBooting
  4. Wikipedia's page on BIOS Boot partition

External Links

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