From 994b82643247f936e07aa9652451a9d724bda615 Mon Sep 17 00:00:00 2001 From: Colin Watson Date: Tue, 29 Mar 2011 14:32:38 +0100 Subject: [PATCH] * docs/grub.texi (BIOS installation): New section, partly based on previous text in other sections. (Installing GRUB using grub-install): Replace BIOS discussion with a cross-reference. (Images): Likewise. --- ChangeLog | 8 ++++ docs/grub.texi | 100 +++++++++++++++++++++++++++++++++++-------------- 2 files changed, 79 insertions(+), 29 deletions(-) diff --git a/ChangeLog b/ChangeLog index a7ed9fc94..552d5dc7c 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,11 @@ +2011-03-29 Colin Watson + + * docs/grub.texi (BIOS installation): New section, partly based on + previous text in other sections. + (Installing GRUB using grub-install): Replace BIOS discussion with a + cross-reference. + (Images): Likewise. + 2011-03-29 Vladimir Serbinenko * grub-core/kern/emu/hostdisk.c (find_partition_start) diff --git a/docs/grub.texi b/docs/grub.texi index 83bd80023..cac4ffbf3 100644 --- a/docs/grub.texi +++ b/docs/grub.texi @@ -550,6 +550,7 @@ the @dfn{boot directory}. * Installing GRUB using grub-install:: * Making a GRUB bootable CD-ROM:: * Device map:: +* BIOS installation:: @end menu @@ -565,13 +566,8 @@ always. Therefore, GRUB provides you with a map file called the @dfn{device map}, which you must fix if it is wrong. @xref{Device map}, for more details. -On BIOS platforms GRUB has to use a so-called embedding zone. On msdos -partition tables, this is the space between the MBR and the first partition -(called the MBR gap or the boot track), while on GPT partition tables it -uses a BIOS Boot Partition (a partition with GUID -21686148-6449-6e6f-744e656564454649). If you use GRUB on a BIOS system, make -sure that the embedding zone is at least 31 KiB (512KiB or more -recommended). +For information on where GRUB should be installed on PC BIOS platforms, +@pxref{BIOS installation}. If you still do want to install GRUB under a UNIX-like OS (such as @sc{gnu}), invoke the program @command{grub-install} (@pxref{Invoking @@ -744,6 +740,72 @@ comments in the file if needed, as the GRUB utilities assume that a line is just a comment if the first character is @samp{#}. +@node BIOS installation +@section BIOS installation + +@heading MBR + +The partition table format traditionally used on PC BIOS platforms is called +the Master Boot Record (MBR) format; this is the format that allows up to +four primary partitions and additional logical partitions. With this +partition table format, there are two ways to install GRUB: it can be +embedded in the area between the MBR and the first partition (called by +various names, such as the "boot track", "MBR gap", or "embedding area", and +which is usually at least 31 KiB), or the core image can be installed in a +file system and a list of the blocks that make it up can be stored in the +first sector of that partition. + +Each of these has different problems. There is no way to reserve space in +the embedding area with complete safety, and some proprietary software is +known to use it to make it difficult for users to work around licensing +restrictions; and systems are sometimes partitioned without leaving enough +space before the first partition. On the other hand, installing to a +filesystem means that GRUB is vulnerable to its blocks being moved around by +filesystem features such as tail packing, or even by aggressive fsck +implementations, so this approach is quite fragile; and this approach can +only be used if the @file{/boot} filesystem is on the same disk that the +BIOS boots from, so that GRUB does not have to rely on guessing BIOS drive +numbers. + +The GRUB development team generally recommends embedding GRUB before the +first partition, unless you have special requirements. You must ensure that +the first partition starts at least 31 KiB (63 sectors) from the start of +the disk; on modern disks, it is often a performance advantage to align +partitions on larger boundaries anyway, so the first partition might start 1 +MiB from the start of the disk. + +@heading GPT + +Some newer systems use the GUID Partition Table (GPT) format. This was +specified as part of the Extensible Firmware Interface (EFI), but it can +also be used on BIOS platforms if system software supports it; for example, +GRUB and GNU/Linux can be used in this configuration. With this format, it +is possible to reserve a whole partition for GRUB, called the BIOS Boot +Partition. GRUB can then be embedded into that partition without the risk +of being overwritten by other software and without being contained in a +filesystem which might move its blocks around. + +When creating a BIOS Boot Partition on a GPT system, you should make sure +that it is at least 31 KiB in size. (GPT-formatted disks are not usually +particularly small, so we recommend that you make it larger than the bare +minimum, such as 1 MiB, to allow plenty of room for growth.) You must also +make sure that it has the proper partition type. Using GNU Parted, you can +set this using a command such as the following: + +@example +# @kbd{parted /dev/@var{disk} set @var{partition-number} bios_grub on} +@end example + +If you are using gdisk, set the partition type to @samp{0xEF02}. With +partitioning programs that require setting the GUID directly, it should be +@samp{21686148-6449-6e6f-744e656564454649}. + +@strong{Caution:} Be very careful which partition you select! 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. + + @node Booting @chapter Booting @@ -2021,28 +2083,8 @@ target operating systems, and so on) from the file system at run-time. The modular design allows the core image to be kept small, since the areas of disk where it must be installed are often as small as 32KB. -On PC systems using the traditional MBR partition table format, the core -image is usually installed in the "MBR gap" between the master boot record -and the first partition, or sometimes it is installed in a file system and -read directly from that. The latter is not recommended because GRUB needs -to encode the location of all the core image sectors in @file{diskboot.img}, -and if the file system ever moves the core image around (as it is entitled -to do) then GRUB must be reinstalled; it also means that GRUB will not be -able to reliably find the core image if it resides on a different disk than -the one to which @file{boot.img} was installed. - -On PC systems using the more recent GUID Partition Table (GPT) format, the -core image should be installed to a BIOS Boot Partition. This may be -created by GNU Parted using a command such as the following: - -@example -# @kbd{parted /dev/@var{disk} set @var{partition-number} bios_grub on} -@end example - -@strong{Caution:} Be very careful which partition you select! 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. +@xref{BIOS installation}, for details on where the core image can be +installed on PC systems. @item *.mod Everything else in GRUB resides in dynamically loadable modules. These are