240 lines
10 KiB
Text
240 lines
10 KiB
Text
4 Installation
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**************
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In order to install GRUB as your boot loader, you need to first install
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the GRUB system and utilities under your UNIX-like operating system
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(*note Obtaining and Building GRUB::). You can do this either from the
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source tarball, or as a package for your OS.
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After you have done that, you need to install the boot loader on a
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drive (floppy or hard disk) by using the utility 'grub-install' (*note
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Invoking grub-install::) on a UNIX-like OS.
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GRUB comes with boot images, which are normally put in the directory
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'/usr/lib/grub/<cpu>-<platform>' (for BIOS-based machines
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'/usr/lib/grub/i386-pc'). Hereafter, the directory where GRUB images
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are initially placed (normally '/usr/lib/grub/<cpu>-<platform>') will be
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called the "image directory", and the directory where the boot loader
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needs to find them (usually '/boot') will be called the "boot
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directory".
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4.1 Installing GRUB using grub-install
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======================================
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For information on where GRUB should be installed on PC BIOS platforms,
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*note BIOS installation::.
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In order to install GRUB under a UNIX-like OS (such as GNU), invoke
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the program 'grub-install' (*note Invoking grub-install::) as the
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superuser ("root").
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The usage is basically very simple. You only need to specify one
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argument to the program, namely, where to install the boot loader. The
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argument has to be either a device file (like '/dev/hda'). For example,
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under Linux the following will install GRUB into the MBR of the first
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IDE disk:
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# grub-install /dev/sda
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Likewise, under GNU/Hurd, this has the same effect:
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# grub-install /dev/hd0
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But all the above examples assume that GRUB should put images under
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the '/boot' directory. If you want GRUB to put images under a directory
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other than '/boot', you need to specify the option '--boot-directory'.
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The typical usage is that you create a GRUB boot floppy with a
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filesystem. Here is an example:
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# mke2fs /dev/fd0
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# mount -t ext2 /dev/fd0 /mnt
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# mkdir /mnt/boot
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# grub-install --boot-directory=/mnt/boot /dev/fd0
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# umount /mnt
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Some BIOSes have a bug of exposing the first partition of a USB drive
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as a floppy instead of exposing the USB drive as a hard disk (they call
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it "USB-FDD" boot). In such cases, you need to install like this:
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# losetup /dev/loop0 /dev/sdb1
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# mount /dev/loop0 /mnt/usb
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# grub-install --boot-directory=/mnt/usb/bugbios --force --allow-floppy /dev/loop0
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This install doesn't conflict with standard install as long as they
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are in separate directories.
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Note that 'grub-install' is actually just a shell script and the real
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task is done by other tools such as 'grub-mkimage'. Therefore, you may
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run those commands directly to install GRUB, without using
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'grub-install'. Don't do that, however, unless you are very familiar
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with the internals of GRUB. Installing a boot loader on a running OS may
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be extremely dangerous.
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On EFI systems for fixed disk install you have to mount EFI System
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Partition. If you mount it at '/boot/efi' then you don't need any
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special arguments:
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# grub-install
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Otherwise you need to specify where your EFI System partition is
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mounted:
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# grub-install --efi-directory=/mnt/efi
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For removable installs you have to use '--removable' and specify both
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'--boot-directory' and '--efi-directory':
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# grub-install --efi-directory=/mnt/usb --boot-directory=/mnt/usb/boot --removable
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4.2 Making a GRUB bootable CD-ROM
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=================================
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GRUB supports the "no emulation mode" in the El Torito specification(1)
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(*note Making a GRUB bootable CD-ROM-Footnote-1::). This means that you
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can use the whole CD-ROM from GRUB and you don't have to make a floppy
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or hard disk image file, which can cause compatibility problems.
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For booting from a CD-ROM, GRUB uses a special image called
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'cdboot.img', which is concatenated with 'core.img'. The 'core.img'
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used for this should be built with at least the 'iso9660' and 'biosdisk'
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modules. Your bootable CD-ROM will usually also need to include a
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configuration file 'grub.cfg' and some other GRUB modules.
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To make a simple generic GRUB rescue CD, you can use the
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'grub-mkrescue' program (*note Invoking grub-mkrescue::):
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$ grub-mkrescue -o grub.iso
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You will often need to include other files in your image. To do
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this, first make a top directory for the bootable image, say, 'iso':
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$ mkdir iso
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Make a directory for GRUB:
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$ mkdir -p iso/boot/grub
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If desired, make the config file 'grub.cfg' under 'iso/boot/grub'
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(*note Configuration::), and copy any files and directories for the disc
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to the directory 'iso/'.
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Finally, make the image:
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$ grub-mkrescue -o grub.iso iso
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This produces a file named 'grub.iso', which then can be burned into
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a CD (or a DVD), or written to a USB mass storage device.
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The root device will be set up appropriately on entering your
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'grub.cfg' configuration file, so you can refer to file names on the CD
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without needing to use an explicit device name. This makes it easier to
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produce rescue images that will work on both optical drives and USB mass
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storage devices.
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(1) El Torito is a specification for bootable CD using BIOS
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functions.
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4.3 The map between BIOS drives and OS devices
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==============================================
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If the device map file exists, the GRUB utilities ('grub-probe', etc.)
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read it to map BIOS drives to OS devices. This file consists of lines
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like this:
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(DEVICE) FILE
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DEVICE is a drive specified in the GRUB syntax (*note Device
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syntax::), and FILE is an OS file, which is normally a device file.
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Historically, the device map file was used because GRUB device names
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had to be used in the configuration file, and they were derived from
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BIOS drive numbers. The map between BIOS drives and OS devices cannot
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always be guessed correctly: for example, GRUB will get the order wrong
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if you exchange the boot sequence between IDE and SCSI in your BIOS.
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Unfortunately, even OS device names are not always stable. Modern
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versions of the Linux kernel may probe drives in a different order from
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boot to boot, and the prefix ('/dev/hd*' versus '/dev/sd*') may change
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depending on the driver subsystem in use. As a result, the device map
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file required frequent editing on some systems.
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GRUB avoids this problem nowadays by using UUIDs or file system
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labels when generating 'grub.cfg', and we advise that you do the same
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for any custom menu entries you write. If the device map file does not
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exist, then the GRUB utilities will assume a temporary device map on the
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fly. This is often good enough, particularly in the common case of
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single-disk systems.
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However, the device map file is not entirely obsolete yet, and it is
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used for overriding when current environment is different from the one
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on boot. Most common case is if you use a partition or logical volume
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as a disk for virtual machine. You can put any comments in the file if
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needed, as the GRUB utilities assume that a line is just a comment if
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the first character is '#'.
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4.4 BIOS installation
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=====================
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MBR
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===
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The partition table format traditionally used on PC BIOS platforms is
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called the Master Boot Record (MBR) format; this is the format that
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allows up to four primary partitions and additional logical partitions.
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With this partition table format, there are two ways to install GRUB: it
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can be embedded in the area between the MBR and the first partition
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(called by various names, such as the "boot track", "MBR gap", or
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"embedding area", and which is usually at least 31 KiB), or the core
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image can be installed in a file system and a list of the blocks that
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make it up can be stored in the first sector of that partition.
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Each of these has different problems. There is no way to reserve
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space in the embedding area with complete safety, and some proprietary
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software is known to use it to make it difficult for users to work
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around licensing restrictions; and systems are sometimes partitioned
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without leaving enough space before the first partition. On the other
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hand, installing to a filesystem means that GRUB is vulnerable to its
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blocks being moved around by filesystem features such as tail packing,
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or even by aggressive fsck implementations, so this approach is quite
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fragile; and this approach can only be used if the '/boot' filesystem is
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on the same disk that the BIOS boots from, so that GRUB does not have to
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rely on guessing BIOS drive numbers.
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The GRUB development team generally recommends embedding GRUB before
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the first partition, unless you have special requirements. You must
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ensure that the first partition starts at least 31 KiB (63 sectors) from
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the start of the disk; on modern disks, it is often a performance
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advantage to align partitions on larger boundaries anyway, so the first
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partition might start 1 MiB from the start of the disk.
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GPT
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===
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Some newer systems use the GUID Partition Table (GPT) format. This was
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specified as part of the Extensible Firmware Interface (EFI), but it can
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also be used on BIOS platforms if system software supports it; for
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example, GRUB and GNU/Linux can be used in this configuration. With
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this format, it is possible to reserve a whole partition for GRUB,
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called the BIOS Boot Partition. GRUB can then be embedded into that
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partition without the risk of being overwritten by other software and
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without being contained in a filesystem which might move its blocks
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around.
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When creating a BIOS Boot Partition on a GPT system, you should make
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sure that it is at least 31 KiB in size. (GPT-formatted disks are not
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usually particularly small, so we recommend that you make it larger than
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the bare minimum, such as 1 MiB, to allow plenty of room for growth.)
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You must also make sure that it has the proper partition type. Using
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GNU Parted, you can set this using a command such as the following:
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# parted /dev/DISK set PARTITION-NUMBER bios_grub on
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If you are using gdisk, set the partition type to '0xEF02'. With
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partitioning programs that require setting the GUID directly, it should
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be '21686148-6449-6e6f-744e656564454649'.
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*Caution:* Be very careful which partition you select! When GRUB
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finds a BIOS Boot Partition during installation, it will automatically
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overwrite part of it. Make sure that the partition does not contain any
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other data.
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