118 lines
4.5 KiB
Text
118 lines
4.5 KiB
Text
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13 Filesystem syntax and semantics
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**********************************
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GRUB uses a special syntax for specifying disk drives which can be
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accessed by BIOS. Because of BIOS limitations, GRUB cannot distinguish
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between IDE, ESDI, SCSI, or others. You must know yourself which BIOS
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device is equivalent to which OS device. Normally, that will be clear
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if you see the files in a device or use the command 'search' (*note
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search::).
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13.1 How to specify devices
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===========================
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The device syntax is like this:
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(DEVICE[,PARTMAP-NAME1PART-NUM1[,PARTMAP-NAME2PART-NUM2[,...]]])
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'[]' means the parameter is optional. DEVICE depends on the disk
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driver in use. BIOS and EFI disks use either 'fd' or 'hd' followed by a
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digit, like 'fd0', or 'cd'. AHCI, PATA (ata), crypto, USB use the name
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of driver followed by a number. Memdisk and host are limited to one
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disk and so it's refered just by driver name. RAID (md), ofdisk
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(ieee1275 and nand), LVM (lvm), LDM, virtio (vdsk) and arcdisk (arc) use
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intrinsic name of disk prefixed by driver name. Additionally just
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"nand" refers to the disk aliased as "nand". Conflicts are solved by
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suffixing a number if necessarry. Commas need to be escaped. Loopback
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uses whatever name specified to 'loopback' command. Hostdisk uses names
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specified in device.map as long as it's of the form [fhc]d[0-9]* or
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hostdisk/<OS DEVICE>. For crypto and RAID (md) additionally you can use
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the syntax <driver name>uuid/<uuid>. For LVM additionally you can use
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the syntax lvmid/<volume-group-uuid>/<volume-uuid>.
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(fd0)
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(hd0)
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(cd)
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(ahci0)
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(ata0)
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(crypto0)
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(usb0)
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(cryptouuid/123456789abcdef0123456789abcdef0)
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(mduuid/123456789abcdef0123456789abcdef0)
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(lvm/system-root)
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(lvmid/F1ikgD-2RES-306G-il9M-7iwa-4NKW-EbV1NV/eLGuCQ-L4Ka-XUgR-sjtJ-ffch-bajr-fCNfz5)
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(md/myraid)
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(md/0)
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(ieee1275/disk2)
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(ieee1275//pci@1f\,0/ide@d/disk@2)
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(nand)
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(memdisk)
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(host)
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(myloop)
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(hostdisk//dev/sda)
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PART-NUM represents the partition number of DEVICE, starting from
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one. PARTNAME is optional but is recommended since disk may have
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several top-level partmaps. Specifying third and later component you
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can access to subpartitions.
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The syntax '(hd0)' represents using the entire disk (or the MBR when
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installing GRUB), while the syntax '(hd0,1)' represents using the first
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partition of the disk (or the boot sector of the partition when
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installing GRUB).
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(hd0,msdos1)
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(hd0,msdos1,msdos5)
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(hd0,msdos1,bsd3)
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(hd0,netbsd1)
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(hd0,gpt1)
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(hd0,1,3)
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If you enabled the network support, the special drives
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'(PROTOCOL[,SERVER])' are also available. Supported protocols are
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'http' and 'tftp'. If SERVER is omitted, value of environment variable
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'net_default_server' is used. Before using the network drive, you must
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initialize the network. *Note Network::, for more information.
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If you boot GRUB from a CD-ROM, '(cd)' is available. *Note Making a
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GRUB bootable CD-ROM::, for details.
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13.2 How to specify files
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=========================
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There are two ways to specify files, by "absolute file name" and by
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"block list".
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An absolute file name resembles a Unix absolute file name, using '/'
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for the directory separator (not '\' as in DOS). One example is
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'(hd0,1)/boot/grub/grub.cfg'. This means the file '/boot/grub/grub.cfg'
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in the first partition of the first hard disk. If you omit the device
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name in an absolute file name, GRUB uses GRUB's "root device"
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implicitly. So if you set the root device to, say, '(hd1,1)' by the
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command 'set root=(hd1,1)' (*note set::), then '/boot/kernel' is the
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same as '(hd1,1)/boot/kernel'.
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On ZFS filesystem the first path component must be
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VOLUME'@'[SNAPSHOT]. So '/rootvol@snap-129/boot/grub/grub.cfg' refers
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to file '/boot/grub/grub.cfg' in snapshot of volume 'rootvol' with name
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'snap-129'. Trailing '@' after volume name is mandatory even if
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snapshot name is omitted.
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13.3 How to specify block lists
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===============================
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A block list is used for specifying a file that doesn't appear in the
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filesystem, like a chainloader. The syntax is
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'[OFFSET]+LENGTH[,[OFFSET]+LENGTH]...'. Here is an example:
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0+100,200+1,300+300
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This represents that GRUB should read blocks 0 through 99, block 200,
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and blocks 300 through 599. If you omit an offset, then GRUB assumes
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the offset is zero.
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Like the file name syntax (*note File name syntax::), if a blocklist
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does not contain a device name, then GRUB uses GRUB's "root device". So
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'(hd0,2)+1' is the same as '+1' when the root device is '(hd0,2)'.
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