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DISKLABEL(8)		FreeBSD	System Manager's Manual		  DISKLABEL(8)

     disklabel -- read and write disk pack label

     disklabel [-r] disk
     disklabel -w [-r] disk disktype [packid]
     disklabel -e [-r] disk
     disklabel -R [-r] disk protofile
     disklabel [-NW] disk

     disklabel -B [-b boot1 [-s	boot2]]	disk [disktype]
     disklabel -w -B [-b boot1 [-s boot2]] disk	disktype [packid]
     disklabel -R -B [-b boot1 [-s boot2]] disk	protofile [disktype]

     Disklabel can be used to install, examine or modify the label on a	disk
     drive or pack.  When writing the label, it	can be used to change the
     drive identification, the disk partitions on the drive, or	to replace a
     damaged label.  On	some systems, disklabel	can be used to install boot-
     strap code	as well.  There	are several forms of the command that read
     (display),	install	or edit	the label on a disk.  Each form	has an addi-
     tional option, -r,	which causes the label to be read from or written to
     the disk directly,	rather than going through the system's in-core copy of
     the label.	 This option may allow a label to be installed on a disk with-
     out kernel	support	for a label, such as when labels are first installed
     on	a system; it must be used when first installing	a label	on a disk.
     The specific effect of -r is described under each command.	 The read and
     install forms also	support	the -B option to install bootstrap code.
     These variants are	described later.

     The first form of the command (read) is used to examine the label on the
     named disk	drive (e.g. da0	or /dev/rda0c).	 It will display all of	the
     parameters	associated with	the drive and its partition layout.  Unless
     the -r flag is given, the kernel's	in-core	copy of	the label is dis-
     played; if	the disk has no	label, or the partition	types on the disk are
     incorrect,	the kernel may have constructed	or modified the	label.	If the
     -r	flag is	given, the label from the raw disk will	be displayed rather
     than the in-core label.

     The second	form of	the command, with the -w flag, is used to write	a
     standard label on the designated drive.  The required arguments to
     disklabel are the drive to	be labeled (e.g. da0), and the drive type as
     described in the disktab(5) file.	The drive parameters and partitions
     are taken from that file.	If different disks of the same physical	type
     are to have different partitions, it will be necessary to have separate
     disktab entries describing	each, or to edit the label after installation
     as	described below.  The optional argument	is a pack identification
     string, up	to 16 characters long.	The pack id must be quoted if it con-
     tains blanks.  If the -r flag is given, the disk sectors containing the
     label and bootstrap will be written directly.  A side-effect of this is
     that any existing bootstrap code will be overwritten and the disk ren-
     dered unbootable.	If -r is not specified,	the existing label will	be
     updated via the in-core copy and any bootstrap code will be unaffected.
     If	the disk does not already have a label,	the -r flag must be used.  In
     either case, the kernel's in-core label is	replaced.

     For a virgin disk that is not known to disktab(5),	disktype can be	speci-
     fied as ``auto''.	In this	case, the driver is requested to produce a
     virgin label for the disk.	 This might or might not be successful,
     depending on whether the driver for the disk is able to get the required
     data without reading anything from	the disk at all.  It will likely suc-
     ceed for all SCSI disks, most IDE disks, and vnode	devices.  Writing a
     label to the disk is the only supported operation,	and the	disk itself
     must be provided as the canonical name, i.e. not as a full	path name.

     An	existing disk label may	be edited by using the -e flag.	 The label is
     read from the in-core kernel copy,	or directly from the disk if the -r
     flag is also given.  The label is formatted and then supplied to an edi-
     tor for changes.  If no editor is specified in an EDITOR environment
     variable, vi(1) is	used.  When the	editor terminates, the formatted label
     is	reread and used	to rewrite the disk label.  Existing bootstrap code is
     unchanged regardless of whether -r	was specified.

     With the -R flag, disklabel is capable of restoring a disk	label that was
     formatted in a prior operation and	saved in an ascii file.	 The prototype
     file used to create the label should be in	the same format	as that	pro-
     duced when	reading	or editing a label.  Comments are delimited by # and
     newline.  As with -w, any existing	bootstrap code will be clobbered if -r
     is	specified and will be unaffected otherwise.

     The -NW flags for disklabel explicitly disallow and allow,	respectively,
     writing of	the pack label area on the selected disk.

     The final three forms of disklabel	are used to install bootstrap code on
     machines where the	bootstrap is part of the label.	 The bootstrap code is
     comprised of one or two boot programs depending on	the machine.  The -B
     option is used to denote that bootstrap code is to	be installed.  The -r
     flag is implied by	-B and never needs to be specified.  The name of the
     boot program(s) to	be installed can be selected in	a variety of ways.
     First, the	names can be specified explicitly via the -b and -s flags.  On
     machines with only	a single level of boot program,	-b is the name of that
     program.  For machines with a two-level bootstrap,	-b indicates the pri-
     mary boot program and -s the secondary boot program.  If the names	are
     not explicitly given, standard boot programs will be used.	 The boot pro-
     grams are located in /boot.  The names of the programs are	taken from the
     ``b0'' and	``b1'' parameters of the disktab(5) entry for the disk if
     disktype was given	and its	disktab	entry exists and includes those	param-
     eters.  Otherwise,	the default boot image names are used, these being:
     /boot/boot1 and /boot/boot2 for the standard stage1 and stage2 boot
     images (details may vary on architectures like the	Alpha, where only a
     single-stage boot is used).

     The first of the three boot-installation forms is used to install boot-
     strap code	without	changing the existing label.  It is essentially	a read
     command with respect to the disk label itself and all options are related
     to	the specification of the boot program as described previously.	The
     final two forms are analogous to the basic	write and restore versions
     except that they will install bootstrap code in addition to a new label.


	   disklabel da0

     Display the in-core label for da0 as obtained via /dev/rda0c.

	   disklabel -w	-r /dev/rda0c da2212 foo

     Create a label for	da0 based on information for ``da2212''	found in
     /etc/disktab.  Any	existing bootstrap code	will be	clobbered.

	   disklabel -e	-r da0

     Read the on-disk label for	da0, edit it and reinstall in-core as well as
     on-disk.  Existing	bootstrap code is unaffected.

	   disklabel -r	-w da0 auto

     Try to auto-detect	the required information from da0, and write a new
     label to the disk.	 Use another disklabel -e command to edit the parti-
     tioning and file system information.

	   disklabel -R	da0 mylabel

     Restore the on-disk and in-core label for da0 from	information in
     mylabel.  Existing	bootstrap code is unaffected.

	   disklabel -B	da0

     Install a new bootstrap on	da0.  The boot code comes from /boot/boot1 and
     possibly /boot/boot2.  On-disk and	in-core	labels are unchanged.

	   disklabel -w	-B /dev/rda0c -b newboot da2212

     Install a new label and bootstrap.	 The label is derived from disktab
     information for ``da2212''	and installed both in-core and on-disk.	 The
     bootstrap code comes from the file	/boot/newboot.

     disklabel(5), disktab(5)

     The kernel	device drivers will not	allow the size of a disk partition to
     be	decreased or the offset	of a partition to be changed while it is open.
     Some device drivers create	a label	containing only	a single large parti-
     tion if a disk is unlabeled; thus,	the label must be written to the ``a''
     partition of the disk while it is open.  This sometimes requires the
     desired label to be set in	two steps, the first one creating at least one
     other partition, and the second setting the label on the new partition
     while shrinking the ``a'' partition.

     On	some machines the bootstrap code may not fit entirely in the area
     allocated for it by some filesystems.  As a result, it may	not be possi-
     ble to have filesystems on	some partitions	of a ``bootable'' disk.	 When
     installing	bootstrap code,	disklabel checks for these cases.  If the
     installed boot code would overlap a partition of type FS_UNUSED it	is
     marked as type FS_BOOT.  The newfs(8) utility will	disallow creation of
     filesystems on FS_BOOT partitions.	 Conversely, if	a partition has	a type
     other than	FS_UNUSED or FS_BOOT, disklabel	will not install bootstrap
     code that overlaps	it.

     When a disk name is given without a full pathname,	the constructed	device
     name uses the ``a'' partition on the Tahoe, the ``c'' partition on	all

     For the i386 architecture,	the primary bootstrap sector contains an
     embedded fdisk table.  Disklabel takes care to not	clobber	it when
     installing	a bootstrap only (-B), or when editing an existing label (-e),
     but it unconditionally writes the primary bootstrap program onto the disk
     for -w or -R, thus	replacing the fdisk table by the dummy one in the
     bootstrap program.	 This is only of concern if the	disk is	fully dedi-
     cated, so that the	BSD disklabel starts at	absolute block 0 on the	disk.

4.2 Berkeley Distribution	April 19, 1994	     4.2 Berkeley Distribution


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