DISKLABEL(8) BSD System Manager's Manual DISKLABEL(8)
disklabel - read and write disk pack label
disklabel [-c | -d | -r | -t] [-v] [-p unit] disk
disklabel -w [-c | -d | -r] [-nv] disk disktype [packid]
disklabel -e [-c | -d | -r] [-nv] disk
disklabel -E [-c | -d | -r] [-nv] [-f tempfile] disk
disklabel -R [-nrv] disk protofile
disklabel -N | -W [-nv] disk
disklabel -B [-nv] [-b boot1] [-s boot2] disk [disktype]
disklabel -Bw [-nv] [-b boot1] [-s boot2] disk disktype [packid]
disklabel -BR [-nv] [-b boot1] [-s boot2] disk protofile [disktype]
The disklabel utility can be used to install, examine, or modify the la-
bel on a disk drive or pack. The disk label contains information about
disk characteristics (size, type, etc.) and the slice layout, stored on
the disk itself. It is used by the operating system to optimize disk I/O
and locate the filesystems resident on the disk.
The options are as follows:
-B Install bootstrap code. The -r flag is implied by -B and never
needs to be specified.
-b Specify the single level boot program, or the primary boot pro-
gram, depending on the system boot architecture (single or two-
level).
-c Clear the system's in-core copy of the label and update it based
on the on-disk label. May not be used in conjunction with the -r
flag.
-d Use the default label. This ignores any existing MirBSD slices on
the disk. Note that this option will only work for disks that are
capable of reporting their geometry, such as SCSI, IDE, and ESDI.
May not be used in conjunction with the -r flag.
-E Use a simple initial label editor, using the command-driven
built-in editor described below.
-e Edit an existing disk label using the editor specified in the
EDITOR environment variable, or vi(1) if none is specified.
-f tempfile
Write entries to tempfile in fstab(5) format for any slices for
which mount point information has been specified. The -f flag is
only valid when used in conjunction with the -E flag. If tempfile
already exists, it will be overwritten.
-N Disallow writing of the pack label area on the selected disk.
-n Make no permanent changes to the disklabel (useful for debugging
purposes).
-p unit
Print slice sizes and offsets in unit instead of sectors. Valid
units are b(ytes), c(ylinders), k(ilobytes), m(egabytes) and
g(igabytes). For operations other than displaying a slice the '%'
(percent of total) and '&' (percent of free) units are also ac-
cepted.
-R Restore a disk label that was formatted in a prior operation and
saved in an ASCII file.
-r 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 without
kernel support for a label, such as when labels are first in-
stalled on a system. This flag does not work on a number of ar-
chitectures, thus it is not considered the right way to put a new
label on a disk. Its use is discouraged.
-s On machines with a two-level bootstrap (such as i386-based
systems), specify the secondary boot program.
-t Format the label as a disktab(5) entry.
-v Print additional information during operation (verbose mode).
-W Allow writing of the pack label area on the selected disk.
-w Write a standard label on the designated drive.
disk Specify the disk to operate on. It can be specified either by its
full pathname or an abbreviated disk form. In its abbreviated
form, the path to the device, the 'r' denoting "raw device", and
the slice, can all be omitted. For example, the first IDE disk
can be specified as either /dev/rwd0c, /dev/wd0c, or wd0.
disktype
Specify a disktype entry from the disktab(5) database.
packid Specify a pack identification string for the device (see below).
protofile
Used with the restore option (-R) to specify a file to read an
ASCII label from.
The first form of the command (read) is used to examine the label on the
named disk drive. It will display all of the parameters associated with
the drive and its slice layout. Unless the -r flag is given, the kernel's
in-core copy of the label is displayed; if the disk has no label, or the
slice types on the disk are incorrect, the kernel may have constructed or
modified the label.
The second form of the command (write) is used to write a standard label
on the designated drive. The drive parameters and slices are taken from
that file. If different disks of the same physical type are to have dif-
ferent slices, 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 contains 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 rendered 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 al-
ready have a label, the -r flag must be used. In either case, the
kernel's in-core label is replaced.
In the third form of the command (edit), 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 editor 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.
The initial label editor mode (fourth form) is only intended for new
disks as it will move slices around as necessary to maintain a contiguous
pool of free blocks. Some commands or prompts take an optional unit.
Available units are 'b' for bytes, 'c' for cylinders, 'k' for kilobytes,
'm' for megabytes, and 'g' for gigabytes. Quantities will be rounded to
the nearest cylinder when units are specified for sizes (or offsets).
Commands may be aborted by entering '^D' (Control-D). Entering '^D' at
the main '>' prompt will exit the editor. At prompts that request a size,
'*' may be entered to indicate the rest of the available space. The edi-
tor commands are as follows:
? [command]
Display help message with all available commands. A command
may be specified to get more detailed help. There is also
(simple) context-sensitive help available at most prompts.
a [part] Add new slice. This option adds a new BSD slice. If no letter
is specified (a-p), the user will be prompted for one.
b Set MirBSD disk boundaries. This option tells disklabel which
parts of the disk it is allowed to modify. This option is
probably only useful for ports with fdisk(8) partition tables
where the ending sector in the MBR is incorrect. The user may
enter '*' at the "Size" prompt to indicate the entire size of
the disk (minus the starting sector). This is useful for disks
larger than 8 gigabytes where the fdisk partition table is in-
capable of storing the real size.
c [part] Change the size of an existing slice. If no slice is speci-
fied, the user will be prompted for one. The new size may be
in terms of the aforementioned units and may also be prefixed
with '+' or '-' to change the size by a relative amount.
D Sets the disk label to the default values as reported by the
kernel. This simulates the case where there is no disk label.
d [part] Delete an existing slice (or '*' to delete all slices). If no
slice is specified, the user will be prompted for one. The 'c'
slice cannot be deleted.
e Edit drive parameters. This option is used to set the follow-
ing parameters: disk type, a descriptive label string,
sectors/track, tracks/cylinder, sectors/cylinder, number of
cylinders, total sectors, rpm, and interleave.
g [b|d|u] Set disk geometry based on what the BIOS, disk, or user thinks
(the user geometry is simply what the label said before
disklabel made any changes).
M Display this manual page.
m [part] Modify parameters for an existing slice. If no slice is speci-
fied, the user will be prompted for one. This option allows
the user to change the filesystem type, starting offset, size,
and mount point for the specified slice. If expert mode is en-
abled (see X below), then block fragment size, block size, and
cylinders per group can also be modified. Note that not all
parameters are configurable for non-BSD slices.
n [part] Name the mount point for an existing slice. If no slice is
specified, the user will be prompted for one. This option is
only valid if disklabel was invoked with the -f flag.
p [unit] Print the current disk label. If a unit is given, the size and
offsets are displayed in terms of the specified unit.
q Quit the editor. If any changes have been made, the user will
be asked whether or not to save the changes to the on-disk la-
bel.
r Recalculate free space. This option should really not be
necessary under normal circumstances.
s [path] Save the label to a file in ASCII format (suitable for loading
via the -R option). If no path is specified, the user will be
prompted for one.
u Undo (or redo) last change. Entering u once will undo the last
change. Entering it again will restore the change.
w Write the label to disk. This option will commit any changes
to the on-disk label.
X Toggle "expert mode". By default, some settings are reserved
for experts only (such as the block and fragment size on ffs
filesystems).
x Exit the editor without saving any changes to the label.
z Zeroes out the existing disklabel, leaving only the 'c' slice.
The drive parameters are not changed.
In the restore form of the command (fifth form), the prototype file used
to create the label should be in the same format as that produced 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 sixth form of the command (protect) is used to control write access
to the label area of a disk so that the label cannot be inadvertently
overwritten. The -N and -W options are only available on architectures
that support this feature, such as vax, hp300 and some sparc models.
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.
When installing bootstrap code with the -B flag, if the names are not ex-
plicitly given, standard boot programs will be used. The boot programs
are located in /usr/mdec. 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 parameters.
Otherwise, boot program names are derived from the name of the disk.
These names are of the form basenameboot for the primary (or only)
bootstrap, and bootbasename for the secondary bootstrap; for example,
/usr/mdec/sdboot and /usr/mdec/bootsd if the disk device is sd0.
The first of the three boot-installation forms is used to install
bootstrap 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.
Note that when a disk has no real BSD disklabel, the kernel creates a de-
fault label so that the disk can be used. This default label will include
other slices found on the disk if they are supported on your architec-
ture. For example, on systems that support fdisk(8) partitions the de-
fault label will also include DOS and Linux partitions. However, these
entries are not dynamic, they are fixed at the time disklabel is run.
That means that subsequent changes that affect non-MirBSD slices will not
be present in the default label, though they may be updated by hand. To
see the default label, run disklabel with the -d flag. disklabel can then
be run with the -e flag and any entries pasted as desired from the de-
fault label into the real one.
/etc/disklabels Directory for backup labels.
/etc/disktab Disk description file.
/usr/mdec/xxboot Primary bootstrap.
/usr/mdec/bootxx Secondary bootstrap.
Display the in-core label for sd0 as obtained via /dev/rsd0c:
# disklabel sd0
Create a label for sd0 based on information for "sd2212" found in
/etc/disktab. Any existing bootstrap code will be clobbered. (Normally
you do not want to use the -r flag though.)
# disklabel -w -r /dev/rsd0c sd2212 foo
Read the on-disk label for sd0, edit it and reinstall in-core as well as
on-disk. (Normally you do not want to use the -r flag though.) Existing
bootstrap code is unaffected.
# disklabel -e -r sd0
Restore the on-disk and in-core label for sd0 from information in
mylabel. Existing bootstrap code is unaffected.
# disklabel -R sd0 mylabel
Install a new bootstrap on sd0. The boot code comes from /usr/mdec/sdboot
and possibly /usr/mdec/bootsd. On-disk and in-core labels are unchanged,
but on some systems other information may be destroyed. Use with care.
# disklabel -B sd0
Install a new label and bootstrap. The label is derived from disktab in-
formation for "sd2212" and installed both in-core and on-disk. The
bootstrap code comes from the file /usr/mdec/newboot.
# disklabel -w -B /dev/rsd0c -b newboot sd2212
The kernel device drivers will not allow the size of a disk slice to be
decreased or the offset of a slice to be changed while it is open. Some
device drivers create a label containing only a single large slice if a
disk is unlabeled; thus, the label must be written to the 'a' slice 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 slice, and
the second setting the label on the new slice while shrinking the 'a'
slice.
On some machines the bootstrap code may not fit entirely in the area al-
located for it by some filesystems. As a result, it may not be possible
to have filesystems on some slices of a "bootable" disk. When installing
bootstrap code, disklabel checks for these cases. If the installed boot
code would overlap a slice of type FS_UNUSED it is marked as type
FS_BOOT. The newfs(8) utility will disallow creation of filesystems on
FS_BOOT slices. Conversely, if a slice has a type other than FS_UNUSED or
FS_BOOT, disklabel will not install bootstrap code that overlaps it.
disklabel(5), disktab(5), scan_ffs(8)
On i386 machines, installboot(8) is normally used to install boot code.
The -B option to disklabel can still be used to install old style boot
code, but this usage is deprecated.
On some machines, such as the sparc, disklabels may not exhibit the full
functionality that is described above.
disklabel only supports up to a maximum of 15 slices, 'a' through 'p',
excluding 'c'. The 'c' slice is reserved for the entire physical disk. By
convention, the 'a' slice of the boot disk is the root filesystem, and
the 'b' slice of the boot disk is the swap partition, but all other
letters can be used in any order for any other slices as desired.
When a disk name is given without a full pathname, the constructed device
name uses the 'c' slice. In -E mode, disklabel is far too quick to shuf-
fle slices around; it should keep a free block list and only move slices
around with the user's permission.
MirBSD #10-current October 27, 1997 5