FMTHARD(8) Maintenance Commands and Procedures FMTHARD(8)


fmthard - populate label on hard disks


fmthard -d data | -n volume_name | -s datafile [-i] /dev/rdsk/c?[t?]d?s2


The fmthard command updates the VTOC (Volume Table of Contents) on hard
disks. One or more of the options -s datafile, -d data, or -n volume_name
must be used to request modifications to the disk label. To print disk
label contents, see prtvtoc(8). The /dev/rdsk/c?[t?]d?s2 file must be the
character special file of the device where the new label is to be
installed. On x86 systems, fdisk(8) must be run on the drive before

If you are using an x86 system, note that the term `partition' in this page
refers to slices within the x86 fdisk partition on x86 machines. Do not
confuse the partitions created by fmthard with the partitions created by


The following options are supported:

-d data
The data argument of this option is a string representing the
information for a particular partition in the current VTOC. The
string must be of the format part:tag:flag:start:size where part is
the partition number, tag is the ID TAG of the partition, flag is
the set of permission flags, start is the starting sector number of
the partition, and size is the number of sectors in the partition.
See the description of the datafile below for more information on
these fields.

-i This option allows the command to create the desired VTOC table,
but prints the information to standard output instead of modifying
the VTOC on the disk.

-n volume_name
This option is used to give the disk a volume_name up to 8
characters long.

-s datafile
This option is used to populate the VTOC according to a datafile
created by the user. If the datafile is - (a hyphen), fmthard
reads from standard input. The datafile format is described below.
This option causes all of the disk partition timestamp fields to be
set to zero.

Every VTOC generated by fmthard will also have partition 2, by
convention, that corresponds to the whole disk. If the input in
datafile does not specify an entry for partition 2, a default
partition 2 entry will be created automatically in VTOC with the
tag V_BACKUP and size equal to the full size of the disk.

The datafile contains one specification line for each partition,
starting with partition 0. Each line is delimited by a new-line
character (\n). If the first character of a line is an asterisk
(*), the line is treated as a comment. Each line is composed of
entries that are position-dependent, separated by white space and
having the following format:

partition tag flag starting_sector size_in_sectors

where the entries have the following values:

The partition number. Currently, for Solaris SPARC, a disk
can have up to 8 partitions, 0-7. Even though the
partition field has 4 bits, only 3 bits are currently used.
For x86, all 4 bits are used to allow slices 0-15. Each
Solaris fdisk partition can have up to 16 slices.

tag The partition tag: a decimal number. The following are
reserved codes: 0 (V_UNASSIGNED), 1 (V_BOOT), 2 (V_ROOT), 3
(V_SWAP), 4 (V_USR), 5 (V_BACKUP), 6 (V_STAND), 7 (V_VAR),
and 8 (V_HOME).

flag The flag allows a partition to be flagged as unmountable or
read only, the masks being: V_UNMNT 0x01, and V_RONLY 0x10.
For mountable partitions use 0x00.

The sector number (decimal) on which the partition starts.

The number (decimal) of sectors occupied by the partition.

You can save the output of a prtvtoc(8) command to a file, edit the
file, and use it as the datafile argument to the -s option.


uname(1), attributes(7), format(8), installboot(8), prtvtoc(8)

x86 Only


Special care should be exercised when overwriting an existing VTOC, as
incorrect entries could result in current data being inaccessible. As a
precaution, save the old VTOC.

For disks under two terabytes, fmthard cannot write a VTOC on an unlabeled
disk. Use format(8) for this purpose.

illumos March 30, 2022 illumos