Go to main content

man pages section 8: System Administration Commands

Exit Print View

Updated: Wednesday, July 27, 2022



format - disk partitioning and maintenance utility


format [-f command-file
] [-l log-file] [
-d disk-name]
     [-s] [-m] [-M] [
-e] [disk-list]
format -L label-type
 -d disk-name


format enables you to format, label, repair, and analyze disks on your system. Unlike previous disk maintenance programs, format runs under Oracle Solaris. Because there are limitations to what can be done to the system disk while the system is running, format is also supported within the memory-resident system environment. For most applications, however, running format under Oracle Solaris is the more convenient approach.

disk-list is a list of disks in the form c?t?d?, /dev/rdsk/c?t?d?s?, or /dev/chassis/?/disk. With the last two forms, shell wildcard specifications are supported. For example, specifying /dev/rdsk/c2* causes format to work on all drives connected to controller c2 only. If no disk-list is specified, format lists all the disks present in the system that can be administered by format.

Removable media devices are listed only when users execute format in expert mode (option –e). This feature is provided for backward compatibility. Use rmformat(1) for rewritable removable media devices.


The following options are supported:

–d disk-name

Specify which disk should be made current upon entry into the program. The disk is specified by its logical name (for instance, –d c0t1d0 or /dev/chassis/SYS/HD0/disk). This can also be accomplished by specifying a single disk in the disk list.


This option switches the behavior of several format command features to expert mode.

  • Enables SCSI expert menu

  • Shows removable media devices

  • The label menu entry allows changing a label type from SMI/VTOC to EFI. This can also be achieved by using the –L option non-interactively

  • Prints partition table in expert mode

Note -  The –e option is not recommended for casual use.
–f command-file

Take command input from command-file rather than the standard input. The file must contain commands that appear just as they would if they had been entered from the keyboard. With this option, format does not issue continue? prompts; there is no need to specify y(es) or n(o) answers in the command-file. In non-interactive mode, format does not initially expect the input of a disk selection number. The user must specify the current working disk with the –d disk-name option when format is invoked, or specify disk and the disk selection number in the command-file. The last command in the command-file should be quit or q.

–l log-file

Log a transcript of the format session to the indicated log-file, including the standard input, the standard output and the standard error.

–L label-type

Immediately, and non-interactively, write a default label of type label-type, to the disk specified with –d. label-type must be either efi or vtoc. Existing label, if any, will be overwritten with label-type. On an x86 machine, the whole disk will default to one Solaris partition labeled with label-type; all fdisk partitions will be lost.


Enable extended messages. Provides more detailed information in the event of an error.


Enable extended and diagnostic messages. Provides extensive information on the state of a SCSI device's mode pages, during formatting.


Silent. Suppress all of the standard output. Error messages are still displayed. This is generally used in conjunction with the –f option.


When you invoke format with no options or with the –e, –l, –m, –M, or –s options, the program displays a numbered list of available disks and prompts you to specify a disk by list number. If the machine has more than a screenful of disks, press SPACE to see the next screenful of disks.

You can specify a disk by list number even if the disk is not displayed in the current screenful. For example, if the current screen shows disks 11-20, you can enter 25 to specify the twenty-fifth disk on the list. If you enter a number for a disk that is not currently displayed, format prompts you to verify your selection. If you enter a number from the displayed list, format silently accepts your selection.

After you specify a disk, format displays its main menu. This menu enables you to perform the following tasks:


Run read, write, compare tests, and data purge. The data purge function implements the National Computer Security Center Guide to Understanding Data Remnance (NCSC-TG-025 version 2) Overwriting Algorithm. See NOTES.


Search for backup labels.


Enable, disable, and query the state of the write cache and read cache. This menu item only appears when format is invoked with the –e option, and is only supported on SCSI devices.


Display the device name, the disk geometry, and the pathname to the disk device.


Retrieve and print defect lists. This option is supported only on SCSI devices. IDE disks perform automatic defect management. Upon using the defect option on an IDE disk, you receive the message:

Controller does not support defect management
or disk supports automatic defect management.

Choose the disk that will be used in subsequent operations (known as the current disk.)


Run the fdisk(8) program to create a fdisk partition for Solaris software (x86 based systems only).


Format and verify the current disk. This option is supported only on SCSI devices. IDE disks are pre-formatted by the manufacturer. Upon using the format option on an IDE disk, you receive the message:

Cannot format this drive. Please use your
manufacturer-supplied formatting utility.

Display the vendor, product name, and revision level of the current drive.


Write a new label to the current disk.


Create and modify slices.


Exit the format menu.


Repair a specific block on the disk.


Select (define) a disk type.


Read and display labels. Print information such as the number of cylinders, alternate cylinders, heads, sectors, and the partition table.


Label the disk with a new eight character volume name.

Exit Status

The following exit values are returned:


Successful completion.


An error occurred. A non-zero exit status is also returned in case format encounters EOF while reading input, e.g., if it is terminated with ^D instead of quit or q in interactive mode or, in the case of non-interactive mode (option -f), if the command file does not end with a quit or q command.


See attributes(7) for descriptions of the following attributes:


See Also

rmformat(1), sd(4D), attributes(7), fmthard(8), prtvtoc(8)

Managing Devices in Oracle Solaris 11.4

x86 Only



Cylinder 0 contains the partition table (disk label), which can be overwritten if used in a raw disk partition by third party software. On x86-based systems, this usage could cause the cylinder information to be off by one, and some difference in the capacity as a consequence, depending on whether the disk is labeled and whether the whole disk is designated as a single Oracle Solaris partition. Note that the CHS (Cylinder/Head/Sector) geometry might be logical only to maintain backward compatibility, which has no physical bearing to the actual disk device.

format supports writing EFI-compliant disk labels in order to support disks or LUNs with capacities greater than one terabyte. However, care should be exercised since many software components, such as filesystems and volume managers, are still restricted to capacities of two terabyte or less.

By default, on an unlabeled disk, EFI labels will be written on disks larger than 2 TB. When format is invoked with the –e option, on writing the label, the label type can be chosen. GPT (EFI) enabled SPARC firmware and UEFI x86 firmware are required to boot these EFI-labeled drives.


format provides a help facility you can use whenever format is expecting input. You can request help about what information is expected by simply entering a question mark (?) and format prints a brief description of what type of input is needed. If you enter a ? at the menu prompt, a list of available commands is displayed.

For SCSI disks, formatting is done with both Primary and Grown defects list by default. However, if only Primary list is extracted in defect menu before formatting, formatting will be done with Primary list only.

Changing the state of the caches is only supported on SCSI devices, and not all SCSI devices support changing or saving the state of the caches.

The NCSC-TG-025 algorithm for overwriting meets the DoD 5200.28-M (ADP Security Manual) Eraser Procedures specification. The NIST Guidelines for Media Sanitization (NIST SP 800-88) also reference this algorithm.