fdisk

Create and manage partitions on a hard disk

Note: In order to run this utility, you must be logged in as root or have read/write permissions for the block-special file concerned.

Syntax:

fdisk [-fz] [-B loader] drive [cmd [args]]

Runs on:

Neutrino

Options:

-B loader
Use the 512-byte file named by loader as the primary bootstrap loader for the device when instructed to write a boot loader to the disk. The default is to install a loader that's built into the fdisk utility.
-f
Force the boot loader to be written on command, even if it isn't possible to save an existing old loader to a mounted filesystem. In non-interactive mode, execute the given add command, even if this would involve overwriting an existing partition slot.
-z
Zero the partition table (interactive mode only).
drive
The disk drive to partition. This must name a block-special file (e.g., /dev/fd1, /dev/hd0).
cmd [args]
An installation command, as described below.

Description:

The fdisk utility lets you create and manage partitions on a hard disk (typically a rotating medium, but fdisk works on other devices, such as compact flash and USB flash, if they support PC-style Master Boot Records (MBRs) and partitions). The partition information, which is kept in the disk's first physical block, matches that used by DOS.

On some platforms, fdisk supports a full-screen interface; see “Interactive mode,” below.

Caution:
  • The installer for Microsoft Windows overwrites any existing Master Boot Record with its own. If you want your disk to contain bootable DOS and bootable QNX (or other non-DOS) partitions, you should install Windows first, and then create the other partitions. If you create a QNX partition first and then install Windows, you can restore the boot loader by running QNX Neutrino from the installation disk and explicitly using dloader.
  • On some x86 machines, you can boot only from OS images that are loaded from within the first 1024 cylinders of the disk. This means that while you may be able to initially install and boot from a partition which extends past the 1024th cylinder, it will someday fail when you go to update the boot image because the location of some of its blocks may change. When this happens you will have a system that's no longer bootable.

    Avoid this problem by creating a separate partition to boot from that lies entirely within the first 1024 cylinders of the hard drive, and use a second partition to access the additional space on the drive. (The boot partition may be quite small — just a few megabytes will suffice.)

Before creating a partition for the first time, you must first start the hard disk driver: 

devb-eide &

You should then execute the fdisk command to partition your disk. For example: 

fdisk /dev/hd0 add -t 179 -p 50

New or changed partitions aren't immediately recognized and/or mounted. You must either slay and restart the filesystem/driver (devb-*), use mount -e /dev/hd0 to recognize the new partitions and update the contents of /dev, or reboot.

Partition types

The fdisk utility recognizes the following partition types. If you add a partition, use the command shown to initialize it.

Type Filesystem Shared object Initialize with: Check with:
1, 4, or 6 DOS fs-dos.so mkdosfs chkdosfs
5 DOS extended N/A N/A N/A
7 Windows NTa fs-nt.so N/A N/A
8 or 9 QNX 2 N/A N/A N/A
11, 12, or 14 FAT32 fs-dos.so mkdosfs chkdosfs
15 Windows 95 extended N/A N/A N/A
77, 78, or 79 QNX 4 fs-qnx4.so dinit chkfsys
99 UNIX N/A N/A N/A
130 Linux swap N/A N/A N/A
131 Linux (Ext2) fs-ext2.so N/A N/A
133 Linux extended N/A N/A N/A
165 BSD N/A N/A N/A
175 Apple Macintosh HFS or HFS Plusa fs-mac.so N/A N/A
177, 178, or 179 Power-Safe fs-qnx6.so mkqnx6fs chkqnx6fsb

a Read-only.

b Not usually necessary.

For more information, see the Filesystems chapter of the System Architecture guide.

Commands

The fdisk utility supports the following commands directly from the command line:

add [args]
Add a new partition entry of the size and type specified. If fdisk can't locate sufficient unallocated disk space to satisfy your request, it allocates the largest available portion of the disk (if any). Here are the arguments for add:
-b
Make the added partition bootable. If another partition was already flagged as the primary boot partition, the flag is turned off for it.
-c start,end
The start and end for the partition to use.
-e extended_slot
The index into the extended partition (1–N).
-l
(“el”) Use blocks instead of cylinders as the units.
-n count
The number of cylinders to allocate (extended partitions only).
-p percent
The percentage of the largest contiguous space the added partition should use. The default is 100%.

If you specify the -c option, the -p option is ignored.

-s slot
The slot (1–4) in the partition table to use. The default is the last free slot.
-t type
The type of partition to add (0–255). The default is 77.

Note that extended partition indexes may change due to additions.

boot [args]
Turn on the boot flag for the indicated partition. If another partition was already flagged as the primary boot partition, the flag is turned off for it. Here are the arguments for boot:
-e extended_slot
The index into the extended partition (1–N).
-s slot
Boot the partition in the selected slot.
-t type
Boot the partition of the selected type.
delete [args]
Delete the specified partitions. Here are the arguments for delete:
-a
Delete all partitions.
-e extended_slot
The index into the extended partition (1–N).
-s slot
Delete the partition in the selected slot.
-t type
Delete this type of partition.

Note that extended partition indexes may change due to deletions.

info
Show the mount information for the raw drive.

The fdisk utility makes a devctl(DCMD_CAM_DEVINFO) call to obtain the cylinder, head, sectors per track, and total sectors counts. Multiplying the first three values together is the classic method of calculating the total number of sectors.

However, some hard drives employ zoned bit recording, so it's impossible to precisely map the number of sectors per track and other fields. As a result, the total number of sectors returned from devctl() and the total number of sectors that were calculated might not match. In this case, fdisk displays a warning.

loader
Write the QNX loader to the disk.
query [args]
Print the number of cylinders to standard output. Here are the arguments for query:
-e extended_slot
The index into the extended partition (1–N).
-f
Display the total number of free cylinders.
-l
(“el”) Use blocks instead of cylinders as the units.
-s slot
Query the partition in the selected slot.
-T
Display the total number of cylinders.
-t type
Query the partition of the selected type.
show [args]
Display the partition table. The argument to show is:
-l
(“el”) Use blocks instead of cylinders as the units.

Interactive mode

On some platforms, fdisk is a fullscreen, interactive program that's fairly self-explanatory. When you invoke fdisk, you'll see a screen similar to this one (assuming your disk is already partitioned): 

FDISK
Ignore Next Prev 1 2 3 4 Change Delete Boot Unboot Restore Loader Save Quit

        _____OS_____     Start      End     ______Number_____    Size    Boot
        name    type    Cylinder  Cylinder  Cylinders  Blocks

--> 1.  QNX6   (177)          0      7648      7649   122881122  60000 MB
    2.  QNX6   (178)       7649      9963      2315    37190475  18159 MB  *
    3.  ______ (___)    _______   _______   _______   _________  _____
    4.  ______ (___)    _______   _______   _______   _________  _____


 Choose a partition by typing the partition number OR moving the pointer
 with the UP/DOWN arrows.
 Then, choose one of the actions on the top line of the screen.



Drive : /dev/hd0                    Config:   255 Heads
Size  : 78159 Mbytes                           63 Sectors/track
Loader: Unknown                              9964 Cylinders
                                              512 Block Size

                                    Last cylinder is 9963

You'll see the available commands displayed at the top of the screen. To select a command, either type its first letter or move the cursor to the command (with the arrow keys) and press Enter.

The commands are:

Command: Action:
Next Move the pointer to the next entry.
Prev Move the pointer to the previous entry.
1, 2, 3, or 4 Move the pointer to the indicated entry.
Change Change the selected partition (see below).
Delete Delete the selected partition.
Boot Turn on the boot flag for the selected partition. If another partition was already flagged as the primary boot partition, the flag is turned off for it.
Unboot Turn off the boot flag for the selected partition.
Restore Restore the previous non-QNX bootstrap loader.
Loader Change the bootstrap loader to the QNX loader.
Save Save all changes and quit. This writes to the device and is irrevocable.
Quit Quit without saving changes.
Note: If you're changing a partition entry, note the following:
  • Save the details about the partition (e.g., by writing them on a piece of paper), because fdisk blanks the fields as you edit them.
  • You have to enter the partition's type number and the start and end cylinders; fdisk calculates the other information for you. Press Enter after typing each value.
  • If the partition was bootable before you changed it, use the Boot command to make it bootable again.

Examples:

Create a QNX 4 partition that occupies half the disk, or the largest available space if there isn't a space big enough for a new partition that occupies half the disk: 

fdisk /dev/hd0 add -t 77 -p 50

Do the same, but make the partition bootable: 

fdisk /dev/hd0 add -b -t 77 -p 50

Continuing from either of the above examples, reread the partition table, set up a QNX 4 filesystem on the new partition, and then mount it: 

mount -e /dev/hd0
dinit -h /dev/hd0t77
mount -t qnx4 /dev/hd0t77 /mnt/q4fs

Create a bootable partition for a Power-Safe filesystem, reread the partition table, format the new partition, and then mount it: 

fdisk /dev/hd0 add -b -t 179 -p 50
mount -e /dev/hd0
mkqnx6fs /dev/hd0t179
mount -t qnx6 /dev/hd0t179 /mnt/psfs

Exit status:

0
Success.
>0
An error occurred; fdisk writes error messages to standard error.

Caveats:

After changing any partition information, you must either slay and restart the filesystem/driver (devb-*) or use mount -e to make the filesystem reread the partition table.

See also:

chkdosfs, chkfsys, chkqnx6fs, devb-*, df, dinit, dloader, fs-dos.so, fs-ext2.so, fs-mac.so, fs-nt.so, fs-qnx4.so, fs-qnx6.so, mkdosfs, mkqnx6fs, mount

Filesystems chapter of the System Architecture guide

Working with Filesystems and Backing Up and Recovering Data chapters of the QNX Neutrino User's Guide