fdisk - Unix, Linux Command


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NAME

fdisk - Partition table manipulator for Linux

SYNOPSIS

fdisk [-uc] [-b sectorsize] [-C cyls] [-H heads] [-S sects] device

fdisk -l [-u] [device...]

fdisk -s partition...

fdisk -v

fdisk -h

DESCRIPTION

Hard disks can be divided into one or more logical disks called partitions. This division is described in the partition table found in sector 0 of the disk.

OPTIONS

TAG DESCRIPTION
-b sectorsize Specify the sector size of the disk. Valid values are 512, 1024, 2048 or 4096. (Recent kernels know the sector size. Use this only on old kernels or to override the kernel's ideas.) Since util-linux-ng 2.17 fdisk differentiates between logical and physical sector size. This option changes both sector sizes to sectorsize..
-h Print help and then exit..

-c Switch off DOS-compatible mode. (Recommended)
-C cyls Specify the number of cylinders of the disk. I have no idea why anybody would want to do so
-H heads Specify the number of heads of the disk. (Not the physical number, of course, but the number used for partition tables.) Reasonable values are 255 and 16.
-S sects Specify the number of sectors per track of the disk. (Not the physical number, of course, but the number used for partition tables.) A reasonable value is 63.
-l List the partition tables for the specified devices and then exit. If no devices are given, those mentioned in /proc/partitions (if that exists) are used

EXAMPLES

EXAMPLE-1:

To list all existing disk partition on your system.

# fdisk -l

output:

# fdisk -l
Disk /dev/sda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000dd3ab

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      499711      248832   83  Linux
/dev/sda2          501758    41940991    20719617    5  Extended
/dev/sda5          501760    41940991    20719616   8e  Linux LVM

Disk /dev/sdb: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/sdb doesn't contain a valid partition table
Disk /dev/mapper/ubuntu--vg-root: 20.1 GB, 20124270592 bytes
255 heads, 63 sectors/track, 2446 cylinders, total 39305216 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/mapper/ubuntu--vg-root doesn't contain a valid partition table
Disk /dev/mapper/ubuntu--vg-swap_1: 1069 MB, 1069547520 bytes
255 heads, 63 sectors/track, 130 cylinders, total 2088960 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/mapper/ubuntu--vg-swap_1 doesn't contain a valid partition table

EXAMPLE-2:

To view all partitions of specific hard disk use the option ‘-l‘ with device name.

# fdisk -l /dev/sda

output:


Disk /dev/sda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000dd3ab

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      499711      248832   83  Linux
/dev/sda2          501758    41940991    20719617    5  Extended
/dev/sda5          501760    41940991    20719616   8e  Linux LVM

EXAMPLE-3:

To view all commands which are available for fdisk.

# fdisk /dev/sda

Type ‘m‘ to see the list of all available commands of fdisk which can be operated on /dev/sda hard disk:

output:

# fdisk /dev/sda
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x18b2eab2.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): m Command action a toggle a bootable flag b edit bsd disklabel c toggle the dos compatibility flag d delete a partition l list known partition types m print this menu n add a new partition o create a new empty DOS partition table p print the partition table q quit without saving changes s create a new empty Sun disklabel t change a partition's system id u change display/entry units v verify the partition table w write table to disk and exit

EXAMPLE-4:

To print all partition table of hard disk, you must be on command mode of specific hard disk say /dev/sda.:

# fdisk /dev/sda

From the command mode, enter ‘p‘ instead of ‘m‘ as we did earlier. As I enter ‘p‘, it will print the specific /dev/sda partition table.

output:
Command (m for help): p Disk /dev/sda: 637.8 GB, 637802643456 bytes 255 heads, 63 sectors/track, 77541 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Device Boot Start End Blocks Id System /dev/sda1 * 1 13 104391 83 Linux /dev/sda2 14 2624 20972857+ 83 Linux /dev/sda3 2625 4582 15727635 83 Linux /dev/sda4 4583 77541 586043167+ 5 Extended /dev/sda5 4583 5887 10482381 83 Linux /dev/sda6 5888 7192 10482381 83 Linux

EXAMPLE-5:

enter ‘d‘ to delete any given partition name from the system:

# fdisk /dev/sda

output:
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x18b2eab2.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): d Partition number (1-4): 4 Command (m for help): w

EXAMPLE-6:

After entering in command mode, now press “n” command to create a new partition under /dev/sda with specific size. This can be demonstrated with the help of following given output.:

# fdisk /dev/sda

output:

Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x18b2eab2.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): n Command action e extended p primary partition (1-4) e

After the new partition is created, don’t skip to format the newly created partition using ‘mkfs‘ command. Type the following command in the terminal to format a partition. Here /dev/sda4 is my newly created partition.:

	# mkfs.ext4 /dev/sda4

EXAMPLE-7:

To check the size of that partition using flag ‘s‘ (displays size in blocks) with fdisk command. This way you can check size of any specific device.:

# fdisk -s /dev/sda2

output:

5194304

EXAMPLE-8:

To Fix Partition Table Order:

# fdisk /dev/sda

output:
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x18b2eab2.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help): x Done.

EXAMPLE-9:

To Quit without saving changes.

# fdisk /dev/sda

output:
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x18b2eab2.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): q Done.

EXAMPLE-10:

To verify partition table
 
# fdisk /dev/sda
 
output:
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x18b2eab2.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): v
Remaining 41439231 unallocated 512-byte sectors


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