fdisk

Related articles:
• File systems




• GNU Parted




• Partitioning

util-linux fdisk is a dialogue-driven command-line utility that creates and manipulates partition tables and partitions on a hard disk. Hard disks are divided into partitions and this division is described in the partition table.

GPT fdisk, as implemented in the gdisk program and its associated utilities, works "on Globally Unique Identifier (GUID) Partition Table (GPT) disks, rather than on the more common (through at least early 2013) Master Boot Record (MBR) partition tables."

This article covers fdisk and its related sfdisk utility, as well as the analogous gdisk and sgdisk utilities.

Tip: For basic partitioning functionality with a graphical interface, cfdisk and cgdisk can be used.

1 Installation

To use fdisk and its associated utilities, the util-linux package, which is part of the base group is required.

To use gdisk and its associated utilities, install the gptfdisk package.

2 List partitions

To list partition tables and partitions on a device, you can run the following, where device is a name like /dev/sda:

# fdisk -l /dev/sda

Note: If the device is not specified, fdisk will list all partitions in /proc/partitions.

Or for the gdisk:

# gdisk -l /dev/sda

3 Backup and restore partition table

Before making changes to a hard disk, you may want to backup the partition table and partition scheme of the drive. You can also use a backup to copy the same partition layout to numerous drives.

3.1 Using dd

Because the MBR is located on the disk it can be backed up and later recovered.

To backup the MBR:

# dd if=/dev/sda of=/path/mbr-backup bs=512 count=1

Restore the MBR:

# dd if=/path/mbr-backup of=/dev/sda bs=512 count=1

Warning: Restoring the MBR with a mismatching partition table will make your data unreadable and nearly impossible to recover. If you simply need to reinstall the bootloader see their respective pages as they also employ the DOS compatibility region: GRUB or Syslinux.

To erase the MBR (may be useful if you have to do a full reinstall of another operating system) only the first 446 bytes are zeroed because the rest of the data contains the partition table:

# dd if=/dev/zero of=/dev/sda bs=446 count=1

3.2 Using sfdisk

For both GPT and MBR you can use sfdisk to save the partition layout of your device to a file with the --dump option. Run the following command for device /dev/sda:

# sfdisk -d /dev/sda > sda.dump

The file should look something like this for a single ext4 partition that is 1GB in size:

sda.dump

label: gpt
label-id: AAAAAAAA-BBBB-CCCC-DDDD-EEEEEEEEEEEE
device: /dev/sda
unit: sectors
first-lba: 34
last-lba: 1048576

/dev/sda1 : start=2048, size=1048576, type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, uuid=BBF1CD36-9262-463E-A4FB-81E32C12BDE7

To later restore this layout you can run:

# sfdisk /dev/sda < sda.dump

3.3 Using sgdisk

Using sgdisk you can create a binary backup consisting of the protective MBR, the main GPT header, the backup GPT header, and one copy of the partition table:

# sgdisk -b=sgdisk-sda.bak

You can later restore the backup by running:

# sgdisk -l=sgdisk-sda.bak

If you want to clone your current device's partition layout (/dev/sda in this case) to another drive (/dev/sdc) run:

# sgdisk -R=/dev/sdc /dev/sda

If both drives will be in the same computer, you need to randomize the GUID's:

# sgdisk -G /dev/sdc

4 Create a partition table and partitions

The first step to partitioning a disk is making a partition table. After that, the actual partitions are created according to the desired partition scheme. See the partition table article to help decide whether to use MBR or GPT.

Before beginning, you may wish to backup your current partition table and scheme.

The following shows how to use both gdisk and fdisk to perform both the creation of a partition table and the creation of the actual partitions. Differences are noted when necessary.

4.1 Start the partition manipulator

Start either fdisk or gdisk as instructed in the following sections. Then continue with #Create new table.

4.1.1 fdisk

Using MBR, the utility for editing the partition table is called fdisk. Recent versions of fdisk have abandoned the deprecated system of using cylinders as the default display unit, as well as MS-DOS compatibility by default. The latest fdisk automatically aligns all partitions to 2048 sectors, or 1024 KiB, which should work for all EBS sizes that are known to be used by SSD manufacturers. This means that the default settings will give you proper alignment.

Start fdisk against your drive as root. In this example we are using /dev/sda:

# fdisk /dev/sda

This opens the fdisk dialogue where you can type in commands.

4.1.2 gdisk

Using GPT, the utility for editing the partition table is called gdisk. Alternatively, you may use the curses-based version called cgdisk; however, the following instructions do not apply to it. See man 8 cgdisk for its usage.

gdisk performs partition alignment automatically on a 2048 sector (or 1024KiB) block size base which should be compatible with the vast majority of SSDs if not all. GNU Parted also supports GPT, but is less user-friendly for aligning partitions.

To use gdisk, run the program with the name of the device you want to change/edit. This example uses /dev/sda:

# gdisk /dev/sda

4.2 Create new table

To create a new MBR partition table and clear all current partition data, type o at the prompt. Skip this step if the table you require has already been created.

Warning: If you create a new partition table on a disk with data on it, it will erase all the data on the disk. Make sure this is what you want to do.

4.3 Create partitions

Create a new partition with the n command. You enter a partition type (fdisk only), partition number, starting sector, and an ending sector.

For fdisk, when prompted, specify the partition type, type p to create a primary partition or e to create an extended one. There may be up to four primary partitions.

Both start and end sectors can be specified in absolute terms as sector numbers or as positions measured in kibibytes (K), mebibytes (M), gibibytes (G), tebibytes (T), or pebibytes (P); for instance, 40M specifies a position 40MiB from the start of the disk. You can specify locations relative to the start or end of the specified default range by preceding the number by a + or - symbol, as in +2G to specify a point 2GiB after the default start sector, or -200M to specify a point 200MiB before the last available sector. Pressing the Enter key with no input specifies the default value, which is the start of the largest available block for the start sector and the end of the same block for the end sector.

Select the partition's type id. The default, Linux filesystem, should be fine for most use. Press l to show the codes list.

Tip:

• When partitioning it is always a good idea to follow the default values for first and last partition sectors. Additionally, specify partition sizes with the +<size>{M,G,...} notation. Such partitions are always aligned according to the device properties.
• EFI System Partition requires code ef00 with gdisk and EFI System with fdisk.
• GRUB requires a BIOS boot partition with code ef02 with gdisk and BIOS boot with fdisk when installing GRUB to a disk.
• It is recommended to use 8200 with gdisk and Linux swap with fdisk for any swap partitions, since systemd will automount it.

See the respective articles for considerations concerning the size and location of these partitions.

Repeat this procedure until you have the partitions you desire.

4.4 Write changes to disk

Write the table to disk and exit via the w command.

5 Tips and tricks

5.1 Convert between MBR and GPT

gdisk, sgdisk and cgdisk have the ability to convert MBR and BSD disklabels to GPT without data loss. Upon conversion, all the MBR primary partitions and the logical partitions become GPT partitions with the correct partition type GUIDs and Unique partition GUIDs created for each partition. See Rod Smith's Converting to or from GPT for more info.

After conversion, the bootloaders will need to be reinstalled to configure them to boot from GPT.

Note:

• GPT stores a secondary table at the end of disk. This data structure consumes 33 512-byte sectors by default. MBR doesn't have a similar data structure at its end, which means that the last partition on an MBR disk sometimes extends to the very end of the disk and prevents complete conversion. If this happens to you, you must abandon the conversion and resize the final partition.
• If your boot loader is GRUB, it needs a BIOS Boot Partition.
• There are known corruption issues with the backup GPT table on laptops that are Intel chipset based, and run in RAID mode. The solution is to use AHCI instead of RAID, if possible.

To convert an MBR partition table to GPT, use sgdisk.

# sgdisk -g /dev/sda

To convert GPT to MBR use the m option. Note that it is not possible to convert more than four partitions from GPT to MBR.

# sgdisk -m /dev/sda

If the device will be bootable you will need to set the bootable flag with fdisk.

5.2 Sort partitions

This applies for when a new partition is created in the space between two partitions or a partition is deleted.

MBR

# sfdisk -r /dev/sda

GPT

# sgdisk -s /dev/sda

After sorting the partitions if you are not using Persistent block device naming, it might be required to adjust the /etc/fstab and/or the /etc/crypttab configuration files.

5.3 Recover GPT header

In case main GPT header or backup GPT header gets damaged, you can recover one from the other with gdisk.

# gdisk /dev/sda

choose r for recovery and transformation options (experts only). From there choose either

• b: use backup GPT header (rebuilding main)
• d: use main GPT header (rebuilding backup)

When done write the table to disk and exit via the w command.

6 See also

• GPT fdisk Tutorial - offical webpage of gdisk with detailed walkthroughs.
• Manually Partitioning Your Hard Drive with fdisk

7 Acknowledgement

This wiki article is based on ArchWiki. We may have removed non-FSDG bits from it.