fdisk -l [device...]
Block devices can be divided into one or more logical disks called partitions. This division is recorded in the partition table, usually found in sector 0 of the disk. (In the BSD world one talks about `disk slices' and a `disklabel'.)
All partitioning is driven by device I/O limits (the topology) by default. fdisk is able to optimize the disk layout for a 4K-sector size and use an alignment offset on modern devices for MBR and GPT. It is always a good idea to follow fdisk's defaults as the default values (e.g. first and last partition sectors) and partition sizes specified by the +<size>{M,G,...} notation are always aligned according to the device properties.
Note that partx(8) provides a rich interface for scripts to print disk layouts, fdisk is mostly designed for humans. Backward compatibility in the output of fdisk is not guaranteed. The input (the commands) should always be backward compatible.
The partition is a device name followed by a partition number. For example, /dev/sda1 is the first partition on the first hard disk in the system. See also Linux kernel documentation (the Documentation/devices.txt file).
If the size is prefixed by '+' then it is interpreted as relative to the partition first sector. In this case the size is expected in bytes and the number may be followed by the multiplicative suffixes KiB=1024, MiB=1024*1024, and so on for GiB, TiB, PiB, EiB, ZiB and YiB. The "iB" is optional, e.g. "K" has the same meaning as "KiB".
The relative sizes are always aligned according to device I/O limits. The +<size>{K,B,M,G,...} notation is recommended.
For backward compatibility fdisk also accepts the suffixes KB=1000, MB=1000*1000, and so on for GB, TB, PB, EB, ZB and YB. These 10^N suffixes are deprecated.
Note that the first sector is still reserved for a protective MBR in the GPT specification. It prevents MBR-only partitioning tools from mis-recognizing and overwriting GPT disks.
GPT is always a better choice than MBR, especially on modern hardware with a UEFI boot loader.
DOS-type (MBR)
In a DOS-type partition table the starting offset and the size of each partition is stored in two ways: as an absolute number of sectors (given in 32 bits), and as a Cylinders/Heads/Sectors triple (given in 10+8+6 bits). The former is OK -- with 512-byte sectors this will work up to 2 TB. The latter has two problems. First, these C/H/S fields can be filled only when the number of heads and the number of sectors per track are known. And second, even if we know what these numbers should be, the 24 bits that are available do not suffice. DOS uses C/H/S only, Windows uses both, Linux never uses C/H/S. The C/H/S addressing is deprecated and may be unsupported in some later fdisk version.
Please, read the DOS-mode section if you want DOS-compatible partitions. fdisk does not care about cylinder boundaries by default.
BSD/Sun-type
IRIX/SGI-type
A sync() and an ioctl(BLKRRPART) (rereading the partition table from disk) are performed before exiting when the partition table has been updated.
The DOS 6.x FORMAT command looks for some information in the first sector of the data area of the partition, and treats this information as more reliable than the information in the partition table. DOS FORMAT expects DOS FDISK to clear the first 512 bytes of the data area of a partition whenever a size change occurs. DOS FORMAT will look at this extra information even if the /U flag is given -- we consider this a bug in DOS FORMAT and DOS FDISK.
The bottom line is that if you use fdisk or cfdisk to change the size of a DOS partition table entry, then you must also use dd(1) to zero the first 512 bytes of that partition before using DOS FORMAT to format the partition. For example, if you were using fdisk to make a DOS partition table entry for /dev/sda1, then (after exiting fdisk and rebooting Linux so that the partition table information is valid) you would use the command "dd if=/dev/zero of=/dev/sda1 bs=512 count=1" to zero the first 512 bytes of the partition.
fdisk usually obtains the disk geometry automatically. This is not necessarily the physical disk geometry (indeed, modern disks do not really have anything like a physical geometry, certainly not something that can be described in the simplistic Cylinders/Heads/Sectors form), but it is the disk geometry that MS-DOS uses for the partition table.
Usually all goes well by default, and there are no problems if Linux is the only system on the disk. However, if the disk has to be shared with other operating systems, it is often a good idea to let an fdisk from another operating system make at least one partition. When Linux boots it looks at the partition table, and tries to deduce what (fake) geometry is required for good cooperation with other systems.
Whenever a partition table is printed out in DOS mode, a consistency check is performed on the partition table entries. This check verifies that the physical and logical start and end points are identical, and that each partition starts and ends on a cylinder boundary (except for the first partition).
Some versions of MS-DOS create a first partition which does not begin on a cylinder boundary, but on sector 2 of the first cylinder. Partitions beginning in cylinder 1 cannot begin on a cylinder boundary, but this is unlikely to cause difficulty unless you have OS/2 on your machine.
For best results, you should always use an OS-specific partition table program. For example, you should make DOS partitions with the DOS FDISK program and Linux partitions with the Linux fdisk or Linux cfdisk programs.
See terminal-colors.d(5) for more details about colorization configuration. The logical color names supported by fdisk are:
The original version was written by Andries E. Brouwer, A. V. Le Blanc and others.