NAME fdisk - Partition table manipulator for Linux
SYNOPSIS
fdisk [-u] [-b sectorsize ] [-C cyls ] [-H heads ] [-S sects ] device
fdisk -l [-u] [ device ... ]
fdisk -s partition ...
fdisk -v
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.
In the BSD world one talks about 'disk slices' and a 'disklabel'.
Linux needs at least one partition, namely for its root file system. It can use swap files and/or swap partitions, but the latter are more efficient. So, usually one will want a second Linux parti- tion dedicated as swap partition. On Intel compatible hardware, the BIOS that boots the system can often only access the first 1024 cylinders of the disk. For this reason people with large disks often create a third partition, just a few MB large, typically mounted on /boot , to store the kernel image and a few auxiliary files needed at boot time, so as to make sure that this stuff is accessible to the BIOS. There may be reasons of security, ease of administration and backup, or testing, to use more than the minimum number of partitions.
fdisk (in the first form of invocation) is a menu driven program for creation and manipulation of partition tables. It understands DOS type partition tables and BSD or SUN type disklabels.
fdisk doesn't understand GUID Partition Table (GPT) and it is not designed for large partitions. In particular case use more advanced GNU parted(8) .
The device is usually /dev/sda, /dev/sdb or so. A device name refers to the entire disk. The old systems without libata (a library used inside the Linux kernel to support ATA host controllers and devices) make a difference between IDE and SCSI disks. In such a case the device name will be /dev/hd* (IDE) or /dev/sd* (SCSI).
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 Documenta- tion/devices.txt file).
A BSD/SUN type disklabel can describe 8 partitions, the third of which should be a 'whole disk' par- tition. Do not start a partition that actually uses its first sector (like a swap partition) at cylinder 0, since that will destroy the disklabel.
An IRIX/SGI type disklabel can describe 16 partitions, the eleventh of which should be an entire 'volume' partition, while the ninth should be labeled 'volume header'. The volume header will also cover the partition table, i.e., it starts at block zero and extends by default over five cylinders. The remaining space in the volume header may be used by header directory entries. No partitions may overlap with the volume header. Also do not change its type and make some file system on it, since you will lose the partition table. Use this type of label only when working with Linux on IRIX/SGI machines or IRIX/SGI disks under Linux.
A DOS type partition table can describe an unlimited number of partitions. In sector 0 there is room for the description of 4 partitions (called 'primary'). One of these may be an extended partition; this is a box holding logical partitions, with descriptors found in a linked list of sectors, each preceding the corresponding logical partitions. The four primary partitions, present or not, get numbers 1-4. Logical partitions start numbering from 5.
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 lat- ter has two different problems. First of all, these C/H/S fields can be filled only when the number of heads and the number of sectors per track are known. Secondly, 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.
If possible, fdisk will obtain 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 simplistic Cylinders/Heads/Sectors form), but 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, 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 the 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 bound- ary, but this is unlikely to cause difficulty unless you have OS/2 on your machine.
A sync() and a BLKRRPART ioctl() (reread partition table from disk) are performed before exiting when the partition table has been updated. Long ago it used to be necessary to reboot after the use of fdisk. I do not think this is the case anymore - indeed, rebooting too quickly might cause loss of not-yet-written data. Note that both the kernel and the disk hardware may buffer data.
DOS 6.x WARNING
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 to change the size of a DOS partition table entry, then you must also use dd to zero the first 512 bytes of that partition before using DOS FORMAT to format the partition. For example, if you were using disk 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.
BE EXTREMELY CAREFUL if you use the dd command, since a small typo can make all of the data on your disk useless.
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 pro- gram.
OPTIONS
-b sectorsize
Specify the sector size of the disk. Valid values are 512, 1024, or 2048. (Recent kernels know the sector size. Use this only on old kernels or to override the kernel's ideas.)
-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.
-u
When listing partition tables, give sizes in sectors instead of cylinders.
-s partition
The size of the partition (in blocks) is printed on the standard output.
-v
Print version number of fdisk program and exit.
BUGS
There are several *fdisk programs around. Each has its problems and strengths. Try them in the order parted , fdisk , sfdisk .
The IRIX/SGI type disklabel is currently not supported by the kernel. Moreover, IRIX/SGI header directories are not fully supported yet.
The option 'dump partition table to file' is missing.
SEE ALSO mkfs(8) , parted(8) , sfdisk(8)
Linux中Fdisk命令的功能是极其强大的，用它可以划分出最复杂的分区，下面简要介绍一下它的用法：
对于IDE硬盘，每块盘有一个设备名：对应于主板的四个IDE接口，设备名依次为：/dev/hda,/dev/hdb,/dev/hdc,/dev/hdd等，如果还有IDE Raid卡，则依 次为：/dev/hde,/dev/hdf,/dev/hdg,/dev/hdh。对于SCSI硬盘，则设备名依次为/dev/sda,/dev/sdb...等等
Fdisk的命令行用法为： Fdisk 硬盘设备名
进入Fdisk后，首先键入'm'，即可显示Fdisk全部菜单。
再键入'p',显示当前分区表状态。
键入'n',增加一个分区，然后会提示你选择分区类型(基本分区或扩展分区)，再选择分区号(1-4)。注：每块硬盘最多可划分四个主分区(包括基本分区和扩展分区)，其中：基本分区最多可划分四个，扩展分区最多可划分一个，但扩展分区内可再划分多个逻辑分区(最多几个我没试过，总之很多)。选中你要建立的分区类型和分区号后，会提示输入起始柱面，从1开始；然后再输入终止柱面，此时可输入实际的柱面数，也可用" 分区尺寸"的方式输入，如： 1024M表示在起始柱面后加上1024M。主分区的设备名依次为：/dev/hda1,/dev/hda2,/dev/hda3,/dev/hda4，逻辑分区的设备名依次为：/dev/hda5,/dev/hda6,/dev/hda7...等等。
键入’d‘,删除分区，输入分区号即可删除。注意，删除扩展分区时，将会同时删除所有的逻辑分区。
键入’t‘，改变分区标志(这是Linux的Fdisk最精华的部份!)，新建的分区默认标志是83(Linux Ext2)，你可以把它改为82(Linux 交换区)、或是'b'(FAT32)、'f'(FAT32 Extend,只限于扩展分区)、'86'(NTFS)。。。等几十种类型。这样一来，使用多操作系统的朋友们就可以用Linux的Fdisk划分出你想要的所有分区了!
键入'a',切换分区激活开关。请注意：每键入一次，被选的分区就会在激活与非激活间变化一次，但你必须保证最后只有一个分区被激活。这时就用得到'p'命令了，被激活的分区上会有个'*'号。
除以上的几个命令外，还有其它几个，但不太常用。
最后，键入’w',你对分区所做的改变被写入硬盘；键入'q'，则放弃所有的修改。
灵活应用Fdisk，还可以修复一些损坏的分区表，前提是你必须准确记住原有每个分区的起始柱面和终止柱面。
再附加一下对硬盘进行格式化的方法：
要把分区格式化成Linux Ext2格式，用： mkext2fs /dev/hda?
要把分区格式化成FAT32格式，用： mkfs.vfat /dev/hda?
/sbin/mkfs.ext3 /dev/sda2
mkdir /test
修改/etc/fstab如下重新启动计算机就行了
/dev/sda2 /test ext3 defaults 1 1
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