最近由于工作的需要，初步研究了uboot中的fastboot实现方式。研究fastboot不可避免的需要了解磁盘分区的相关知识点，在linux下可以使用fdisk命令实现磁盘的分区。好了，下面步入正题。

1. 查看帮助信息（fdisk --help）

linux@linux-System-Product-Name:~$ fdisk --help

Usage:
 fdisk [options] <disk>      change partition table
 fdisk [options] -l [<disk>] list partition table(s)

Display or manipulate a disk partition table.

Options:
 -b, --sector-size <size>      physical and logical sector size
 -B, --protect-boot            don't erase bootbits when creating a new label
 -c, --compatibility[=<mode>]  mode is 'dos' or 'nondos' (default)
 -L, --color[=<when>]          colorize output (auto, always or never)
                                 colors are enabled by default
 -l, --list                    display partitions and exit
 -o, --output <list>           output columns
 -t, --type <type>             recognize specified partition table type only
......

2. 查看磁盘分区

通过命令 sudo fdisk -l可以查看磁盘的详细分区情况，如下所示，我电脑目前存在两个磁盘：分别为sda和sdb（其中sda即为240G的固态硬盘，为系统盘，而sdb则为一个容量为16G的SD卡）。

linux@linux-System-Product-Name:~$ sudo fdisk -l
[sudo] password for linux:
Disk /dev/sda: 232.9 GiB, 250059350016 bytes, 488397168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: DE19ADF1-DDE6-4899-BC1B-C6B608AD5C31

Device       Start       End   Sectors   Size Type
/dev/sda1     2048   1050623   1048576   512M EFI System
/dev/sda2  1050624 488396799 487346176 232.4G Linux filesystem

Disk /dev/sdb: 14.6 GiB, 15646851072 bytes, 30560256 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
Disklabel type: dos
Disk identifier: 0x9b9208de

Device     Boot Start     End Sectors Size Id Type
/dev/sdb1        2048 2099199 2097152   1G 83 Linux
linux@linux-System-Product-Name:~$

以sdb为例进行详细的说明如下：

磁盘容量为14.6GiB，合计共15646851072 字节，每个“扇区”的大小为512字节，总共30560256个扇区；
扇区的大小（物理 / 逻辑）：512字节 / 512字节
I / O大小（最小值 / 典型值）：512字节 / 512字节
磁盘标签类型：dos （sda的磁盘标签类型为gpt）
磁盘标识符：0x9b9208de
该磁盘共分了一个“分区”，分区名称为sdb1, 该分区的起始扇区号为2048，结束扇区号为2099199，共2097152个扇区（sector），大小为1GiB，分区ID为0x83（linux native分区），类型为Linux

3. 磁盘分区

需求举例：

将sdb磁盘分为4个区，其中1，2，3分区为主分区，4分区为扩展分区；
分区1的大小为512M字节，分区2的大小为2G字节，分区3的大小为4G字节，分区4的大小为剩余的磁盘空间；
创建DOS类型的分区表（MBR）

步骤1：执行命令 sudo fdisk /dev/sdb，输入 m 获取帮助信息，如下：

linux@linux-System-Product-Name:~$ sudo fdisk /dev/sdb

Welcome to fdisk (util-linux 2.31.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): m

Help:

  DOS (MBR)
   a   toggle a bootable flag
   b   edit nested BSD disklabel
   c   toggle the dos compatibility flag

  Generic
   d   delete a partition
   F   list free unpartitioned space
   l   list known partition types
   n   add a new partition
   p   print the partition table
   t   change a partition type
   v   verify the partition table
   i   print information about a partition

  Misc
   m   print this menu
   u   change display/entry units
   x   extra functionality (experts only)

  Script
   I   load disk layout from sfdisk script file
   O   dump disk layout to sfdisk script file

  Save & Exit
   w   write table to disk and exit
   q   quit without saving changes

  Create a new label
   g   create a new empty GPT partition table
   G   create a new empty SGI (IRIX) partition table
   o   create a new empty DOS partition table
   s   create a new empty Sun partition table


Command (m for help):

步骤2：输入 p，查看磁盘当前的分区表

Command (m for help): p
Disk /dev/sdb: 14.6 GiB, 15646851072 bytes, 30560256 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
Disklabel type: dos
Disk identifier: 0x9b9208de

Device     Boot Start     End Sectors Size Id Type
/dev/sdb1        2048 2099199 2097152   1G 83 Linux

当前磁盘共分了一个“分区”，分区名称为sdb1, 该分区的起始扇区号为2048，结束扇区号为2099199，共2097152个扇区（sector），大小为1GiB，分区ID为0x83（linux native分区），类型为Linux

步骤3：输入 o，创建一个新的GPT分区表

Command (m for help): o

Created a new DOS disklabel with disk identifier 0x6ade9f76.
The old dos signature will be removed by a write command.

步骤4：输入 n，添加一个新的分区（添加我们的第1个分区，大小为512M）

Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p   // 主分区
Partition number (1-4, default 1):	// 分区号为1，直接按“回车”即可
First sector (2048-30560255, default 2048): // 直接按“回车”即可
Last sector, +sectors or +size{K,M,G,T,P} (2048-30560255, default 30560255): +512M // 分配的空间大小为512M

Created a new partition 1 of type 'Linux' and of size 512 MiB.

Command (m for help): p // 查询分区表
Disk /dev/sdb: 14.6 GiB, 15646851072 bytes, 30560256 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
Disklabel type: dos
Disk identifier: 0x6ade9f76

Device     Boot Start     End Sectors  Size Id Type
/dev/sdb1        2048 1050623 1048576  512M 83 Linux

步骤5：输入 n，依次添加2，3，4分区

Command (m for help): n
Partition type
   p   primary (1 primary, 0 extended, 3 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (2-4, default 2):	// 创建第2个分区
First sector (1050624-30560255, default 1050624):
Last sector, +sectors or +size{K,M,G,T,P} (1050624-30560255, default 30560255): +2G // 分区大小为2G

Created a new partition 2 of type 'Linux' and of size 2 GiB.

Command (m for help): n
Partition type
   p   primary (2 primary, 0 extended, 2 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (3,4, default 3): // 创建第3个分区
First sector (5244928-30560255, default 5244928):
Last sector, +sectors or +size{K,M,G,T,P} (5244928-30560255, default 30560255): +4G // 分区大小为4G

Created a new partition 3 of type 'Linux' and of size 4 GiB.

Command (m for help): n
Partition type
   p   primary (3 primary, 0 extended, 1 free)
   e   extended (container for logical partitions)
Select (default e): e // 创建扩展分区

Selected partition 4	// 创建第3个分区，MBR最多只能创建4个分区
First sector (13633536-30560255, default 13633536):
Last sector, +sectors or +size{K,M,G,T,P} (13633536-30560255, default 30560255):

Created a new partition 4 of type 'Extended' and of size 8.1 GiB. // 分区大小为“磁盘剩余空间”

Command (m for help): p
Disk /dev/sdb: 14.6 GiB, 15646851072 bytes, 30560256 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
Disklabel type: dos
Disk identifier: 0x6ade9f76

Device     Boot    Start      End  Sectors  Size Id Type
/dev/sdb1           2048  1050623  1048576  512M 83 Linux
/dev/sdb2        1050624  5244927  4194304    2G 83 Linux
/dev/sdb3        5244928 13633535  8388608    4G 83 Linux
/dev/sdb4       13633536 30560255 16926720  8.1G  5 Extended

步骤6：输入 w，将分区表写入磁盘，至此磁盘分区完成。

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.
linux@linux-System-Product-Name:~$  // 退出了磁盘的命令模式

步骤7：再次确认“磁盘分区表”是否真正的写入磁盘

linux@linux-System-Product-Name:~$ sudo fdisk /dev/sdb
[sudo] password for linux:

Welcome to fdisk (util-linux 2.31.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/sdb: 14.6 GiB, 15646851072 bytes, 30560256 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
Disklabel type: dos
Disk identifier: 0x6ade9f76

Device     Boot    Start      End  Sectors  Size Id Type
/dev/sdb1           2048  1050623  1048576  512M 83 Linux
/dev/sdb2        1050624  5244927  4194304    2G 83 Linux
/dev/sdb3        5244928 13633535  8388608    4G 83 Linux
/dev/sdb4       13633536 30560255 16926720  8.1G  5 Extended

Command (m for help):