fdisk 挺好学的，因为基本上按个m它就能告诉你该怎么做了。我这里有一个20g的虚拟磁盘。实际操作下。
开始对磁盘/dev/sdb分区
[root@rhel6 sjb]# fdisk /dev/sdb
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').
Command (m for help): m
Command action
a toggle a bootable flag 设置为启动分区
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition 删除分区
l list known partition types 显示已知的分区类型以及对应的id号
m print this menu 显示选项菜单
n add a new partition 新建分区
o create a new empty DOS partition table
p print the partition table 显示分区表
q quit without saving changes 不保存退出
s create a new empty Sun disklabel
t change a partition's system id 改变分区id，即分区类型
u change display/entry units
v verify the partition table
w write table to disk and exit 写入分区表并退出
x extra functionality (experts only)
显示磁盘分区
Command (m for help): p
Disk /dev/sdb: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xce4aaddb
Device Boot Start End Blocks Id System
/dev/sdb1 * 1 131 1048576 83 Linux
Partition 1 does not end on cylinder boundary.
/dev/sdb2 131 784 5242880 83 Linux
Partition 2 does not end on cylinder boundary.
/dev/sdb3 784 1045 2097152 82 Linux swap / Solaris
Partition 3 does not end on cylinder boundary.
/dev/sdb4 1045 2611 12580864 f W95 Ext'd (LBA)
Partition 4 does not end on cylinder boundary.
/dev/sdb5 1045 2611 12579840 83 Linux
删除磁盘分区
Command (m for help): d
Partition number (1-5): 1
Command (m for help): d
Partition number (1-5): 2
Command (m for help): d
Partition number (1-5): 3
Command (m for help): d
Partition number (1-5): 4
Command (m for help): d
Partition number (1-5): 5
查看删除情况
Command (m for help): p
Disk /dev/sdb: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xce4aaddb
Device Boot Start End Blocks Id System
新建主分区1，起始磁柱为1，分区大小我们用+100M来指定分区大小为100M.
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-2610, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-2610, default 2610): +100M
指定其为活动分区
Command (m for help): a
Partition number (1-6): 1
建立主分区2，大小为1G
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (15-2610, default 15):
Using default value 15
Last cylinder, +cylinders or +size{K,M,G} (15-2610, default 2610): +1G