说一台很旧的RedHat机器硬盘空间不足，去df -m查看下
[root@192.168.14.117:/root]#df -m
Filesystem 1M-blocks Used Available Use% Mounted on
/dev/sda3 17599 15619 1072 94% /
/dev/sda1 251 16 223 7% /boot
tmpfs 760 0 760 0% /dev/shm
/dev/sdb3 30236 23542 5159 83% /data
原来是因为本来空间就不大，只有50多个G，du一路查下去，发现是cgi的日志文件和so的core文件占用了很大的空间，但是想想也没啥可清理的了。(注：检查磁盘空间占用，可以用du -ah --max-depth=1，打印当前目录下，各个文件大小和目录的磁盘空间占用情况，也可以在后面指定显示某个目录的子目录和文件空间占用信息)
因为还有一块20G的老硬盘闲置在那里，所以就干脆把它挂上去。
1、拆机，硬盘挂上
2、重启机器，fdisk -l 查看
[root@192.168.14.117:/dev]#fdisk -l
Disk /dev/sda: 21.4 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 33 265041 83 Linux
/dev/sda2 34 294 2096482+ 82 Linux swap / Solaris
/dev/sda3 295 2610 18603270 83 Linux
Disk /dev/sdb: 32.2 GB, 32212254720 bytes
255 heads, 63 sectors/track, 3916 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb3 1 3916 31455238+ 83 Linux
Disk /dev/sdc: 21.4 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk /dev/sdc doesn't contain a valid partition table
很好,刚挂上去的第三块盘认到了，sdc，21.4G,不过盘上还没有任何分区。
3、创建分区。执行 fdisk /dev/sdc
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.
The number of cylinders for this disk is set to 2610.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help):
提示我输入命令，可怜的记不住命令，只能打一个m，for help了 ^-^
Command (m for help): m
Command action
a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
l list known partition types
m print this menu
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition's system id
u change display/entry units
v verify the partition table
w write table to disk and exit
x extra functionality (experts only)
大概看了一个m出来的命令，毫不犹豫选择了 n ,添加一个新分区