使用DD 创建SWAP

1创建所需swap空间的文件

　　　　　　　　　　　　if=获取数据　 of=输出位置　 　块大小(每次复制大小)　　块个数（复制次数）　　
[root@web01 ~]# dd if=/dev/zero of=/tmp/100m　　 bs=1M 　　　　　　count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 2.01386 s, 52.1 MB/s
[root@web01 ~]# ll -h /tmp/100m 
-rw-r--r--. 1 root root 100M Apr 21 13:44 /tmp/100m

2 格式化文件成为SWAP

[root@web01 ~]# mkswap  /tmp/100m 
mkswap: /tmp/100m: warning: don't erase bootbits sectors
        on whole disk. Use -f to force.
Setting up swapspace version 1, size = 102396 KiB
no label, UUID=f90d8d0c-4972-42fc-83f8-4b98c651554e
[root@web01 ~]# file /tmp/100m   查看文件类型是否更改为swap
/tmp/100m: Linux/i386 swap file (new style) 1 (4K pages) size 25599 pages

3 让文件生效成SWAP

[root@web01 ~]# free -h    
             total       used       free     shared    buffers     cached
Mem:          3.7G       2.2G       1.6G       232K       1.0G       164M
-/+ buffers/cache:       972M       2.8G
Swap:         1.5G         0B       1.5G

[root@web01 ~]# swapon /tmp/100m 
[root@web01 ~]# free -h
total       used       free     shared    buffers     cached
Mem:          3.7G       2.2G       1.6G       232K       1.0G       164M
-/+ buffers/cache:       972M       2.8G
Swap:         1.6G         0B       1.6G

4 检查swap 是由及部分组成

[root@web01 ~]# swapon -s
Filename                Type        Size    Used    Priority
/dev/sda2               partition   1048572   0      -1
/tmp/500m               file        511996    0      -2
/tmp/100m               file        102396    0      -3

5 永久挂载/开机挂载

方法1：写入 /etc/rc.local
[root@web01 ~]# cat /etc/rc.local
#!/bin/sh
#
# This script will be executed *after* all the other init scripts.
# You can put your own initialization stuff in here if you don't
# want to do the full Sys V style init stuff.

touch /var/lock/subsys/local
#bin/mount    /dev/sdc1    /date
swapon        /tmp/100m
方法2 
[root@web01 ~]# cat /etc/fstab
/tmp/100m		swap			swap	defaults	0 0