内存交换空间（swap）的构建

一、使用物理分区构建swap

1、先进行分区的行为。

 [root@iZ255cppmtxZ ~]# fdisk /dev/xvdb
 Welcome to fdisk (util-linux 2.23.).

 Changes will remain in memory only, until you decide to write them.
 Be careful before using the write command.

 Command (m for help): n
 Partition type:
    p   primary ( primary,  extended,  free)
    e   extended
 Select (default p): p
 Partition number (,,, default ):
 First sector (-, default ):
 Using default value
 Last sector, +sectors or +size{K,M,G} (-, default ): +512M Partition  of type Linux and of size  GiB is set

 Command (m for help): p

 Disk /dev/xvdb: 32.2 GB,  bytes,  sectors
 Units = sectors of  *  =  bytes
 Sector size (logical/physical):  bytes /  bytes
 I/O size (minimum/optimal):  bytes /  bytes
 Disk label type: dos
 Disk identifier: 0x25a2caf5

     Device Boot      Start         End      Blocks   Id  System
 /dev/xvdb2                         Linux
 /dev/xvdb4                     Linux

 Command (m for help): t           <==修改系统ID
 Partition number (,, default ): 4
 Hex code (type L to list all codes): 82           <==改成swap的ID
 Changed type of partition 'Linux' to 'Linux swap / Solaris'

 Command (m for help): p

 Disk /dev/xvdb: 32.2 GB,  bytes,  sectors
 Units = sectors of  *  =  bytes
 Sector size (logical/physical):  bytes /  bytes
 I/O size (minimum/optimal):  bytes /  bytes
 Disk label type: dos
 Disk identifier: 0x25a2caf5

     Device Boot      Start         End      Blocks   Id  System
 /dev/xvdb2                         Linux
 /dev/xvdb4                     Linux swap / Solaris

 Command (m for help): w
 The partition table has been altered!

 Calling ioctl() to re-read partition table.
 Syncing disks.

强制内核更新分区表：

[root@iZ255cppmtxZ ~]# partprobe

2、开始构建swap格式。

[root@iZ255cppmtxZ ~]# mkswap /dev/xvdb4
Setting up swapspace version , size =  KiB
no label, UUID=033a1d75-88fd---08d856cb9ad1

3、查实查看与加载。

 [root@iZ255cppmtxZ ~]# swapon /dev/xvdb4
 [root@iZ255cppmtxZ ~]# free
              total       used       free     shared    buffers     cached
 Mem:
 -/+ buffers/cache:
 Swap:                  

[root@iZ255cppmtxZ ~]# swapon -s
Filename                Type        Size    Used    Priority
/dev/xvdb4                                 partition            -

二、使用文件系统构建swap

1、使用dd这个命令来新增一个128MB的文件在/data下面：

 [root@iZ255cppmtxZ ~]# dd if=/dev/zero of=/data/swap bs=1M count=
 + records in
 + records out
  bytes ( MB) copied, 7.82149 s, 68.6 MB/s

2、使用mkswap将/data/swap这个文件格式化为swap的文件格式：

 [root@iZ255cppmtxZ ~]# mkswap /data/swap
 Setting up swapspace version , size =  KiB
 no label, UUID=ede63d44-cf78-4d08-92ca-15fb38a625f4

3、使用swapon来将/data/swap启动

 [root@iZ255cppmtxZ ~]# swapon /data/swap
 swapon: /data/swap: insecure permissions ,  suggested.
 [root@iZ255cppmtxZ ~]# free -m
              total       used       free     shared    buffers     cached
 Mem:
 -/+ buffers/cache:
 Swap:
 [root@iZ255cppmtxZ ~]# swapon -s
 Filename                Type        Size    Used    Priority
 /data/swap                                 file            -

使用swapoff关掉swapfile

 [root@iZ255cppmtxZ ~]# swapoff /dev/xvdb4
 [root@iZ255cppmtxZ ~]# swapoff /data/swap 

为了能够让swap自动挂载，要修改/etc/fstab文件

在文件末尾加上

/data/swap swap swap default 0 0 
这样就算重启系统，swap分区就不用手动挂载了。