服务器评测
一、Linux中swap分区的基础作用：
Linux swap分区是Linux交换分区：Linux系统物理内存不够用时，系统会自动启用swap分区，来缓解物理内存的压力，系统把物理内存里的访问频率低的内存对象移动到swap分区中，再在物理内存里产生新的连接指向swap分区中的特定的对象；
二、
相对于繁忙的服务器来说，会出现物理内存和物理分区同时不够用的情况，这时候我们就需要临时扩增swap分区的大小，达到这种目的有两种方法：
1.当硬盘的扩展分区还有剩余的内存可用，可以用fdisk命令创建新的分区，并调整分区类型为Linux-swap,然后启用即可。
具体步骤：
[root@linuxidc ~]# free -m //查看物理内存和swap分区的使用率
total used free shared buffers cached
Mem: 502 474 28 0 76 274
-/+ buffers/cache: 124 378
Swap: 1019 0 1019
[root@linuxidc ~]# fdisk /dev/sdb
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)
Command (m for help): p //列出当前已创建的分区
Disk /dev/sdb: 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
Command (m for help): n //新建一个分区
Command action
e extended
p primary partition (1-4)
p //主分区
Partition number (1-4): 1
First cylinder (1-2610, default 1):
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-2610, default 2610): +3G
Command (m for help): t //改变分区类型
Selected partition 1
Hex code (type L to list codes): L //列出内核所支持的分区
0 Empty 1e Hidden W95 FAT1 80 Old Minix bf Solaris
1 FAT12 24 NEC DOS 81 Minix / old Lin c1 DRDOS/sec (FAT-
2 XENIX root 39 Plan 9 82 Linux swap / So c4 DRDOS/sec (FAT-
3 XENIX usr 3c PartitionMagic 83 Linux c6 DRDOS/sec (FAT-
4 FAT16 <32M 40 Venix 80286 84 OS/2 hidden C: c7 Syrinx
5 Extended 41 PPC PReP Boot 85 Linux extended da Non-FS data
6 FAT16 42 SFS 86 NTFS volume set db CP/M / CTOS / .
7 HPFS/NTFS 4d QNX4.x 87 NTFS volume set de Dell Utility
8 AIX 4e QNX4.x 2nd part 88 Linux plaintext df BootIt
9 AIX bootable 4f QNX4.x 3rd part 8e Linux LVM e1 DOS access
a OS/2 Boot Manag 50 OnTrack DM 93 Amoeba e3 DOS R/O
b W95 FAT32 51 OnTrack DM6 Aux 94 Amoeba BBT e4 SpeedStor
c W95 FAT32 (LBA) 52 CP/M 9f BSD/OS eb BeOS fs
e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a0 IBM Thinkpad hi ee EFI GPT
f W95 Ext’d (LBA) 54 OnTrackDM6 a5 FreeBSD ef EFI (FAT-12/16/
10 OPUS 55 EZ-Drive a6 OpenBSD f0 Linux/PA-RISC b
11 Hidden FAT12 56 Golden Bow a7 NeXTSTEP f1 SpeedStor
12 Compaq diagnost 5c Priam Edisk a8 Darwin UFS f4 SpeedStor
14 Hidden FAT16 <3 61 SpeedStor a9 NetBSD f2 DOS secondary
16 Hidden FAT16 63 GNU HURD or Sys ab Darwin boot fb VMware VMFS
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fc VMware VMKCORE
18 AST SmartSleep 65 Novell Netware b8 BSDI swap fd Linux raid auto
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep
1c Hidden W95 FAT3 75 PC/IX be Solaris boot ff BBT
Hex code (type L to list codes): 82
Changed system type of partition 1 to 82 (Linux swap / Solaris)
Command (m for help): w //保存分区
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.
[root@linuxidc ~]# partprobe /dev/sdb //让内核重读分区表
[root@linuxidc ~]# cat /proc/partitions //确保内核重读分区表完成
major minor #blocks name
8 0 20971520 sda
8 1 305203 sda1
8 2 19615365 sda2
8 3 1044225 sda3
8 16 20971520 sdb
8 17 2939863 sdb1
[root@linuxidc ~]#mkswap /dev/sdb1 //格式化
Setting up swapspace version 1, size = 3010412 kB
[root@linuxidc ~]# swapon /dev/sdb1 //启用该swap分区
[root@linuxidc ~]# free -m
total used free shared buffers cached
Mem: 502 394 107 0 30 273
-/+ buffers/cache: 90 412
Swap: 3890 0 3890
[root@linuxidc ~]# swapoff /dev/sdb1 //关闭该swap分区
[root@linuxidc ~]# free -m
total used free shared buffers cached
Mem: 502 393 108 0 30 273
-/+ buffers/cache: 89 413
Swap: 1019 0 1019
2.当硬盘没有剩余的存储可创建新分区时，可以利用dd命令在已存的分区中创建一个文件，充当swap分区。
具体步骤：（现已脚本的形式呈现）
[root@linuxidc ~]# vi createswap.sh
#!/bin/bash
echo -n “Please input your number: “
read number
echo -n “Please input your swapfile name and the whole path: “
read path
dd if=/dev/zero of=$path bs=1M count=$number
mkswap $path
swapon $path
free -m
echo “The swap created”
结束语：到此教程完毕。
Linux dd命令制作U盘系统启动盘 http://www.linuxidc.com/Linux/2015-02/113585.htm
Linux/UNIX: 使用 dd 命令创建 1GB 大小的二进制 http://www.linuxidc.com/Linux/2014-12/110147.htm
如何在Ubuntu 14.04中创建SWAP交换分区文件 http://www.linuxidc.com/Linux/2014-08/105223.htm
如何扩展/删除SWAP分区 http://www.linuxidc.com/Linux/2014-03/98311.htm
在OpenStack虚拟机实例中创建SWAP分区的一种方法 http://www.linuxidc.com/Linux/2013-07/87380.htm
Linux 中交换空间 （SWAP）应该分多大才好？ http://www.linuxidc.com/Linux/2013-05/84252.htm
Linux SWAP 分区建立及释放内存 http://www.linuxidc.com/Linux/2013-03/81890.htm
Linux SWAP 交换分区配置说明 http://www.linuxidc.com/Linux/2013-03/82008.htm
本文永久更新链接地址：http://www.linuxidc.com/Linux/2015-03/114326.htm
