1、swap可以在安装操作系统的时候划分单独分区创建；也可以安装好操作系统后划分剩余硬盘创建；还可以创建一个文件当swap分区使用
2、建议创建一个新的分区当swap使用，如果想使用一个文件当swap分区用的话最好将文件放在固态硬盘上，使用文件充当swap的话可以随意变大变小，移动也方便，但性能不如分区好
一、使用free -h查看当前swap
当前系统有4G的swap空间
[root@centos7 ~]# free -h
total used free shared buff/cache available
Mem: 1.9G 180M 1.2G 19M 545M 1.6G
Swap: 4.0G 12M 4.0G使用swapon -s显示当前系统的swap
[root@centos7 ~]# swapon -s
Filename Type Size Used Priority
/dev/dm-0 partition 419430012676 -2二、使用lsblk查看当前系统的硬盘
可以看到，sda总共200G，现在才划分了150多G，还有可以用的空间
[root@centos7 ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 200G 0 disk
├─sda1 8:1 0 1G 0 part /boot
├─sda2 8:2 0 100G 0 part /
├─sda3 8:3 0 50G 0 part /data
├─sda4 8:4 0 1K 0 part
└─sda5 8:5 0 4G 0 part
└─centos-swap
253:0 0 4G 0 lvm [SWAP]
sdb 8:16 0 20G 0 disk
└─sdb2 8:18 0 2G 0 part 三、使用fdisk对/dev/sda硬盘进行创建分区操作
[root@centos7 ~]# fdisk /dev/sda
Welcome to fdisk (util-linux 2.23.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): n
All primary partitions are in use
Adding logical partition 6
First sector (325072896-419430399, default 325072896):
Using default value 325072896
Last sector, +sectors or +size{K,M,G} (325072896-419430399, default 419430399): +2G
Partition 6 of type Linux and of size 2 GiB is set
Command (m for help): p
Disk /dev/sda: 214.7 GB, 214748364800 bytes, 419430400 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000f14f7
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 2099199 1048576 83 Linux
/dev/sda2 2099200 211814399 104857600 83 Linux
/dev/sda3 211814400 316671999 52428800 83 Linux
/dev/sda4 316672000 419430399 51379200 5 Extended
/dev/sda5 316674048 325070847 4198400 8e Linux LVM
/dev/sda6 325072896 329267199 2097152 83 Linux
Command (m for help): w
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 or after you run partprobe(8) or kpartx(8)
Syncing disks.四、执行两下partprobe(CentOS6执行part /dev/sda -a)
[root@centos7 ~]# partprobe
Warning: Unable to open /dev/sr0 read-write (Read-only file system). /dev/sr0 has been opened read-only.
Error: Invalid partition table - recursive partition on /dev/sr0.
Warning: Unable to open /dev/sr1 read-write (Read-only file system). /dev/sr1 has been opened read-only.
[root@centos7 ~]# partprobe
Warning: Unable to open /dev/sr0 read-write (Read-only file system). /dev/sr0 has been opened read-only.
Error: Invalid partition table - recursive partition on /dev/sr0.
Warning: Unable to open /dev/sr1 read-write (Read-only file system). /dev/sr1 has been opened read-only.五、创建文件系统
[root@centos7 ~]# ls /dev/sda6
/dev/sda6
[root@centos7 ~]# mkswap /dev/sda6
Setting up swapspace version 1, size = 2097148 KiB
no label, UUID=b98996a2-a548-4266-b636-b2cb75cd0626六、写入/etc/fstab，并mount -a测试
[root@centos7 ~]# blkid /dev/sda6
/dev/sda6: UUID="b98996a2-a548-4266-b636-b2cb75cd0626" TYPE="swap"
[root@centos7 ~]# vim /etc/fstab
[root@centos7 ~]# tail -1 /etc/fstab
UUID=b98996a2-a548-4266-b636-b2cb75cd0626 swap swap defaults 0 0
# 被挂载的设备名 挂载点 文件系统类型 挂载选项 转储频率 系统自检选项
[root@centos7 ~]# mount -a七、swapon -a
此时执行free -h，swap分区还没显示出来，执行swapon -a，启用所有swap
[root@centos7 ~]# free -h
total used free shared buff/cache available
Mem: 1.9G 176M 1.2G 19M 547M 1.6G
Swap: 4.0G 12M 4.0G
# 执行swapon -a
[root@centos7 ~]# swapon -a
[root@centos7 ~]# free -h
total used free shared buff/cache available
Mem: 1.9G 178M 1.2G 19M 547M 1.6G
Swap: 6.0G 12M 6.0G八、卸载这个swap
# 使用swapoff关闭/dev/sda6这个swap分区
[root@centos7 ~]# swapoff /dev/sda6
# 使用sed删除fstab最后加的一行
[root@centos7 ~]# sed -ri ‘$d‘ /etc/fstab
# mount -a
[root@centos7 ~]# mount -a
# 此时swap已变成原来的4G一、使用dd命令创建一个文件100M，当swap用
[root@centos7 data]# dd if=/dev/zero of=/data/swapfile bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 2.74665 s, 38.2 MB/s
# swap文件权限修改为600，安全
[root@centos7 data]# chmod 600 swapfile二、对该文件创建文件系统
[root@centos7 data]# mkswap swapfile
Setting up swapspace version 1, size = 102396 KiB
no label, UUID=a16538e7-685e-4141-aaeb-e1b7896cffdf三、写入/etc/fstab,挂载（这里要注意，挂载设备不能写UUID，只能写文件名）
[root@centos7 data]# tail -1 /etc/fstab
/data/swapfile swap swap defaults 0 0
[root@centos7 data]# mount -a四、执行swapon -a 开启所有swap
[root@centos7 data]# swapon -a
[root@centos7 data]# swapon -s
Filename Type Size Used Priority
/dev/dm-0 partition 4194300 12672 -2
/data/swapfile file 102396 0 -3
[root@centos7 data]# free -h
total used free shared buff/cache available
Mem: 1.9G 176M 1.1G 19M 650M 1.6G
Swap: 4.1G 12M 4.1G五、增大swap，需要先取消挂载
# 必须先卸载，不然报错了
[root@centos7 data]# dd if=/dev/zero of=/data/swapfile bs=1M count=200
dd: failed to open ‘/data/swapfile’: Text file busy
# 卸载
[root@centos7 data]# swapoff /data/swapfile
[root@centos7 data]# dd if=/dev/zero of=/data/swapfile bs=1M count=200
200+0 records in
200+0 records out
209715200 bytes (210 MB) copied, 3.23377 s, 64.9 MB/s
# 创建文件系统
[root@centos7 data]# mkswap swapfile
Setting up swapspace version 1, size = 204796 KiB
no label, UUID=79d0f287-c998-42d3-aabc-b3b2d60b9cb2
# 执行swapon -a启用所有swap
[root@centos7 data]# swapon -a
[root@centos7 data]# free -h
total used free shared buff/cache available
Mem: 1.9G 176M 1.0G 19M 752M 1.6G
Swap: 4.2G 12M 4.2G六、卸载
# 取消挂载
[root@centos7 data]# swapoff /data/swapfile
[root@centos7 data]# sed -ri ‘$d‘ /etc/fstab
[root@centos7 data]# mount -a
[root@centos7 data]# rm -f swapfile
[root@centos7 data]# free -h
total used free shared buff/cache available
Mem: 1.9G 176M 1.2G 19M 547M 1.6G
Swap: 4.0G 12M 4.0G原文：https://blog.51cto.com/14012942/2428343