CentOS7的swap分区管理（分区或文件）

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

创建分区来划分swap

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

创建一个文件充当swap分区

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