Linux_交换分区SWAP

一、交换分区SWAP

1️⃣：交换分区SWAP就是LINUX下的虚拟内存分区，它的作用是在物理内存使用完之后,将磁盘空间(也就是SWAP分区)虚拟成内存来使用。

2️⃣：交换分区一般指定虚拟内存的大小为实际内存的1~1.5倍。

3️⃣：如果实际内存超过8GB，可以直接划分16GB给虚拟内存即可，如果虚拟内存不够用的情况，须增加一个虚拟磁盘，由于不能给原有的磁盘重新分区，所以可以选择新建。

二、创建SWAP

1、方式一：创建SWAP文件

使用dd if=/dev/zero of=/root/swap bs=1M count=2048创建2G大小的文件
- if：指定源- -般写/dev/zero
- of：指定目标
- bs：定义块大小
- count：数量

[root@localhost ~]# dd if=/dev/zero of=/root/swap bs=1M count=2048
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB, 2.0 GiB) copied, 44.8512 s, 47.9 MB/s
[root@localhost ~]# du -sh /root/swap
2.0G    /root/swap

格式化刚刚创建的swap文件

[root@localhost ~]# mkswap -f /root/swap       // -f ：指定格式化文件（目标是文件,则加-f ；若为磁盘分区，则不需要加-f）
mkswap: /root/swap: insecure permissions 0644, 0600 suggested.
Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=20e1675b-3206-497c-b33b-9175be73083f

根据提示设置改格式化后文件的权限为600（此步骤也可以不做）

[root@localhost ~]# ll swap
-rw-r--r-- 1 root root 2147483648 Aug 20 03:03 swap
[root@localhost ~]# chmod 600 /root/swap
[root@localhost ~]# ll swap
-rw------- 1 root root 2147483648 Aug 20 03:03 swap

查看刚刚格式化swap文件的属性

[root@localhost ~]# blkid /root/swap
/root/swap: UUID="20e1675b-3206-497c-b33b-9175be73083f" TYPE="swap"

查看当前SWAP分区情况

[root@localhost ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:          1.8Gi       207Mi        65Mi       5.0Mi       1.5Gi       1.4Gi
Swap:         2.0Gi       3.0Mi       2.0Gi

挂载SWAP分区

[root@localhost ~]# swapon /root/swap
[root@localhost ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:          1.8Gi       209Mi        64Mi       5.0Mi       1.5Gi       1.4Gi
Swap:         4.0Gi       3.0Mi       4.0Gi

卸载SWAP分区

[root@localhost ~]# swapoff /root/swap
[root@localhost ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:          1.8Gi       207Mi       110Mi       5.0Mi       1.5Gi       1.4Gi
Swap:         2.0Gi       3.0Mi       2.0Gi

2、方式二：使用磁盘分区创建SWAP分区

创建一个磁盘主分区

[root@localhost ~]# fdisk /dev/nvme0n2 

Welcome to fdisk (util-linux 2.32.1).
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 (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-104857599, default 2048): 
Last sector, +sectors or +size{K,M,G,T,P} (2048-104857599, default 104857599): +4G

Created a new partition 1 of type 'Linux' and of size 4 GiB.
Partition #1 contains a swap signature.

The signature will be removed by a write command.

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

调整刚刚创建的磁盘分区ID为82

[root@localhost ~]# fdisk /dev/nvme0n2
Welcome to fdisk (util-linux 2.32.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): p      //查看分区列表
Disk /dev/nvme0n2: 50 GiB, 53687091200 bytes, 104857600 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
Disklabel type: dos
Disk identifier: 0x8f03f9d8

Device         Boot Start     End Sectors Size Id Type
/dev/nvme0n2p1       2048 8390655 8388608   4G 83 Linux

Command (m for help): t      //更改分区ID
Selected partition 1       //默认显著磁盘的第一个分区；如果有多个分区可选，就需要手动选择分区
Hex code (type L to list all codes): 82      //输入分区编号82；可以使用 ‘l’查看看所有的分区ID
Changed type of partition 'Linux' to 'Linux swap / Solaris'.

Command (m for help): p     //查看分区列表 
Disk /dev/nvme0n2: 50 GiB, 53687091200 bytes, 104857600 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
Disklabel type: dos
Disk identifier: 0x8f03f9d8

Device         Boot Start     End Sectors Size Id Type
/dev/nvme0n2p1       2048 8390655 8388608   4G 82 Linux swap / Solaris       //id 为82 ;type 为 Linux swap

Command (m for help): w      //保存退出
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

格式化刚刚创建的磁盘分区

[root@localhost ~]# mkswap /dev/nvme0n2p1 
Setting up swapspace version 1, size = 4 GiB (4294963200 bytes)
no label, UUID=64bff483-41ba-4180-ae1c-eab2e1075c84

[root@localhost ~]# blkid /dev/nvme0n2p1 
/dev/nvme0n2p1: UUID="64bff483-41ba-4180-ae1c-eab2e1075c84" TYPE="swap" PARTUUID="8f03f9d8-01"

在/etc/fstab文件写入永久挂载（开机自动挂载）

//先查看一下SWAP分区的UUID
UUID="64bff483-41ba-4180-ae1c-eab2e1075c84"

 //在/etc/fstab文件写入内容
[root@localhost ~]# vim /etc/fstab 
..........
UUID="64bff483-41ba-4180-ae1c-eab2e1075c84"	swap	swap	defaults	0 0

挂载SWAP分区

 //手下查看一下SWAP分区情况
[root@localhost ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:          1.8Gi       204Mi       1.3Gi       8.0Mi       253Mi       1.4Gi
Swap:         2.0Gi          0B       2.0Gi

 //挂载SWAP分区
[root@localhost ~]# swapon /dev/nvme0n2p1 

 //查看挂载后的SWAP分区情况
[root@localhost ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:          1.8Gi       208Mi       1.3Gi       8.0Mi       253Mi       1.4Gi
Swap:         6.0Gi          0B       6.0Gi

卸载SWAP分区

 //查看SWAP分区情况
[root@localhost ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:          1.8Gi       208Mi       1.3Gi       8.0Mi       253Mi       1.4Gi
Swap:         6.0Gi          0B       6.0Gi

 //卸载SWAP分区
[root@localhost ~]# swapoff /dev/nvme0n2p1 

 //查看卸载后SWAP分区情况
[root@localhost ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:          1.8Gi       204Mi       1.3Gi       8.0Mi       253Mi       1.4Gi
Swap:         2.0Gi          0B       2.0Gi

使用swapon -s 查看所有在使用交换分区

[root@localhost ~]# swapon -s
Filename				Type		Size	Used	Priority
/dev/dm-1                              	partition	2146300	0	-2
/dev/nvme0n2p1                         	partition	4194300	0	-3        //这是刚刚创建的交换分区