# Linux Swap 启停及swappiness设置
Date: 2020-06-21


#### **生成swap分区**

可以通过磁盘分区和文件两种方式进行操作

##### 1\. 通过磁盘分区

- 划出一块4G磁盘**fdisk /dev/sdb**
    
    > sdb磁盘对应的文件
    

```C
[root@centosgpt ~]# fdisk /dev/sdb
Command (m for help): n
Partition number (1-128, default 1):
First sector (34-41943006, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-41943006, default 41943006): +4G
Created partition 1
...
Command (m for help): p
...
#         Start          End    Size  Type            Name
 1         2048      8390655      4G  Linux filesyste
 ..
Command (m for help): w
The partition table has been altered!

```

- 创建分区**mkswap /dev/sdb1**
    
    > sdb1对应分区
    

```C
[root@centosgpt ~]# mkswap /dev/sdb1
Setting up swapspace version 1, size = 1020 KiB
no label, UUID=5dabc5b1-d763-4757-9e0c-383f0cacb0ea

```

##### 2\. 通过文件生成

- 生成文件**dd if=/dev/zero of=/swap bs=1MB count=1024**
    
    > bs 以1M为单位, count多少个1MB块
    

```C
[root@centosgpt ~]# dd if=/dev/zero of=/swap bs=1MB count=1024
1024+0 records in
1024+0 records out
1024000000 bytes (1.0 GB) copied, 1.36373 s, 751 MB/s

```

- 赋予权限**chown root:root /swap** **chmod 600 /swap**

```c
[root@centosgpt ~]# chown root:root /swap
[root@centosgpt ~]# chmod 600 /swap
```

- 创建分区 **mkswap -L swap /swap**

```C
[root@centosgpt ~]# mkswap -L swap /swap
Setting up swapspace version 1, size = 999996 KiB
LABEL=swap, UUID=e382380e-c729-40e6-bf3b-823d5cd9b55f
```

##### 3\. 通过LVM2创建

```
1. Create the LVM2 logical volume of size 2 GB:
# lvcreate VolGroup00 -n LogVol02 -L 2G
2. Format the new swap space:
# mkswap /dev/VolGroup00/LogVol02
```

> #### https://access.redhat.com/documentation/en-us/red\_hat\_enterprise\_linux/7/html/storage\_administration\_guide/ch-swapspace

#### 开启关闭swap分区

##### 1.开启分区

**swapon -s**

```C
[root@centosgpt ~]# swapon -s
Filename                                Type            Size    Used    Priority
/dev/dm-1                               partition       4194300 0       -2
[root@centosgpt ~]# swapon /dev/sdb1
[root@centosgpt ~]# swapon -s
Filename                                Type            Size    Used    Priority
/dev/dm-1                               partition       4194300 0       -2
/dev/sdb1                               partition       1020    0       -3
```

##### 2 永久生效

**/etc/fstab**

```C
[root@centosgpt ~]# cat /etc/fstab |grep swap
/dev/mapper/centos-swap swap    swap    defaults        0 0
/dev/sdb1 none swap sw 0 0
```

##### 3.关闭分区

**swapoff**

```C
[root@centosgpt ~]# swapon
NAME      TYPE        SIZE USED PRIO
/swap     file      976.6M   0B   -2
/dev/sdb1 partition  1020K   0B   -3
/dev/dm-1 partition     4G   0B   -4
[root@centosgpt ~]# swapoff /swap
[root@centosgpt ~]# swapon
NAME      TYPE       SIZE USED PRIO
/dev/sdb1 partition 1020K   0B   -2
/dev/dm-1 partition    4G   0B   -3
[root@centosgpt ~]# swapoff /dev/sdb1
[root@centosgpt ~]# swapon
NAME      TYPE      SIZE USED PRIO
/dev/dm-1 partition   4G   0B   -2
```

#### swappiness参数

swappiness参数指导如何使用swap分区, 值越小越偏向使用物理内存， 越大越趋向使用swap分区.

##### 1\. 查看

```C
[root@centosgpt ~]# sysctl -n vm.swappiness
30
```

```C
cat /proc/sys/vm/swappiness
```

##### 1\. 临时调整

```C
sysctl vm.swappiness=40
```

##### 2\. 永久调整

```C
/etc/sysctl.conf
vm.swappiness = 10
sysctl -p 
```

### 参考引用

[Linux交换空间（swap space）的那些优缺点](https://yq.aliyun.com/articles/194733) [Linux 创建交换（swap）分区](http://kuanghy.github.io/2019/11/16/linux-swap)