linux系统中添加交换分区

什么是交换分区？

SWAP（交换）分区是一种通过在硬盘中预先划分一定的空间，然后把内存中暂时不常用的数据临时存放到硬盘中，以便腾出物理内存空间让更活跃的程序服务来使用的技术，其设计的目的是为了解决真实物理内存不足的问题。但由于交换分区毕竟是通过硬盘设备读写数据的，速度肯定比物理内存慢，所以只有当真实的物理内存耗尽后才会调用交换分区的资源。

交换分区能够划分多大？

在生产环境中，交换分区的大小一般为真实物理内存的1.5-2倍。

1、对/dev/sdb添加一个磁盘分区

[root@PC1linuxprobe dev]# fdisk /dev/sdb
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): p

Disk /dev/sdb: 21.5 GB, 21474836480 bytes, 41943040 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: 0xe287b3a9

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     4196351     2097152   83  Linux

Command (m for help): n
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p): p
Partition number (2-4, default 2): 2
First sector (4196352-41943039, default 4196352): ## 此处回车
Using default value 4196352
Last sector, +sectors or +size{K,M,G} (4196352-41943039, default 41943039): +5G
Partition 2 of type Linux and of size 5 GiB is set

Command (m for help): p

Disk /dev/sdb: 21.5 GB, 21474836480 bytes, 41943040 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: 0xe287b3a9

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     4196351     2097152   83  Linux
/dev/sdb2         4196352    14682111     5242880   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.

2、查看添加的磁盘分区

[root@PC1linuxprobe dev]# find sd*
sda
sda1
sda2
sdb
sdb1
[root@PC1linuxprobe dev]# partprobe 
Warning: Unable to open /dev/sr0 read-write (Read-only file system).  /dev/sr0 has been opened read-only.
Warning: Unable to open /dev/sr0 read-write (Read-only file system).  /dev/sr0 has been opened read-only.
Warning: Unable to open /dev/sr0 read-write (Read-only file system).  /dev/sr0 has been opened read-only.
[root@PC1linuxprobe dev]# find sd*
sda
sda1
sda2
sdb
sdb1
sdb2

3、对磁盘分区进行交换分区格式化

[root@PC1linuxprobe dev]# mkswap /dev/sdb2
Setting up swapspace version 1, size = 5242876 KiB
no label, UUID=208a06d0-30e7-473a-b90a-bf920bf545a8

4、挂载

[root@PC1linuxprobe dev]# free -h
             total       used       free     shared    buffers     cached
Mem:          1.9G       1.1G       859M        10M       1.7M       293M
-/+ buffers/cache:       833M       1.1G
Swap:         2.0G         0B       2.0G
[root@PC1linuxprobe dev]# swapon /dev/sdb2
[root@PC1linuxprobe dev]# free -h
             total       used       free     shared    buffers     cached
Mem:          1.9G       1.1G       855M        10M       1.7M       293M
-/+ buffers/cache:       837M       1.1G
Swap:         7.0G         0B       7.0G

5、设为开机自动挂载

[root@PC1linuxprobe dev]# cat /etc/fstab 

#
# /etc/fstab
# Created by anaconda on Thu Nov  5 15:23:01 2020
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/rhel-root   /                       xfs     defaults        1 1
UUID=0ba20ae9-dd51-459f-ac48-7f7e81385eb8 /boot                   xfs     defaults        1 2
/dev/mapper/rhel-swap   swap                    swap    defaults        0 0
/dev/sdb1    /devide    xfs    defaults    0    0
[root@PC1linuxprobe dev]# echo -e "/dev/sdb\tswap\tswap\tdefaults\t0\t0" >> /etc/fstab 
[root@PC1linuxprobe dev]# cat /etc/fstab 

#
# /etc/fstab
# Created by anaconda on Thu Nov  5 15:23:01 2020
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/rhel-root   /                       xfs     defaults        1 1
UUID=0ba20ae9-dd51-459f-ac48-7f7e81385eb8 /boot                   xfs     defaults        1 2
/dev/mapper/rhel-swap   swap                    swap    defaults        0 0
/dev/sdb1    /devide    xfs    defaults    0    0
/dev/sdb    swap    swap    defaults    0    0