CentOS7的swap分區管理（分區或文件）

CentOS7的swap分區管理（分區或文件）
1、swap可以在安裝操作系統的時候劃分單獨分區創建；也可以安裝好操作系統后劃分剩余硬盤創建；還可以創建一個文件當swap分區使用

2、建議創建一個新的分區當swap使用，如果想使用一個文件當swap分區用的話最好將文件放在固態硬盤上，使用文件充當swap的話可以隨意變大變小，移動也方便，但性能不如分區好

創建分區來劃分swap
一、使用free -h查看當前swap

當前系統有4G的swap空間

[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顯示當前系統的swap

[root@centos7 ~]# swapon -s
Filename Type Size Used Priority
/dev/dm-0 partition 419430012676 -2
二、使用lsblk查看當前系統的硬盤

可以看到，sda總共200G，現在才劃分了150多G，還有可以用的空間

[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對/dev/sda硬盤進行創建分區操作

[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 (35072896-419430399, 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、執行兩下partprobe(CentOS6執行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、創建文件系統

[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、寫入/etc/fstab，并mount -a測試

[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

被掛載的設備名 掛載點 文件系統類型 掛載選項 轉儲頻率 系統自檢選項

[root@centos7 ~]# mount -a
七、swapon -a

此時執行free -h，swap分區還沒顯示出來，執行swapon -a，啟用所有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

執行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、卸載這個swap

使用swapoff關閉/dev/sda6這個swap分區

[root@centos7 ~]# swapoff /dev/sda6

使用sed刪除fstab最后加的一行

[root@centos7 ~]# sed -ri '$d' /etc/fstab

mount -a

[root@centos7 ~]# mount -a

此時swap已變成原來的4G

創建一個文件充當swap分區
一、使用dd命令創建一個文件100M，當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文件權限修改為600，安全

[root@centos7 data]# chmod 600 swapfile
二、對該文件創建文件系統

[root@centos7 data]# mkswap swapfile
Setting up swapspace version 1, size = 102396 KiB
no label, UUID=a16538e7-685e-4141-aaeb-e1b7896cffdf
三、寫入/etc/fstab,掛載（這里要注意，掛載設備不能寫UUID，只能寫文件名）

[root@centos7 data]# tail -1 /etc/fstab
/data/swapfile swap swap defaults 0 0
[root@centos7 data]# mount -a
四、執行swapon -a 開啟所有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，需要先取消掛載

必須先卸載，不然報錯了

[root@centos7 data]# dd if=/dev/zero of=/data/swapfile bs=1M count=200
dd: failed to open ‘/data/swapfile’: Text file busy

卸載

[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

創建文件系統

[root@centos7 data]# mkswap swapfile
Setting up swapspace version 1, size = 204796 KiB
no label, UUID=79d0f287-c998-42d3-aabc-b3b2d60b9cb2

執行swapon -a啟用所有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、卸載

取消掛載

[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