[root@sannian mnt]# dd if=/dev/zero of=/mnt/swapfile bs=1M count=20480
20480+0 records in
20480+0 records out
21474836480 bytes (21 GB) copied, 193.865 s, 111 MB/s

开机自挂载：

[root@sannian swap]# mkswap   swapfile
[root@sannian swap]# vim /etc/fstab 
/mnt/swap/swapfile   swap              swap        defaults        0 0

挂载

[root@sannian swap]# swapon  /mnt/swap/swapfile 
swapon: /mnt/swap/swapfile: insecure permissions 0644, 0600 suggested.

去除：

[root@sannian swap]# swapoff /mnt/swap/swapadd

查看是不事挂上去了？

[root@sannian swap]# free -m
              total        used        free      shared  buff/cache   available
Mem:           1839         196         999           0         642        1471
Swap:         20479           0       20479