http://blog.sina.com.cn/s/blog_6e4388910100tsk7.html
Swap is generally in a dedicated swap area, which may be because the system prompts you to create a swap area during installation. But in fact any file can be used as swap ( swap device ) , be it a partition or a simple file. Nevertheless, for better experience and sensing speed, it is recommended to use a large amount of memory instead of relying on swap . Swap can be increased by adding a swap file
four steps
1) Create a file of your preset size.
2) Format the file as swap ( swap device ) .
3) Add swap to the existing system.
4) Make a permanent change in the system.
Example: To add a 512M swap
Create a 512M file
We will create a swap file at /mnt/512Mb.swap .
sudo dd if=/dev/zero of=/mnt/512Mb.swap bs=1M count=512
The count=512 in the code means that we want to create a file that contains 512 blocks of bs=1M (bs = block size ; 1M = 1mebibyte = 1048576 bytes ) . Be careful not to use the command dd of=/mnt/512Mb.swap bs=1M seek=512 count=0 . Although the file will immediately grow to 512Mb , this is buggy and may render it unusable.
Format the file to make it swap ( swap device ):
sudo mkswap /mnt/512Mb.swap
Activate swap to an existing system now :
sudo swapon /mnt/512Mb.swap
Now the new swap can be seen by " cat /proc/meminfo " command.
Make permanent changes :
Edit the /etc/fstab file :
gksudo gedit /etc/fstab
Add the following line to the end of the file :
/mnt/512Mb.swap none swap sw 0 0
Save and restart.