First step is to create empty file (I’ll create 1GB one). You can do that by issuing one of the following commands (you’ll need to be root):

fallocate -l 1G /swapfile


dd if=/dev/zero of=/swapfile bs=1M count=1024

After that change permissions on that file so nobody else can read it:

chmod 600 /swapfile

Make swap:

mkswap /swapfile

And at last, activate it:

swapon /swapfile

If you want your system to mount that swap automatically on boot you should add following entry to your /etc/fstab file:

/swapfile    swap    swap    defaults    0 0