Swap file creation
As root use dd to create a swap file the size of your choosing (M = Megabytes, G = Gigabytes). For example, creating a 512 MB swap file:
# dd if=/dev/zero of=/swapfile bs=1M count=512
Set the right permissions
# chmod 600 /swapfile
After creating the correctly sized file, format it to swap:
# mkswap /swapfile
Activate the swap file:
# swapon /swapfile
Edit fstab to add an entry for the swap file:
# vim /etc/fstab
/swapfile swap swap defaults 0 0
Remove swap file
To remove a swap file, the current swap file must be turned off.
As root:
# swapoff -a
Remove swap file:
# rm -f /swapfile
Finally remove the relevant entry from /etc/fstab.