What is swap?
Swap space is the area on a hard disk which is part of the Virtual memory of your machine, which is a combination of accessible physical memory (RAM) and the swap space. Swap space temporarily holds memory pages that are inactive. Swap space is used when your system decides that it needs physical memory for active processes and there is insufficient unused physical memory available. If the system happens to need more memory resources or space, inactive pages in physical memory are then moved to the swap space therefore freeing up that physical memory for other uses. Note that the access time for swap is slower therefore do not consider it to be a complete replacement for the physical memory. Swap space can be a dedicated swap partition (recommended), a swap file, or a combination of swap partitions and swap files.
Create the Swap File on Ubuntu 12.04
1) Using the dd command
sudo dd if=/dev/zero of=/swapfile bs=1024 count=256k
2) Prepare the swap file by creating a linux swap area:
sudo mkswap /swapfile
3) The results display:
Setting up swapspace version 1, size = 262140 KiB no label, UUID=103c4545-5fc5-47f3-a8b3-dfbdb64fd7eb
4) Activating the swap file:
sudo swapon /swapfile