Ubuntu 14.04 Encrypted Swapfile Setup
In the installed system, first make a swap container. N is the size you want in megabytes and if you've got 4GB or more of memory and you're not working on a server, then a minimum swap size of half your system's RAM is realistically sufficient. Below 4GB, a swap size of 75 to 100 percent of the RAM available is good.
sudo dd if=/dev/urandom of=/swapfile bs=1M count=N
Then make the actual swap filesystem and restrict its permissions so that only the root user can read and write to it.
sudo mkswap /swapfile sudo chmod 0600 /swapfile
Add it to fstab.
/swapfile none swap sw 0 0
And last, switch it on. No reboot necessary.
sudo swapon /swapfile