Creating a Swap file and making it permanent (tested in Ubuntu 14.04)

This creates a 2 GB Swap file. You can change this in the first line and write 4G instead of 2G for a 4 GB Swap for example.

sudo fallocate -l 2G /swapfile

sudo chmod 600 /swapfile

sudo mkswap /swapfile

sudo swapon /swapfile

sudo nano /etc/fstab    ->   add at bottom: /swapfile   none    swap    sw    0   0