This is part of my complete guide to Setting up a CentOS Digital Ocean droplet with Nginx for beginners.

If you just need the commands, here they are. Read on for an explanation of what is happening.

sudo fallocate -l 1G /swapfile  
sudo chmod 600 /swapfile  
sudo mkswap /swapfile  
sudo swapon /swapfile  
sudo sh -c 'echo "/swapfile none swap sw 0 0" >> /etc/fstab'  

I am not going to bother repeating the excellent explanation of these commands from their source guide. If you are interested, check it out.