Here are a few commands I have in my notes for adding swap memory on low resource Linux servers. I've used these on low end VPS's like the cheaper offerings by Amazon Lightsail.
sudo dd if=/dev/zero of=/swapfile bs=1M count=6114
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo echo '/swapfile swap swap defaults 0 0' | sudo tee --append /etc/fstab
sudo swapon -a