Turn on swap on small virtual machines (e.g. letsencrypt command 'x86_64-linux-gnu-gcc' failed with exit status 4)

gistfile1.txt

Digitalocean, 512MB - need to turn on swap:

sudo dd if=/dev/zero of=/swapfile bs=1024 count=524288
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

Sources: https://community.letsencrypt.org/t/installation-via-letsencrypt-auto-fails-with-error-code-1/5919, http://stackoverflow.com/a/26762938