Add swap memory on Ubuntu

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

Check that the swap file is active:

sudo swapon --show
free -h

To enable it after reboot, add it to /etc/fstab:

/swapfile none swap sw 0 0

To remove it later:

sudo swapoff /swapfile
sudo rm /swapfile