Swap

 swapon --show
 swapoff /swapfile
 sudo fallocate -l 4G /swapfile
 sudo fallocate -l 8G /swapfile
 sudo dd if=/dev/zero of=/swapfile bs=1024 count=4194304
 sudo chmod 600 /swapfile
 sudo mkswap /swapfile
 sudo swapon /swapfile

 # /etc/fstab
 /swapfile swap swap defaults 0 0

 sudo swapon --show
 sudo free -h

 cat /proc/sys/vm/swappiness
 sudo sysctl vm.swappiness=10

 sudo swapoff -v /swapfile
 # and remove the entry from /etc/fstab
 sudo rm /swapfile