Create an ad-hoc swap file for AWS nano / micro servers

make-fake-swap-file.sh

#!/bin/bash -ue

####################
# For small AWS EC2 instances that have no swap space by default.
# A tiny, slow swap file may be preferable to having the server's OOM killer shutting down processes.
# A real swap on ephemeral storage is better, but this will do in a pinch. 
# The disadvantage is that if a server starts using swap, it will burn through it's EBS disk burst credits very quickly. 
# Works on Ubuntu 14,16,18, LTS. Not tested on any other platform.
####################


SWAP_FILE="/swapfile"

function main () {
  test -e "$SWAP_FILE" && {
    echo "Swap file already exists."
    exit 0
  }
  grep swap /etc/fstab && {
    echo "Not running because I found the word 'swap' in /etc/fstab."
    exit 1
  }

  set -x
  dd if=/dev/zero of="$SWAP_FILE" bs=1M count=1024
  chmod 600 "$SWAP_FILE"
  mkswap "$SWAP_FILE"
  swapon "$SWAP_FILE"
  echo "$SWAP_FILE swap swap defaults 0 0" >> /etc/fstab
  
}

main

Not working on OpenVZ

@SalimF it wasn't designed for or tested on OpenVZ. I've updated the header to include where the script works.

See also:
https://www.softwaretestinghelp.com/how-to-write-good-bug-report/