Function to create and configure swap file on Linux. Useful on VPS' and the like where images normally don't come configured with swap by default.

add_swapfile.sh

#! /bin/bash

test "$(id -u)" -eq 0 || exit 1

# Create and configurat swapfile
create_add_swapfile() {
  test -z $1 && return 1

  local size=$(echo ${1} | grep -o -E '^[0-9]*')
  local unit=$(echo ${1} | grep -o -E '[^0-9](.*)?$' || echo M)
  local file="/swapfile.${size}${unit}"

  if [[ -f "$file" ]]; then
    echo "Error: File exists: ${file}" >&2
    return 1
  fi

  # Create the actual file
  fallocate -l "${size}${unit}" "${file}"
  chmod 0600 "${file}"
  chown root:root "${file}"
  mkswap "${file}"
  swapon "${file}"

  # Comment out existing entry in /etc/fstab
  sed -i -e "/^\\${file}/s/^/#/" /etc/fstab
  printf "%s\tnone\tswap\tdefaults\t0 0\n" ${file} >> /etc/fstab
}


grep -q -E '^SwapTotal: * 0 kB' /proc/meminfo
test $? -eq 0 \
  && create_add_swapfile 1024MiB

exit $?