Swapsetup

swapsetup.sh

#!/bin/sh
set -e 

SWAPNAME="swapfile"
SWAPFILE="/var/swapfile.crypt"

MEMORY=`cat /proc/meminfo | grep MemTotal | sel -c 2`
# Next power of 2 Megabytes above reported memory
MEGABYTES=$(perl -e "use POSIX; print 2**ceil(log(ceil($MEMORY/(2**10)))/log(2))")

# status, on, or off
TYPE="$1"
if [ -z "$TYPE" ]; then
  TYPE="on"
fi

enabled_p() {
  SWAPS=$(sudo swapon -s | tail -n +2 | wc -l)
  if [ $SWAPS -gt "0" ]; then
    return 0;
  else
    return 1;
  fi
}

status() {
  # SWAPS=$(swapon -s | tail -n +2 | wc -l)
  if enabled_p; then
    swapon -s | tail -n +2 | sel -c 1 3 | xargs -n2 echo swap enabled
  else
    echo "swap disabled"
  fi
}

cleanup() {
  if [ -f /var/swap_loops ]; then
    for loop_i in $(sudo cat /var/swap_loops); do
      if sudo losetup "$loop_i" >/dev/null 2>&1; then
        echo removing loopback $loop_i
        sudo losetup -d "$loop_i"
      fi
    done
    sudo rm /var/swap_loops
  fi
  if sh -c "sudo cryptsetup status $SWAPNAME >/dev/null 2>&1"; then
    echo closing crypto $SWAPNAME
    sudo cryptsetup close $SWAPNAME
  fi
}

make_swapfile() {
  echo "creating a swap of size ${MEGABYTES}mB"
  sudo dd if=/dev/zero of=$SWAPFILE bs=1M count=$MEGABYTES
}

ensure_swapfile() {
  if [ -f $SWAPFILE ]; then
    SIZE=$(ls -l $SWAPFILE | sel -c 5)
    MBACT=$(perl -e "use POSIX; print floor($SIZE/1048576)")
    if [ "$MBACT" -lt "$MEGABYTES" ]; then
      make_swapfile
    fi
  else
    make_swapfile
  fi
  sudo chmod 600 $SWAPFILE
}

# run main operations
if [ "$TYPE" = "status" ]; then
  status
elif [ "$TYPE" = "on" ]; then
  if enabled_p; then
    status
  else 
    cleanup
    ensure_swapfile
    LOOP=$(sudo losetup -f)
    echo using loopback device $LOOP
    sudo sh -c "echo $LOOP >> /var/swap_loops"
    sudo losetup $LOOP $SWAPFILE
    echo setting up crypto
    sudo cryptsetup open --type plain --key-file /dev/urandom $LOOP $SWAPNAME
    echo mkswap on /dev/mapper/$SWAPNAME
    sudo mkswap -f /dev/mapper/$SWAPNAME
    echo swapon on /dev/mapper/$SWAPNAME
    sudo swapon /dev/mapper/$SWAPNAME
    status
  fi
elif [ "$TYPE" = "off" ]; then
  for swap_i in $(swapon -s | tail -n +2 | sel -c 1); do
    echo swapoff on $swap_i
    sudo swapoff $swap_i
  done
  cleanup
  status
fi