setup-swap.sh

#!/usr/bin/env bash
# ---------------------------------------------------------------------------
#
# RUN THIS SCRIPT VIA: setup-swap.sh, THIS SCRIPT IS USED BY setup-swap.sh
# READ THE NOTES AND DISCLAIMER WITHIN setup-swap.sh BEFORE RUNNING!
#

#remove disable swap, remove it and remove entry from fstab
removeSwap() {
    echo "Will remove swap and backup fstab."
    echo ""

    #get the date time to help the scripts
    backupTime=$(date +%y-%m-%d--%H-%M-%S)

    #get the swapfile name
    swapSpace=$(swapon -s | tail -1 |  awk '{print $1}' | cut -d '/' -f 2)
    #debug: echo $swapSpace

    #turn off swapping
    swapoff "/$swapSpace"

    #make backup of fstab
    cp /etc/fstab /etc/fstab."$backupTime"

    #remove swap space entry from fstab
    sed -i "/swap/d" /etc/fstab

    #remove swapfile
    rm -f "/$swapSpace"

    echo ""
    echo "--> Done"
    echo ""
}

#spinner by: https://www.shellscript.sh/tips/spinner/
setupSwapSpinner() {
  spinner="/|\\-/|\\-"
  while :
  do
    for i in $(seq 0 7)
    do
      echo -n "${spinner:$i:1}"
      echo -en "\010"
      sleep 1
    done
  done
}


#identifies available ram, calculate swap file size and configure
createSwap() {
    echo "Will create a swap and setup fstab."
    echo ""

    #get available physical ram
    availMemMb=$(grep MemTotal /proc/meminfo | awk '{print $2}')
    #debug: echo $availMemMb

    #convert from kb to mb to gb
    gb=$(awk "BEGIN {print $availMemMb/1024/1024}")
    #debug: echo $gb

    #round the number to nearest gb
    gb=$(echo "$gb" | awk '{print ($0-int($0)<0.499)?int($0):int($0)+1}')
    #debug: echo $gb

    echo "-> Available Physical RAM: $gb Gb"
    echo ""
    if [ "$gb" -eq 0 ]; then
        echo "Something went wrong! Memory cannot be 0!"
        exit 1;
    fi

    if [ "$gb" -le 2 ]; then
        echo "   Memory is less than or equal to 2 Gb"
        let swapSizeGb=$gb*2
        echo "   -> Set swap size to $swapSizeGb Gb"
    fi
    if [ "$gb" -gt 2 -a "$gb" -lt 32 ]; then
        echo "   Memory is more than 2 Gb and less than to 32 Gb."
        let swapSizeGb=4+$gb-2
        echo "   -> Set swap size to $swapSizeGb Gb."
    fi
    if [ "$gb" -gt 32 ]; then
        echo "   Memory is more than or equal to 32 Gb."
        let swapSizeGb=$gb
        echo "   -> Set swap size to $swapSizeGb Gb."
    fi
    echo ""

    echo "Creating the swap file! This may take a few minutes."
    echo ""

    #implement swap file

    #start the spinner:
    setupSwapSpinner &

    #make a note of its Process ID (PID):
    SPIN_PID=$!

    #kill the spinner on any signal, including our own exit.
    trap "kill -9 $SPIN_PID" $(seq 0 15)

    #convert gb to mb to avoid error: dd-memory-exhausted-by-input-buffer-of-size-bytes
    let mb=$gb*1024

    #create swap file on root system and set file size to mb variable
    echo "-> Create swap file."
    echo ""
    dd if=/dev/zero of=/swapfile bs=1M count=$mb

    #set read and write permissions
    echo "-> Set swap file permissions."
    echo ""
    chmod 600 /swapfile

    #create swap area
    echo "-> Create swap area."
    echo ""
    mkswap /swapfile

    #enable swap file for use
    echo "-> Turn on swap."
    echo ""
    swapon /swapfile

    echo ""

    #update the fstab
    if grep -q "swap" /etc/fstab; then
        echo "-> The fstab contains a swap entry."
        #do nothing
    else
        echo "-> The fstab does not contain a swap entry. Adding an entry."
        echo "/swapfile swap swap defaults 0 0" >> /etc/fstab
    fi

    echo ""
    echo "--> Done"
    echo ""

    exit 1
}

#the main function that is run by the calling script.
function setupSwapMain() {
    #check if swap is on
    isSwapOn=$(swapon -s | tail -1)

    if [[ "$isSwapOn" == "" ]]; then
        echo "No swap has been configured! Will create."
        echo ""

        createSwap
    else
        echo "Swap has been configured. Will remove and then re-create the swap."
        echo ""

        removeSwap
        createSwap
    fi

    echo "Setup swap complete! Check output to confirm everything is good."
}

# ---------------------------------------------------------------------------
#
# This script will create swap file if the swap file does not exist.
# It will disable the swap file and re-create it if it does exist.
#
# Re-create the swap to adjust the size when you change AWS instance types.
#
# Based on advice from:
# https://aws.amazon.com/premiumsupport/knowledge-center/ec2-memory-swap-file/
#
# USE THIS SCRIPT AT YOUR OWN RISK AND STUDY THE CODE CAREFULLY.
#
# For usage, login as root, run "./setupSwap.sh"
#
# Note the following assumptions:
# - you have enough disk-space for the new swap
#   - less than 2 Gb RAM - swap size: 2x the amount of RAM
#   - more than 2 GB RAM, but less than 32 GB - swap size: 4 GB + (RAM – 2 GB)
#   - 32 GB of RAM or more - swap size: 1x the amount of RAM
# - you are running as root user
# - your swap file is called: swapfile
#
# Revision history:
# 2019-04-15 Created (v0.1)
# 2019-04-15 Read total physical memory using /proc/meminfo instead
#
# Tested on:
# - Ubuntu Server 18.04 (On-Premise and Cloud (AWS)) - 2019-04-15
# - Amazon Linux 2 Cloud (AWS) - 2019-04-15
#
# DISCLAIMER:
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License at <http://www.gnu.org/licenses/> for
# more details.

#main start

#check permissions
if [[ $EUID -ne 0 ]]; then
    echo ""
    echo "This script must be run as root! Login as root, sudo or su."
    echo ""
    exit 1;
fi


echo ""
echo "--------------------------------------------------------------------------"
echo "setupSwap - creates swap space on your server based on AWS guidelines"
echo "--------------------------------------------------------------------------"
echo ""
echo "This will remove an existing swap file and then create a new one. "
echo "Please read the disclaimer and review the code before proceeding."
echo ""

echo -n "Do you want to proceed? (y/n): "; read proceed
if [ "$proceed" == "y" ]; then
    echo ""

    setupSwapMain

else

    echo "You chose to exit. Bye!"

fi

echo ""
echo "--------------------------------------------------------------------------"
echo ""

exit 0