enable-swap.sh

#!/bin/bash

##
# Usage
# # enable-swap.sh 1024M
##

SWAPFILE="/swapfile.swp"
SWAPSIZE=$1

die () {
    RED='\033[0;31m'
    NC='\033[0m'
    echo -e >&2 "${RED}$@${NC}\n"
    exit 1
}

[ "$(id -u)" -eq "0" ] || die "This script must be run as root"

[ "$#" -eq 1 ] || die "Swap size parameter required, $# argument provided"

echo $1 | grep -E -q '^[0-9]+(B|K|M|G|T)$' || die "Swap size should look like 1024M or 2G, $1 is WRONG"

[ ! -f $SWAPFILE ] || die "Swap file exists, disable swap first"

free | grep -E -q "^Swap:[[:blank:]]*0"
[ $? -eq 0 ] || die "Swap is already enabled."

fallocate -l "$SWAPSIZE" $SWAPFILE
[ $? -eq 0 ] || die "Unable to fallocate $SWAPFILE"

chmod 600 $SWAPFILE
[ $? -eq 0 ] || die "Unable to chmod 600 $SWAPFILE"

mkswap $SWAPFILE
[ $? -eq 0 ] || die "Unable to mkswap $SWAPFILE"

swapon $SWAPFILE
[ $? -eq 0 ] || die "Unable to swapon $SWAPFILE"

echo "$SWAPFILE none swap sw 0 0" | tee -a /etc/fstab
[ $? -eq 0 ] || die "Unable to write to fstab $SWAPFILE"

sysctl vm.swappiness=10
[ $? -eq 0 ] || die "Unable to adjust swappiness $SWAPFILE"