#!/bin/bash
###############
# DESCRIPTION: configure swappiness to 0 (= only swap when no memory is free)
###############
set -euo pipefail

PRECONFIG=$( ( grep -P '^[ \t]*vm.swappiness[ \t]*=' /etc/sysctl.conf || : ) |sed -r 's/.+=[ \t]*//g')
PREACTIVE=$(cat /proc/sys/vm/swappiness)

if [[ -z "${PRECONFIG+x}" ]] || [[ -z "${PRECONFIG// }" ]]; then
	PRECONFIG="unconfigured"
	echo 'vm.swappiness=0' >> /etc/sysctl.conf
	printf "/etc/sysctl.conf: 'vm.swappiness' changed from $PRECONFIG to 0.\n"
elif [[ -n "${PRECONFIG##*[!0-9]*}" ]]; then
	if [[ $PRECONFIG -ne 0 ]]; then
		sed -i 's/^[ \t]*vm.swappiness[ \t]*=.*$/vm.swappiness=0/g' /etc/sysctl.conf
		printf "/etc/sysctl.conf: 'vm.swappiness' changed from $PRECONFIG to 0.\n"
	else
		printf "/etc/sysctl.conf: 'vm.swappiness' already set to 0.\n"
	fi
else
	sed -i 's/^[ \t]*vm.swappiness[ \t]*=.*$/vm.swappiness=0/g' /etc/sysctl.conf
	printf "/etc/sysctl.conf: 'vm.swappiness' set to non numerical value \"$PRECONFIG\". Changed to 0.\n"
fi

if [[ -z "${PREACTIVE+x}" ]] || [[ -z "${PREACTIVE// }" ]]; then
	PREACTIVE="unconfigured"
	echo '0' >> /proc/sys/vm/swappiness
	printf "/proc/sys/vm/swappiness: changed from $PREACTIVE to 0.\n"
elif [[ -n "${PREACTIVE##*[!0-9]*}" ]]; then
	if [[ $PREACTIVE -ne 0 ]]; then
		echo '0' >> /proc/sys/vm/swappiness
		printf "/proc/sys/vm/swappiness: changed from $PREACTIVE to 0.\n"
	else
		printf "/proc/sys/vm/swappiness: already set to 0.\n"
	fi
else
	echo '0' >> /proc/sys/vm/swappiness
	printf "/etc/sysctl.conf: set to non numerical value \"$PREACTIVE\". Changed to 0.\n"
fi