pmaports/main/postmarketos-base/rootfs-sbin-swapfile

#!/bin/sh
#################################################################################
# Copyright 2017 Clayton Craft <clayton@craftyguy.net>
#
# This file is part of postmarketos-base
#
# postmarketos-base 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.
#
# postmarketos-base 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 for more details.
# You should have received a copy of the GNU General Public License
# along with this postmarketos-base.  If not, see <http://www.gnu.org/licenses/>.
#################################################################################

# $1 = swap file location
function remove_old_swap() {
	local _swap_file=$1
	swapoff ${_swap_file} 2>/dev/null
	rm ${_swap_file}
	if [ -e ${_swap_file} ]; then
		echo "Unable to remove old swap file!"
		exit 1
	fi
}

# $1 = swap file location
# $2 = swap file size
function make_swap() {
	local _swap_file=$1
	local _swap_size=$2

	# Allocate space on disk for swap
	fallocate -l ${_swap_size}M ${_swap_file}

	# Set correct file permissions for swap file
	chown root:root ${_swap_file}
	chmod 600 ${_swap_file}

	#format swap file
	mkswap ${_swap_file} 1>/dev/null
}

if [ "$(id -u)" != "0" ]; then
	echo "This script can only be run as root"
	exit 1
fi

config=/etc/conf.d/swapfile
if [ ! -f ${config} ]; then
	echo "Unable to find config at: ${config}"
	exit 1
fi

# deviceinfo is a pmOS-specific thing, but it's not *required*
. /usr/share/misc/source_deviceinfo
source /etc/conf.d/swapfile

# Configure swap size. Size is in MB
# If size in config is unset then use value from deviceinfo,
# or default to 0 if neither is set
if [ -z "${swap_size}" ]; then
	if [ -n "${deviceinfo_swap_size_recommended}" ]; then
		swap_size=${deviceinfo_swap_size_recommended}
	else
		swap_size=0
	fi
fi

if [ "${swap_size}" == "0" ]; then
	echo "Configured swap file size is 0, skipping creation."
	exit 0
fi

swap_file="${swap_file:-/swapfile}"

echo "Setting up swap file of size ${swap_size}MB at ${swap_file}..."

# Clean up old swap file
if [ -f ${swap_file} ]; then
	remove_old_swap ${swap_file}
fi

# Create swap file
make_swap ${swap_file} ${swap_size}

# Activate swap file
swapon ${swap_file}

echo "Successfully activated swap file!"
exit 0