swapfile automation

swapper.sh

#!/bin/bash
# Swapfile generator
#
# Copyright 2019 Ismo Vuorinen <[email protected]>
# Licensed under MIT <https://opensource.org/licenses/MIT>

_err () {
    echo "(!) Error: $1" >&2; exit 1
}

# Check that the user is logged in as root
if [[ $(id -u) -ne 0 ]] ; then _err "Please run as root" ; fi

_command_exists () {
    type "$1" &> /dev/null;
}

# Check that our system has all the required commands available
required_applications=( "dd" "chown" "chmod" "swapon" "mkswap" )
for i in "${required_applications[@]}"
do
    if ! _command_exists "$i"; then
        _err "I require $i but it's not installed. Aborting."
    fi
done

# Get arguments
while getopts s:f: option
    do
    case "${option}"
    in
        s) SIZE=${OPTARG};;
        f) FILE=$OPTARG;;
        *) echo "$0 -s (Size in GB) -f (Full path to swap file)";;
    esac
done

# Check that the size given is a number
reSize='^[0-9]+$'
if ! [[ $SIZE =~ $reSize ]] ; then
   _err "Swap size (-s) was not a number! Aborting."
fi

# No filename was given, use default (/swapfile-YYYY-MM)
if [ -z "$FILE" ]; then
    FILE="/swapfile-$(date +%Y-%m)"
fi

# Check that we are not accidentally overriding anything
if [ -f "$FILE" ]; then
    _err "File $FILE already exists! Aborting."
fi

# Fix variables for commands
FILESIZE=$((SIZE*1024*1024))
FILE=$(realpath "$FILE")

# The filename is empty, how about that?
if ! [ "$FILE" ]; then
    _err "Something went wrong"
fi

SLASHES=$(echo "${FILE}" | awk -F"/" '{print NF-1}')

if ! [[ $SLASHES == 1 ]] ; then
    _err "You should use root path, not inside subfolders. (Slashes in $FILE = $SLASHES)"
fi

echo
echo "Changes about to be made:"
echo " -> Swap file: $FILE"
echo " -> Swap size: $SIZE GB ($FILESIZE bytes)"
echo " -> Change ownership to root:root and make it writable only to root"
echo " -> mkswap and swapon"
echo " -> Add it to /etc/fstab to persist the change across boots"
echo " -> List swapfiles present on the system"
echo

read -p "Continue and make changes? [y/N] " -n 1 -r
echo    # (optional) move to a new line
if [[ $REPLY =~ ^[Yy]$ ]]
then
    dd if=/dev/zero of="$FILE" bs=1024 count=$FILESIZE \
      && chown root:root "$FILE" \
      && chmod 0600 "$FILE" \
      && mkswap "$FILE" \
      && swapon "$FILE" \
      && echo "$FILE none swap sw 0 0" >> /etc/fstab \
      && swapon -s
fi