• Bash
  • mkfswap.sh

    Swap file. Good for VM that has no Swap assigned.

---

wget -q https://kps.makz.net/run/mkfswap.sh -O - | bash

#!/bin/bash
#
# Create and enable a swap file.
#
set -euo pipefail

readonly SWAPFILE="/swapfile"
readonly SIZE_GB="${1:-2}"
readonly FSTAB_LINE="${SWAPFILE} none swap sw 0 0"

die()  { echo "Error: $*" >&2; exit 1; }
info() { echo "$*"; }

# ---------- preflight ----------
[[ $EUID -eq 0 ]] || die "Must be run as root."
[[ "$SIZE_GB" =~ ^[0-9]+$ ]] && (( SIZE_GB > 0 )) \
    || die "Size must be a positive integer (GB). Got: $SIZE_GB"

if [[ -e "$SWAPFILE" ]]; then
    info "Swap file ${SWAPFILE} already exists."
    swapon --show
    exit 0
fi

# ---------- free-space check ----------
# Need SIZE_GB * 1024 * 1024 KiB free on the target filesystem.
need_kib=$(( SIZE_GB * 1024 * 1024 ))
avail_kib=$(df -Pk -- "$(dirname "$SWAPFILE")" | awk 'NR==2 {print $4}')
(( avail_kib >= need_kib )) \
    || die "Not enough free space: need ${need_kib} KiB, have ${avail_kib} KiB."

# ---------- create ----------
info "Allocating ${SIZE_GB}G at ${SWAPFILE}..."
if command -v fallocate >/dev/null && fallocate -l "${SIZE_GB}G" "$SWAPFILE" 2>/dev/null; then
    :  # fast path on ext4/xfs/btrfs
else
    # Fallback for filesystems where fallocate is unsupported (e.g. some tmpfs/zfs setups).
    rm -f "$SWAPFILE"
    dd if=/dev/zero of="$SWAPFILE" bs=1M count="$(( SIZE_GB * 1024 ))" status=progress
fi

chmod 600 "$SWAPFILE"
mkswap "$SWAPFILE"
swapon "$SWAPFILE"

# ---------- persist in fstab ----------
if grep -qE "^[[:space:]]*${SWAPFILE}[[:space:]]" /etc/fstab; then
    info "fstab entry for ${SWAPFILE} already present."
else
    info "Adding fstab entry: ${FSTAB_LINE}"
    printf '%s\n' "$FSTAB_LINE" >> /etc/fstab
fi

swapon --show --bytes
info "Done."