Create swap on VPS

swap.sh

#!/usr/bin/env bash
#==============================================================================
# title: swap.sh
# description: This script automatically creates a swap size that's 20% of total RAM
# and comments out the old swap device in /etc/fstab.
# author: Kawin Viriyaprasopsook <[email protected]>
# usage: bash swap.sh
# notes: need `sudo dd sed` packages
#==============================================================================

# Exit immediately if a command exits with a non-zero status.
# Treat unset variables as an error when substituting.
# The exit status of a pipeline is the exit status of the last command that exited with a non-zero status,
# or zero if all commands in the pipeline exit successfully.
set -euo pipefail

# Determine if sudo is needed
SUDO=""
if [ "$(whoami)" != "root" ]; then
    if command -v sudo &>/dev/null; then
        SUDO="sudo"
    else
        echo "Error: This script requires root privileges or the 'sudo' command." >&2
        exit 1
    fi
fi

# Define constants
SWAP_FILE="/swapfile"
MIN_SWAP_MB=1024 # Minimum swap size in MB (1GB)

# Function to add or update a sysctl parameter
add_sysctl_param() {
    local param="$1"
    local value="$2"
    local description="$3"

    if grep -q "^${param}" /etc/sysctl.conf; then
        echo "Sysctl config for '${param}' already exists, skipping addition."
    else
        echo "${param} = ${value}" | ${SUDO} tee -a /etc/sysctl.conf >/dev/null
        echo "Added sysctl config: ${param} = ${value} (${description})"
    fi
}

echo "Starting swap file creation process..."

# Check and disable existing swap devices
if swapon -s | grep -q '/'; then
    echo "Existing swap devices detected. Disabling them now..."
    ${SUDO} swapoff -a
else
    echo "No active swap devices found. Proceeding..."
fi

# Get the amount of RAM in MB
ram_mb=$(free -m | awk '/Mem:/ {print $2}')
echo "Detected RAM: ${ram_mb} MB"

# Calculate the swap size in MB (20% of RAM), ensuring a minimum size
swap_mb=$((ram_mb / 5))
if [ "${swap_mb}" -lt "${MIN_SWAP_MB}" ]; then
    swap_mb="${MIN_SWAP_MB}"
    echo "Calculated swap size is less than ${MIN_SWAP_MB}MB. Setting to ${MIN_SWAP_MB}MB."
fi
echo "Calculated swap size: ${swap_mb} MB ($((swap_mb / 1024)) GB)"

# Create the swap file
echo "Creating swap file at ${SWAP_FILE}..."
${SUDO} dd if=/dev/zero of="${SWAP_FILE}" bs=1M count="${swap_mb}" status=none
${SUDO} chmod 0600 "${SWAP_FILE}"
echo "Swap file created and permissions set."

# Format the swap file
echo "Formatting ${SWAP_FILE} as swap..."
${SUDO} mkswap "${SWAP_FILE}"

# Enable the swap file
echo "Enabling the new swap file..."
${SUDO} swapon "${SWAP_FILE}"

# Comment out old swap config from fstab
echo "Commenting out old swap entries in /etc/fstab..."
# This sed command comments out any line containing the word 'swap'.
${SUDO} sed -i '/swap/s/^/#/' /etc/fstab

# Add the new swap file entry to /etc/fstab
echo "Adding new swap file entry to /etc/fstab..."
echo "${SWAP_FILE}	none	swap	sw	0	0" | ${SUDO} tee -a /etc/fstab >/dev/null

# Configure sysctl parameters for swap and inotify
echo "Configuring sysctl parameters..."
add_sysctl_param "vm.swappiness" "10" "Controls how often the system swaps"
add_sysctl_param "fs.inotify.max_user_watches" "524288" "Increases max watches for inotify (e.g., for IDEs)"

# Apply sysctl changes
echo "Applying sysctl changes..."
${SUDO} sysctl -p

echo "Swap file created and enabled successfully!"
echo "Current swap status:"
free -h

exit 0