This script will automate the process of creating a swap file, ensuring that it is run with the necessary permissions and handling user input effectively.

create_swap.sh

#!/bin/bash

# Ensure the script is run as root
if [ "$EUID" -ne 0 ]; then
    echo "Please run as root (use sudo)."
    exit 1
fi

# Function to create or resize the swap file
create_swap() {
    local size=$1

    # Disable current swap
    swapoff -a

    # Create or resize the swap file
    fallocate -l "${size}" /swapfile

    # Set correct permissions
    chmod 600 /swapfile

    # Set up the swap file
    mkswap /swapfile

    # Enable the swap file
    swapon /swapfile

    # Verify the swap
    echo "Swap file created and enabled. Current swap status:"
    free -h
}

# Check if the swap file already exists
if [ -f /swapfile ]; then
    current_size=$(du -h /swapfile | cut -f1)
    echo "The swap file already exists with a size of: $current_size"
    read -p "Do you want to resize the swap file? (yes/no): " confirm
    confirm=${confirm,,}  # Convert to lowercase
    if [[ "$confirm" != "yes" && "$confirm" != "y" ]]; then
        echo "Operation canceled."
        exit 0
    fi

    # Prompt for the new size if the user wants to overwrite
    while true; do
        read -p "What size would you like the new swap file? (In Gigabytes): " size
        size=${size^^}  # Convert to uppercase
        if [[ "$size" =~ ^[0-9]+G$ ]]; then
            create_swap "$size"
            break
        else
            echo "Invalid input. Please enter a number followed by 'G' (e.g., 5G)."
        fi
    done
else
    # Prompt the user for the size of the swap file
    while true; do
        read -p "What size would you like the swap file? (In Gigabytes): " size
        size=${size^^}  # Convert to uppercase
        if [[ "$size" =~ ^[0-9]+G$ ]]; then
            create_swap "$size"
            break
        else
            echo "Invalid input. Please enter a number followed by 'G' (e.g., 5G)."
        fi
    done
    # Make the change permanent
    echo "/swapfile none swap sw 0 0" >> /etc/fstab
    exit 0
fi

# If the swap file exists, resize it
create_swap "$size"