Bash script to create a swap file on Linux (debian/ubuntu)

create_swap.sh

#!/bin/bash

# Bash script to create a swap file on Linux (debian/ubuntu)
# Author: 	Mohamed Elashri
# Date:      2022-09-27

# use free -m to check the memory and see if there is enough memory (less than 2G) to create swap
# Logic is simple
# if there is no enough memory, then create swap
# if there is enough memory, delete swap

if [ $mem -lt 2048 ]
then
        if [ $swap -eq 0 ]
        then
                echo "Creating swap file of 4G"
                sudo fallocate -l 4G /swapfile
                sudo chmod 600 /swapfile
                sudo mkswap /swapfile
                sudo swapon /swapfile
                echo "/swapfile none swap sw 0 0" | sudo tee -a /etc/fstab
        else
                echo "There is already a swap file, do you want to delete it and create a new one of 4G? (y/n)"
                read ans
                if [ $ans == "y" ]
                then
                        echo "Deleting the old swap file"
                        sudo swapoff -a
                        sudo rm /swapfile
                        sudo fallocate -l 4G /swapfile
                        sudo chmod 600 /swapfile
                        sudo mkswap /swapfile
                        sudo swapon /swapfile
                        echo "/swapfile none swap sw 0 0" | sudo tee -a /etc/fstab
                else
                        echo "Ok, no swap file created"
                fi
        fi
else
        echo "There is enough memory, no need to create swap"
fi

# check the memory again
mem=`free -m | grep Mem | awk '{print $2}'`
swap=`free -m | grep Swap | awk '{print $2}'`

echo "Memory: $mem MB"
echo "Swap: $swap MB"

swap.sh

#!/bin/bash

# Bash script to create a swap file on Linux (debian/ubuntu)
# Author:    Mohamed Elashri
# Date:      2022-09-27

# use free -m to check the memory and see if there is enough memory (less than 2G) to create swap
# Logic is simple
# if there is no enough memory, then create swap
# if there is enough memory, delete swap

# check the memory
mem=`free -m | grep Mem | awk '{print $2}'`
swap=`free -m | grep Swap | awk '{print $2}'`


# if there is no enough memory (less than 2G), then create swap memory of 4G
if [ $mem -lt 2048 ]; then
    if [ $swap -eq 0 ]; then
        dd if=/dev/zero of=/swapfile bs=1024 count=4194304
        # Give the correct permission (secure)
        chmod 600 /swapfile
        mkswap /swapfile
        swapon /swapfile
        echo "/swapfile swap swap defaults 0 0" >> /etc/fstab
        # Tune linux krenel swappiness parameter
        sysctl vm.swappiness=80
        echo "vm.swappiness = 80" >> /etc/sysctl.conf
        # set cache pressure
        sysctl vm.vfs_cache_pressure=50
        echo "vm.vfs_cache_pressure = 50" >> /etc/sysctl.conf
    fi
fi

# if there is enough memory, make user choose to delete swap or not
if [ $mem -ge 2048 ]; then
    if [ $swap -gt 0 ]; then
        echo "There is enough memory, and swap memory exists do you want to delete swap?"
        echo "1) Y"
        echo "2) N"
        read -p "Please choose:" choice
        case $choice in
            1)
                swapoff /swapfile
                rm -rf /swapfile
                sed -i '/swap/d' /etc/fstab
                ;;
            2)
                exit 0
                ;;
        esac
    fi
fi


echo "Done!"

Usage.md

Usage:

For create_swap.sh script

• run the script

chmod +x create_swap.sh
 ./create_swap.sh

if everything is ok, we should see something like this

 Memory: 2048 MB
 Swap: 4096 MB

if there is no swap file, we should see something like this

 Memory: 2048 MB
 Swap: 0 MB

if there is already a swap file, we should see something like this

 Memory: 2048 MB
 Swap: 4096 MB

If we want to do this manually without the scrip

• check the swap file sudo swapon --show

• delete the swap file

sudo swapoff -a
sudo rm /swapfile
sudo sed -i '/swapfile/d' /etc/fstab

Then check the memory again free -m