Ubuntu 20.04: add swap space

In this tutorial, I will walk you through how to add swap space on Ubuntu 20.04 and above.

A swap space on Linux is a location on the disk, which allows the OS to load the random access memory (RAM), on Windows we find this type of file pagefile.sys

By default, on server versions of Ubuntu, space is no longer added by default.

Adding swap space to an SSD can reduce its lifespan.

Check if swap space is present

Before embarking on the creation of a swap space, we will check if it already exists and for this there are several solutions.

With htop :

sudo htop

On the capture below, we can see the Swp is at 0K.

With the swapon command:

sudo swapon --show

If no swap is configured, the command returns nothing

With the command free

sudo free -h

The command returns the available memory as well as the swap is 0.

We are sure not to have any swap on our machine.

Create swap space

To create a swap space, it comes down to creating a file of a defined size on our disk and then configuring Linux to tell it that it can unload its RAM into this file.

Creating the swap file:

sudo fallocate -l 4G /swapfile

This command creates a 4G file named swapfile at the root of disk /.

It is possible to check the creation of the file with the command:

ls -lh /swapfile

Modify rights

Enter the command below to allow only the root user:

sudo chmod 600 /swapfile

You can use this command again to check the permissions:

ls -lh /swapfile

Enable swap space

We will now tell the system that we have a swap space:

sudo mkswap /swapfile

You can enable swap with the command:

sudo swapon /swapfile

To check that it is activated, enter:

sudo swapon --show

The swap space is functional.

Configure Boot Swap

For the moment, the swap is not permanent, if you restart your Linux, the swap space will not be mounted, to make it permanent, you must add a record to the file /etc/fstab.

To add this line, enter the following command:

echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

With this line, at the next boot, the swap will be available.

Setting up swap usage

This part is optional, but if you want to optimize the use in order to use it more or less, you must adjust the swappiness parameter.

swappiness is parameter between 0 and 100, it will determine the frequency of exchange between the ram and the swap. The closer the value approaches 100, for the swap is used. By default the value is 60.

To display the current value of swappiness enter:

cat /proc/sys/vm/swappiness

To temporarily change the value enter the command:

sudo sysctl vm.swappiness=30

To apply the value permanently, you must write the value in the /etc/sysctl.conf file.

Open file:

sudo nano /etc/sysctl.conf

Add at the end:

vm.swappiness=30

If the parameter already exists, modify the value

Now you know how to set up a swap file on Ubuntu.