How to add Swap Space on Ubuntu 20.04


An example of allocating additional memory for system to use, by creating a SWAP space.

Warning: Flash RAM cells used in SSDs drives have a limited lifespan. Using SWAP files on such devices can lead to issues with hardware degradation over time, faster wear of memory cells and at critical hardware failure.

What is Swap?

Swap is an amount of hard drive storage used as operating system memory to temporarily store data that don't have enough room in available operative memory.



Step 1 – Prepare

Before start, need to check if there is enough disk space and if SWAP space is already in use. In most conditions one SWAP space file should be enough, it is possible to have multiple swap files or swap partitions in a system.

Check free disk space
df -h

Check if the system have enough free disk space

Check if the system have enough free disk space
Check if the system have enough free disk space for our SWAP space file
Show SWAP space files
sudo swapon --show

Check if SWAP space file is already created

Check if SWAP space file is already created
Check if SWAP space file is already created



Step 2 – Creating a Swap File

We will allocate a file of the size 1G, with the name "swapfile" in our root (/) directory. Using "fallocate" application. This command will create a file with defined size and in selected location. (File size and location can be adjusted to your needs)

Create SWAP space file & verify
sudo fallocate -l 1G /swapfile
ls -lh /swapfile

We will create a 1G file, after verify the creation and amount of space that was reserved.

Creating a SWAP File & verify
Creating a SWAP File & verify



Step 3 – Enabling the Swap File

Now when we have the file(/swapfile) with defined size, we need to turn this file into swap space file.
Important to set right permissions to prevent normal users from being able to access/edit the file, which will lead to security implications.

Enabling the Swap File
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo swapon --show

Enable swap space file and verify that the swap is available and has been set up successfully.

Enabling the Swap File
Enabling the Swap File



Step 4 - Configuration

Tuning your Swap Settings

Few options that can be helpful with default Swap configuration. Option to autoload Swap space file on system boot, settings to control swap system usage and effectiveness.

Make the Swap Space File Permanent and autoloaded on system boot
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

This command is required to be able to use our Swap space after system reboot. We can change this by adding a configuration line to /etc/fstab file.

Adjusting the Swappiness Property
sudo sysctl vm.swappiness=10

The swappiness setting control how often your system swaps data out of RAM to the swap space. Possible values  0 and 100.
Close to 0 system will not swap data to the disk unless absolutely necessary.
Values closer to 100 will try to put more data into swap in an effort to keep more RAM space free.

Adjusting the Cache Pressure Setting
sudo sysctl vm.vfs_cache_pressure=50

This setting will control amount of cache inode and dentry information to store in Swap. This will help files system work faster.

Check of newly created SWAP space file
Check of newly created SWAP space file.




This guide will give you a showcase of creating a swap file, activation and basic configuration on your Ubuntu 20.04 system, to protect against out-of-memory issues that can lead to execution errors or system freeze.

Bear in mind, that swap file is last stand option, and can lead to server performance decline as disk IO operations are significantly slower than ones kept in RAM, so the best solution is to optimize your applications or upgrade your server.