Swap is a space on a disk that is used when the amount of physical RAM memory is full. When a Linux system runs out of RAM, inactive pages are moved from the RAM to the swap space.
Swap space can take the form of either a dedicated swap partition or a swap file. Typically, when running Ubuntu on a virtual machine, a swap partition is not present, and the only option is to create a swap file.
This tutorial explains how to add a swap file on Ubuntu 20.04 systems.
Before You Begin
Swap should not be seen as a replacement to physical memory. Since swap space is a section of the hard drive, it has a slower access time than physical memory. If your system constantly runs out of memory, you should add more RAM.
Generally, the size of the swap file depends on how much RAM your system has:
- Systems with less than 2 GB RAM – 2 times the amount of RAM.
- Systems with 2 to 8 GB RAM – the same size as the amount of RAM.
- Systems with more than 8 GB RAM – at least 4 GB of Swap.
Only root or user with sudo privileges can activate the swap file.
Creating a Swap File
In this example, we will create
2 GB swap file. If you want to add more swap, replace
2G with the size of the swap space you need.
Complete the steps below to add swap space on Ubuntu 20.04:
- First, create a file that will be used as swap:
sudo fallocate -l 2G /swapfile
fallocateutility is not present on your system, or you get an error message saying
fallocate failed: Operation not supported, use the following command to create the swap file:
sudo dd if=/dev/zero of=/swapfile bs=1024 count=2097152
- Set the file permissions to
600to prevent regular users to write and read the file:
sudo chmod 600 /swapfile
- Create a Linux swap area on the file:
sudo mkswap /swapfile
Setting up swapspace version 1, size = 2 GiB (2147479552 bytes) no label, UUID=fde7d2c8-06ea-400a-9027-fd731d8ab4c8
- Activate the swap file by running the following command:
sudo swapon /swapfile
To make the change permanent open the
sudo nano /etc/fstab
and paste the following line:
/swapfile swap swap defaults 0 0
- Verify that the swap is active by using either the
freecommand, as shown below:
sudo swapon --show
NAME TYPE SIZE USED PRIO /swapfile file 2G 0B -1
sudo free -h
total used free shared buff/cache available Mem: 981Mi 97Mi 68Mi 0.0Ki 814Mi 735Mi Swap: 2.0Gi 10Mi 1.9Gi
Adjusting the Swappiness Value
Swappiness is a Linux kernel property that defines how often the system will use the swap space. It can have a value between 0 and 100. A low value will make the kernel to try to avoid swapping whenever possible, while a higher value will make the kernel to use the swap space more aggressively.
On Ubuntu, the default swappiness value is set to
60. You can check the current value by typing the following command:
cat /proc/sys/vm/swappiness 60
While the swappiness value of
60 is OK for most Linux systems, for production servers, you may need to set a lower value.
For example, to set the swappiness value to
sudo sysctl vm.swappiness=10
To make this parameter persistent across reboots, append the following line to the
The optimal swappiness value depends on your system workload and how the memory is being used. You should adjust this parameter in small increments to find an optimal value.
Removing a Swap File
To deactivate and delete the swap file, follow these steps:
- First, deactivate the swap space:
sudo swapoff -v /swapfile
- Next, remove the swap file entry
/swapfile swap swap defaults 0 0from the
- Finally, remove the actual swapfile file using the
sudo rm /swapfile
We have shown you how to create a swap file and activate and configure swap space on your Ubuntu 20.04 system.
If you hit a problem or have feedback, leave a comment below.