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. In most cases when running Ubuntu on a virtual machine a swap partition is not present so the only option is to create a swap file.
This tutorial covers the steps necessary to add a swap file on Ubuntu 18.04 systems.
Before continuing with this tutorial, check if your Ubuntu installation already has swap enabled by typing:
sudo swapon --show
If the output is empty, it means that your system does not have swap space enabled.
Otherwise, if you get something like below, you already have swap enabled on your machine.
NAME TYPE SIZE USED PRIO /dev/sda2 partition 1.9G 0B -2
Although possible, it is not common to have multiple swap spaces on a single machine.
The user you are logged in as must have sudo privileges to be able to activate swap. In this guide, we will add
1G of swap, if you want to add more swap, replace
1G with the size of the swap space you need.
Perform the steps below to add swap space on Ubuntu 18.04.
- Start by creating a file which will be used for swap:
sudo fallocate -l 1G /swapfile
fallocateis not installed or you get an error message saying
fallocate failed: Operation not supportedthen use the following command to create the swap file:
sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576
- Only the root user should be able to write and read the swap file. Set the correct permissions by typing:
sudo chmod 600 /swapfile
- Use the
mkswaputility to set up a Linux swap area on the file:
sudo mkswap /swapfile
- Activate the swap file using the following command:
sudo swapon /swapfile
To make the change permanent open the
sudo nano /etc/fstab
and paste the following line:/etc/fstab
/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 1024M 507.4M -1
sudo free -h
total used free shared buff/cache available Mem: 488M 158M 83M 2.3M 246M 217M Swap: 1.0G 506M 517M
Swappiness is a Linux kernel property that defines how often the system will use the swap space. Swappiness 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.
The default swappiness value is 60. You can check the current swappiness value by typing the following command:
While the swappiness value of 60 is OK for Desktops, for production servers you may need to set a lower value.
For example, to set the swappiness value to 10, type:
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.
To deactivate and remove the swap file, follow these steps:
- Start by deactivating the swap space by typing:
sudo swapoff -v /swapfile
- Next, remove the swap file entry
/swapfile swap swap defaults 0 0from the
- Finally, delete the actual swapfile file:
sudo rm /swapfile