In Linux, swap space is used when the system starts running out of physical memory (RAM). In that case, any inactive data stored in RAM are moved into the swap space, freeing up physical memory for other uses. Swap is also used during hibernation, where all data in RAM are copied to swap, just before powering off the computer.

It is almost always a good idea to have some disk space allocated as swap, but how much swap space is needed depends on your particular circumstances. You can find some example scenarios here.

Sometimes the swap space can be on a separate disk partition, however recent versions of Linux distributions, including Ubuntu, use a special swap file in the root partition as swap space.

Find swap file location

Typically, a swap file should have been created during installation. We can find where that file is located, using the swapon command.

swapon --show
NAME      TYPE SIZE USED PRIO
/swap.img file   8G 7.3M   -2

If for some reason you don’t have any swap space allocated, swapon shouldn’t show any output, in which case feel free to create a new file.

Create a new swap file

1. Deactivate the existing swap file. Obviously, skip this step if you are creating a swap file for the first time.

   sudo swapoff /swap.img
   

2. Create an empty file with a size of 8G (8GB) - update this value as required. Run man fallocate for more information on how to use this command.

   sudo fallocate -l 8G /swap.img
   

3. Format the file as swap space.

   sudo mkswap /swap.img
   

4. Activate the new swap file.

   sudo swapon /swap.img
   

Confirm swap file activated

You can use swapon or free to confirm that the new swap file has been activated.

free -h
               total        used        free      shared  buff/cache   available
Mem:            15Gi       5.4Gi       3.3Gi       250Mi       7.4Gi        10Gi
Swap:          8.0Gi       7.2Mi       8.0Gi