Creating a swap partition in Linux

This guide explains how to set up SWAP on an existing Linux system.

1. Check if SWAP already exists

Run the following command to see if any swap space is currently active:

sudo swapon --show

If nothing is returned, there is no active swap.

2. Create the SWAP file

Create a new swap file using fallocate:

sudo fallocate -l 1G /swapfile

Replace 1G with the desired size, e.g. 2G or 4G. If the command fails (for example, on older filesystems), use dd instead:

sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576

3. Secure the SWAP file

Restrict access so only root can read and write to it:

sudo chmod 600 /swapfile

4. Set up the swap area

Initialize the file as swap space:

sudo mkswap /swapfile

5. Activate the SWAP

Enable the swap file immediately:

sudo swapon /swapfile

6. Make the change permanent

Edit /etc/fstab and add the following line:

/swapfile swap swap defaults 0 0

This ensures the swap file is automatically enabled at boot.

7. Verify

Confirm that the swap is active:

sudo swapon --show

Or check total swap space with:

free -h