To set up a 4 GB swap file on an Azure Debian 12 virtual machine, follow these steps:

1. Check for Existing Swap

Before creating a new swap file, check if swap space is already enabled:

sudo swapon --show

If nothing is returned, then no swap space is currently active.

2. Create a Swap File

You can create a swap file using the fallocate command:

sudo fallocate -l 4G /swapfile

If fallocate is not available or if you want a more secure way, you can use dd:

sudo dd if=/dev/zero of=/swapfile bs=1M count=4096

This command creates a 4 GB swap file at /swapfile.

3. Secure the Swap File

Set the correct permissions so that only the root user can read and write to the swap file:

sudo chmod 600 /swapfile

4. Set Up the Swap Area

Format the file as swap:

sudo mkswap /swapfile

5. Enable the Swap File

Activate the swap file so it can be used immediately:

sudo swapon /swapfile

Verify that the swap is active:

sudo swapon --show

6. Make the Swap Permanent

To ensure that the swap file is used at boot time, add it to the /etc/fstab file:

echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

7. Adjust Swap Settings (Optional)

You can adjust the swappiness value, which defines how often the swap is used. The default value is 60. To change it, edit /etc/sysctl.conf:

sudo nano /etc/sysctl.conf

Add or change the following line to your preferred swappiness value:

vm.swappiness=10

Save and apply the changes:

sudo sysctl -p

8. Verify Swap

Finally, check the swap summary to ensure everything is working as expected:

free -h

This will display the available swap and RAM on your system. Your 4 GB swap file should be listed here.