Adding SWAP size - Ubuntu/Debian

One of the simplest ways to enhance your application's memory protection is by adding Swap memory. Swap is an area on your hard drive used for temporarily storing operating system data when the required data doesn't fit into the RAM.

By configuring Swap memory, you increase the amount of information your server can retain. Disk space is primarily used when there's a shortage of RAM.

Data written to the disk is slower than data stored in RAM, but the operating system uses Swap for older data.

Checking Swap

You can have multiple Swap files or Swap partitions, but typically, one should suffice.

Check if the system has Swap configured using:

Another way to verify Swap is by using the "free" tool, which shows system memory usage:

Checking Available Disk Space

The traditional way to allocate space for Swap is by creating a separate partition. However, modifying the partition structure isn't always possible.

You can easily create a Swap file on an existing partition. Before creating a Swap file, check the available disk space:

The initial value for Swap is either equal to or double the amount of RAM on your system.

Creating a Swap File

Once you know the available disk space, you can proceed to create a Swap file.

Create a file and name it "swapfile" in your root (/) directory. The file must be allocated with the amount of space you want for your Swap file; in this case, it's 4GB.

There are two methods to achieve this:

Slower Method

Traditionally, you create a file with allocated space using the "dd" command. Set the file size by combining the "bs" parameter for block size and "count" for the number of blocks.

For a 4GB file, you can set the block size to 1GB and the count to 4:

Confirm that 4GB has been allocated by using:

This command will take some time to complete as it writes 4GB of zeros to the disk. If you want to create the file faster, you can delete the one you just created:

Faster Method

A quicker way to create the same file is by using the "fallocate" program. You can create a 4GB file with:

Check the file size with:

Enabling the Swap File

Before enabling it, you need to adjust the permissions. Allowing regular users to read and write to the swapfile would be a security risk, so change the permissions to make it readable only by the root user.

Set up the Swap space using:

Enable the Swap file with:

Verify that Swap is active with:

You should see the newly created /swapfile in the output.

Permanent Swap File Enablement

Now, your Swap file is running. However, when you restart your server, the Swap file won't be enabled automatically. To make it persistent, you need to edit the "fstab" file.

Edit the file with root privileges in a text editor:

Add a line at the end of the file, instructing the system to automatically enable the file you created:

Save and close the file. When you restart the device, the Swap file will be active.

Adjusting Swap Settings

There are a few options you can set that will impact your system's performance when it's swapping.

The "swappiness" parameter determines when the system will move data from RAM to Swap. The value for this parameter is a percentage between 0 and 100.

With values closer to 0, the kernel won't move data to Swap until it's necessary. With values closer to 100, the kernel will prioritize saving data to Swap over RAM.

You can check the current swappiness value with:

For VPS, it's better to have a swappiness value closer to 0. For a quick change, you can use:

This change will be lost on reboot. To keep the change after a reboot, you can use:

Add the line to the end of the file:

Save and close the file.

Done.