Introduction

Swap space is a Linux feature that acts as additional virtual memory by using disk storage. When your system's physical RAM is fully utilized, swap space temporarily stores less-used data, ensuring smooth system performance and preventing crashes during heavy workloads.

This guide shows you how to create and configure swap space on Rocky Linux 9 to expand your system RAM and efficiently run memory-intensive applications.

Prerequisites

Before you begin:

• Deploy a Digital Ocean VPS server running Rocky Linux 9.
• Create a non-root sudo user. For guidance, refer to the following guide:
  • How to Create a Non-Root Sudo User on Rocky Linux.

Check for Existing Swap Space

1. SSH into your server as a non-root sudo user.

2. Check whether a swap space is already active.

   CONSOLE

   $ sudo swapon --show
   

   If there's no output, it means no swap space is currently active. If swap is already enabled, you'll see output like this.

   NAME      TYPE      SIZE   USED   PRIO
   /swapfile file      2G     0B     -2
   

   If swap exists but you'd prefer to create a new one:

   • Disable the current swap space:

     CONSOLE

     $ sudo swapoff -a
     

   • Delete the swap file (if applicable):

     CONSOLE

     $ sudo rm /swapfile
     

Allocate Disk Space for Swap

Decide how much swap space to allocate based on your system’s RAM and workload:

• For systems with ≤ 2GB RAM, set swap to 2× RAM.
• For systems with > 2GB RAM, set swap to 1–1.5× RAM.

For instance:

• A system with 1GB RAM benefits from a 2GB swap.
• A system with 4GB RAM may need 4–6GB swap.

To allocate swap space:

1. Create a swap file. Replace 2G with your desired size.

   CONSOLE

   $ sudo fallocate -l 2G /swapfile
   

   If fallocate isn’t available, use:

   CONSOLE

   $ sudo dd if=/dev/zero of=/swapfile bs=1M count=2048
   

2. . Verify the file exists.

   CONSOLE

   $ ls -lh /swapfile
   

   Output:

   -rw------- 1 root root 2.0G ... /swapfile
   

Secure the Swap File

Protect sensitive data in the swap file by restricting access to the root user.

1. Adjust permissions.

   CONSOLE

   $ sudo chmod 600 /swapfile
   

2. Verify the permissions.

   CONSOLE

   $ ls -lh /swapfile
   

   Output:

   -rw------- 1 root root 2.0G ... /swapfile
   

Set Up the Swap File

1. Format the file as a swap space.

   CONSOLE

   $ sudo mkswap /swapfile
   

2. Activate the swap file.

   CONSOLE

   $ sudo swapon /swapfile
   

3. Ensure the swap file is active.

   CONSOLE

   $ sudo swapon --show
   

   Output:

   NAME      TYPE      SIZE   USED   PRIO
   /swapfile file      2G     0B     -2
   

Make the Swap File Permanent

The next step is ensuring your swap space is automatically enabled at boot.

1. Open the /etc/fstab file with a text editor.

   CONSOLE

   $ sudo nano /etc/fstab
   

2. Add this line to the end of the file.

   INI

   /swapfile none swap sw 0 0
   

3. Save and close the file by pressing Ctrl + X, Y , and Enter.

Optimize Swap Usage

Swappiness determines how aggressively Linux uses swap space. The default value is 60, but you can adjust it for your needs:

• Low RAM (≤ 4GB): Use higher swappiness (For instance, 60) to prioritize disk usage.

• High RAM (≥ 8GB): Lower the swappiness (For instance, 10–20) to favor RAM.

• Check the current swappiness value.

  CONSOLE

  $ cat /proc/sys/vm/swappiness
  

  Output:

  60
  

• Temporarily set swappiness to 10.

  CONSOLE

  $ sudo sysctl vm.swappiness=10
  

• Edit /etc/sysctl.conf for a permanent change.

  CONSOLE

  $ sudo nano /etc/sysctl.conf
  

• Add this line.

  INI

  vm.swappiness=10
  

• Apply the settings:

  CONSOLE

  $ sudo sysctl -p
  

General Swappiness Recommendations

Systems with Low RAM (≤ 4GB)

• Use a swappiness of 60 to offload inactive data to disk.

Systems with High RAM (≥ 8GB)

• Use a swappiness of 10–20 to minimize disk usage.

SSD vs HDD

• SSD: Use swappiness 30–40 for faster swap performance.
• HDD: Use swappiness 10–20 to reduce bottlenecks.

Conclusion

This guide explained how to set up and optimize swap space on Rocky Linux 9, including verifying existing swap, creating and securing a swap file, making it permanent, and tuning swappiness for better performance. With properly configured swap, your system can now handle memory-intensive tasks smoothly and efficiently.