How to add swap memory on AlmaLinux 8.5

What is swap space/memory?

When the amount of physical memory (RAM) is full, swap space in Linux is used. Non-active pages in memory are moved to the swap memory if the system requires more memory resources and also the RAM is complete.

While swap memory can help devices with a percentage of RAM, it should not be thought about a substitute for more RAM. Swap memory is located on hard disk drives, which have a slower accessibility time than physical memory.

Table of Contents

• What is swap space/memory?
• Swap memory calculation formula
• Identifying Current Swap Space
• Creating swap file on AlmaLinux 8.5
• Swappiness configuration
• Removing Swap File on AlmaLinux 8.5
• Conclusion

Swap memory calculation formula

Use the following formula to calculate the required swap memory:

# MEMORY = Amount of RAM in GB
# SWAP_MEMORY = Amount of Swap Memory in GB

if MEMORY < 2:
   SWAP_MEMORY = MEMORY * 2
elif MEMORY > 32:
  SWAP_MEMORY = MEMORY / 2
else:
  SWAP_MEMORY = MEMORY

Examples:

• If you have 2 GB of RAM, you need 4 GB of swap memory
• If you have 3 GB of RAM, you need 3 GB of swap memory
• If you have 64 GB of RAM, you need 32 GB of swap memory

Identifying Current Swap Space

Before adding swap space, check if your system already has swap configured. You can use any of these commands:

cat /proc/swaps

Or:

swapon --show

Or:

free

If no swap is configured, these commands will show empty output or zero swap space.

Creating swap file on AlmaLinux 8.5

Follow these steps to create and enable a swap file:

Step 1: Create swap space directory

sudo mkdir /swap-space

Step 2: Install required utility

Install the util-linux package which provides the fallocate command:

sudo dnf install util-linux -y

Step 3: Create the swap file

Create a 2GB swap file (adjust the size according to your needs):

sudo fallocate -l 2G /swap-space/swapfile

Step 4: Set proper permissions

For security reasons, the swap file should only be readable and writable by root:

sudo chmod 600 /swap-space/swapfile

Step 5: Configure the swap file

Set up the file as a swap area:

sudo mkswap /swap-space/swapfile

You should see output similar to:

Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=6e965805-2ab9-450f-aed6-577e74089dbf

Step 6: Activate the swap file

Enable the swap file immediately:

sudo swapon /swap-space/swapfile

Step 7: Verify swap is active

Check that the swap is now active:

sudo swapon --show

Output should show:

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

Step 8: Make swap permanent

To ensure the swap file is activated on system boot, add it to /etc/fstab:

echo '/swap-space/swapfile swap swap defaults 0 0' | sudo tee -a /etc/fstab

Swappiness configuration

Swappiness is a Linux kernel parameter that controls how aggressively the system uses swap space. The value ranges from 0 to 100:

• 0: Swap is used only when RAM is completely full
• 100: System will use swap space aggressively

Check current swappiness value

cat /proc/sys/vm/swappiness

Default value is usually 60.

Temporarily change swappiness

To change swappiness for the current session:

sudo sysctl vm.swappiness=60

Permanently change swappiness

To make the change permanent, edit /etc/sysctl.conf:

sudo vi /etc/sysctl.conf

Add or modify this line:

vm.swappiness=60

Apply the changes:

sudo sysctl -p

Recommended swappiness values

• Desktop systems: 60 (default)
• Server systems: 10-30
• Database servers: 10 or lower

Removing Swap File on AlmaLinux 8.5

If you need to remove the swap file:

Step 1: Deactivate the swap file

sudo swapoff /swap-space/swapfile

Step 2: Remove the fstab entry

Edit /etc/fstab and remove the line:

/swap-space/swapfile swap swap defaults 0 0

Step 3: Delete the swap file

sudo rm /swap-space/swapfile

Step 4: Remove the directory (optional)

sudo rmdir /swap-space

Troubleshooting

Issue: “fallocate: fallocate failed: Operation not supported”

Some file systems don’t support fallocate. Use dd instead:

sudo dd if=/dev/zero of=/swap-space/swapfile bs=1M count=2048

Issue: “swapon: /swap-space/swapfile: swapon failed: Invalid argument”

This usually means the file permissions are incorrect. Ensure:

sudo chmod 600 /swap-space/swapfile
sudo chown root:root /swap-space/swapfile

Issue: System is still slow despite having swap

Remember that swap is much slower than RAM. If your system frequently uses swap:

• Consider adding more physical RAM
• Reduce the number of running applications
• Optimize your applications’ memory usage

Best Practices

1. Monitor swap usage: Regularly check swap usage with free -h or vmstat
2. Size appropriately: Don’t create swap that’s too large; it wastes disk space
3. Use SSD if possible: Swap on SSD is faster than on traditional HDD
4. Multiple swap spaces: You can have multiple swap files or partitions with different priorities
5. Regular maintenance: Monitor for high swap usage which indicates RAM shortage

Conclusion

Adding swap space to AlmaLinux 8.5 is a straightforward process that can help your system handle memory pressure more gracefully. While swap is not a replacement for adequate RAM, it provides a safety net for occasional memory spikes and can prevent out-of-memory errors.

Remember to:

• Calculate the appropriate swap size for your system
• Monitor swap usage regularly
• Adjust swappiness based on your workload
• Consider adding physical RAM if swap is frequently used

With proper configuration, swap space can significantly improve your AlmaLinux system’s stability and performance under memory-intensive workloads.