How to add swap space on CentOS Stream 8

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.

Before You Begin

Swap should not be seen as a replacement to physical memory. Since swap space is on the hard drive, it has slower access time than physical memory.

Calculating Swap Space

Generally, swap space should be:

• 2x physical RAM for up to 2 GB of RAM
• Additional 1x physical RAM above 2 GB
• Never less than 32 MB
• For systems with >32 GB RAM, around 1/2 physical RAM

Creating the Swap File

Steps to create swap space:

1. Create swap file:

sudo dd if=/dev/zero of=/swapfile bs=1024 count=2097152

2. Set permissions:

sudo chmod 600 /swapfile

3. Set up swap area:

sudo mkswap /swapfile

4. Activate swap:

sudo swapon /swapfile

5. Add to /etc/fstab:

/swapfile swap swap defaults 0 0

Verifying Swap Space

Check if swap is active:

free -h
swapon --show

Adjusting Swappiness

The swappiness parameter controls the tendency of the kernel to move processes out of physical memory:

# Check current swappiness
cat /proc/sys/vm/swappiness

# Temporarily change swappiness
sudo sysctl vm.swappiness=60

To make it permanent, add to /etc/sysctl.conf:

vm.swappiness=60

Removing Swap File

If you need to remove the swap file:

sudo swapoff /swapfile
sudo rm /swapfile

Also remove the entry from /etc/fstab.

Conclusion

Adding swap space to CentOS Stream 8 can help improve system performance when physical memory is limited. Remember to monitor your system’s memory usage and adjust swap size accordingly.