How to Add Swap Space to Your VPS

Swap is disk space the Linux kernel uses as overflow when RAM is full. Without swap, a memory spike (a busy WordPress site, a composer install, an npm build) makes the kernel kill a process, often MariaDB, and your site goes down. A modest swap file gives the server breathing room.

Swap is much slower than RAM, so it is a safety net, not a replacement for memory.

Which VPS is this for? These steps are for an Unmanaged VPS, where you log in as root and look after the server yourself. On a Managed VPS we take care of the operating system and server software, and you manage your websites in StackCP instead.

Step 1: Check what you have

free -h
swapon --show
df -h /

                        
                    

If swapon --show prints nothing, the VPS has no swap. Make sure you have enough free disk space for the file.

How big should it be?

Step 2: Create the swap file

Ubuntu and Debian (ext4)

sudo fallocate -l 2G /swapfile

                        
                    

AlmaLinux and Rocky Linux (usually XFS)

Write the file out in full with dd, which works on every file system:

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

                        
                    

All systems: secure and enable it

sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
swapon --show

                        
                    

The chmod 600 step matters: swap can contain passwords and other data from memory, so only root may read it.

Step 3: Make it permanent

Add the swap file to /etc/fstab so it is used after every reboot:

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

                        
                    

A typo in /etc/fstab can stop the server from booting, which is why we keep a copy. Check the file with cat /etc/fstab before rebooting.

Step 4: Tune swappiness (optional)

vm.swappiness controls how eagerly Linux moves memory to swap (0–100, default 60). On a server, a lower value keeps active data in RAM longer:

echo 'vm.swappiness=10' | sudo tee /etc/sysctl.d/99-swappiness.conf
sudo sysctl --system
cat /proc/sys/vm/swappiness

                        
                    

Changing the size or removing swap

sudo swapoff /swapfile
# to resize: create it again with the new size, then mkswap and swapon
# to remove completely:
sudo rm /swapfile
sudo nano /etc/fstab   # delete the /swapfile line

                        
                    

Is swap enough, or do I need more RAM?

Watch the server for a few days with free -h and vmstat 5. Occasional small swap use is fine. Signs you need more RAM:

• Swap usage stays high all day and keeps growing.
• The si/so columns in vmstat 5 are constantly above zero (the server is actively swapping).
• Pages load slowly even though CPU usage is low.
• The kernel log shows out-of-memory kills: sudo journalctl -k | grep -i 'out of memory'.

If you see these, reduce memory use (fewer PHP-FPM workers, smaller database buffers, fewer containers) or move to a bigger plan: How to Upgrade or Downgrade Your VPS Plan.

Common problems

• swapon: /swapfile: insecure permissions: run sudo chmod 600 /swapfile.
• swapon failed: Invalid argument: the file system did not accept a file made with fallocate (this can happen on XFS). Remove it and create it again with dd.
• fallocate failed: Text file busy: the swap file is in use. Run sudo swapoff /swapfile first.

Need help?

If something about the VPS itself is not working (it won't start, you can't reach it, or you need console access, an upgrade or a reinstall), open a support ticket from your client area or message us on WhatsApp at 01818160926. Include your VPS IP address and what you have already tried so we can help faster.