How to Add or Resize Swap on Your Server

Swap is disk space the server uses as overflow memory when RAM is full. It keeps the server from killing processes (and taking websites down) during short memory spikes. It is much slower than RAM, so it's a safety net - not a replacement for more memory.

OpenPanel creates a swap file automatically during installation and monitors it afterwards. This guide shows how to check, resize and clear swap.

How Much Swap Do You Need?​

The installer creates /swapfile automatically, sized by RAM:

That's a good starting point. If the server regularly uses a lot of swap, add RAM instead of more swap - see System requirements and sizing.

To choose the size yourself when installing, use the --swap flag (1-10 GB):

bash <(curl -sSL https://openpanel.org) --swap=4

From OpenAdmin​

Go to OpenAdmin → System → Swap:

• Current usage - total, used and free swap, and every active swap device.
• Change allocation - enter a new size to recreate /swapfile at that size. It's added to /etc/fstab so it survives reboots. Swap is briefly turned off while the file is recreated.
• Drop swap - moves swapped-out data back into RAM (swapoff -a; swapon -a) without changing the size.

See Swap.

From the Terminal​

Check the current swap:

free -h
swapon --show

Create or resize the swap file (example: 4 GB):

swapoff /swapfile 2>/dev/null
fallocate -l 4G /swapfile
chmod 600 /swapfile
mkswap /swapfile
swapon /swapfile
grep -q '^/swapfile' /etc/fstab || echo '/swapfile none swap sw 0 0' >> /etc/fstab

Clear swap (only when enough RAM is free to hold what's in swap):

swapoff -a && swapon -a

Swappiness​

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

sysctl vm.swappiness=10
echo 'vm.swappiness=10' > /etc/sysctl.d/99-swappiness.conf

How OpenPanel Monitors Swap​

The Sentinel monitoring script (opencli sentinel) runs every 5 minutes and checks swap usage against the SWAP % threshold in OpenAdmin → Settings → Notifications → Resource Usage (default 85%):

1. Swap is below the threshold - nothing happens.
2. Swap is above the threshold - Sentinel sends a High SWAP usage notification, then clears the page cache and swap (swapoff -a; swapon -a), and reports the new usage.
3. Not enough free RAM to clear it safely - Sentinel skips the cleanup and notifies you instead, so clearing swap can never run the server out of memory.
4. Swap is turned off but configured in /etc/fstab - Sentinel turns it back on (swapon -a) and notifies you.

Change the threshold from OpenAdmin, or from the terminal:

opencli admin notifications update swap 70

Run the checks manually with:

opencli sentinel

See Notifications settings.

Swap Keeps Filling Up?​

Frequent high swap usage means the server needs more memory than it has. Find out what's using it:

grep VmSwap /proc/*/status 2>/dev/null | sort -k2 -hr | head

Then see Find which site is using high CPU or RAM - often a single account, a leaking app or a service like ClamAV. Lower that account's memory limit, or upgrade the server's RAM.

Related​

• Free up disk space - swap files use disk space too
• System cron jobs