> ## Documentation Index
> Fetch the complete documentation index at: https://docs.opus-host.de/llms.txt
> Use this file to discover all available pages before exploring further.

# Add Swap and Tune Performance on Your Opus Host VPS

> Add a swap file to survive memory spikes, tune swappiness, and use built-in tools to diagnose slow performance on your Opus Host VPS.

A free VPS gives you a modest amount of RAM, and it does not take much to hit the ceiling. When memory runs out, the Linux kernel starts killing processes, usually the one you cared about most. A swap file gives the kernel breathing room by letting it move inactive memory to disk.

<Warning>
  Swap uses disk space and is much slower than RAM. Use it as a safety net for occasional spikes, not as a substitute for enough memory. Check your [resource limits](/vps/resource-limits) before adding a large swap file.
</Warning>

## Add a swap file

<Steps>
  <Step title="Check current swap">
    ```bash theme={null}
    free -h
    swapon --show
    ```
  </Step>

  <Step title="Create a 1 GB swap file">
    ```bash theme={null}
    sudo fallocate -l 1G /swapfile
    sudo chmod 600 /swapfile
    sudo mkswap /swapfile
    sudo swapon /swapfile
    ```
  </Step>

  <Step title="Make it persistent across reboots">
    ```bash theme={null}
    echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
    ```
  </Step>

  <Step title="Verify">
    ```bash theme={null}
    free -h
    ```
  </Step>
</Steps>

## Tune swappiness

Swappiness controls how eagerly the kernel moves memory to swap. On a server, a lower value keeps active data in RAM longer.

```bash theme={null}
# Check current value (default is usually 60)
cat /proc/sys/vm/swappiness

# Set to 10 for this session
sudo sysctl vm.swappiness=10

# Make it permanent
echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.conf
```

## Diagnose slow performance

### Check memory and CPU

```bash theme={null}
free -h        # memory usage
uptime         # load average
top            # live process view (press q to quit)
htop           # nicer top; install with: sudo apt install htop
```

### Find the biggest memory hogs

```bash theme={null}
ps aux --sort=-%mem | head -n 10
```

### Find the biggest CPU hogs

```bash theme={null}
ps aux --sort=-%cpu | head -n 10
```

### Check disk usage

```bash theme={null}
df -h          # disk space by mount
du -sh /*      # size of each top-level directory
```

### Check disk I/O

```bash theme={null}
sudo apt install sysstat -y
iostat -x 2 5
```

## Remove a swap file

```bash theme={null}
sudo swapoff /swapfile
sudo sed -i '/\/swapfile/d' /etc/fstab
sudo rm /swapfile
```