# Add a swap file

> Create a swap file on Ubuntu 24.04 or Debian 12, make it permanent, and tune swappiness so it is used only when needed.

Source: https://vpsnine.com/help/add-swap · Updated: 2026-10-09

Swap is disk space the kernel borrows when RAM runs out. It's far slower than RAM, but it turns a sudden out-of-memory kill into a short slowdown, which is much easier to recover from. On a server with 2 to 4 GB of RAM, a swap file the size of the RAM (up to 2 GB) is a good start.

## See if you already have some

```bash
swapon --show
free -h
```

If `swapon --show` prints nothing, there's no swap yet. If it lists one, you can stop here, or jump to the end to resize it.

## Create the file

This makes a 2 GB file at `/swapfile`. Change `2G` if you want a different size.

```bash
fallocate -l 2G /swapfile
chmod 600 /swapfile
mkswap /swapfile
swapon /swapfile
```

Don't skip the `chmod 600`. Swap can hold anything that was in memory, passwords included, so only root should be able to read it.

`fallocate` works on ext4, which is what you'll almost certainly have. If it says `Operation not supported`, use `dd if=/dev/zero of=/swapfile bs=1M count=2048` instead and carry on from `chmod`.

## Keep it after a reboot

Right now swap is on, but only until the next boot. Add it to `/etc/fstab`:

```bash
echo '/swapfile none swap sw 0 0' >> /etc/fstab
```

Then check the line went in once, not twice (easy to do if you ran it again):

```bash
grep swapfile /etc/fstab
```

## Tell the kernel to go easy on it

`vm.swappiness` is how keen the kernel is to move memory out to swap. The default is 60. On a server, 10 keeps your busy programs in RAM and leaves swap for emergencies:

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

The first line changes it now. The file makes it stick.

Check both:

```bash
swapon --show
cat /proc/sys/vm/swappiness
```

You want to see `/swapfile` at 2G, and `10`. Reboot once and check again, just to be sure it all survives.

## Removing or resizing it

```bash
swapoff /swapfile
sed -i '/^\/swapfile /d' /etc/fstab
rm /swapfile
```

To resize, remove it like that and create it again at the new size. `swapoff` needs enough free RAM to take back what's in swap, so if it fails, stop a service or two first.

A few messages you might meet:

- `insecure permissions 0644, fix with: chmod 0600 /swapfile`: just a warning, swap is on. Run the `chmod` anyway.
- `read swap header failed`: the file was never formatted. Run `mkswap /swapfile`.

And if swap is always full and the server crawls, swap is hiding a real memory shortage. Find the culprit with `top` (press `M` to sort by memory), or [move to a bigger plan](https://vpsnine.com/help/choosing-a-plan).