How to Set Up Swap on Ubuntu 24.04

Out of the box Ubuntu Server 24.04 ships without a swap file on most cloud images. For workloads that occasionally spike, a small swap file is the cheapest insurance against the OOM-killer.

Prerequisites

• Ubuntu Server 22.04 or 24.04 with sudo access.
• At least 2 GiB of free space on the root filesystem.
• An idea of how much swap you actually want — for general use, swap = min(RAM, 4G).

Step 1: Check existing swap

free -h
swapon --show

If swapon --show returns nothing, you have zero swap. Continue.

Step 2: Create the swap file

We will allocate 2 GiB. Use fallocate for speed; fall back to dd if the filesystem (some tmpfs, NFS, etc.) does not support it.

sudo fallocate -l 2G /swapfile
# fallback if fallocate fails:
# sudo dd if=/dev/zero of=/swapfile bs=1M count=2048 status=progress

sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

Confirm:

swapon --show
free -h

Step 3: Persist across reboots

swapon is in-memory only. Add a line to /etc/fstab:

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

Verify the entry is correct and the file mounts cleanly:

sudo swapoff /swapfile
sudo swapon -a
swapon --show

Step 4: Tune swappiness

vm.swappiness controls how aggressively the kernel swaps. The default of 60 is too eager for servers; 10 is a sensible production value.

sudo sysctl vm.swappiness=10
echo 'vm.swappiness=10' | sudo tee /etc/sysctl.d/99-skyline-swap.conf

Verify

cat /proc/swaps
sysctl vm.swappiness

/proc/swaps should list /swapfile, and vm.swappiness should return 10.

Conclusion

A right-sized swap file (with low swappiness) costs nothing and stops the OOM-killer from picking off your application during a brief memory spike. Keep an eye on swapon --show over the first week — chronic swap-in is a sign you actually need more RAM.

Next steps

• Lock the box down with SSH and UFW hardening.
• Pair this with unattended security upgrades.
• See the systemd services guide to expose memory targets per service.