How to Add Swap Space on Ubuntu (5GB Example)

Why Swap Matters

Swap is disk space that your OS uses as overflow when physical RAM fills up. Without it, the kernel may start killing processes (the dreaded OOM killer) when memory is exhausted. With it, your system degrades gracefully instead of crashing.

My setup: 7.57 GB RAM, 0 KB swap. Adding 5 GB swap gives the system room to breathe under heavy loads.

Step 1: Create the Swap File

sudo fallocate -l 5G /swapfile

fallocate instantly allocates the space on disk without writing zeroes — fast and efficient. If for some reason fallocate isn't available, use dd as a fallback:

sudo dd if=/dev/zero of=/swapfile bs=1M count=5120

Step 2: Lock Down Permissions

sudo chmod 600 /swapfile

This ensures only root can read/write the swap file — important for security. A world-readable swap file is a potential data leak.

Step 3: Format as Swap

sudo mkswap /swapfile

You should see output like:

Setting up swapspace version 1, size = 5 GiB (5368705024 bytes)
no label, UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

Step 4: Enable the Swap

sudo swapon /swapfile

Step 5: Make It Permanent

Without this step, your swap disappears after a reboot.

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

This appends the swap entry to /etc/fstab, which is read at boot time.

Step 6: Verify

free -h

You should see something like:

               total        used        free      shared  buff/cache   available
Mem:           7.5Gi       3.2Gi       1.1Gi       512Mi       3.2Gi       3.6Gi
Swap:          5.0Gi          0B       5.0Gi

Swap is now active. ✅

Bonus: Tune Swappiness

By default, Ubuntu sets vm.swappiness=60, which tells the kernel to start using swap when RAM usage hits ~40%. For a desktop or workstation with plenty of RAM, that's too aggressive — you want to stay in RAM as long as possible.

Check your current value:

cat /proc/sys/vm/swappiness

Set it to 10 (apply immediately):

sudo sysctl vm.swappiness=10

Make it permanent across reboots:

echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.conf

Swappiness reference

| Value | Behavior | |-------|----------| | 0 | Avoid swap entirely (only use in emergencies) | | 10 | Prefer RAM strongly — great for desktops/workstations | | 60 | Ubuntu default — balanced | | 100 | Swap aggressively |

For most desktop users with 4GB+ RAM, 10 is the sweet spot.

Quick Summary

# 1. Create
sudo fallocate -l 5G /swapfile

# 2. Secure
sudo chmod 600 /swapfile

# 3. Format
sudo mkswap /swapfile

# 4. Enable
sudo swapon /swapfile

# 5. Persist
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

# 6. Verify
free -h

# Bonus: tune swappiness
sudo sysctl vm.swappiness=10
echo 'vm.swappiness=10' | sudo tee -a /etc/sysctl.conf