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

#devops #ubuntu

Article from blog

Description

A step-by-step guide to creating a swap file on Ubuntu, making it persistent across reboots, and tuning swappiness for better performance.

Disclamer

This article was made with Ai, but I have tested all these commands since I needed swap too

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
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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
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Step 2: Lock Down Permissions 

sudo chmod 600 /swapfile
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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
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You should see output like:

Setting up swapspace version 1, size = 5 GiB (5368705024 bytes)
no label, UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
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Step 4: Enable the Swap 

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

Step 6: Verify 

free -h
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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
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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
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Set it to 10 (apply immediately):

sudo sysctl vm.swappiness=10
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Make it permanent across reboots:

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