How To Add Swap Space on Ubuntu 22.04 LTS

Adding swap space to your Ubuntu 22.04 LTS system is a crucial skill for any Linux user who wants to optimize their system’s performance. Swap space serves as a vital safety net for your system when physical memory becomes insufficient. This comprehensive guide walks you through the process of adding, configuring, and optimizing swap space on Ubuntu 22.04 LTS. By following these instructions, you’ll ensure your system remains stable even under memory-intensive workloads.

Understanding Swap Space in Ubuntu 22.04

Swap space functions as a virtual extension of your system’s RAM. When your physical memory fills up, the Linux kernel transfers inactive memory pages to the swap space, freeing up valuable RAM for active processes. This mechanism prevents system crashes due to memory exhaustion and allows your Ubuntu system to handle larger workloads than it could with just physical RAM alone.

In Ubuntu 22.04 LTS, swap space can exist in two primary forms:

Swap files are the most common and flexible approach. These are regular files created on your existing filesystem that are designated for swap usage. Swap files are particularly advantageous because they can be easily resized, created, or removed without altering your disk partitioning scheme.

Swap partitions are dedicated disk partitions specifically formatted for swap use. While slightly more efficient in some scenarios, they require partitioning your disk, making them less flexible than swap files for most users.

For most modern Ubuntu installations, especially desktop environments and virtual machines, swap files are the recommended approach due to their flexibility and ease of management. The days when swap partitions offered significant performance advantages are largely behind us, especially with modern SSDs and file systems.

How Much Swap Space Do You Need?

The ideal swap size depends on several factors, including your system’s RAM, workload patterns, and whether you need hibernation support. Here are some general guidelines:

• Systems with less than 2GB RAM: Use swap equal to 2× RAM size
• Systems with 2GB to 8GB RAM: Use swap equal to RAM size
• Systems with more than 8GB RAM: Use at least 4GB swap space, or more if hibernation is required

For systems that use hibernation (suspend-to-disk), your swap size should be at least equal to your RAM size to accommodate the memory dump during hibernation.

Prerequisites for Adding Swap Space

Before proceeding with adding swap space, ensure you have these prerequisites in place:

Administrative Privileges: You’ll need root or sudo access to execute the commands in this tutorial. Most commands will be prefixed with sudo.

Available Disk Space: Check your current disk space to ensure you have enough room for the swap file:

df -h

This command shows available space on all mounted filesystems. You’ll need free space at least equal to your planned swap size.

Current Swap Status: Determine whether swap space already exists on your system:

sudo swapon --show

If this command returns no output, it means no swap space is currently configured. Otherwise, it will display details about existing swap spaces.

For a more comprehensive view of memory allocation, use:

free -h

This shows your system’s RAM and swap usage in human-readable format (GB/MB).

Checking Current Swap Configuration

Before creating new swap space, it’s crucial to thoroughly examine your current setup. This prevents potential conflicts and helps determine the appropriate size for your new swap space.

Start by checking if any swap space is already active on your system:

sudo swapon --show

This command displays information about all active swap spaces, including type (file or partition), size, used space, and priority. If nothing is returned, your system currently has no swap space enabled.

For detailed statistics on your system’s memory allocation:

free -h

The output shows total, used, and available RAM along with swap information. The -h flag ensures the sizes are displayed in human-readable units rather than bytes.

You can also examine the /proc/swaps file for comprehensive swap information:

cat /proc/swaps

This file contains details about all active swap spaces on your system, including their paths and usage statistics.

If you discover existing swap space, you can either add more swap or disable the current swap and replace it. For systems with multiple swap spaces, you can prioritize them using the priority parameter when enabling them.

Creating a Swap File in Ubuntu 22.04

Creating a swap file is the recommended approach for most Ubuntu 22.04 systems. This method offers flexibility without requiring disk repartitioning. Follow these detailed steps to create and configure a swap file:

Step 1: Create the Swap File

You have two methods to create a swap file: using fallocate (faster) or dd (more compatible). Let’s explore both options:

Option 1: Using fallocate (Recommended)

The fallocate command is the quicker way to create a swap file:

sudo fallocate -l 4G /swapfile

This creates a 4GB swap file at the root directory. Adjust the size according to your needs by changing the 4G value.

Option 2: Using dd (Alternative method)

If fallocate isn’t available or doesn’t work on your filesystem, use the dd command:

sudo dd if=/dev/zero of=/swapfile bs=1M count=4096

This creates a 4GB swap file (4096 × 1MB). The process might take longer than fallocate but works on all filesystems.

Step 2: Secure the Swap File

Set appropriate permissions to prevent unauthorized access to your swap file:

sudo chmod 600 /swapfile

This command restricts read and write permissions to the root user only, which is critical for security. Skipping this step could potentially allow regular users to access sensitive information that might be written to the swap file.

Step 3: Set Up the Swap Area

Format the file as swap space:

sudo mkswap /swapfile

This command prepares the file for use as swap space. You should see output confirming the swap file creation along with its UUID.

Step 4: Enable the Swap File

Activate the swap file immediately:

sudo swapon /swapfile

This makes the swap space available for immediate use by the system. The change remains active until the next system reboot unless you make it permanent.

Step 5: Make the Swap File Permanent

To ensure your swap file persists across system reboots, you need to add it to the /etc/fstab file:

sudo nano /etc/fstab

Add the following line at the end of the file:

/swapfile swap swap defaults 0 0

Save and close the file. This entry tells Ubuntu to automatically activate this swap file during the boot process.

Step 6: Verify the Swap Configuration

Confirm that your new swap space is active and properly configured:

sudo swapon --show

And:

free -h

These commands should now display your newly created swap space. The swapon --show command will indicate the path, type, size, and usage of the swap, while free -h will show how much swap space is available to your system.

Your swap file is now successfully created and will be available even after system reboots, providing your Ubuntu system with additional memory resources when needed.

Resizing an Existing Swap File

As your system requirements change, you might need to adjust your swap size. Unlike swap partitions, swap files can be easily resized without repartitioning your disk. Here’s how to increase or decrease an existing swap file:

Step 1: Deactivate the Current Swap File

First, disable the current swap file:

sudo swapoff /swapfile

This safely deactivates the swap file, allowing it to be modified. Ensure your system has enough RAM to handle operations while swap is disabled.

Step 2: Resize the Swap File

Delete the existing swap file and create a new one with the desired size:

Using fallocate:

sudo rm /swapfile
sudo fallocate -l 8G /swapfile

Or using dd:

sudo rm /swapfile
sudo dd if=/dev/zero of=/swapfile bs=1M count=8192

This example increases the swap size to 8GB. Adjust the size according to your needs.

Step 3: Reinitialize the Swap File

Format the newly resized file as swap space:

sudo mkswap /swapfile

This prepares the resized file for use as swap space.

Step 4: Set Secure Permissions

Ensure the swap file has secure permissions:

sudo chmod 600 /swapfile

This restricts access to the root user only, which is essential for security.

Step 5: Reactivate the Swap File

Enable the resized swap file:

sudo swapon /swapfile

This activates the newly resized swap space for immediate use.

Step 6: Verify the Changes

Confirm that your swap file has been resized correctly:

sudo swapon --show
free -h

These commands should display the updated swap size.

If you’ve kept the same swap file path, the existing entry in /etc/fstab will still work without modifications. The swap file will be automatically activated with its new size at system boot.

Optimizing Swap Performance in Ubuntu 22.04

After setting up swap space, you can fine-tune its behavior to match your system’s needs. One key parameter to adjust is “swappiness,” which controls how aggressively Ubuntu uses the swap space:

Understanding Swappiness

Swappiness is a kernel parameter that defines how much the system prefers swap over RAM. It accepts values from 0 to 100:

• Higher values (closer to 100): The system will be more aggressive in moving memory pages to swap, potentially freeing up more RAM but increasing disk I/O.
• Lower values (closer to 0): The system will avoid using swap until absolutely necessary, keeping more data in RAM for faster access.

Checking Current Swappiness Value

See your current swappiness setting with:

cat /proc/sys/vm/swappiness

The default value in Ubuntu 22.04 is typically 60.

Temporarily Adjusting Swappiness

To change swappiness temporarily (until next reboot):

sudo sysctl vm.swappiness=10

This sets a lower swappiness value, making the system less likely to use swap when RAM is available.

Making Swappiness Changes Permanent

For permanent changes, edit the system configuration:

sudo nano /etc/sysctl.conf

Add or modify this line:

vm.swappiness=10

Save and close the file. The change will take effect after the next reboot, or you can apply it immediately with:

sudo sysctl -p

Recommended Swappiness Values

• Desktop systems: 10-20 provides better responsiveness
• Servers with sufficient RAM: 10-30 balances performance and stability
• Systems with limited RAM: 60 (default) may be necessary to prevent out-of-memory conditions
• Systems with SSDs: Can use higher values with less performance penalty due to faster disk speeds

Monitor your system’s performance after adjusting swappiness to find the optimal value for your specific workload patterns.

Removing Swap Space

If you need to remove swap space from your Ubuntu system, follow these steps:

Step 1: Deactivate the Swap File

First, disable the swap file:

sudo swapoff /swapfile

This safely disables the swap file, returning any data to RAM if possible.

Step 2: Remove the Swap Entry from System Configuration

Edit the fstab file to remove the swap entry:

sudo nano /etc/fstab

Find and delete or comment out the line containing the swap file information:

/swapfile swap swap defaults 0 0

Save and close the file.

Step 3: Delete the Swap File

Remove the swap file from your system:

sudo rm /swapfile

This permanently deletes the swap file, freeing up disk space.

Step 4: Verify Removal

Confirm that swap space has been successfully removed:

sudo swapon --show
free -h

These commands should no longer show any swap space if all swap has been properly removed.

Before removing swap space, ensure your system has enough RAM to handle your workload without swap. Consider temporarily disabling swap with swapoff first to test system stability before permanent removal.

Troubleshooting Common Swap Issues

When working with swap space on Ubuntu 22.04, you might encounter these common issues:

Permission Errors

If you see “Permission denied” errors, ensure you’re using sudo with the commands:

sudo mkswap /swapfile
sudo swapon /swapfile

Also verify that you’ve set the correct permissions on the swap file:

sudo chmod 600 /swapfile

Swap Not Persisting After Reboot

If your swap space disappears after rebooting, check your /etc/fstab entry:

sudo cat /etc/fstab

Ensure the entry is correctly formatted:

/swapfile swap swap defaults 0 0

Look for any syntax errors or misplaced characters in the file.

“Cannot Allocate Memory” Errors

These typically occur when the system has insufficient RAM and swap. Add more swap space or optimize the memory usage of your applications. Checking logs can help identify the processes consuming memory:

sudo dmesg | grep -i memory

fallocate Command Not Working

Some filesystems don’t support fallocate. If you encounter errors, use the alternative dd command:

sudo dd if=/dev/zero of=/swapfile bs=1M count=4096

This works on all filesystems but may take longer.

System Performance Degradation

If your system is constantly using swap space, resulting in sluggish performance, you’re likely experiencing “swap thrashing.” This indicates insufficient RAM for your workload. Consider:

1. Adding more physical RAM
2. Reducing the number of running applications
3. Optimizing applications to use less memory
4. Adjusting swappiness to a higher value temporarily

Monitor swap usage with:

watch -n 1 free -h

This updates memory statistics every second, helping you identify patterns in swap usage.

Failed Hibernation

If your system fails to hibernate or resume from hibernation, ensure your swap size is at least equal to your RAM size. For systems with compressed hibernation, swap should still be at least 60% of RAM size.

Best Practices and Recommendations

Follow these best practices for optimal swap configuration on Ubuntu 22.04:

Right-Size Your Swap Space

• General use: Match your RAM size up to 8GB, use at least 4GB for systems with more RAM
• Hibernation support: Use at least 1× RAM size (1.5× for safety margin)
• Servers with large RAM (>16GB): Consider using a percentage (50% or less) of RAM size unless memory-intensive applications are used

Secure Your Swap File

Always set restrictive permissions to prevent unauthorized access:

sudo chmod 600 /swapfile

This ensures only the root user can read or write to the swap file, protecting potentially sensitive data.

Monitor Swap Usage Regularly

Use these commands to keep an eye on swap utilization:

free -h
sudo swapon --show

Consider setting up monitoring tools like Netdata, Prometheus, or Grafana for long-term tracking. Consistent high swap usage indicates you may need more RAM rather than more swap.

Consider Storage Type Impact

• SSD-based swap: Performs significantly better than HDD-based swap
• For HDDs: Consider dedicating a separate disk or partition for swap to reduce I/O contention
• ZRAM/ZSWAP: Consider enabling these compressed swap technologies for better performance on systems with limited resources

Maintain Sufficient Free Space

Ensure at least 25% free space on the filesystem containing your swap file to prevent fragmentation issues and allow for potential growth.

Set Appropriate Mount Options

In /etc/fstab, you can add optional parameters to optimize swap behavior:

/swapfile swap swap defaults,pri=10 0 0

The pri parameter sets priority (higher values indicate higher priority) when multiple swap spaces exist.