How to Configure Swap Space in Ubuntu 24.04?

Prerequisites

Before starting, ensure you have:

• Ubuntu 24.04 is installed and running
• Terminal access with sudo privileges
• Sufficient disk space for the swap file (usually 1-2 times your RAM size)
• Basic understanding of command-line operations

Step 1: Check Current Memory and Swap Status

First, examine your system's current memory configuration to understand what resources are already available.

1.1 View the current memory usage, including any existing swap:

sudo free -h

The swap total is 0B, which means no swap is enabled.

This command displays memory information in a human-readable format. You'll see output similar to above:

1.2 Check specifically for active swap spaces:

sudo swapon --show

If no output appears, your system does not have any active swap files or partitions. If you see output, it displays currently active swap spaces, along with their sizes and priorities.

1.3 Verify available disk space to ensure you have enough room for the swap file:

df -h

Look for the root filesystem (/) and ensure you have adequate free space. A good rule of thumb is to have at least 1-2GB of free space beyond your intended swap size.

Step 2: Create the Swap File

Now, create a dedicated swap file. The size depends on your system's needs, but here are standard guidelines:

• Systems with 2 GB RAM or less: Create a swap equal to 2x RAM
• Systems with 2-8 GB RAM: Create a swap equal to the RAM size
• Systems with 8 GB+ RAM: Create 2-4GB swap (unless specific applications require more)

2.1 Create a 2GB swap file using the fallocate command:

sudo fallocate -l 2G /swapfile  

The fallocate command immediately allocates the specified space. If fallocate doesn't work, use the alternative dd method:

sudo dd if=/dev/zero of=/swapfile bs=1M count=2048

This creates the same 2GB file but may take longer as it writes zeros to the entire file.

2.2 Verify the file was created with the correct size:

ls -lh /swapfile

You should see output showing the file size as 2.0 G.

Step 3: Set Proper File Permissions

Swap files contain sensitive data from your system's memory, so securing them is crucial.

3.1 Set restrictive permissions so only the root user can read and write the file:

Sudo chmod with code 600 is used to keep any file private

sudo chmod 600 /swapfile 

3.2 Verify the permissions are correctly set:

ls -lh /swapfile

The output should show -rw-------, indicating only root has read/write access.

Step 4: Format and Enable the Swap File

Transform your regular file into a swap space that the system can use.

4.1 Format the file as swap space:

sudo mkswap /swapfile

This command prepares the file for use as swap and displays information about the created swap space, including its UUID.

4.2 Enable the swap file for immediate use:

sudo swapon /swapfile 

4.3 Verify the swap is now active:

sudo swapon --show

You should see your new swap file listed with its size and priority.

4.4 Check the updated memory information:

sudo free -h

The swap line should now show the additional space available.

Step 5: Set up Permanent Swap

Currently, your swap file is only active for this session. To ensure it remains active after reboots, add it to the system's file system table.

5.1 First, create a backup of the fstab file:

sudo cp /etc/fstab /etc/fstab.backup 

5.2 Add the swap file to the fstab configuration:

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

This line instructs the system to mount the swap file at boot time automatically. The fields mean:

• /swapfile: The swap file location
• none: No mount point (swap doesn't mount to a directory)
• swap: File system type
• sw: Swap-specific mount options
• 0 0: No backup needed, no fsck required

Step 6: How to Optimize Swap?

Fine-tune your swap configuration for optimal performance based on your system's usage patterns.

Adjust Swappiness

Swappiness controls how aggressively the system uses swap space. The value ranges from 0 to 100:

• 0-10: Minimal swapping, prefer RAM
• 10-50: Moderate swapping for balanced performance
• 60 (default): Aggressive swapping, suitable for desktops
• 90-100: Very aggressive swapping

Check the current swappiness value:

6.1 cat /proc/sys/vm/swappiness

For servers or systems where you want to minimize swap usage, set a lower value:

sudo sysctl vm.swappiness=10

6.2 Make this change permanent by adding it to the sysctl configuration:

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

6.3 Adjust Cache Pressure

The cache pressure setting controls how quickly the system removes cached file system data. Lower values keep the cache longer, improving file system performance.

Check the current cache pressure:

cat /proc/sys/vm/vfs_cache_pressure

Set a more conservative value:

sudo sysctl vm.vfs_cache_pressure=50

Make this permanent:

echo 'vm.vfs_cache_pressure=50' | sudo tee -a /etc/sysctl.conf

Step 7: Test Your Swap Configuration

Verify everything is working correctly and will persist across reboots.

Test automatic mounting without rebooting:

sudo swapoff /swapfile

sudo swapon -a

The first command disables your swap file, and the second command enables all swap spaces listed in the fstab file. Check that your swap is active again:

sudo swapon --show

Monitor swap usage in real-time:

watch -n 1 'free -h'

Press Ctrl+C to exit the watch command.

Managing Swap Space

Disabling Swap (If Needed)

If you need to remove swap space later:

# Disable the swap file

sudo swapoff /swapfile

# Remove the file

sudo rm /swapfile

Remove the swap entry from fstab by editing the file:

sudo nano /etc/fstab

Delete the line containing /swapfile none swap sw 0 0.

Troubleshooting Common Issues

Issue: The fallocate command fails. Solution: Use the dd method instead, or check if your filesystem supports fallocate.

Issue: Swap file doesn't activate after reboot. Solution: Verify the fstab entry is correct and the file permissions are set to 600.

Issue: The System becomes slow after enabling swap. Solution: Reduce the swappiness value to minimize swap usage, or consider adding more RAM.

Issue: "Operation not permitted" when creating a swap file. Solution: Ensure you're using sudo and have sufficient disk space.

Best Practices

1. Size appropriately: Don't create unnecessarily large swap files(> 4G) that waste disk space.
    
2. Monitor usage: Regularly check swap usage to ensure it's helping rather than hindering performance.
    
3. Consider SSD wear: On systems with SSDs, monitor swap usage to avoid excessive wear on your storage device.
    
4. Security: Always set proper permissions on swap files to protect sensitive data.
    
5. Backup fstab: Always backup your fstab file before making changes.

Setting up swap space in Ubuntu 24.04 provides your system with extra memory when it becomes tight. Although Ubuntu now includes zram compression by default, traditional swap files still address real problems, especially for hibernation, low-memory systems, and resource-intensive applications.

Your new swap configuration will start automatically every time you boot up, helping prevent those frustrating moments when programs crash due to memory shortages.