How to Create and Manage Swap Files on Ubuntu 26.04

Swap space serves as an extension of your system’s physical RAM, providing a safety net when memory runs low. On Ubuntu 26.04, using a swap file rather than a dedicated swap partition offers greater flexibility, since you can easily create, resize, or remove it without repartitioning your disk. In this tutorial, you will learn how to swap file create manage ubuntu 26.04 systems effectively, from initial setup through performance tuning.

Software Requirements

What Is Swap Space?

Swap space is a designated area on your storage device that the Linux kernel uses as an overflow for RAM. When your system’s physical memory is fully utilized, the kernel moves less frequently accessed memory pages to swap, thereby freeing RAM for active processes. This mechanism prevents out-of-memory crashes and keeps the system responsive under heavy load.

There are two primary ways to provide swap on Linux: a dedicated swap partition or a swap file. Historically, swap partitions were the standard approach. However, swap files offer several advantages. Consequently, they have become the preferred method on modern Ubuntu installations. You can create, resize, or delete a swap file without touching your partition table, which makes capacity planning far more flexible.

When Do You Need Swap?

Several scenarios make swap space essential. Servers with limited RAM benefit from swap as a safety net during traffic spikes. Desktop users running memory-intensive applications like video editors or virtual machines may also need extra breathing room. Furthermore, swap is a requirement for hibernation, where the entire contents of RAM are written to disk before the system powers off.

As a general guideline, systems with 2 GB of RAM or less should have swap equal to double the RAM size. Systems with 4-8 GB can use a swap file equal to the RAM size. For systems with more than 8 GB, a swap file of 2-4 GB is typically sufficient unless hibernation is planned.

Checking Existing Swap on Ubuntu 26.04

Before creating a new swap file, you should first verify whether your Ubuntu 26.04 system already has swap configured. There are several commands to inspect the current swap setup.

1. Check active swap devices: The swapon --show command provides a clean summary of all active swap areas, including their type, size, and priority.

   $ sudo swapon --show

   If the command produces no output, your system currently has no active swap.

2. View memory and swap summary: The free command shows both RAM and swap usage at a glance.

   $ free -h

   Look at the “Swap” row. If it shows all zeros, no swap is active.

3. Inspect /proc/swaps: For a more detailed view, read the kernel’s swap information directly.

   $ cat /proc/swaps

   This file lists each swap area with its filename, type, size, usage, and priority.

Creating a Swap File on Ubuntu 26.04

Creating a swap file on Ubuntu 26.04 involves allocating a file of the desired size, setting proper permissions, formatting it as swap, and then activating it. Follow these steps to create and manage a swap file on your system.

1. Allocate the swap file: Use the dd command to create a file filled with zeros. The following example creates a 2 GB swap file at /swapfile.

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

   The bs=1M parameter sets the block size to 1 megabyte, and count=2048 writes 2048 blocks, resulting in a 2 GB file. The status=progress flag displays the write progress. Adjust the count value to match your desired swap size. For instance, use count=4096 for a 4 GB swap file.

2. Set correct permissions: The swap file must only be readable and writable by root. If the permissions are too open, you may encounter permission denied errors or security warnings.

   $ sudo chmod 600 /swapfile

   This ensures that no regular user can read or modify the swap file contents.

3. Format the file as swap: The mkswap command writes a swap signature to the file, preparing it for use.

   $ sudo mkswap /swapfile

   You should see output confirming the swap area size and UUID.

4. Activate the swap file: Use swapon to enable the swap file immediately.

   $ sudo swapon /swapfile

5. Verify the swap is active: Confirm that the swap file is now in use.

   $ sudo swapon --show

   The output should list /swapfile with the correct size. You can also run free -h to verify the total swap shown matches your new file size.

Making Swap Permanent via /etc/fstab

The swapon command activates swap only for the current session. To ensure the swap file is activated automatically after a restart, you must add an entry to /etc/fstab.

1. Back up your fstab file: Before making any changes, create a backup of the existing file.

   $ sudo cp /etc/fstab /etc/fstab.bak

2. Add the swap entry: Append the swap file entry to /etc/fstab.

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

   This line tells the system to mount /swapfile as swap space during boot.

3. Verify the fstab entry: Review the file to confirm the entry was added correctly.

   $ cat /etc/fstab

   You should see a line reading /swapfile none swap sw 0 0 at the end of the file.

Resizing or Removing a Swap File

One of the key advantages of swap files over swap partitions is the ability to resize or remove them without modifying your disk layout. Whether you need more swap space or want to reclaim disk space, the process is straightforward.

Resizing a Swap File

To resize an existing swap file, you must first deactivate it, recreate it at the new size, and then reactivate it.

1. Deactivate the current swap file: Turn off the swap file before making changes.

   $ sudo swapoff /swapfile

2. Recreate the file at the new size: For example, to increase the swap to 4 GB:

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

3. Set permissions and format: Repeat the permission and format steps.

   $ sudo chmod 600 /swapfile
   $ sudo mkswap /swapfile

4. Reactivate the swap file:

   $ sudo swapon /swapfile

   No changes to /etc/fstab are needed since the filename remains the same.

   

Removing a Swap File

If you no longer need the swap file, remove it completely with these steps.

1. Deactivate the swap file:

   $ sudo swapoff /swapfile

2. Remove the fstab entry: Edit /etc/fstab and delete the line containing /swapfile.

   $ sudo nano /etc/fstab

   Remove the line /swapfile none swap sw 0 0, then save and exit.

3. Delete the swap file:

   $ sudo rm /swapfile

Tuning Swappiness and Cache Pressure

The Linux kernel exposes tunable parameters that control how aggressively it uses swap. Adjusting these values can improve performance depending on your workload.

Understanding Swappiness

The vm.swappiness parameter controls the kernel’s tendency to move processes from physical memory to swap. The value ranges from 0 to 200, with the default set to 60 on most Ubuntu systems. A lower value tells the kernel to prefer keeping data in RAM, while a higher value encourages more swap usage.

1. Check the current swappiness value:

   $ cat /proc/sys/vm/swappiness

2. Change swappiness temporarily: To set swappiness to 10 for the current session:

   $ sudo sysctl vm.swappiness=10

3. Make the change permanent: Create a configuration file in /etc/sysctl.d/ to persist the setting across reboots.

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

Adjusting VFS Cache Pressure

The vm.vfs_cache_pressure parameter controls how aggressively the kernel reclaims memory used for caching directory and inode objects. The default value is 100. Lowering it makes the kernel prefer to retain these caches, which can improve filesystem performance.

1. Check the current value:

   $ cat /proc/sys/vm/vfs_cache_pressure

2. Set a lower cache pressure: A value of 50 is a common recommendation for desktop use.

   $ sudo sysctl vm.vfs_cache_pressure=50

3. Persist the change:

   $ echo 'vm.vfs_cache_pressure=50' | sudo tee -a /etc/sysctl.d/99-swappiness.conf

   This appends the setting to the same file used for swappiness, keeping all swap-related tuning in one place.

Conclusion

In this tutorial, you learned how to create and manage swap files on Ubuntu 26.04. You checked your existing swap configuration, created a new swap file with dd, set proper permissions, formatted and activated it, and added it to /etc/fstab for persistence. Additionally, you explored how to resize or remove swap files and how to tune vm.swappiness and vm.vfs_cache_pressure for optimal performance. Swap files provide a simple yet powerful way to extend your system’s memory capacity without repartitioning your disk. For further reading, consult the Ubuntu Swap FAQ on the official community documentation.

Frequently Asked Questions

1. How much swap space do I need on Ubuntu 26.04? The recommended size depends on your RAM and use case. Systems with 2 GB or less should have swap equal to double the RAM. Systems with 4-8 GB can match the RAM size. For systems with more than 8 GB, 2-4 GB of swap is usually enough unless you plan to use hibernation, which requires swap at least equal to your total RAM.
2. Can I have multiple swap files on Ubuntu 26.04? Yes, Linux supports multiple swap areas simultaneously. You can create additional swap files with different filenames (for example, /swapfile2) and activate them alongside the first. Use the priority option in /etc/fstab to control which swap area is used first, such as /swapfile2 none swap sw,pri=10 0 0.
3. Does swap slow down my system? Swap on disk is significantly slower than RAM. However, having swap available prevents out-of-memory errors that could crash your applications. The performance impact depends on how frequently swap is used. By tuning the vm.swappiness value to a lower number, you can minimize unnecessary swapping and keep your system performing well.
4. Why does mkswap fail when I use fallocate? On some filesystems, fallocate creates files with holes (sparse allocations) rather than contiguous blocks. The mkswap command detects this and refuses to proceed because swap requires fully allocated space. Use dd if=/dev/zero instead, which writes actual data to every byte of the file.
5. How do I check if my swap is being used? Run free -h and look at the “Swap” row. The “used” column indicates how much swap is currently occupied. Alternatively, swapon --show displays each swap area with its total and used space. If you want to monitor swap usage over time, use vmstat 1 and watch the si (swap in) and so (swap out) columns.