Use the Linux Persistent USB File Creator to make a casper-rw persistent file or writable persistence loop file for Ubuntu based distributions. Written for use from within Windows, this tool enables you to quickly create a loopback filesystem image (Overlay Image) that can save and restore Ubuntu changes while booted from a live USB. With persistence enabled, your live Ubuntu USB can remember system settings, installed software, and personal files across reboots.
This is one of the easiest methods to create Ubuntu persistence from Windows without needing any Linux command line tools or partitioning utilities.
What is Casper-RW Persistence?
Casper-rw is a term associated with Ubuntu based live USB drives. It refers to a special loop file or partition that acts as a virtual block device. Also known as a persistent overlay image, a casper rw (read/write) file works as a companion to your live bootable Ubuntu USB, allowing you to save changes, settings, and files between sessions.
While running from a live USB version of Ubuntu or one of its derivatives, this unique feature enables the live system to act more like a full installation. There are some limitations; for example, you cannot upgrade the kernel or perform full system upgrades because these remain outside of the overlaid image.
Persistent storage on Ubuntu live USBs is an extremely popular solution for users who want a portable Linux environment, especially when traveling or when running Ubuntu on multiple computers. This feature is commonly used with live linux USB bootable systems created using tools such as the Universal USB Installer, YUMI Multiboot USB Creator, and other similar bootable USB creation tools. Note that UUI and YUMI exFAT already automate this process.
Key Terms Explained
- Live USB Drive: A portable USB flash drive containing a bootable operating system. It allows you to boot Ubuntu without installing it on the internal hard drive.
- Persistence: The ability to save files, installed applications, and customizations across reboots. Without persistence, all changes are lost when the system restarts.
- Casper: A component of Ubuntu's live system that handles booting from USB.
- Casper-rw: A special file or partition added to the live USB to provide a writable overlay.
- Writable: Required for Ubuntu 20.04 and newer.
- Overlay / Loopback File: A filesystem image (ext2/ext3/ext4) stored as a single file.
Comparison: casper-rw vs writable vs live-rw
| Feature | casper-rw | writable | live-rw |
|---|---|---|---|
| Used By | Ubuntu 19.10 and earlier | Ubuntu 20.04 and newer | Debian Live systems |
| File or Partition Name | casper-rw | writable | live-rw |
| Overlay Filesystem Format | ext2/ext3/ext4 loop file | ext4 recommended | ext2/ext3/ext4 loop file |
| Supports Saving Changes | Yes | Yes | Yes |
| Compatibility | Legacy Ubuntu persistence | Current Ubuntu persistence standard | Debian persistence only |
| Maximum File Size (FAT32) | 4GB limit | 4GB limit | 4GB limit |
Why Use Casper-RW?
Casper-rw persistence is especially useful for users who want a portable, customizable Ubuntu environment. For example, you can:
- Install additional applications and keep them across reboots.
- Save personal files, scripts, and documents directly to the USB.
- Customize desktop settings, themes, and preferences.
- Carry a secure and personal Linux environment on the go.
File size considerations: The casper rw file size depends on your allocation. If your USB is formatted with FAT32, the maximum file size is 4GB. Using ext4 or NTFS avoids this limitation and allows larger persistence files.
Casper-RW Persistent File Creator
The Persistent File Creator tool provides an easy way to create casper or writable loopback files directly from Windows. This avoids manual commands such as dd, mkfs.ext4, or partition editing.
Source Code – SHA-256: 69116a284e1d56b8a06730902bc0a5d440463a78d1620df4df1d500066d0dceb
Important: Ubuntu 20.04+ requires the file to be named writable. Ubuntu 19.10 and older use casper-rw.
How to Make a Casper Persistent Block File
- Download Persistence File Creator and run it.
- Select your USB Flash Drive.
- Choose casper-rw or writable.
- Set the desired size.
- Click Create.
Note: You can move the persistence file after creation, but it must remain at the root directory of your USB drive to function properly at boot.
Booting and Using a Casper Persistent Overlay Image
Once you have created your persistence file, the next step is to boot your Ubuntu Live USB with persistence enabled. This determines whether Ubuntu will load the writable casper-rw or writable overlay file during startup. The process is simple, but it varies depending on how the bootable USB was created and which boot menu your system uses.
Enable Persistence at Boot
Depending on how your live USB was created, you may need to manually add the persistent boot option:
- At the boot menu, press F6.
- Press ESC to edit the boot string.
- Add the word persistent at the end of the boot parameters.
- Press Enter to boot with persistence enabled.
Tip: Tools like UUI and YUMI exFAT add this automatically.
Using Persistence
A persistent overlay allows you to:
- Save and restore personalized settings.
- Retain installed software and system tweaks.
- Keep documents, media, and configuration files.
Limitations: Do not upgrade kernels or perform full system upgrades. Because the kernel remains outside the overlay, updates may cause boot failures. Persistence is best for files, apps, and personal settings.
Additional Tips for Better Persistence Performance
- Use a USB 3.0 or USB 3.2 flash drive.
- For best performance, use a portable SSD.
- Lightweight desktop environments (XFCE, LXQt) perform better.
Casper-RW Persistent File FAQ
What is the purpose of a persistent live USB?
A persistent live USB lets you save files, settings, and installed applications across reboots.
How does Casper-RW work?
Casper-RW stores your changes inside a writable overlay file or partition.
What is the difference between casper-rw and writable?
Ubuntu 20.04+ uses writable. Older versions use casper-rw.
Can I upgrade Ubuntu using persistence?
No. Kernel and system upgrades may break the live USB.
What is the maximum size of a casper-rw file?
FAT32 limits files to 4GB.
Can I move the casper-rw file?
Yes, but it must remain in the root directory.
How do I boot with persistence enabled?
Select the persistent option or append persistent manually.
What about Debian live USB persistence?
Debian uses a file named live-rw.
Do I need to reformat my USB?
No. You only need free space to add the file.
Can YUMI or UUI create a persistent Ubuntu USB?
Yes. Both tools support Ubuntu persistent storage.
Final Thoughts
Creating a persistent live USB with Ubuntu based distributions is an excellent way to carry your operating system and personal environment anywhere. Using the Casper-RW persistence feature lets you save settings, install apps, and keep personal files across reboots.
If you need a portable Linux environment while running Ubuntu, creating a casper-rw persistent file is invaluable. When paired with the Persistent File Creator and your preferred USB creation utility, setting up persistence from Windows becomes a piece of cake.
By planning your persistence file size carefully and understanding its limitations, you can unlock the full potential of your portable Ubuntu live bootable USB drive.