The following tutorial explains how to create a larger casper-rw loop file (or writable file) for your Ubuntu based USB flash drive install. For example, on: Ubuntu, Xubuntu, Kubuntu, Lubuntu, Crunchbang, or Linux Mint. A larger casper-rw loop file is particularly useful for those who have performed a Linux install to a large thumb drive using a Windows USB tutorial and need more persistent storage space for saving changes. The default casper-rw loop file we used in the Windows USB installation tutorials is only 1GB.
You will need to perform the following steps from a booted Linux system other than the USB Linux installation. Or simply boot your USB with persistence disabled by removing the persistent boot parameter.
Important Considerations:
- For Ubuntu based distributions from version 20.04 onward, use writable in place of casper-rw throughout this tutorial.
- Persistent file size (count) must be less than =< 4096 MB on a FAT32 formatted flash drive due to the 4GB file size limitation of a FAT32 partition. ExFAT and NTFS formatted drives do not exhibit this limitation.
About Casper Persistence
Casper Persistence is a powerful feature of Linux that allows you to save system changes and files across reboots when running from a live USB. For example, if you install software, customize settings, or download files while using a live USB, these changes can be retained after rebooting. Without persistence, everything you do during the session will be lost once you shut down the system. The casper-rw file is the critical component that enables this persistent storage. It is essentially a virtual disk used to save changes and data, making your live Linux system feel more like a fully installed one, while still running from a USB drive.
What is the casper-rw
file? In simple terms, casper-rw is a loop file used by Ubuntu-based distributions to store your persistent changes. When booting from a live USB, the system is loaded into memory, but without persistence, it only uses the RAM and doesn't retain changes after a reboot. The casper-rw
loop file serves as a storage container that holds everything you modify during the session (e.g., installed programs, configuration changes, or saved documents). The size of this file determines how much data you can store persistently.
Why create a larger casper-rw
file? The default casper-rw
file is typically set to a small size (usually around 1GB), which might not be enough for users who want to install many programs, store large files, or make significant customizations. Expanding this file allows you to increase the amount of storage available for persistent data, ensuring that you have enough space for everything you need.
Why FAT32? FAT32 is the most commonly used file system for USB drives because it offers broad compatibility across various operating systems, including Windows, macOS, and Linux. It is also relatively fast for small files and has been around for a long time. However, FAT32 has a major limitation: it cannot handle files larger than 4GB. This becomes problematic when you want to create a large casper-rw
file because it may exceed this limit, preventing you from creating or expanding the persistent storage beyond 4GB.
Alternatives to FAT32: NTFS and exFAT If you need a larger persistent storage file, you can format your USB drive using other file systems like NTFS or exFAT, both of which support larger file sizes. These file systems are better suited for large files and persistent storage, allowing you to create a larger casper-rw
file that exceeds the 4GB limit imposed by FAT32. However, while these file systems are more flexible in terms of file size, you may encounter compatibility issues with certain systems or devices that don't support NTFS or exFAT. For most modern Linux distributions, however, exFAT is supported out of the box and NTFS can be used with the right drivers.
In Summary, when creating a larger casper-rw
file, it’s important to choose the appropriate file system for your needs. If you don’t need more than 4GB of persistent storage and want maximum compatibility, FAT32 is still a good choice. If you require more space or plan to use larger files, consider using NTFS or exFAT. Always make sure your USB drive has sufficient capacity to handle the desired file size, and keep in mind that the performance of your USB drive can vary depending on its speed and the file system used.
This tutorial assumes you have a basic understanding of how to use the terminal in Linux. If you're unfamiliar with command-line operations, you may want to familiarize yourself with basic terminal commands to follow along smoothly. Don't worry—this tutorial will guide you step by step through the process!
Creating a NEW larger casper-rw overlay file
The following method will create a NEW casper-rw file that will replace the old one. If you want to resize an existing image, see the next section.
- After you are up and running in Linux, insert the flash drive that contains your casper-rw loop file.
- Open a terminal.
- Type the following into the terminal window and press enter:
dd if=/dev/zero of=casper-rw bs=1M count=4096
(replacing 4096 with the "size in MB" you wish to use for saving changes persistently).
Tip: Use a size slightly less than the full capacity of your USB drive to avoid overwriting important areas or causing corruption.
- Type the following into the terminal and press enter:
mkfs.ext3 -F casper-rw
This formats the file with the ext3 filesystem, which is required for persistence.
- Copy the new casper-rw or writable file to your USB flash drive.
- Restart your computer, booting from the USB flash drive, and enjoy using the larger casper-rw loop block file you have just created.
Resize an existing casper-rw overlay file
The following method will allow you to resize your existing casper-rw image (expand casper-rw). You should create a backup just in case before proceeding.
- After you are up and running in Linux, insert the flash drive that contains your casper-rw loop file.
- Open a terminal and change directory (CD) to the location of your casper-rw file.
Tip: Use thecd
command followed by the path to your USB drive. For example:cd /media/username/USB_LABEL
- Type the following into the terminal window and press enter:
dd if=/dev/zero bs=1M count=4096 >> casper-rw
(replacing 4096 with the size in MB you wish to increase the original size by).
Note: This step appends blank space to the existing file. Ensure you have enough free space on your USB drive before proceeding.
- Type the following into the terminal window and press enter to resize the filesystem:
resize2fs casper-rw
This resizes the filesystem inside the casper-rw file to match the new file size.
Troubleshooting
Error: "No space left on device"
Ensure there is sufficient free space on your USB drive before resizing the casper-rw file.
"resize2fs: Device or resource busy"
This error may occur if the file is currently in use. Ensure that the USB drive is not mounted or in use, and try again.
Not enough space even after resizing?
Consider switching to an alternative filesystem like NTFS or exFAT on your USB drive to bypass the FAT32 file size limitation. You can then create even larger casper-rw files.
FAQ
- Q: Can I create a casper-rw file larger than 4GB?
- A: Yes, but only if your USB drive is formatted with a file system that supports larger files, such as NTFS or exFAT. If your drive is formatted as FAT32, the maximum file size is 4GB.
- Q: What happens if I run out of space on my USB drive?
- A: If you run out of space, you’ll need to either reduce the size of your casper-rw file or reformat the USB drive to a larger capacity file system.
- Q: Is it safe to use a casper-rw file on the same USB drive I boot from?
- A: Yes, this is the standard practice for persistence. Just make sure not to overwrite important system files.
- Q: Can I use this method for distributions other than Ubuntu?
- A: This method is designed for Ubuntu-based distributions, but some of the principles may work for other Linux distributions. Always check the documentation for your specific distro.
Final Thoughts
Creating a larger casper-rw file or resizing a casper-rw file is a straightforward way to extend the capabilities of a persistent Linux USB installation. With the steps outlined above, you can ensure you have enough storage to save your changes, install additional software, and customize your Linux environment. Always remember to back up your data before making major changes, and don’t hesitate to experiment to find the configuration that works best for your needs.
I hope this guide was helpful. If you have any additional questions or run into other issues, feel free to reach out. Happy Persistent Linux booting!