A Linux live USB drive is normally a blank slate each time you boot it. You can boot it up, install programs, save files, and change settings. But, as soon as you reboot, all your changes are wiped away and you’re back to a fresh system. This can be useful, but if you want a system that picks up where you left off, you can create a live USB with persistent storage.
How Persistent Storage Works
When you create a USB drive with persistence, you’ll allocate up to 4 GB of the USB drive for a persistent overlay file. Any changes you make to the system—for example, saving a file to your desktop, changing the settings in an application, or installing a program—will be stored in the overlay file. Whenever you boot the USB drive on any computer, your files, settings, and installed programs will be there.
This is an ideal feature if you want to keep a live Linux system on a USB drive and use on different PCs. You won’t have to set up your system up from scratch each time you boot. You don’t need persistence if you’re just using a USB drive to install Ubuntu and then running it from your hard drive afterward.
There are a few limitations. You can’t modify system files, like the kernel. You can’t perform major system upgrades. You also can’t install hardware drivers. However, you can install most applications. You can even update most installed applications, so you can be sure your persistent USB drive has the latest version of the web browser you prefer.
Persistence doesn’t work with every Linux distribution. We’ve tested it with the latest versions of Ubuntu—Ubuntu 18.04 LTS and Ubuntu 19.04—and it works. It should also work with Ubuntu-based Linux distributions. In the past, we had luck with Fedora as well. Just download the appropriate ISO file and follow the instructions below.
How to Make a Persistent Ubuntu USB Drive on Ubuntu
You’ll need a computer already running Ubuntu to perform this process. You’ll also need a USB drive with enough storage capacity to set up persistence. We used a 16 GB drive, but an 8 GB drive would have worked as well. The bigger the drive, the more persistent storage you can have.
The grub, boot and Ubuntu partitions take up less than 2 GB. The remainder of the space on the USB drive will be used for the casper-rw and the usbdata partitions.
The casper-rw partition is used for persistent storage. For example, software you install and settings files will be stored here.
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Source: How-To Geek
