Persistent Linux - What is it? After looking through some of the tutorials offered on Pen Drive Linux, you may be wondering what Persistent Linux means. So in the following segment, I will cover my understanding of persistence in relation to Linux, data storage and recovery. In addition, I will try to explain some of the limitations of using a USB Persistent Overlay partition, Image or other Persistence data storage structure.
Wikipedia definition: "Persistence - in computer science refers to the characteristic of data that outlives the execution of the program that created it. Without this capability, data only exists in RAM, and will be lost when the memory loses power, such as on computer shutdown."
Table of Contents
What does Persistence mean for USB Linux Users?
For USB Linux users, a Persistent Linux install is one that allows its user to save data changes back to the USB storage device instead of leaving the information in system RAM. This data can then be recovered and used again on subsequent boots, even when booting from different machines. Typically a separate Persistent storage space (persistent overlay) image or partition is used in conjunction with a compressed Live Linux OS.
Linux persistence feature advantages & disadvantages
There are several advantages and disadvantages to using a Linux Persistence feature for storage. Here's a breakdown of both:
Advantages of using persistent storage:
- More available storage space - Since the Live Linux Operating System (OS) is compressed with most persistent installs, the entire operating system takes up less space. Enabling operating systems that usually require gigabytes of space to be condensed into storage capacities less than 1GB in many cases.
- Less wear on the USB device - Since most of the operating system is loaded into system memory and only the changes are written back to the USB storage device, the read/write cycles decrease, prolonging your USB flash drives life.
- Independent Overlay - The overlay storage space used for persistent changes is independent of and separated from the OS, allowing users to backup or recover persistent changes on the fly without reinstalling and rebuilding an entire operating system. The operating system should still continue to function like a fresh install if the persistence feature is disabled.
- Portability - Bookmarks, settings, system preferences, customizations and file downloads can in most cases be stored and retrieved when booting from different or multiple machines.
Disadvantages of using persistent storage:
- Limited Protection - Persistent data is left unencrypted in most cases. If you lose your drive, someone could steal and use your data.
- Persistent data is uncompressed - Although the Live OS can be compressed, the persistent data is left uncompressed making it very easy to run out of storage space quickly.
- Some changes are not saved persistently - In some cases, further modification is required to enable things like graphical card settings and network card settings to be saved. In almost all cases, system wide kernel updates and upgrades will not work and could result in a broken boot.
*System and initrd updates appear to be working on recent Ubuntu and related remixes. See how to Create an Ubuntu Persistent USB.