I'm installing multiple operating systems on a usb drive I recently purchased for this purpose and was wondering how to create a usb drive with multiple persistent OS's that will be linux based and have a capacity > 4gb of the casper-rw file and was wondering 1. if this was possible (I have read from 1 source that it wasnt but it was not one that was overly trustworthy), and 2. how to go about doing it (answers should be aimed at ubuntu being the system I create the drive on)
You may want to check Easy2Boot. It's the most versatile and probably also best-documented tool for multiboot things. Specifically, it supports in particular
Boot multiple linux ISOs each with separate persistence files
[in addition, the author is also pretty helpful and really responsive even for in-depth questions] You could misuse that to reference the same casper-rw file for each of the systems.
For similar topics, you might want to check the following links:
An NTFS Easy2boot drive will boot multiple linux ISOs with persistence even if the linux being used does not support NTFS. You can even boot from an exFAT E2B drive to a linux distro that does not support exFAT. E2B creates a 4th partition on the E2B USB drive and 'maps' the ISO to that partition. When the ISO boots, it sees the 4th partition as having a CDFS filesystem and mounts it. It then gets the .sqfs file (or whatever it needs) from that CDFS partition. The same for the persistence file - it maps the persistence file to partition 3 of the E2B USB drive before booting to the ISO. Pretty much all linux ISOs should work with E2B. It also supports UEFI-booting (by converting each linux ISO to a .imgPTN partition image file and 'switching in' that partition.)
You can specify the persistence volume label in the boot parameters:
As far as I know, this works with Debian. More info