Manually creating Casper -rw file

Hello guys. I was wondering if there was a way to create the casper -rw file for persistence manually, i.e. via terminal. I've been using Ubuntu 14.04 Live USB with persistence and it ran fine for the last two weeks. Last night, I was installing a bunch of apps (or at least, I thought I was) and I got a few errors after which the terminal froze. I had no idea what went wrong, so I just forced shut down and fell asleep.

This morning, I tried to boot my netbook and the screen went blank after the grub menu and just stayed like that. I figured I must've accidentally updated the kernel and it messed up the system. So I plugged in another USB with another OS in my netbook, booted, browsed to the drive where the casper -rw file was located and deleted it.

This solved one problem. I could boot into Ubuntu alright, except I just didn't have persistence. So is there a way to manually create the persistence file WHILE I'm running Ubuntu? I don't want to do another fresh install as I only have two drives (one for backup and one for Ubuntu) and my backup drive's running Porteus and it always fails to create bootable USBs due to some module issue.

I would also like to know if there's a way to stop Ubuntu from updating kernel so as not to get in the same situation again in the future. Thanks!