One thing I've noticed with Samsung phones/Ubuntu & file transfers/manipulation is connectivity is hit & miss until I install gMTP. I suspect it's some kind of driver issue & installing gMTP solves that. Once I do that, transferring files/etc is a snap the usual way via the Ubuntu File Manager (I.E drag & drop as per Windoze).
Could also be a simple case of not being able to mount it; sometimes my Ubuntu installation loses the ability to mount external drives temporarily for whatever reason (even the partition my Windoze installation is unable to be mounted), and logout/login again always fixes this. Try this, then the gMTP thing (I'm running Raring Ringtail).
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Most retarded thread on XDA in 2013