I was using Ubuntu 16.04.1 LTS Live DVD on a tower PC, while shutting down Firefox browser the screen froze. The DVD drive has been making grinding noises with the activity light flashing for 3 days, no response from mouse or keyboard.

I have un-exported bookmarks, is it possible to recover the system without losing data?

Or the system get's back on, or your are done.
A live DVD system works on RAM and if you reboot or power off, that info will disappear.

Is the DVD in good conditions? Maybe you can burn another ISO, replace the DVD and hope the reader could read and get un-frozen.

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What if I eject the DVD & re-insert it, would that break the loop while retaining the system in memory then maybe it would continue from where it stopped? Any way to access the data from another system on the network?

If you try and find out...
From the network, I doubt, because the system is frozen...

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See if you can run a port scan aimed at the Linux box. If you see an open ssh port you could try to connect over the network with ssh. But it sounds doubtful.

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Thanks for the suggestions, no idea how to do a port scan, guess I could learn. Is there anyway to mount a Ram drive remotely, like you can with a HDD?

Not really possible in your case. You would have had to export the ram drive for sharing via a network protocol like NFS or CIFS/Samba etc. prior to the freeze. You really want to do a port scan to see what your options are if any.

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On-Line Data Recovery Consultant. RAID / NAS / Linux Specialist.
Serving clients worldwide since 2011
FreeDataRecovery.us

The screen was off & I noticed the DVD light stopped flashing, switched the screen on to be greeted by the login screen & mouse pointer moving. Logged in with the default Ubuntu Livecd login ubuntu/blank & everything was still there so I exported my bookmarks. Next headache is fixing boot loader so I can use Ubuntu on the HDD again.

Thank's for staying on board & I hope we all learned from this experience. If you wait long enough some things fix themselves.

That's great. I wonder what caused the freeze. You might take a look in the log file to see what was going on at the time.... /var/log/syslog

_________________
On-Line Data Recovery Consultant. RAID / NAS / Linux Specialist.
Serving clients worldwide since 2011
FreeDataRecovery.us