I am on my third crash with this . They say it is the not enough space, hard drive bad sector or bad installation. I will tell you Ubuntu Linux is horrible on the recovery. You can only use a live Ubuntu Live CD to recover for back up of filles. You always have to reinstall the operating system which blows. When you do searches on this topic, it appears this is quite common on Ubuntu. When you compare to Fedora, it is not so common. As a result, I am finally switching to from Ubuntu to Fedora since many high speed trading shops use it .
If this a constant problem like I have, you may want to use a new drive. I can onlu recommend Western Digital over Seagate if you will be running this 24 7 days which means never turning it off. Here are some of the reasons and solutions to fix this problem:
Key difference between Ubuntu and Fedora
Also I choose this Western Digital drive since it s a NAS for 24/7 operational drive https://www.canadacomputers.com/product_info.php?cPath=15_1086_210_212&item_id=063680
As part of the diagnostics, I found certain drive/USB key/devices which were exluded from the BIOS. Press X to switch between excluded and included lists.FACEBOOK ACCOUNT and TWITTER. Don't worry as I don't post stupid cat videos or what I eat!