Do you know how far the render has progressed? Is there a way  to determine that? Is the file an animation or is it a static picture? If it is an animation with a lot of information, the render time might be because of this. If it is a static picture, (not animated), there may be a high amount of data that the software must read and process for the render. If your scene is a simple one there maybe some hidden aspects that are making the render so slow. Other than that, (and I am loath to mention it), your computer may have a virus or other type of malware, or you may need to defragment your hard drive. I don't have Linux on my pc, thus these problems may not be what is happening. At any rate, if I were you, I would check into the things I mentioned to see if any of them could be the cause. I don't quite know about the render to disk option, but when I have a render in the normal setup that will take a while to complete, I will stop the render periodically and save the file at that point of the render. I can then exit the program, and open it later for the purpose of continuing the render. I do this to give my processor a rest, allowing it to cool for a while. For large files with a lot of detail, this is a necessity. 

Maybe the above suggestions will help. Either way, let me know how you do. I definitely hope the render is well worth the wait, and I would love to see it when it is done.

Stay awesome!

Agent 0013.