Hi, I have recently changed system. I was running xwiki on windows 10 with java8 (standalone distribution) and it worked with no problem. I decided to install Ubuntu with java12 and I cannot run it from .sh script. I decided to make virtual machine with java8 (openjdk) only for purpose of hosting xwiki. Unfortunatelly when I start xwiki and go to it’s adddress I get java stack trace: HTTP ERROR 500Problem accessing /xwiki/bin/view/Main/. Reason: Server - Pastebin.com
What is wrong and how can I fix this? If it is not fixable, than how can I get all of my data from wiki and import it to newer version, docker version or whatever.
Would be great if you could report the issue you had with Java 12.
Note that having several versions of Java in Ubuntu is nothing exotic, you just need to tell your application server which version to use.
Hard to tell from this error, looks more like a consequence of something else. You should check the server side log and search for the very first error in it.
today I tried to run this wiki on my windows 10 laptop. I have installed java 8, the same version that it used to work on, but I have the same error once I’m trying to get to this wikis website. How can I check this server side log?
The most important question for now is how can I move database from this instance of Xwiki to another one? I’m scared of loosing data 
and maybe that would be the best solution to fix this problem, just move database to different xwiki? This is standalone version so I belive, that there has to be some file / folder storing my data.
It depends a lot on how XWiki is installed (since it’s not a XWiki choice most of the time), see https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Logging#HLogLocation for some examples.