I would like to update our xWiki to the latest stable version 17.9. When I run the command, it tells me that I already have the latest version with 17.6. What do I need to check? Have I lost an entry?
According to your apt update log, you simply don’t have the XWiki repository. Maybe you upgraded Ubuntu (in which case all your custom repositories were disabled).
Only xWiki runs on that machine. I don’t know why the repository isn’t there anymore. Can I reconfigure it with those two commands?
That’s what it’s for, yes.