The Zimsvlog.zim file
The log file zimsvlog.zim, located in the directory pointed to by the ZIM environment variable, records all events happening with Zim Server like, its start, its end, errors, tracing and other information.
You can browse its contents using a text editor or using ZIMEXPLORE.
After some time using Zim Server, this file can become very large. You should check the size of it from time to time, archive it (if you wish) and erase it. It can be erased any time, even when Zim Server is running. Next time Zim Server needs to log some information, the file will be recreated.