The 2.3 log4j.properties file doesn't specify a file for the FileAppender (because the necessary lines haven't been uncommented). Hence the log files normally generated via the file appender, logs/atlassian-confluence.log, is presently missing?
If you experience this situation and see errors in the logs such as:
log4j:WARN File option not set for appender [confluencelog].
log4j:WARN Are you using FileAppender instead of ConsoleAppender?
log4j:ERROR No output stream or file set for the appender named [confluencelog].
Please uncomment the following lines in the log4j.properties file located under confluence/WEB-INF/classes and restart Confluence
(ie remove the #'s)