I am just trying http://code.google.com/p/enterprise-log-search-and-archive/wiki/Quickstart
It looks as though it could be the business - and runs on multiple flavours of Linux. I haven't got it working / used it yet so can't comment on whether it is any good or not. The features list looks great though; as does the performance.
I am installing on Red Hat 6 from behind a proxy so I have had some small pain. Your mileage may vary.
Just a quick ELSA note: please let me know either personally or via the Google Groups list (http://groups.google.com/group/enterprise-log-search-and-archive) if you would like any assistance getting going with ELSA. I've got a few sites up with it and they are pleased with it thus far. We've been using it in production for over a year.