Lucene "Lock obtain timed out"

Today I had to interrupt my Java search server while it was indexing. Next time when I ran the server, it kept giving me the following messages:

caught a class java.io.IOException
with message: Lock obtain timed out: Lock@/tmp/lucene-bc34bb2d3ec966220086135e748049c5-write.lock

Solution was to delete the /tmp/lucene-* files.