If your software runs on Linux, you do not need the locking code, nor the seeking code. Just open the file in append mode and commit each log entry as a single write. Unix file semantics guarantee that the write will append to the file atomically. (For more information see Re^3: Looking for a simple multiprocess-enabled logging module, in which I explain more and invoke the Single Unix Specification.)

See also "All I want to do is append a small amount of text to the end of a file. Do I still have to use locking?" from perlfaq5.

Cheers,
Tom