There are three ways to use the cyclic log package:
Use of the either of the APIs require that the programmer observes the license that the cyclic log package is released under. The software licence is the GPL. This means that software that uses the cyclic log API is considered to be a derivative work and must therefore also be released under the GPL.
This policy does not prevent cyclic logs being used in proprietary or commercial projects. Such projects are confined to just using the cyclic log commands. This ought to be sufficient for most projects, since the need is to capture server output for later viewing without running the risk of filling up the available disk space.