This paper explores how software developers debug integrated systems, where they have little or no access to the source code of the third-party software the system is composed of. We analyze the practice of debugging integrated systems, identifying five characteristics that set it apart from existing research on debugging: it spans a variety of operating environments, it is collective, social, heterogeneous, and ongoing. We draw implications of this for software maintenance research and debugging practice. The results presented in this paper are based on observations from an ethnographic study of the Gentoo OSS community, a geographically distributed community of over 320 developers developing and maintaining a software system for distributing and integrating third-party software packages with different Unix versions.