@article {Yu:2006:MKO:1150566.1150571, title = {Maintainability of the kernels of open-source operating systems: A comparison of Linux with FreeBSD, NetBSD, and OpenBSD}, journal = {J. Syst. Softw.}, volume = {79}, year = {2006}, note = {"Data regarding the number and total number of lines of code of kernel and nonkernel modules in the four operating systems are provided in Table 1" loc, kloc, number of kernel modules, number of nonkernel modules size c files .h files}, month = {June}, pages = {807{\textendash}815}, publisher = {Elsevier Science Inc.}, address = {New York, NY, USA}, abstract = {We compared and contrasted the maintainability of four open-source operating systems: Linux, FreeBSD, NetBSD, and OpenBSD. We used our categorization of common coupling in kernel-based software to highlight future maintenance problems. An unsafe definition is a definition of a global variable that can affect a kernel module if that definition is changed. For each operating system we determined a number of measures, including the number of global variables, the number of instances of global variables in the kernel and overall, as well as the number of unsafe definitions in the kernel and overall. We also computed the value of each our measures per kernel KLOC and per KLOC overall. For every measure and every ratio, Linux compared unfavorably with FreeBSD, NetBSD, and OpenBSD. Accordingly, we are concerned about the future maintainability of Linux. }, keywords = {abiword, Common coupling, coupling, Definition-use analysis, freebsd, kernel, lines of code, linux, linux kernel, loc, Maintainability, modules, netbsd, Open-source software, openbsd, source code}, issn = {0164-1212}, doi = {http://dx.doi.org/10.1016/j.jss.2005.08.014}, url = {http://dx.doi.org/10.1016/j.jss.2005.08.014}, attachments = {https://flosshub.org/sites/flosshub.org/files/YuSchachChen.pdf}, author = {Yu, Liguo and Schach, Stephen R. and Chen, Kai and Heller, Gillian Z. and Offutt, Jeff} }