sysbuild is a tool to automate the maintenance of the NetBSD sources and the build of releases by means of a single command and a configuration file that tells sysbuild what to do. Since NetBSD 1.6 (released in September 2002), the source tree has included a very flexible script (build.sh) to build a full NetBSD release for the current platform or to cross-build for any of the supported platforms. The flipside of the flexibility is that the script is inconvenient to use on a daily basis because of the myriad of options it takes. Furthermore, managing the source trees that make up NetBSD is not in the scope of build.sh: the user must fetch these trees and keep them up to date by hand. While these details are all fine on their own, rebuilding NetBSD frequently (to keep a system up to date, or just for development tasks) is convoluted. Developers and users usually find themselves writing their own wrapper scripts over build.sh to simplify their daily tasks. sysbuild extends build.sh by adding support for configuration files and source tree management, allowing NetBSD rebuilds with a single and simple command. Make sure to check the sysbuild-user package for a way to trivially set up periodic NetBSD rebuilds under an dedicated, unprivileged user.