runit is an init scheme for Unix-like operating systems that initializes, supervises, and ends processes throughout the operating system. Runit is a "reimplementation" of the "seminal" daemontools process supervision toolkit that runs on the Linux, Mac OS X, *BSD, and Solaris operating systems. Runit features parallelization of the start up of system services, which can speed up the boot time of the operating system.
Runit is an init daemon, so it is the direct or indirect ancestor of all other processes. It is the first process started during booting, and continues running until the system is shut down.
The RubyWorks stack of software required to run Ruby on Rails incorporated Runit into its suite.
Runit focuses on being a small, modular, and portable codebase. Runit is split into three stages: one time initialization, process supervision, and halting or rebooting. While the first and third stages must be adapted to the specific operating system they are running on, the second stage is portable across all POSIX compliant operating systems.
Runit can be used either as a drop-in replacement for sysvinit, or as a service supervisor with sysvinit as the parent PID1 process ran from inittab.