What is "runit"

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.