When comparing Upstart vs s6, the Slant community recommends s6 for most people. In the question“What are the best Linux init systems?” s6 is ranked 5th while Upstart is ranked 6th.
Ranked in these QuestionsQuestion Ranking
Pro Simple .conf file in /etc/init
Pro Event based startup was fantastic.
Since it is event based, it was simple to have interdependent services emit status messages each other. Service start ordering and shutdown was easily managed in one conf file.
The "lazy" start of systemd is BS and is a mess to debug . service unit files have no clue what another service state is. The maintainers add arbitrary timers that add more complexity and more init hangs. The systemd documentation is poor. When a service fails to start (or stop) systemd follows the Microsoft model of not telling the reason why.
Pro Runs on every POSIX system
Pro You can use all its components independently
Pro Rock solid
Portable: Linux, BSD, Solaris
Can be compiled with musl.
A lot of feature including dependencies service management.
Easy to implement with the conjunction of 66 (https://framagit.org/obarun/66.git) which provide frontend file for service declaration, automatic logger creation,nested supervision tree,user service,instantiated services and many more.
Best alternative ever. Work out of the box, PROC was made on Gentoo, Funtoo, Devuan, KISS linux, Adelie, Void, Antix.
Default init system and service manager on Obarun (https://web.obarun.org) and from a long time ago.
Pro The perfect init
s6-rc, provides a real Service Manager, a Services Supervisor with Parallel RC and logging, upon demand. The perfect continuation, of Runit.
ISC License, is not a barrier, Ibut instead, is so friendly to Open Source and Free Software Licence
Con Ubuntu abandoned it
The original developers (Canonical) seem to have abandoned this project. At least they're no longer using it in Ubuntu.
Con It was just sysvinit or systemd in disguise
It really just offered a barely more intuitive way to create init scripts for the actual init system running behind upstart.
Con Not GPL
It depends on libc, has a lot of code.