[ale] Using runit or s6 on top of systemd

[Steve Litt]

Hi all,

One alternative not discussed here is to use the process supervision
portion of runit or s6 to spawn some of your daemons in systemd.

It's pretty simple: 

1) Create a runit or s6 systemd service that starts early.

2) For each service you want to transfer to runit or s6:
	a) Disable it in systemd
	b) Enable it in runit or s6

Over time, more and more of your services will be run from runit or s6.
Be sure to back up the directories that define the runit or s6
supervised processes. On my computer that's a 628K backup.

Runit and s6 are daemontools-inspired init systems with similar
architectures. Runit houses its process supervisor in a process outside
of PID1, while s6 houses its process supervisor inside PID1. Runit is
conceptually simpler, s6 is more robust and withstands greater
challenges. Runit depends on polling much more than s6, although
runit's level of polling has no material effect on machine efficiency.

SteveT