Dependency-based & Event-based init daemons and launchd

“With the recent announcement of systemd, I’ve noticed some
increased confusion around Upstart and what it means to be an
event-based init daemon. Now seems as good a time as any to try and
clear that up by describing what I mean by that.

“Dependency-based init

“Before Upstart came along, the state of the art of init daemon
replacements were the dependency-based init daemons. The two most
well-known at the time was the Service Management Facility (SMF) of
Solaris, and initng on Linux.

“The easiest way to understand how a dependency-based init
daemon works is to look at another dependency-based system you’re
probably more familiar with: the package manager of your Linux
distribution.”

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