From e907de2deb5371f3abf1381d82bdcbd7ec2b925c Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Tue, 24 Aug 2021 13:30:54 +0200
Subject: [PATCH] notes/notes-on-s6-init-talk-fosdem17.md

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+---
+title: "Notes on Laurent Bercot's talk at FOSDEM 2017"
+---
+
+Talk more about s6 and init than s6 and supervision.
+
+We can get to 100% satisfaction with an init system. Lots of people
+are still unhappy with their init system though.
+
+This talk is about design of an init system.
+
+4 elements:
+
+ - /sbin/init (the startup scripts/programs/processes)
+ - PID 1
+ - process supervision
+ - service management
+
+These 4 elements don't have to be in the same process.
+
+02:55
+
+Process supervision: supervision tree, rooted at pid1.
+
+"Supervision only applies to daemons" - huh, interesting
+
+Service management: bring services up/down; More generally, change
+from one state to another.
+
+Services: oneshots (short-lived, with side-effects) or longruns
+(daemons). Have dependencies (enforced by service manager).
+
+ - Ah, a oneshot might be a traditional-init-like "run a program to
+   set things up" so that the service is "running" even though there's
+   no particular process you can point to that *is* the service?
+
+    - 10:30 - Void Linux has only longruns (?) and so "hacks",
+      "longruns that do nothing" are used to emulate oneshots
+
+05:40
+
+Ah this is an interesting perspective. Bercot classifies various
+systems in terms of the 4 elements:
+
+                                   /sbin/init   pid1   supervision   svcmgr
+    Integrated init systems
+    (systemd, launchd, upstart)        ✓         ✓          ✓          ✓
+
+    sysvinit, BSD init                 ✓         ✓          ✓
+      - sysv-rc, /etc/rc                                                ✓
+
+    OpenRC                                                              ✓
+
+08:10
+
+Daemontools family - daemontools (1998!), daemontools-encore, runit,
+perp, s6 - supervision suites; nosh - suite of tools similar to s6
+
+09:55
+
+Supervision suites are not enough - only 1/4 of an init system.
+
+11:40
+
+s6: technical aspects
+
+"reproducible launch environment" even for oneshots