On Mon, 29 Apr 2019 21:19:58 +0200
Jeff <sysinit_at_yandex.com> wrote:
> i came across some interesting claims recently. on
> http://skarnet.org/software/s6/
> it reads
>
> "suckless init is incorrect, because it has no supervision
> capabilities, and thus, killing all processes but init can brick the
> machine."
Oh, that.
First of all, Suckless Init is a PID1 that forks an rc script and then
hangs around reaping zombies. You could use that rc file to run
supervision systems such as daemontools-encore and the supervision part
of runit and s6. So Suckless Init is the PID1 part of an init system.
It's 83 lines of C.
There are three philosophies:
1) The supervision should be done by PID1: Supported by Laurent Bercot
2) The supervision should be done outside of PID1: Perhaps supported by
Rich Felker in his
http://ewontfix.com/about/
>
> a rather bold claim IMO !
> where was the "correct" init behaviour specified ?
> where can i learn how a "correct" init has to operate ?
> or is it true since s6-svscan already provides such respawn
> capabilities ? ;-)
>
> there is actually NO need for a "correct" working init implementation
> to provide respawn capabilities at all IMO.
> this can easily done in/by a subprocess and has 2 advantages:
>
> - it simplyfies the init implementation
>
> - process #1 is the default subprocess reaper on any unix
> implementation and hence a lot of terminated zombie subprocesses
> get assigned to it, subprocesses that were not started by it.
> if it has respawn capabilities it has to find out if any of this
> recently assigned but elsewhere terminated subprocesses is one of its
> own childs to be respawned. if it has lots of services to respawn
> this means lots of unnecessary work that could be also done
> in/by a suprocess aswell.
>
> when do you kill a non supvervised process running with UID 0
> "accidently" ? when calling kill ( -1, SIGTERM ) ?
> the kernel protects special/important processes in this case from
> being killed "accidently", that's true.
> but where do we usually see that ? in the shutdown stage, i guess.
> and that's exactly where one wants to kill all process with PID > 1
> (sometimes excluding the calling process since it has to complete
> more tasks). or when going into single user mode.
>
> so this looks like a rather artificial and constructed argument for
> the necessity of respawn functionality in an init implementation IMO.
>
--
SteveT
Steve Litt
January 2019 featured book: Troubleshooting: Just the Facts
http://www.troubleshooters.com/tjust
Received on Wed May 01 2019 - 07:26:14 UTC