Re: Readiness notification exemplars

From: Serge E. Hallyn <>
Date: Wed, 1 Apr 2020 09:21:22 -0500

I've been considering for several years trying to push a kernel patch
which would provide a way for userspace to find out when someone starts
listening on some port. Based on problems I saw long ago in the late
days of upstart and early days of systemd, that seemed like it would
solve a not infrequent problem without having to make any changes to
the daemons. Upstart tried to solve it by making the daemons send a
sigstop when ready; systemd solves it by making the daemons support
socket notification; listen-notifiers could be entirely handled by
the dependency handler in the init system.

It's *still* on my list of todos. Maybe sufficient ridicule here will
help me knock it off the list :)

On Wed, Apr 01, 2020 at 08:23:26AM -0500, Brett Neumeier wrote:
> I read on
> "...daemons can simply write a line to a file descriptor of their choice,
> then close that file descriptor, when they're ready to serve. This is a
> generic mechanism that some daemons already implement."
> I am curious, does anyone on this list know of examples of such daemons? I
> am considering creating and submitting patches for some daemon programs
> that I use that do *not* support this mechanism as yet, and am curious if
> it is as simple as it looks like it should be.
> Cheers!
> Brett
> --
> Brett Neumeier (
Received on Wed Apr 01 2020 - 14:21:22 UTC

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