Re: Readiness notification for systemd

From: Steve Litt <>
Date: Sat, 13 Jun 2015 16:53:48 -0400

On Sat, 13 Jun 2015 22:35:13 +0200
Laurent Bercot <> wrote:

> On 13/06/2015 21:46, Steve Litt wrote:
> > When I write my own daemons (for use with daemontools,
> > daemontools-encore, runit, and soon to be S6), I use stdout to
> > write to the log. Wouldn't the writenewline/close interfere with
> > that?
> It's more idiomatic to actually use stderr to write to the log.
> stderr is traditionally "the place where I write diagnostic
> messages for an external observer", and stdout is traditionally
> "the place where I write stuff as a part of my workflow".
> Logs fall in the former category, not in the latter; and daemons
> usually have no use for stdout. You could arguably call it a
> misdesign in daemontools (repeated in runit and s6) that the
> logging pipe is tied to the daemon's stdout, not its stderr, by
> default; fortunately, it's very easy to fix in the run script.
> Almost all of my run scripts start with "fdmove -c 2 1", which
> redirects stdout to stderr (the shell equivalent would be
> "exec 2>&1"). That's the behaviour I would also recommend for
> your daemons.
> That said, sdnotify-wrapper, as well as s6-notifywhenup, comes
> with a "-d" option that allows you to choose what descriptor
> the notification will be read on. So if you're dead set on
> logging to stdout, you can write your readiness newline to
> descriptor 3, for instance, and document this; the admin wanting
> to run your daemon will simply give the "-d 3" option to the
> wrapper.
> > How do I take advantage of sdnotify-wrapper if I'm using S6?
> You don't use sdnotify-wrapper, because you're already using
> a kickass supervision suite and have no need for crutches. :)
> > How do I take advantage of sdnotify-wrapper if I'm using
> > daemontools-encore?
> You don't. You only use sdnotify-wrapper if you're an
> administrator using systemd to manage a daemon that refuses to
> use sd_notify() and uses the "write a newline to a file
> descriptor" notification mechanism instead.
> The point of the wrapper is to prevent having to include
> systemd code in the daemon's code to make it systemd-compatible.
> If you've never been tempted to use sd_notify() in the code you
> write, and if you are not using systemd as a supervision
> framework, then you can quietly ignore everything about it. :)

That's easy enough. One problem though: It seems like everything I
write to stderr ends up in my readproctitle display in ps.


Steve Litt
June 2015 featured book: The Key to Everyday Excellence
Received on Sat Jun 13 2015 - 20:53:48 UTC

This archive was generated by hypermail 2.3.0 : Sun May 09 2021 - 19:44:19 UTC