Re: s6 problems logging

From: Peter Pentchev <>
Date: Mon, 28 Jan 2019 13:00:42 +0200

On Sun, Jan 27, 2019 at 02:27:10PM -0500, Roger Pate wrote:
> On Sun, Jan 27, 2019 at 1:56 PM Sean MacLennan <> wrote:
> > So it seems that s6-log does not like buffered output. I modified
> > doorknob to vsnprintf into a buffer and then tried various output
> > methods.
> s6-log (or another program) has no idea about your buffered output.
> Output cannot be read until it has been written, and data still in a
> buffer has not been written. Change your program to flush after
> messages. It is common for stdio to buffer stdout differently
> depending on whether it is a terminal and to not make that distinction
> for stderr. In your terminal, compare "doorknob -fs" (stdout as
> terminal) to "doorknob -fs | cat" (stdout as pipe) to see the
> difference.

If it is not easy to change the program itself, the stdbuf(1)
utility in recent versions of coreutils might help (of course,
if you use some kind of minimal system, it may not always be


Peter Pentchev  roam_at_{,,}
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Received on Mon Jan 28 2019 - 11:00:42 UTC

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