From: "Laurent Bercot" <ska-supervision@skarnet.org>
To: "supervision@list.skarnet.org" <supervision@list.skarnet.org>
Subject: Re: Generic interrupt command?
Date: Sun, 10 Feb 2019 11:41:19 +0000 [thread overview]
Message-ID: <eme17a01d1-68e3-48e2-815f-b393aa59d5fc@elzian> (raw)
In-Reply-To: <CAPCpfp8QiQU_0nV2qw+kfNraww++F09yRAFfbJ=2ETi=8-6BAA@mail.gmail.com>
>That's a tough call. On the one hand, it makes simple constructs safer.
>On the other, it adds complexity to interpreting the data
>programmatically ( the test / [ program errors for integer comparisons
>with text, and using scanf() to pull in the values for libc style
>programs wouldn't be so simple anymore).
That was my thought process originally, but if it makes it riskier
or more annoying for programs to use the result of s6-svstat,
especially in scripts which are its likely users, I'm willing to
change that.
>Also, while thinking about this, I wonder the risk of signaling the
>wrong program. When svc does it via supervise, it can know the right
>program gets the signal because it handles the cleaning of the child
>PID. In a script, there is a chance the child has exited and been
>replaced between the time the PID was queried by svstat and the time
>the kill command gets executed. I don't know how likely a new program
>might get the old PID in that time, this receiving the signal intended
>for the original child.
Well that is one of the reasons for using a supervisor in the first
place. Only the parent of a process can reliably send signals to it.
Any time you're trying to signal a program and you're not a parent,
you are subject to that risk condition. The only 100% safe way is
using s6-svc, there's no changing that.
So far the only real need to customize a signal has been for the
signal that brings a service down, which is now achieved via
./down-signal. I haven't been told of any real use case where
sending a non-supported signal, without intending to terminate the
service, was necessary.
--
Laurent
next prev parent reply other threads:[~2019-02-10 11:41 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-02 2:36 Steve Litt
2019-02-02 9:07 ` Laurent Bercot
2019-02-02 19:30 ` Steve Litt
2019-02-02 21:08 ` Colin Booth
2019-02-02 21:40 ` Steve Litt
2019-02-05 3:09 ` John O'Meara
2019-02-05 4:15 ` Roger Pate
2019-02-05 7:20 ` Laurent Bercot
2019-02-05 14:16 ` John O'Meara
2019-02-05 19:30 ` Laurent Bercot
2019-02-10 4:14 ` John O'Meara
2019-02-10 11:41 ` Laurent Bercot [this message]
2019-02-02 22:31 ` Jonathan de Boyne Pollard
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