Re: Antw: Re: Binary changed since start

[Jetchko Jekov <jetchko.jekov@xxxxxxxxx>]

On Tue, Dec 10, 2019 at 4:27 PM Ulrich Windl
<Ulrich.Windl@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> >>> Lennart Poettering <lennart@xxxxxxxxxxxxxx> schrieb am 10.12.2019 um 12:32
> in
> Nachricht <20191210113234.GA16721@gardel-login>:
> > On Di, 10.12.19 10:38, Ulrich Windl (Ulrich.Windl@xxxxxx‑regensburg.de)
> wrote:
> >
> >> Hi!
> >>
> >> Two questions (In Linux it's possible to replace the image of the binary
> > that is executed on disk):
> >>
> >> 1) It seems my version of systemd (228) does not detect that a
> >> binary has changed since the service was started. In case it's still
> >> true in the current version, is it difficult to indicate that fact
> >> in "systemctl status .."?
> >
> > We don't, no. It has been requested before that we deal with that, but
> > it's not realistic to do this correctly. Thing is, binaries are
>
> Well at least "zypper ps" does that kind of things:
> # zypper ps

Well, that is a zypper (package manager) feature. Why do you need it
in systemd too?
dnf/yum equivalent is:
# dnf needs-restarting

[ -- cut --]
>
> > generally not statically compiled, they link against other libraries
> > which might also be updated, and which would have to be checked
> > too. And they do so via module loading (i.e. dlopen()) and explicitly,
> > we'd have to check both, which already is harder, since you cannot
> > just look at the ELF headers of binaries to determine deps
> > anymore. But they also keep other resources mapped, for example l10n
> > and i18n data, and a lot of other stuff. We'd have to check that
> > too. And then, there are the invisible dependencies too: some file
> > changed that some library a program opens and reads, but only
> > sometimes: how would you ever figure out you need to restart the
> > service? And then, there's also the fact that C is just one
> > programming language and others work very differently, and require
> > other schemes for updating, i.e. Python does something very very
> > different.
> >
> > So in the end: implementing something like that could at best be a
> > heuristic, that works sometimes but not generally. I know that some
> > distros implemented a checker for this in their package manager. But I
> > am very sure this has no place in systemd, since it's black magic and
> > you never could rely on the correctness for that.
> >
> >> 2) Given 1), would it make sense to allow an option like
> >> "RestartIfBinary Changed"?
> >
> > Binding control flow to such a heuristic sounds even more dangerous to
> > me.
>
> I was asking for an option, not for a default.
>
> Regards,
> Ulrich
>
>
> >
> > Lennart
> >
> > ‑‑
> > Lennart Poettering, Berlin
>
>
>
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