openssh bugs - Dec 2022 - [Bug 3509] New: implement RemoteCommandCommand

https://bugzilla.mindrot.org/show_bug.cgi?id=3509

            Bug ID: 3509
           Summary: implement RemoteCommandCommand
           Product: Portable OpenSSH
           Version: 9.1p1
          Hardware: Other
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: Miscellaneous
          Assignee: unassigned-bugs at mindrot.org
          Reporter: calestyo at scientia.org

Hey.

For some configuration options which specify a file, we also have a
corresponding one specifying a command, namely:
  GlobalKnownHostsFile
  UserKnownHostsFile
and
  KnownHostsCommand

I would find it useful, if something similar could be offered for
RemoteCommand (well that's the one I'd have a use case for - for
LocalCommand it doesn't really make sense anyway).

I have some special configurations that set a quite large RemoteCommand
(which starts a remote systemd unit for a VNC server, sets traps on
INT/EXIT/QUIT to stop the server, but a special one for HUP, so that it
can be left running, and later reconnected to, if just the connection
dies... well and it does some more stuff).

AFAICS there is no site limit for the RemoteCommand, but it's still
quite messy to edit within ssh_config.

So one solution would be to have a RemoteCommandCommand, which itself
is executed locally and gives back some string that ssh would use as
RemoteCommand (executed remotely).

Simply reading a script could be done via a RemoteCommandCommand like
"cat myscript.sh".

I'm not sure whether the remote command  could contain in principle
newlines (and just the limitations of RemoteCommand prevent these.
If it can (which I guess9, any script would already work, if not, then
one could perhaps give an example command that "serialises" a script,
though I think that's actually not easy,... at least it's not enough to
replace any newline with ';'.

Thanks,
Chris.

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Darren Tucker <dtucker at dtucker.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dtucker at dtucker.net

--- Comment #1 from Darren Tucker <dtucker at dtucker.net> ---
You can already do this with a trivial shell pipeline:

yourcommand | ssh yourserver /bin/sh

or the equivalent shell wrapper around ssh.  I don't see a general need
for what you're describing.

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https://bugzilla.mindrot.org/show_bug.cgi?id=3509

--- Comment #2 from Christoph Anton Mitterer <calestyo at scientia.org>
---
Well that doesn't work as soon as you want pipe something to the shell
"script's" stdin... or if you want to have an interactive session.

A wrapper command is in principle of course possible, but still less
easy to use (one needs to distribute it everywhere, write it smart
enough so that it only kicks in for the desired connections, etc.)

Anyway... I just reported it because I assumed it would be rather easy
to do... I don't strictly depend on it so just close if you don't like
the idea :-D

Cheers,
Chris.

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Darren Tucker <dtucker at dtucker.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|NEW                         |RESOLVED

--- Comment #3 from Darren Tucker <dtucker at dtucker.net> ---
(In reply to Christoph Anton Mitterer from comment #2)
> Well that doesn't work as soon as you want pipe something to the
> shell "script's" stdin... or if you want to have an
interactive
> session.
That's true, however for those cases you could do

ssh yourserver "$(yourcommandcommand)"

instead.  It still doesn't seem like this is something that would be
generally useful so I'm going to close this bug.  Thanks anyway.

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #4 from Damien Miller <djm at mindrot.org> ---
OpenSSH 9.3 has been released. Close resolved bugs

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