What are port requirements for remote lisp?

Martin Simmons martin at lispworks.com
Tue Mar 31 15:51:01 UTC 2020

>>>>> On Mon, 30 Mar 2020 21:16:00 -0400, Mirko Vukovic said:
> Hello,
> My setup is Sly on Spacemacs with Windows 10 running remote lisp on Linux
> over a corporate network. I have not found a Sly mailing list, and I hope I
> can get an answer here.
> Emacs is running Sly on Spacemacs on Windows 10. Lisp is running on a Linux
> server. But Sly does not connect to the listening Lisp. Corporate network
> security policies have changed. I can ask for IT to accommodate me, but
> first I need to know what to ask for.
> So far, I have opened a tunnel, and started a listening lisp (details
> below).
> In Emacs I get:
> sly-connect RET RET RET
> [sly] Connecting to Slynk on port 4005..
> helm-M-x-execute-command: make client process failed: Connection timed out,
> :name, sly-9, :buffer, nil, :host, hal9000, :service, 4005, :nowait, nil,
> :tls-parameters, nil
> The session transcript:
> > ssh -L4005:localhost:4005 mirko at hal9000
> [mirko at hal9000 .roswell]$ ros -L ccl-bin run --load start-slynk-server.lisp
> SLYNK's ASDF loader finished.
>  Loaded ASDF system
> ;; Slynk started at port: 4005.
>  Created SLYNK server on port 4005
> Clozure Common Lisp Version 1.11.5/v1.11.5  (LinuxX8664)
> For more information about CCL, please see http://ccl.clozure.com.
> CCL is free software.  It is distributed under the terms of the Apache
> Licence, Version 2.0.
> ?
> My question is as follows:
>    1. Do I need bi-directional traffic on 4005?

Assuming you are using the ssh tunnel above, then you don't need port 4005
traffic on the LAN (it is all hidden in the tunnel).

The most likely problem is that some firewall on the Windows machine is
blocking port 4005.  You may need to configure that firewall to allow ssh to
listen on localhost:4005 and/or to accept connections to it from Spacemacs.
In theory you might have similar localhost firewall issues on hal9000, but
that is less likely.

>    2. Do I need bi-directional traffic on 22? (after recent changes I
>    cannot ssh or scp into my Windows machine)

I'm assuming that you ran the ssh command on the Windows 10 machine and it
gave you a working login to hal9000.  If so, then it looks like you already
have what you need for port 22.

Note that bi-directional traffic on a connected socket is different from
whether you can make a connection in both directions.

>    3. What tools can I use to try to narrow down the cause of the problem?
>    For instance, can I send a command to the lisp image, and see its effects
>    on the lisp side?

Firstly, run "netstat -antp" on hal9000 to see if Lisp is listening on port

Secondly, run "netstat -anop tcp" on the Windows 10 machine to see if ssh is
listening on port 4005.

Thirdly, run "ssh -p 4005 localhost" on the Windows 10 machine.  This use a
ssh is very bogus, but it should at least give an error message with some
diagnostics.  (Normally I would use telnet for this, but it is not installed
on Windows 10 by default.)


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