Re: tramp ControlMaster options

[Michael Albinus <michael.albinus@gmx.de>]

Thierry Volpiatto <thierry.volpiatto@gmail.com> writes:

>> In emacs 24.5.1, I see this at line 310 of tramp.el:

Here we are. What I have written is about Emacs 25, the development
branch in git.

> So IIUC tramp is calling ssh at load time when evaling its defcustom ?!!

Not any longer. This is fixed, as I have explained.

>>>> Any reason why we cannot use `ssh -o BatchMode=yes [various flags]
>>>> 0.0.0.0' instead of using a domain name? This would greatly reduce the
>>>> issue.
>>> 
>>> The function (!) `tramp-ssh-controlmaster-options' uses "localhost" for
>>> test. This shall avoid DNS requests.
>>
>> Still connects to a valid host, which might have a daemon running (in
>> fact, I have one on localhost for debugging).
>>
>> If there's no reason to connect to something, call 0.0.0.0.

I've tested. If there is a daemon running on your local host, it *also*
connects using 0.0.0.0. No difference to localhost.

--8<---------------cut here---------------start------------->8---
# ssh -o ControlPath=%C 0.0.0.0
Welcome to Ubuntu 15.04 (GNU/Linux 3.19.0-23-generic x86_64)

 * Documentation:  https://help.ubuntu.com/

0 packages can be updated.
0 updates are security updates.

*** System restart required ***
Last login: Mon Jul 20 20:41:09 2015 from localhost
--8<---------------cut here---------------end--------------->8---

That's why *current* Tramp connects to another port, hoping nobody let
run an sshd on that port.

--8<---------------cut here---------------start------------->8---
# ssh -p 23 -o ControlPath=%C localhost
ssh: connect to host localhost port 23: Connection refused
--8<---------------cut here---------------end--------------->8---

> Isn't it possible to setup the default value of
> `tramp-ssh-controlmaster-options' only when tramp is involved (i.e at
> first connection) instead of evaling this at load time ?

That's the case in recent Tramp.

>> I love that tramp detects ControlMaster support in ssh, but calling
>> external processes on load, if really needed, should /really/ be quick.

It does now.

In order to fix the problem for you, you could upgrade to the
development branch of Emacs (25.0.50). If this is not an option for you,
you might install Tramp 2.2.12, which has been released end of June.

Another Emacs 24.x release is unlikely, as Stefan has said a while ago.

> Thanks.

Best regards, Michael.