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Re: TRAMP and scp

From: Kai Grossjohann
Subject: Re: TRAMP and scp
Date: Thu, 30 Oct 2003 21:19:20 +0000
User-agent: Gnus/5.1003 (Gnus v5.10.3) Emacs/21.2 (gnu/linux)

Michael Powe <> writes:

> thanks for the extended reply.

I'm sorry for answering so late now, lots of todo items on my mind

>>>>>> "Kai" == Kai Grossjohann <> writes:
>     Kai> Michael Powe <> writes:
>     >> Out of band method `scp' not applicable for remote shell asking
>     >> for a password
>     Kai> It seems I failed to describe this correctly.  Here is how
>     Kai> Tramp works:
>     Kai> When you invoke something that invokes Tramp, Tramp first
>     Kai> opens a shell connection to the remote host.  This shell is
>     Kai> used for filename completion and suchlike.  For this shell
>     Kai> connection, Tramp knows how to deal with password prompts.
> okay, so under what circumstances does this occur with scp, which i
> believe is the default method if i don't use tramp-default-method? 

You can specify the method in the filename.  For example, in Emacs you
can say C-x C-f /ssh:michael@otherhost:/some/file RET, then it will
use ssh.  Or C-x C-f /su:root@localhost:/another/file RET -- this uses
the su program.

>     Kai> If you are using an out-of-band method, then on actually
>     Kai> transferring a file, Tramp will open another connection to
>     Kai> the remote host, using scp in your example.  For this
>     Kai> connection, Tramp does NOT support password prompts.
> the message cited is the first message i get from attempting to open a
> file remotely, so i don't actually get a prompt even for the opening
> connection. that confuses me.  from your description, it sounds like i
> should get an initial password prompt and then the secondary attempt
> to connect to the file (after opening the shell) should fail.

Well, Tramp is smart!  It knows that things won't work, so it's
telling you up front.  That way, you won't be disappointed.

>     Kai> So an easy workaround is to choose an inline method, such as
>     Kai> ssh.  (It will use uuencode or mimencode to transfer the file
>     Kai> contents through the shell connection.)
> so, if i (setq default-tramp-method "ssh"), that performs the same
> function? i shall try it forthwith.

Yes, I think it will.

In general, inline methods will be slower for large files and faster
for small files.

> i'm afraid i don't actually know the difference between "inline" and
> "out-of-band" in this context, although your description here of what
> is happening is clear.

Inline means that Tramp uses base64 or uu encoding to transfer the
file right through the shell connection.  Out of band means that Tramp
starts another program, such as rcp or scp or rsync, to actually
transfer the file.

I knew about the different kinds of methods, and I had to find terms
to describe them.  I'm afraid that maybe I've been using confusing
terms.  Maybe I should have called them frumple and blargl methods...

(It just occurs to me that I think that the signal transmission folks
use "in-band" and "out-of-band", is this right?  So maybe inline is
the confusing term here.)


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