Re: TRAMP password caching

[Michael Albinus]

Eli Zaretskii <address@hidden> writes:

>> That was the default until recently. It was changed because people
>> regard ssh (aka plink) methods too slow for copying large files.
>
> I don't understand: didn't you say that you want to change the default
> to ssh, or even already changed it?  I thought you were asking me
> whether a similar change, from pscp to plink, was a good idea for
> Windows.  What am I missing?

Let's try to summarize: Tramp has used ssh and plink as defaults for a
long time. Some weeks ago, there was a discussion that those methods
are not performant enough for large files. So the default has been
changed to scp and pscp.

Then, with this thread, Tramp was blamed that in this case it requires
again and again typing a password. Tramp knows 2 approaches to avoid
retyping passwords: users run ssh-agent or pageant; or Tramp loads
password.el, which caches passwords. Unfortunately, password.el is not
part of GNU Emacs (yet), so it is not a general solution.

Under UNIX, another feature is used now: MasterControl/MasterPath
options of ssh. This allows to reuse an existing ssh connection for
all scp calls, avoiding retyping password. I have submitted the patch
some days ago; no complaints until now, I assume it works.

In the w32 case, plink doesn't seem to offer this feature. So it was
proposed to revert the initial change (i.e. plink becomes the default
again). An optimization could be to set the default depending wether
pageant is running or not - in case it is running, one could keep pscp
as default, otherwise one takes plink.

But I have no ida how to check whether pageant is running.

>> Please do. I hoped it could be determined simply via the existence of
>> environment variables (as it is possible with ssh-agent, environment
>> variables $SSH_AUTHENTICATION_*), but it doesn't seem so easy. And I
>> also don't know a command like 'ps' which returns running processes,
>> in order to check whether pageant is active.
>
> Is there code that does this for Unix?  If so, where's that code?

As I told above, this is not necessary. MasterControl/MasterPath seem
to be sufficient.

>> All Tramp methods provide a whole implementation of primitive file
>> operations. Not only for `copy-file' or `rename-file', but also
>> `file-attributes' or `directory-files' etc. Those functions cannot be
>> implemented by (p)scp, I fear. Because of this, Tramp opens
>> additionally an ssh resp. plink connection.
>
> IMHO, this is just one more reason to move away from pscp as the
> default.

Personally, I don't care. It should be just th convenience of the
majority.

Best regards, Michael.