SFTP Sessions close from Linux server access by Putty

[kleinr]

This is a long shot, but I am getting desperate. We are in the
process of upgrading our Tectia Server for z/OS from 6.1 to 6.2. We
are able to establish an sftp session from an openssh server to a v6.1
server but get a session closed error message when trying to sftp to
the 6.2 server from the same openssh server. This problem occurs for
one of our Linux servers but not another Linux server which is running
the same version of Linux and the same version of ssh as the Linux
server with the problem. Also, we don't have the problem when sftping
from a desktop machine running Linux and using the openssh sftp client
that comes with desktop Linux. I figure there must be some difference
in the environment of the Linux server that works from the environment
on the the Linux server that has the problem. I have
compared .profile settings, ssy_config settings and stty settings but
don't see any difference. If anyone has any idea of what I should be
looking for or change, I would be most appreciative.

Robert Klein
kle...@mail.nih.gov

[Jacob Nevins]

kleinr <klei...@gmail.com> writes:
>We are able to establish an sftp session from an openssh server to a v6.1
>server but get a session closed error message when trying to sftp to

>the 6.2 server from the same openssh server. [...]

How is PuTTY involved?

[mrob...@att.net]

kleinr <klei...@gmail.com> wrote:
> We are in the process of upgrading our Tectia Server for z/OS from

^^^^
> 6.1 to 6.2.

Maybe somebody dropped the JCL deck and put it back together in the
wrong order... :)

> We are able to establish an sftp session from an openssh server to a
> v6.1 server

So you are running sftp from the command line on the "openssh server"
and connecting to the Tectia 6.1 server? In other words, sftp is the
client, and Tectia is the server?

Is this the sftp client that runs on top of the OpenSSH ssh client, and
is the usual command-line sftp client found on Linux? (The man page for
this sftp on my system says it is from the "BSD General Commands
Manual".)

> but get a session closed error message when trying to sftp to the 6.2
> server from the same openssh server.

If you have the sftp client that runs on top of OpenSSH ssh, I have
found the "-v" switch to OpenSSH to be good for diagnosing problems like
this. It will print a lot of details about all the negotiations it is
going through with the server to set up and maintain the connection.
You can use it up to three times to get more details. Try something
like

sftp -v -v -v user@tectiaserver

and be prepared for a lot of output. The same trick works with the
scp client that runs on top of OpenSSH ssh, but you have to give it
a file to transfer to get the scp client to attempt to connect:

touch testfile.txt
scp -v -v -v testfile.txt user@tectiaserver:/tmp

If you have the PuTTY sftp or scp client running on the Linux machine,
then I don't know. I've used PuTTY and its sftp/scp clients on Windows
but not on Linux. The PuTTY docs suggest that pscp has a -v option for
more verbosity, but psftp does not.

> Also, we don't have the problem when sftping from a desktop machine
> running Linux and using the openssh sftp client that comes with
> desktop Linux.

Do the same "-v -v -v" from the desktop machine that works and compare
to the output of the machine that doesn't work.

> I figure there must be some difference in the environment of the Linux
> server that works from the environment on the the Linux server that
> has the problem.

Could be environment; could be that Tectia v6.2 and the scp or sftp
client can't agree for some other reason.

The OpenSSH man page for ssh mentions several environment variables,
and says it will also read from the ~/.ssh/environment file under some
conditions.

Matt Roberds