Deprecation of scp protocol and improving sftp client

Colin Watson cjwatson at
Tue Jun 23 09:34:01 AEST 2020

On Mon, Jun 22, 2020 at 10:47:35AM +0200, Andreas Schneider wrote:
> On Tuesday, 16 June 2020 20:47:24 CEST Colin Watson wrote:
> > On Tue, Jun 16, 2020 at 06:41:09PM +0200, Jakub Jelen wrote:
> > >  * Modify sshd to use some compatibility "scpd" to support old clients
> > 
> > This should be unnecessary.  When an scp client connects to an scp
> > server, it passes the -f (source) or -t (sink) flag as appropriate;
> > neither is part of the documented user-facing interface to scp.  I don't
> > see any particular reason why scp (the program) couldn't continue to
> > speak the scp protocol when invoked with -f/-t, but speak the sftp
> > protocol when invoked in the normal way.
> It is necessary. If you replace the protocol of the scp command with sftp then 
> there are still scp commands out there speaking the scp protocol. You need to 
> keep the server side supported.

I think you must have misread what I wrote.  Let me try to clarify: the
way to keep the server side supported is simply to continue handling the
-f and -t flags appropriately in scp, which can be independent of
whether scp speaks sftp when invoked as an ordinary client.  It isn't
necessary to modify sshd to use a different "scpd" executable.

Colin Watson (he/him)                              [cjwatson at]

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