Difference between executing a command and calling a subsystem?

[Markus Friedl]

On Sun, Jul 06, 2003 at 02:07:56AM -0700, Dan Kaminsky wrote:
> 
> >Subsystems must be pre-defined in sshd_config. They are intended more as
> >a sub-protocol extension mechanism (e.g. sftp) than as a user-visible
> >way to execute commands.
> >
> >As far as execution of commands go, there is very little difference in
> >terms of code executed between a defined subsystem and "ssh somehost
> >command"
> > 
> >
> Isn't their execution environment much more strictly defined, i.e. 
> pathing issues aren't a problem like with scp, and it's fair game to 
> specify _protocols_ rather than _implementations_?
> 
> Is the user's shell still invoked to execute subsystems?

it's not different from remote command execution. there's only one
additional indirection, so the client does not have to worry about
pathnames.