-n vs batch_mode vs batch_flag
Markus Friedl
markus.friedl at informatik.uni-erlangen.de
Sun Apr 8 22:28:33 EST 2001
i did not invent '-n' but the manpage reads:
-n Redirects stdin from /dev/null (actually, prevents reading from
stdin). This must be used when ssh is run in the background. A
common trick is to use this to run X11 programs on a remote ma-
chine. For example, ssh -n shadows.cs.hut.fi emacs & will start
an emacs on shadows.cs.hut.fi, and the X11 connection will be au-
tomatically forwarded over an encrypted channel. The ssh program
will be put in the background. (This does not work if ssh needs
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
to ask for a password or passphrase; see also the -f option.)
^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^
On Fri, Apr 06, 2001 at 08:11:11PM +0900, Tom Holroyd wrote:
> How is -n supposed to work? When you say ssh -n, it sets stdin_null_flag
> but not batch mode. When the client is choosing authmethods, there is a
> batch_flag that is tested to see (presumably) if we are in batch mode or
> perhaps if -n has been given. But nothing sets it. It looks like it's
> supposed to point to options.batch_mode, but it's never even initialized!
>
> Even if it did point to batch_mode, that's independent of -n, so when you
> say -n it still (tries to) ask for a password.
>
> % ssh -n localhost &
> [1] 5220
> % tomh at localhost's password:
> [1] + Suspended (tty input) ssh -n localhost
>
> It seems to me that -n (without -f) should mean "stdin doesn't exist, so
> don't try any authmethods that ask for passwords from stdin", which would
> imply that it should set batch_mode too, and batch_flag should point to
> that. Or maybe batch_mode should be checked instead of batch_flag.
>
> Or is this all supposed to be handled somehow by ssh-askpass (which is
> currently only used by ssh-agent)?
>
> Thanks,
>
> Dr. Tom
>
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