Re: Preferred Backup Method?

[David Brodbeck <brodbd@u.washington.edu>]

On Dec 7, 2007, at 8:02 PM, cls@truffula.sj.ca.us wrote:

> [This message has also been posted to linux.debian.user.]
>  On Wed, Dec 05, 2007 at 03:35:46PM -0800, David Brodbeck wrote:
> > You're close.  Try this:
> >
> > tar cvvf - bar | ssh -e none user@dest "cat >foo.tar"
> >
> > Using - as the filename tells tar to output to stdout.  "-e none"  
> > disables
> > SSH's escape character, making the session fully transparent --  
> > otherwise
> > SSH will go into command mode if your tar output happens to  
> > contain a line
> > that starts with ~.
>
> 	What?  I've moved many gigabytes through
> 	  tar cf - stuff | ssh remotebox tar xf -
> 	If there were a problem with tilde dot in the stream I would
> 	have seen it by now.  Let's try an experiment with
> 	Debian boxes truffula (local) and oobleck (remote).

...

> 	So "ssh host" cares about ~. but "ssh host command" doesn't.
> 	No wonder I've been getting away with tar | ssh tar.
> 	The "-e none" is not necessary.



Hmm, it would seem you're right.

I was going by the ssh manpage, which says:

     -e escape_char
             Sets the escape character for sessions with a pty  
(default: `~').
             The escape character is only recognized at the  
beginning of a
             line.  The escape character followed by a dot (`.')  
closes the
             connection; followed by control-Z suspends the  
connection; and
             followed by itself sends the escape character once.   
Setting the
             character to ``none'' disables any escapes and makes  
the session
             fully transparent.


What I didn't pay attention to was the phrase "for sessions with a  
pty."  It would seem when you call ssh with a command, it doesn't  
allocate a pty by default, so the escape character is not honored.   
Good to know.