[colug-432] terminal resizing notification?

[Jeff Frontz]

I always thought it was SIGWINCH that prompted an app (or, rather, its
library) to go out and query the terminal for [potentially] new
dimensions.  And I'm guessing the "query" is dependent on the TERM
type-- which, if I remember correctly, is sent over by ssh on
interactive login.

When you're running it with "expect", what environment variables are
you seeing on the remote?


Jeff



On Thu, Mar 28, 2013 at 2:41 PM, Rick Hornsby <richardjhornsby at gmail.com> wrote:
>
> Trying to understand the relationship between resizing a terminal, stty, and
> how the remote side gets that information that the window has been resized.
>
> The issue is that I can ssh into a linux host with no issues, resize my
> window all day long and the remote side sees the resize (confirmed by stty
> -a | grep row).
>
> However, we have a very small expect wrapper that we use most of the time to
> log in.  The expect wrapper goes to a credential store to fetch the password
> (yeah, I know, public keys, etc ... that's a long story), and passes the
> password to the prompt.
>
> When I use the expect wrapper to log in, the remote side never sees the
> resize.  I can manually set the window size using stty, but I'm unclear on
> why wrapping it in expect is causing this issue.  The terminal type is the
> same in both cases, and I've confirmed this behavior in two different
> terminal applications (Terminal.app and iTerm2).
>
> How does the remote side know about the resize?  Is it some kind of
> backchannel communication, or is there some kind of escape code getting
> sent?
>
> This is the essence of the expect script, if it helps put it in context:
>
> ---
> spawn -noecho ssh -o PubKeyAuthentication=no -o StrictHostKeyChecking=no
> root@$host $cmd
>
> expect "?*password?*"
> send "$passwd\r"
>
> interact
>
> exit 0
> ---
>
> (yes -- first rule -- never, ever log in as root -- if I could get my giant
> company with our 10s of thousands of servers to understand that life would
> be much easier.)
>
> the $cmd part is ignored if it wasn't provided.
>
> termtype all that behind the scenes stuff re a terminal is a topic I
> admittedly don't understand very well.
>
> thanks
> -rick
>
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