[colug-432] terminal resizing notification?

[Jeff Frontz]

Yeah, someone else ran into this:
http://ubuntuforums.org/showthread.php?t=865420

Summary:  "You have to trap SIGWINCH in your expect script and
propagate this to the child."


Jeff




On Thu, Mar 28, 2013 at 3:34 PM, Jeff Frontz <jeff.frontz at gmail.com> wrote:
> 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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