How to debug mintty or screen freeze

Andy Koppe
Mon Nov 8 12:36:00 GMT 2010

On 8 November 2010 10:15, Henry S. Thompson wrote:
> Bear with me please, this is moderately complex:
> I run mintty out of the Quick Launch bar as follows:
>  C:\Cygwin\bin\mintty.exe  /usr/bin/screen -q
> and in one of the resulting tabs read mail using gnus in xemacs on a
> Debian box remotely via ssh.  About once a week as that remote gnus is
> painting the subject lines in my spam box, the whole thing freezes
> solid.
> screen doesn't respond to escape commands, ~. does nothing, Control-C
> has no effect, trying to close the window results in the "process not
> responding" popup.
> It's not repeatable, in that reconnecting and changing to the same
> gnus Subject buffer will succeed.
> I _presume_ some obscure character code is responsible. . .
> Two questions:
>  1) Anyone else seen anything like this?

Not as such, but it could be to do with the following issue: if you
cat a big file and press any key that sends a character, the terminal
and cat will be deadlocked, like so:

$ ps
O    2408       1    2408       2408    ? 99498 12:27:13 /usr/bin/mintty
O    2672    2772    2672       1580    5 99498 12:27:19 /usr/bin/cat

They're both in write(), waiting for each other to read data from
their side of the pty. Happens with all the pty-based terminals.
Killing the cat resolves the deadlock, and the terminal merrily

>  2) Any easy way to provide useful details?  I would be happy to run a
>    debugging build if supplied, but really can't run for days under
>    strace. . .

So the first thing to check is what state the mintty and screen
processes are in when this happens, using 'ps', and to try killing
first screen and then mintty from the command line.

You could also try hammering the keyboard during the screen updates in
question to see whether you can force the issue.


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