Re: some screen windows freezing

[Michael Parson]

On Fri, 11 Dec 2020, Hauke Laging wrote:
> Hello,
>
> I regularly experience that one of several screen windows freezes. This
> usually happens after some time of inactivity.

What are you doing in those windows that freeze up?  What programs were
runing?  Just sitting at a shell prompt?  An open editor session?  Was
that window local to your computer or had you ssh'd to a remote system?

> ^A q does not solve this problem. Are there any other features which can
> cause this effect?
>
> I don't know whether the cause of the problem was always the same. When
> it happened the last time I attached strace to the respective shell and
> learnt by this that the shell still gets input from screen and writes
> its regular output.

One possibility:

^S can 'freeze' a window/shell session.  It's the 'XOFF' software
flow-control character, a hold-over from back when terminals were
connected via serial lines.  ^Q is the 'XON' character that should
resume output.

Given that on US/QWERTY keyboards, the 'A' and 'S' keys are right next
to each other, it is easy to accidentally hit ^S when reaching for ^A in
screen.  You might have to also try ^A^Q to get the session to resume.
I have had individual windows freeze up in ways that I wasn't able to
fix with combos of those key sequences and wind up having to :kill that
window, but I've also had pretty good luck unfreezing with ^Q and/or
^S^Q, and sometimes ':flow off'.

Check the man page FLOW-CONTROL section as well as about the '-f' screen
flag, the 'defflow' and 'flow' .screenrc options about how to control
and/or disable this feature inside of screen.

--
Michael Parson
Pflugerville, TX
KF5LGQ