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screen defscrollback memory exhaustion

From: Ricardo F. Teixeira
Subject: screen defscrollback memory exhaustion
Date: Thu, 14 Aug 2014 00:53:11 +0100

Hi guys,

Does anyone know how to set the size of the defscrollback buffer to unlimited?

Lookin' through the man page I saw no reference in setting an unlimited value:

defscrollback num
Same as the scrollback command except that the default setting for new
windows is changed. Initial setting is 100.

Clearly by setting the -k value to nothing (screen -h) will throw the
help menu. A negative integer doesn't a solve the problem either,
'cause screen will print an error message and will exit.

[626] if (nwin_options.histheight < 0)
[627]    exit_with_usage(myname, "-h: %s: negative scrollback size?", *av);

The only option left is to assign a higher value to this parameter.
However I learned, from the hard way, that screen -h 10000000 will
just hang a system with low resources - screen consumed more than 1GB
of memory!

Lookin' on the source code for an answer, I noticed that screen
doesn't perform any boundaries check and will try to maintain
scrollback entirely in RAM.

On a bad perspective this leads to (another) problem: anyone with
access to a setuid screen binary (most GNU/Linux distributions have
this by _default_) can literally hang a production system.

So, does anyone have ideas on how to achieve this without freeze the system?



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