screen: Flow Control Summary
15.1 About 'screen' flow control settings
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Each window has a flow-control setting that determines how screen deals
with the XON and XOFF characters (and perhaps the interrupt character).
When flow-control is turned off, screen ignores the XON and XOFF
characters, which allows the user to send them to the current program by
simply typing them (useful for the 'emacs' editor, for instance). The
trade-off is that it will take longer for output from a "normal" program
to pause in response to an XOFF. With flow-control turned on, XON and
XOFF characters are used to immediately pause the output of the current
window. You can still send these characters to the current program, but
you must use the appropriate two-character screen commands (typically
'C-a q' (xon) and 'C-a s' (xoff)). The xon/xoff commands are also
useful for typing C-s and C-q past a terminal that intercepts these
characters.
Each window has an initial flow-control value set with either the
'-f' option or the 'defflow' command. By default the windows are set to
automatic flow-switching. It can then be toggled between the three
states 'fixed on', 'fixed off' and 'automatic' interactively with the
'flow' command bound to 'C-a f'.
The automatic flow-switching mode deals with flow control using the
TIOCPKT mode (like 'rlogin' does). If the tty driver does not support
TIOCPKT, screen tries to determine the right mode based on the current
setting of the application keypad -- when it is enabled, flow-control is
turned off and visa versa. Of course, you can still manipulate
flow-control manually when needed.
If you're running with flow-control enabled and find that pressing
the interrupt key (usually C-c) does not interrupt the display until
another 6-8 lines have scrolled by, try running screen with the
'interrupt' option (add the 'interrupt' flag to the 'flow' command in
your .screenrc, or use the '-i' command-line option). This causes the
output that 'screen' has accumulated from the interrupted program to be
flushed. One disadvantage is that the virtual terminal's memory
contains the non-flushed version of the output, which in rare cases can
cause minor inaccuracies in the output. For example, if you switch
screens and return, or update the screen with 'C-a l' you would see the
version of the output you would have gotten without 'interrupt' being
on. Also, you might need to turn off flow-control (or use auto-flow
mode to turn it off automatically) when running a program that expects
you to type the interrupt character as input, as the 'interrupt'
parameter only takes effect when flow-control is enabled. If your
program's output is interrupted by mistake, a simple refresh of the
screen with 'C-a l' will restore it. Give each mode a try, and use
whichever mode you find more comfortable.
Info Catalog
screen: Flow Control
screen: Flow