Bug 48485

Most users don't expect their shell to freeze when they press Ctrl-S (there 
was more than only one bug report about this). I liked the [one-time] pop-up 
information more than current situation too. 

adding from debian BTS #131562 here, since it touches the same subject:

If one has selected the "Mac Default" keybinding for KDE applications,
there is no apparent way to transmit an XON (Ctrl-Q) character through a
konsole terminal.  Nonetheless, one can transmit XOFF (Ctrl-S), thus
suspending output from the terminal program with no way to restore it.
As far as I can tell, this forces one to abandon whatever one is doing
in the terminal.

One fix would be to add XON/XOFF to the "Session->Send Signal" submenu.

This might be considered a bug with the keybinding, since it steals
standard terminal control characters for application control.  Arguably
it would be more Mac-like to use Alt rather than Ctrl for application
commands anyway:  the Mac itself does not use Ctrl for this purpose,
reserving Ctrl for terminal control.  Please feel free to reassign this
bug to kdebase (or wherever) if you consider this a stronger case.

Hasn't this been fixed?  In Configure->General->Use CTRL+S/+Q flow control; it seems to work fine here.

It's configurable, and most user friendly option is to keep off.  A year and a bit later with no comments, so resolving.

For clarity, this option is in the Settings->"Configure Konsole..." general tab in the Misc section.

All the terminal programs I tested have this Ctrl +s/+q on by default.  Perhaps, Konsole should also.
Tested: mrxvt, gnome-terminal, xterm, rxvt, urxvt, MacOSX terminal and iTerm

Having the terminal suddenly freeze with no indication of what is happening when Ctrl+S is pressed would definitely surprise me - because I until I read this report, I had no idea what flow control is.

Can someone explain why flow control might be useful in a modern environment?

One option might be to enable flow control by default, but display a warning status-message at the top of the terminal widget which includes the keypress needed to deactivate it.

eg.  A FireFox-style yellow warning bar containing the text: "Terminal output was suspended by pressing Ctrl+S.  Press Ctrl+Q to resume output."

Since Ctrl+S / Ctrl+Q is reserved for this in most terminals, it would probably be safe to remove it as an option in Konqueror if it was decided to disable it by default.

Yes, it is quite common.  As I mention in #6, all the terms I tried have this enabled by default.  Linux Virtual console have it also and I'm fairly sure the *BSDs also.

In Powerterm for MS, there is a button "STOP/RESUME" which does the same thing.  I agree some sort of visual notification should be required in Konsole.

I have added the aforementioned warning bar when flow control is enabled which tells users what has happened when they press Ctrl+S and what to press to disable flow control.  It should be safe now to enable Xon/Xoff by default. 

Implemented in KDE 4.

I see the warning for xon/xoff added when I press ctrl-s/q and I also see the option to enable/disable flow control with ctrl-s/q in the edit-profile->advanced tab.  However, this option is selected and grayed out.  As a result, I've lost my ctrl-s mapping that I use in mutt which is slowly driving me mad.  Is there a way to turn off flow control or change the mapping?  I looked around in all the usual places but didn't find anything.

(In reply to comment #11)
> I see the warning for xon/xoff added when I press ctrl-s/q and I also see the
> option to enable/disable flow control with ctrl-s/q in the
> edit-profile->advanced tab.  However, this option is selected and grayed out. 
> As a result, I've lost my ctrl-s mapping that I use in mutt which is slowly
> driving me mad.  Is there a way to turn off flow control or change the mapping?
>  I looked around in all the usual places but didn't find anything.

See Bug 165457.