I think this is a tmux question, though it may be a zsh question, or a question relating to both.

I SSH to a server from a Windows box using PuTTY. In the PuTTY configuration window, in the Data panel, I have terminal speeds set to "230400, 230400".

At the server end, in my .zprofile, I have "stty speed 230400". When I enter "stty -a" at my zsh prompt, it shows "speed 230400 baud;" (among several other stty settings).

When I log in to the server, I see (below a welcome banner) "230400" on a line by itself just above my shell prompt.

I assume (somewhat uncertainly) from this that I am connecting at or close to that speed.

So why is it that when I open tmux from my zsh prompt, just before the child zsh prompt appears (inside tmux), I see, on a line just above the child zsh prompt, "9600"?

Do I need to -export- the "stty speed 230400" command that's in my .zprofile? I'm not sure I can do that (or I don't know how to do that), since "stty speed 230400" is not an environment variable setting.

Or, can I / do I need to set from within tmux the speed at which the shell opens tmux?

Or am I better off not trying to set these speeds at all? (The PuTTY manual says, for example, about its "terminal speeds" setting:

"This parameter does not affect the actual speed of the connection, which is always ‘as fast as possible’; it is just a hint that is sometimes used by server software to modify its behaviour. For instance, if a slow speed is indicated, the server may switch to a less bandwidth-hungry display mode.

"The value is usually meaningless in a network environment, but PuTTY lets you configure it, in case you find the server is reacting badly to the default value. *"The format is a pair of numbers separated by a comma, for instance, 38400,38400. The first number represents the output speed (from the server) in bits per second, and the second is the input speed (to the server)."**

In any event, I find the "9600" odd. I also am not really sure if these supposed connection speeds have any real meaning or bear accurately on my real connection speeds.

So, what is the source of the appearance of the "9600" speed indicator, and why that speed when all settings are at the higher number, and appear to be working at that higher number?

  • I'm pretty sure these old baud settings persist just for backwards compatibility reasons, and don't actually control anything anymore. I'm quite certain zsh doesn't care. Commented Apr 3, 2014 at 15:06

1 Answer 1


These speeds are a configuration setting for serial lines and are irrelevant for any terminal that isn't connected through a serial line, such as terminal multiplexer software, remote terminals, GUI terminal emulator, or any other kind of software terminal. Because serial lines were once the norm for terminals, the speed is a parameter in the terminal configuration. While in theory some applications might use the setting, which is why PuTTY allows you to change it, in practice, I've yet to encounter one that does. You can safely ignore this setting, and don't include any stty speed … line in any configuration file.

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