In my shell I have flow control disabled using stty -ixon. This works perfectly in the shell and when I launch tmux and start programs within tmux.

However, when starting a new session from the command line and directly launching a command, the flow control setting is not respected and ctrl-s freezes the terminal.

This works:

tmux new-session -s foo

This does not respect the stty flow control setting:

tmux new-session -s foo vim

How can I disable flow control even in the latter case?

  • Is it sufficient to disable flow control all together within tmux for all cases, or are you interested in nailing down why it works in the first example but not the second?
    – slm
    May 14, 2013 at 0:12
  • @slm In the first place I'd like to have it fixed. Nevertheless, I'm interested why tmux behaves as it does.
    – Marco
    May 14, 2013 at 6:51

2 Answers 2


If you have stty -ixon in your shell's initialization, it's rather simple: when tmux creates new terminals, it runs user's default shell by default and that in turn disables the control flow during the initialization. However, when you ask tmux to run a specific command (ViM in your case), no initialization takes place and the default terminal settings (flow control enabled) apply.

tmux new-session -s foo "stty -ixon; vim"

should fix your problem.


A workaround which does not require changing the tmux call is to include the stty call in the file $HOME/.zshenv. This file is parsed by ZSH and used even for non-interactive shells.

echo 'stty -ixon' | tee -a ~/.zshenv
# ... or ...
echo 'stty -ixon' >> ~/.zshenv

BASH users have to set the environment variable BASH_ENV=$HOME/.zshenv to make this work.

  • 2
    I don't know what it does, but it did the trick. Added it to both .zshrc and .zshenv. Be careful with > though. Use: echo 'stty -ixon' >> ~/.zshenv
    – firedev
    Apr 12, 2015 at 9:32

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