According to man tmux to check the launch option:

-C: Start in control mode (see the CONTROL MODE section). Given twice (-CC) disables echo.

Then in the control mode section of the man tmux, there is the following description:

     tmux offers a textual interface called control mode.  This allows
     applications to communicate with tmux using a simple text-only protocol.

     In control mode, a client sends tmux commands or command sequences
     terminated by newlines on standard input.  Each command will produce one
     block of output on standard output.  An output block consists of a %begin
     line followed by the output (which may be empty).  The output block ends
     with a %end or %error.  %begin and matching %end or %error have two
     arguments: an integer time (as seconds from epoch) and command number.
     For example:

           %begin 1363006971 2
           0: ksh* (1 panes) [80x24] [layout b25f,80x24,0,0,2] @2 (active)
           %end 1363006971 2

     The refresh-client -C command may be used to set the size of a client in
     control mode.

     In control mode, tmux outputs notifications.  A notification will never
     occur inside an output block.

I'm not sure what it means, but at least as far as I try a few commands and try to see the looks and feels of it via (tmux -CC), it looks like the same as when I launch via tmux new-session.

So what is the "control mode" and what makes it different from the normal mode?


I found that the session and the window that was launched via the control mode (-CC) does not react to the keyboard shortcut of the tmux commands, such as window split. So what is the point of using the control mode in the first place?

  • 1
    tmux does support copy and paste, see capture-pane and save-buffer and related commands – thrig Jul 4 '18 at 13:44
  • @thrig Sorry what I read was wrong; tmux does support it but does not the mouse-based copy & paste. It seems feasible via third-party plugins like tmux-yank, though I have not tried it yet. – Blaszard Jul 4 '18 at 13:54
  • Do you already have a tmux session running when you try tmux -C or tmux -CC? – JigglyNaga Jul 4 '18 at 17:07
  • @JigglyNaga I tried both situations but the result was consistent. – Blaszard Jul 4 '18 at 17:31
  • @Blaszard if you enable mouse support, you can enable copy by highlighting with your mouse. – rovr138 Jul 4 '18 at 18:08

I'm on a Mac and I use iTerm2. As far as I know it's the only terminal emulator that has tmux integration. You start by doing tmux -CC and iTerm will control your tmux session. This means you can use iTerm2 normally as you usually do (CMD-D to split a window vertically, CMD-SHIFT-D split it horizontally). You can use your mouse to reposition the panes instead of using C-b {. You don't need to use the prefix at all. You don't have any problems with copy and paste either when you're dealing with panes.

tl;dr Using tmux -CC allows you to use tmux "natively" on terminals that support it. So far I haven't seen any linux terminals that support it, only iTerm2 on a Mac.


The interesting aspect of control mode is that you can write a background process that listens to a real tmux process. It gets notifications of things happening in the real tmux, and it can then send commands. If you use 2 terminals and run a normal session in one

tmux new -s mysession

and in the other

tmux -C attach -t mysession

then when you split windows, add new ones, or close them in the normal tmux you will get lines like

%layout-change @2 91a8,80x23,0,0[80x11,0,0,5,80x11,0,12,7]
%window-add @3
%window-close @1

in the control tmux, to which you can react by writing a program. To help there is a python library to exploit this mechanism. See the examples there.


You are seeing similar results from tmux -CC as you would from tmux new-session because you didn't specify a command, so tmux uses the default, which is new-session:

command [flags]

This specifies one of a set of commands used to control tmux, as described in the following sections. If no commands are specified, the new-session command is assumed.

Adding -CC doesn't appear to change that. To control the existing session, you should attach to it in control mode:

tmux -C attach

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