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Presentation notes from JMU Unix Users Group meetings


What is Tmux?

Tmux stands for terminal multiplexer. Anyone who has taken 261 might recognize the word multiplexer, but just in case you dont; multiplexers take one thing and split it into many. In 261 it’s referring to circuits, here we’re referring to your terminal.

Why should I use it?

Because it pains me physically:

Both of these problems are easily solved with Tmux, and they don’t even require much technical overhead.

Using Tmux

To start Tmux, simply type Tmux on the command line.

Wow! A bottom bar!

What you have now is simply a regular terminal running inside what Tmux calls a ‘session’. Sessions contain windows and windows contain terminals. None of this is complicated in theory and Tmux doesn’t complicate it in practice either.

Splitting your view

We will start with the most useful part of Tmux, before we go into how it works.

To split your view horizontally, simply press CTRL + b followed by %.

BAM, 2 terminals!


Note that you are not pressing CTRL + b + %. This is because Tmux works off a ‘prefix’ hotkey system, where CTRL + b is the default ‘prefix’ input. This simply means that (by default) Tmux wont pay attention to any keystroke not preceded by the prefix.

So now that you are sitting there with two terminals, how do you get between them?

Start with your prefix, and follow it with the left arrow key.

And like magic, your cursor moves to the left terminal. This works for all arrow keys exactly like you would imagine.

To split your current terminal vertically, simply enter the prefix followed by " (denoted from here on as prefix + "). This makes it easy to remember which one splits which way because they divide the keyboard in the direction they divide your terminal.

Try splitting the terminal a couple times and moving around with the arrow keys.

Now I’m sure you’ve opened an ungodly number of terminals and are wondering how to close them, well prefix + x has you there, will close the current terminal after a confirmation window pops up on the bottom in a different color. Type y if you are sure you want your window closed. You can also type exit directly into the terminal and Tmux will handle the pane closing perfectly.

Quick ref:

Opening new windows

To open a new window in Tmux, type prefix + c. You will be greeted with a new terminal as well as a new entry in the bottom information bar. This bar shows open windows and their names. By default the names are generated from whatever the last active terminal in use was on that window, they can be changed by entering prefix + ,. This will prompt for a new name to call the window.

This is not strictly necessary, and may even be a waste of time unless you have 6+ windows at a time you are continuously working out of, but it is an option.

Moving between windows is as easy as prefix + 0-9, selecting the number listed next to the window you want to move to. By default this is indexed at 0 for some reason, so for now just deal with that and we’ll fix it later.

You can also create a new window using a terminal from another one with prefix + !.

Closing windows is the same as closing terminals, using prefix + &

Quick ref:


Sessions are a sometimes useful, sometimes frustrating part of Tmux that can be very powerful if used correctly, and can bring your system to it’s knees if used incorrectly.

Sessions are basically how Tmux saves your current set of windows and allows you to return to them later

To list all current sessions use prefix + s. If you have attempted to use Tmux before you might even see a few sessions open! You can hit enter on the current attached one to re-enter where you left off.

If you do you can type prefix + :, which will open Tmux command entry, and type kill-session -a. This will simply kill all sessions besides the current.

Let’s detach from the current session. Enter the prefix + d to manually detach from the current session, you will return to the command line with a line of output from Tmux that we don’t particularly care about.

Now open Tmux again. You will be greeted with a new Tmux session. To move to a different session while already in a Tmux session you can do prefix + s and move to the old one and hit enter to attach.

These sessions will stay open once detached until they are manually closed. Every once in a while I hear there is a purge on stu, so be sure to save your work even if you are using sessions.

When are they useful?

One last quick sidenote, sessions are automatically kept if a terminal is lost. This is most useful when stu or your internet are being dumb, and you get disconnected. Your session will be automatically kept and can be accessed by ssh-ing again or on the lab computers.

How can they hurt me?

Let’s say you keep losing connection to stu, but never re-attach your session. This means you will keep creating new Tmux sessions and slowly but surely load stu with terminal sessions simply waiting for you to return.

So make sure to close sessions and periodically check for open ones.


Here are some quick options from my ~/.Tmux.conf that I think are nice QOL improvements over base functionality.

# set base index to 1 for windows
set -g base-index 1

# rebind prefix to ctrl+a
unbind C-b
set -g prefix C-a
bind C-a send-prefix

# Switch panes using alt+arrow keys
bind -n M-Left select-pane -L
bind -n M-Right select-pane -R
bind -n M-UP select-pane -U
bind -n M-Down select-pane -D

# Allow mouse control
set -g mouse on

# Turn off audio bell
set -g bell-action none

# turn visual bell on
set -g visual-bell on

# when I had Tmux wrap any shell I used, this command was useful to attatch
# Tmux to my current directory
# Binds to prefix + p
bind p attach -c "#{pane_current_path}"