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@seanh
Created May 18, 2016
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tmux

Notes about tmux from various sources, including:

Commands

All tmux commands can be entered in any of four ways:

  1. By hitting a bound keyboard shortcut such as ctrl-a c to create a new window.

  2. By hitting Ctrl-a : to enter tmux's command-line, then typing the command and hitting Enter.

  3. As a subcommand of the tmux command in a shell, eg. tmux split-window.

    Running tmux commands from zsh is usually better than using tmux's command-line, in zsh there is tab-completion of tmux subcommands and options with docstrings.

  4. As a line in your .tmux.conf configuration file.

The names of the commands and their options are the same, however the command is entered.

You can see a list of all tmux commands by doing:

  • :list-commands on the tmux command-line (i.e. type Ctrl-a :list-commands<Enter> in tmux)

  • $ tmux list-commands in a shell

  • or just $ tmux <tab> in zsh

Configuration File

The tmux system-wide and user config files are:

/etc/tmux.conf
~/.tmux.conf

The set-option command (alias: set) sets config options. For example, to change tmux's prefix from the default Ctrl-b to Ctrl-a, put this in your .tmux.conf file:

# Bind Ctrl-a instead of Ctrl-b as prefix key.
unbind C-b
set -g prefix C-a

then restart tmux. -g means "global" which means set this option for all new tmux sessions.

Install the configuration file from this folder

To install the .tmux.conf file from this folder, run this command in a shell:

$ wget 'https://raw.github.com/seanh/content-addressable/master/tmux/tmux.conf' -O ~/.tmux.conf

Reload your tmux.conf while tmux is running

If you've changed your .tmux.conf file, you can reload it without leaving your tmux session with this command:

source-file ~/.tmux.conf

You can create a keyboard shortcut Ctrl-a r to reload your .tmux.conf file, by putting this in your .tmux.conf file:

# Bind `Ctrl-a r` to reload the tmux.conf file.
bind r source-file ~/.tmux.conf \; display "~/.tmux.conf reloaded!"

256 colours

To make sure 256-colour mode works inside tmux, add this to your .tmux.conf:

# Enable 256 colours in tmux.
set -g default-terminal "screen-256color"

and always run tmux with the command TERM=screen-256color-bce tmux. You can alias tmux to this command in your zshrc or bashrc:

alias tmux="TERM=screen-256color-bce tmux"

Keybindings

Tmux commands can be bound to keyboard shortcuts, such as Ctrl-a c to open a new window. The bind-key and unbind-key commands change keyboard shortcuts.

The list-keys command (bound to ctrl-a ? by default) lists all current keybindings.

bindkey -n binds a key without having to press the prefix key first, eg:

# Use Ctrl-PgDn and Ctrl-PgUp to change windows.
bind-key -n C-PgDn next-window
bind-key -n C-PgUp previous-window

This completely disables these key combinations in any app inside tmux that might want to use them, so take care and use few of these.

-r makes a keybinding repeatable, so you can enter it multiple times without having to hit Ctrl-a each time.

Sessions

Create a new session named foobar:

new-session -s foobar
new -s foobar

Create a new session named foo, and name the session's first window bar:

new -s foo -n bar

List all currently running sessions:

list-sessions
ls

Attach to an already-running session named foobar:

attach-session -t foobar
attach -t foobar

attach works both from within a tmux session (to change to a different session) or from outside of any tmux session (to join one) (in this case attach has to be run from the shell, e.g. $ tmux attach -t foobar).

In zsh, $ tmux attach -t <tab> will autocomplete the names of currently running sessions to attach to.

Kill a session named foobar:

kill-session -t foobar

Windows

"Tabs" in tmux are called windows. The new-window command creates a new window and changes to it (this is bound to Ctrl-a c by default).

By default a shell will be run in the new window. To run some other program instead, give it as argument:

new-window htop

So you can make keybindings to, for example, move to a joined window named "mutt" or create a new window running mutt if there isn't one already.

Ctrl-a , renames the current window. From the command line you can rename any window:

rename-window -t 1 foo

(without the -t option it would rename the current window).

There are various commands and keyboard shortcuts for moving between windows:

ctrl-a ctrl-a
ctrl-a n
ctrl-a p
ctrl-a 0...9
ctrl-a f    List windows matching a search
ctrl-a w    List all windows
select-window -t 0..9

Kill a window:

ctrl-a &

Panes

Add this to your config to get easier-to-remember key bindings for splitting windows:

# Bind `Ctrl-a |` and `Ctrl-a -` to split the current window vertically and
# horizontally.
bind | split-window -h
bind - split-window -v

To move between panes, use:

Ctrl-a {left,right,up,down}

Cycle through built-in pane layouts:

ctrl-a space

Select a specific layout directly:

select-layout main-horizontal

(if you do this from zsh, you can tab-complete the layout names).

Kill a pane:

ctrl-a x

(also closes the pane's window, if the window doesn't have any other panes).

"Pop out" a pain into its own window:

ctrl-a !

Move the current pane "up" or "down":

ctrl-a }
ctrl-a {

(panes are numbered in the order they're created, these commands move the current pane up and down in this sequence by swapping it with "adjacent" panes).

Turn a window into a pane within another window:

join-pane -s panes:1

"panes" is the name of the session you want to take a window from, 1 is the number of the window you want to take. The window will become a pane in the current window.

To join a specific pane instead of an entire window, do:

join-pane -s panes:1.2

to take pane 2 of window 1 of session "panes".

Resizing Panes

Add this to your config:

# Bind `Ctrl-a shift-{left,right,up,down}` to resize the current pane.
# These are repeatable (-r), for example you can do `Ctrl-a shift-left` and
# then, without releasing shift, keep pressing left, up, down and right to
# resize the pane as much as you want.
bind -r S-Left resize-pane -L 1
bind -r S-Right resize-pane -R 1
bind -r S-Up resize-pane -U 1
bind -r S-Down resize-pane -D 1

"Maximising" and Unmazimising Panes

Note: tmux 1.8 (not yet available in Ubuntu 12.04, unless you install from source) has a built-in "zoom pane" feature that replaces this.

Bind ctrl-a M and ctrl-m to temporarily maximise and then unmaximise the current pane:

bind M new-window -d -n tmp \; swap-pane -s tmp.1 \; select-window -t tmp
bind m last-window \; swap-pane -s tmp.1 \; kill-window -t tmp

These bindings work by creating a new window called tmp, then swapping the current pane with the new pane that tmux automatically created in the new window. Unmaximising swaps the panes back then kills the temporary window.

(Unfortunately I think these keybindings misbehave if you change windows or panes while the pane is maximised, or if you try to unmaximise a pane that is not maximised.)

Managing Multple Sessions

Show a list of all running sessions so you can choose one to go to:

ctrl-a s

Move window 9 of the ckan session to window 3 of the foobar session:

tmux move-window -s ckan:9 -t foobar:3

Create or attach to a named session

This bit of shell script will attach to a session named foobar if one exists, or create a new session named foobar otherwise:

$ tmux attach -t foobar || tmux new -s foobar

Automatically connect to a named tmux session when starting your shell

Sometimes you open a new terminal emulator window, start working in a shell or terminal app, then realise you want to open another tmux window or pane within the terminal emulator window. To do so you have to quit the app you're running and start tmux, which is annoying.

You can put this in your zshrc or bashrc file to automatically connect to a named tmux session whenever you open a new shell:

# Automatically connect to tmux when starting zsh.
# If tmux is installed, and we're not already in a tmux session, then
# attach to a named tmux session (creating it if it doesn't already exist)
# when starting zsh.
if tmux -V >/dev/null 2>&1; then
  if [[ "$TERM" != "screen-256color" ]]
  then
    tmux attach-session -t "$USER" || tmux new-session -s "$USER"
    exit
  fi
fi

This is perfectly safe, the code won't execute if tmux isn't installed, you'll just get a normal non-tmux shell.

Warning, this is a little weird:

  • Remember to use ctrl-a d not ctrl-d to close a terminal window, ctrl-d will close all the terminal windows attached to the session!

  • If you have multiple terminal windows open and attached to the same tmux session, tmux will force each terminal to be as small as the smallest one

  • If you want to get out of the default session and attach to some other tmux session, just use the attach -t <session_name> command or ctrl-a s. Or to start a new session and join it, use the new command. You can also use tmuxinator (below) from a shell to move from one session into another, e.g. mux my_project.

Manage projects with tmuxinator

Tmuxinator lets you create named "projects", where each project defines (in a yaml file) a tmux session with a set of programs to run in a layout of windows and panes. You then use the mux command (an alias for tmuxinator) to open a project, and tmuxinator starts the tmux session, creates the windows and panes and runs the programs specified in the yaml file.

You can also specify pre commands that should be run before starting the session, a project root dir (that new shells in the session will start in) and a socket name to use for the session.

To create the yaml file for a project (or edit it, if the project already exists):

$ mux open ckan

To attach to a project's tmux session (starting the session if it isn't already running):

$ mux ckan

(like tmux's attach -t command, this also works for switching between sessions if you're already in another tmux session).

To list all defined projects:

$ mux list

Copy Mode

Config:

# Enable vi-mode when in copy mode.
set-window-option -g mode-keys vi

Enter copy mode:

ctrl-a [

Leave copy mode:

Enter

Moving around in copy mode (with vi-mode active):

Arrows or h, j, k, l           Move slowly
w and b                        Move by word
f followed by any character    Jump to the next occurence of that character
                               (on the same line)
F                              Jump backwards
Page Up, Page Down             Move a page at a time
gg                             Jump to top of buffer
G                              Jump to bottom of buffer
?                              Search upwards
/                              Search downwards
n                              Jump to next search match
N                              Jump to previous search match
$
^
etc (see :list-keys -t vi-copy)

Copying and Pasting

Add this to your config to enable vim-like key bindings for copying (yanking) and pasting text in copy mode:

# Select and copy text with v and y (instead of Space and Enter) like in vim.
bind -t vi-copy v begin-selection
bind -t vi-copy y copy-selection

# Bind Escape to exit copy mode.
bind -t vi-copy Escape cancel

# Paste text with `ctrl-a p`.
unbind p
bind p paste-buffer

To copy text: enter copy mode (Ctrl-a [), move the cursor to where you want your text selection to start from, press v, move the cursor to where you want your selection to end, press y, tmux copies the text and leaves copy mode.

To copy an entire pane's text:

capture-pane

To show the current contents of the paste buffer:

show-buffer

Save the paste buffer to a file:

save-buffer buffer.txt

From a shell, you can capture the contents of the current page and save them to a file in one command:

$ tmux capture-pane && tmux save-buffer buffer.txt

Tmux actually copies text into a new paste buffer each time you copy, and saves all the old paste buffers in a paste buffer stack. With the choose-buffer command tmux will show you the list of paste buffers and their contents, and let you choose one to paste from.

ctrl-a =
choose-buffer

The paste buffers are shared across all running tmux sessions, so you can copy text from one session and paste it into another.

Using the X Windows Clipboard

Note: this doesn't work on OS X.

First, install xclip:

sudo apt-get install xclip

Copying text in tmux's copy mode copies it into tmux's own paste buffer, not into the system clipboard. Pasting text in tmux pastes from tmux's paste buffer. If your terminal emulator supports it, you can still copy-paste with the system clipboard using terminal emulator shortcuts. (In my terminal emulator, select text with the mouse, right-click, and choose copy. To paste from the system clipboard, Shift-Ctrl-v.) But this doesn't recognise the boundaries between tmux panes, it will copy parts of text from adjacent tmux panes at once, including the border characters between the panes. So these key bindings can sometimes be useful to move text between tmux's paste buffer and the system clipboard:

# Copy text from tmux's paste buffer into the X clipboard with `ctrl-a y`.
bind y run "tmux save-buffer - | xclip -i -sel clipboard" \; display "Text copied to X clipboard"

# Paste text from the system clipboard into tmux with `ctrl-a P`.
bind P run "tmux set-buffer \"$(xclip -o -sel clipboard)\"; tmux paste-buffer"

Note: as your terminal emulator's text copying isn't aware of tmux's panes, borders and status line and will copy them as if they're part of the content, tmux's copy mode isn't aware of vim's gutter, status line, split windows, etc. So if you want to copy text from vim into the system clipboard, it's best to do this using vim keybindings.

Pair Programming

Unlike screen sharing, using tmux for pair-programming works even with slow or unreliable network connections. It uses much less bandwidth.

With a shared user account

The simplest way is to have a shared user account on a shared remote machine, both ssh into the same user account and simply attach to the same tmux session:

  • Create user account tmux on the shared remote server
  • Add a ~/ssh/authorized_keys file to the tmux account, with the right permissions
  • Add both user's ssh public keys to the file
  • First user ssh's into the tmux account on the remote machine and does tmux new-session -s foobar
  • Second user ssh's into the tmux account on the remote machine and does tmux attach -t foobar

Grouped Sessions

When you're both attached to the same session, you both see the same thing at the same time. For example, if one user changes to a new window, all users will change. If you don't want this, then instead of attaching to the other user's session you can create a new session and attach that session to their session:

tmux new-session -t foo -s bar

Now users can switch windows independently, but if one user creates a new window all users will see it in their status bar.

Tmux Sockets

With sockets different users (with different unix accounts) can connect to the same tmux session. Instead of launching tmux with the new-session and attach commands, both users launch tmux specifying the socket file to user for the session with -S:

tmux -S /var/tmux/pairing           (Creates the session)
tmux -S /var/tmux/pairing attach    (Attaches to the session)

The socket file needs to be one that both users have permission to read and write. The easiest way is to make a unix group called tmux, set the group of /var/tmux to tmux, set g+ws permissions on /var/tmux, and add all the users to the tmux group.

Unfortunately all sessions sharing the socket will use the .tmux.conf of the user who started the first session.

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