tmux

tmux is a terminal multiplexer, similar to GNU screen but with window management. It serves two needs:

Enabling any number of terminals to be accessed from a single terminal.
Allowing the user to detach from a session, which will continue to run in the background, and can later be resumed.

Concepts

Sessions are made up of one or more windows. tmux exits when there are no longer any running sessions.
Windows host one or more panes. Only one window may be visible at any given time.
Panes can host pseudo terminals. Panes may be navigated within a window.
Pseudo terminals are managed as child processes of the tmux server.
The Status line shows the active and available windows, and can show additional information about the machine tmux is running on.
The Prefix key precedes a tmux command.

Commands

ls lists sessions.
new-session [-d] [-n WINDOW_NAME] [-s SESSION_NAME] creates a new session.
new-window [-a] [-t TARGET] [-n WINDOW_NAME] creates a new session.
attach [-t TARGET] attaches to a session.
kill-session [-t TARGET] kills a session.
kill-server kills the server.

Modes

Each pane has a mode:

Direct terminal access is the default. Keys are sent directly to the pseudo terminal.
Copy mode (entered with copy-mode) allows copying a selection of the pane's history to a paste buffer.
View mode behaves like copy mode, but can only be entered by running a command that produces output.
Choose mode allows picking items from a list, and can be entered only from the choose-* commands.

Key bindings

Key bindings execute commands. For consistency with the documentation key bindings are denoted in emacs syntax. They're triggered with the prefix key (C-b by default) followed by a command key:

C-b passes the prefix key sequence to the terminal.
? shows the key bindings.
: enters a command.
r forces the client to redraw.
~ shows messages from the tmux server.
d detaches the current client.
D selects a client to detach from the server.
L switch the attached client back to the last session.

Cursor keys navigate between panes.
q briefly shows pane numbers.
o navigates to the next pane in the window.
; returns to the previously active pane.
{ swaps the current pane with the previous pane.
} swaps the current pane with the next pane.
M-n jumps to the next window with a bell/activity marker.
M-p jumps to the previous window with a bell/activity marker.

Pane management

These commands operate within the current pane:

t shows the time.
% splits vertically.
" splits horizontally.
z toggles the pane's zoom (full screen) state (note *Z in the status line).
! moves the pane to a new window.
x kills the pane.

Pane arrangement

M-1 through M-5 arrange panes in a preset layout:
- even-horizontal
- even-vertical
- main-horizontal
- main-vertical
- tiled
Space arranges windows in the next layout.
C-Up, C-Down, C-Left, and C-Right resize the current pane in one cell steps.
M-Up, M-Down, M-Left, M-Right resize the current pane in five cell steps.

0 through 9 switch to the specified window.
' prompts for a window to switch to.
w changes window interactively.
f searches for text in open windows.
l moves to the previously selected window.
n moves to the next window.
p moves to the previous window.

Window management

These commands operate on the current window:

c creates a new window.
i shows some information about the window.
, renames the window.
& kills the window.
. moves the window.

s interactively selects a new session for the client to attach to.
( selects the previous session.
) selects the next session.

Session management

$ renames the session.

Copy/paste

[ enters copy mode, also allowing scrollback through history.
- PgUp enters copy mode and scrolls one page up.
] pastes.
= interactively selects the buffer to paste.
# lists all paste buffers.
- deletes the most recently copied buffer.

Implementation

Terminals run in a server, to which the client connects. The server exits when there are no longer any active sessions.

Configuration

Configuration is stored in ~/.tmux.conf, and can execute any commands.

Some interesting options:

set-option -g mouse on enables mouse support for pane navigation and resizing.
set-option -g pane-border-status top shows the pane title and number above each pane.
- set-option -g pane-border-format " [ (#P) #T ] " shows the pane index and title enclosed in square brackets.
bind-key C-k "send-keys -R C-l; clear-history clears the screen and tmux scrollback buffer in one go.
bind-key -n C-a send-prefix allows hitting C-a in the root tmux session to pass the prefix key to a nested session.