🖥️ tmux

tmux is a terminal multiplexer — it lets you run multiple terminal sessions inside a single window, split the screen into panes, and detach/reattach to sessions so work keeps running in the background.

Core Concepts

Session — a collection of windows. You can detach from a session and reattach later; everything keeps running.
Window — like a tab inside a session. Each window fills the full terminal.
Pane — a split within a window. Multiple panes can be visible side-by-side or stacked.

All tmux commands are prefixed with a key combination called the prefix key. The default is Ctrl+B.

Sessions

Command	Description
`tmux`	Start a new session
`tmux new-session -s <name>`	Start a named session
`tmux list-sessions` / `tmux ls`	List all sessions
`tmux attach`	Re-attach to the most recent session
`tmux attach -t <name>`	Re-attach to a named session
`Ctrl+B, D`	Detach from the current session
`Ctrl+B, $`	Rename the current session
`Ctrl+B, S`	Show an interactive session list to switch between sessions
Inside session: `tmux rename-session <new-name>`	Rename session from the command line

Windows

Command	Description
`Ctrl+B, C`	Create a new window
`tmux new-window`	Create a new window (from the command line inside a session)
`Ctrl+B, N`	Switch to the next window
`Ctrl+B, P`	Switch to the previous window
`Ctrl+B, ,`	Rename the current window
`exit` or `Ctrl+B, &`	Close the current window

Panes

Command	Description
`Ctrl+B, %`	Split pane vertically (side by side)
`Ctrl+B, "`	Split pane horizontally (top and bottom)
`Ctrl+B, <arrow>`	Move focus to the pane in that direction
`Ctrl+B` (hold), `<arrow>`	Resize the current pane in that direction
`exit`	Close the current pane

Configuration

tmux reads its configuration from ~/.tmux.conf at startup.

Note

Good resource for customization: Learn tmux Part 5 — How to Customize tmux and Make it Your Own

Enable mouse support:

set -g mouse on

With mouse support enabled you can click to focus a pane or window, and drag pane borders to resize them.

Scripting

tmux is scriptable, which makes it useful for launching reproducible development environments. The example below sets up a three-pane layout — a common pattern for running a broker alongside two clients.

Example: launch a multi-pane tmux session from a script

#!/bin/bash

SESSION="my-session"

# Kill any existing session to start clean
tmux kill-session -t $SESSION 2>/dev/null

# Create a new detached session (200 cols × 50 rows)
tmux new-session -d -s $SESSION -x 200 -y 50

# Split right: creates pane 2
tmux split-window -t $SESSION -h -l 100

# Split pane 2 vertically: creates pane 3 below
tmux split-window -t $SESSION:1.2 -v -l 25

# Send commands to each pane
tmux send-keys -t $SESSION:1.1 "echo 'hello from pane 1'" Enter
tmux send-keys -t $SESSION:1.2 "echo 'hello from pane 2'" Enter
tmux send-keys -t $SESSION:1.3 "echo 'hello from pane 3'" Enter

# Attach to the session
tmux attach-session -t $SESSION

Key scripting commands:

tmux new-session -d -s <name> -x <cols> -y <rows> — create a detached session with a given size
tmux split-window -t <target> -h -l <cols> — split horizontally, new pane on the right
tmux split-window -t <target> -v -l <rows> — split vertically, new pane below
tmux send-keys -t <target> "<command>" Enter — send a command to a pane
tmux attach-session -t <name> — attach to a session
tmux set-hook -t <name> session-closed 'run-shell "<cmd>"' — run a shell command when the session closes

The <target> format is <session>:<window>.<pane> (e.g. my-session:1.2 means window 1, pane 2 of session my-session).