tmux

tmux — Terminal Multiplexer

Selective Reading Rule

Start with:

• references/senior-master-standard.md
• references/usage-routing.md
• references/quality-checklist.md

Then load only the inherited docs, scripts, assets, or examples that match the user's actual task.

Overview

tmux keeps terminal sessions alive across SSH disconnects, splits work across multiple panes, and enables fully scriptable terminal automation. This skill covers session management, window/pane layout, keybinding patterns, and using tmux non-interactively from shell scripts — essential for remote servers, long-running jobs, and automated workflows.

When to Use This Skill

• Use when setting up or managing persistent terminal sessions on remote servers
• Use when the user needs to run long-running processes that survive SSH disconnects
• Use when scripting multi-pane terminal layouts (e.g., logs + shell + editor)
• Use when automating tmux commands from bash scripts without user interaction

How It Works

tmux has three hierarchy levels: sessions (top level, survives disconnects), windows (tabs within a session), and panes (splits within a window). Everything is controllable from outside via tmux <command> or from inside via the prefix key (Ctrl-b by default).

Session Management

# Create a new named session
tmux new-session -s work

# Create detached (background) session
tmux new-session -d -s work

# Create detached session and start a command
tmux new-session -d -s build -x 220 -y 50 "make all"

# Attach to a session
tmux attach -t work
tmux attach          # attaches to most recent session

# List all sessions
tmux list-sessions
tmux ls

# Detach from inside tmux
# Prefix + d   (Ctrl-b d)

# Kill a session
tmux kill-session -t work

# Kill all sessions except the current one
tmux kill-session -a

# Rename a session from outside
tmux rename-session -t old-name new-name

# Switch to another session from outside
tmux switch-client -t other-session

# Check if a session exists (useful in scripts)
tmux has-session -t work 2>/dev/null && echo "exists"

Window Management

# Create a new window in the current session
tmux new-window -t work -n "logs"

# Create a window running a specific command
tmux new-window -t work:3 -n "server" "python -m http.server 8080"

# List windows
tmux list-windows -t work

# Select (switch to) a window
tmux select-window -t work:logs
tmux select-window -t work:2       # by index

# Rename a window
tmux rename-window -t work:2 "editor"

# Kill a window
tmux kill-window -t work:logs

# Move window to a new index
tmux move-window -s work:3 -t work:1

# From inside tmux:
# Prefix + c     — new window
# Prefix + ,     — rename window
# Prefix + &     — kill window
# Prefix + n/p   — next/previous window
# Prefix + 0-9   — switch to window by number

Pane Management

# Split pane vertically (left/right)
tmux split-window -h -t work:1

# Split pane horizontally (top/bottom)
tmux split-window -v -t work:1

# Split and run a command
tmux split-window -h -t work:1 "tail -f /var/log/syslog"

# Select a pane by index
tmux select-pane -t work:1.0

# Resize panes
tmux resize-pane -t work:1.0 -R 20   # expand right by 20 cols
tmux resize-pane -t work:1.0 -D 10   # shrink down by 10 rows
tmux resize-pane -Z                   # toggle zoom (fullscreen)

# Swap panes
tmux swap-pane -s work:1.0 -t work:1.1

# Kill a pane
tmux kill-pane -t work:1.1

# From inside tmux:
# Prefix + %     — split vertical
# Prefix + "     — split horizontal
# Prefix + arrow — navigate panes
# Prefix + z     — zoom/unzoom current pane
# Prefix + x     — kill pane
# Prefix + {/}   — swap pane with previous/next

Sending Commands to Panes Without Being Attached

# Send a command to a specific pane and press Enter
tmux send-keys -t work:1.0 "ls -la" Enter

# Run a command in a background pane without attaching
tmux send-keys -t work:editor "vim src/main.py" Enter

# Send Ctrl+C to stop a running process
tmux send-keys -t work:1.0 C-c

# Send text without pressing Enter (useful for pre-filling prompts)
tmux send-keys -t work:1.0 "git commit -m '"

# Clear a pane
tmux send-keys -t work:1.0 "clear" Enter

# Check what's in a pane (capture its output)
tmux capture-pane -t work:1.0 -p
tmux capture-pane -t work:1.0 -p | grep "ERROR"

Scripting a Full Workspace Layout

This is the most powerful pattern: create a fully configured multi-pane workspace from a single script.

#!/usr/bin/env bash
set -euo pipefail

SESSION="dev"

# Bail if session already exists
tmux has-session -t "$SESSION" 2>/dev/null && {
  echo "Session $SESSION already exists. Attaching..."
  tmux attach -t "$SESSION"
  exit 0
}

# Create session with first window
tmux new-session -d -s "$SESSION" -n "editor" -x 220 -y 50

# Window 1: editor + test runner side by side
tmux send-keys -t "$SESSION:editor" "vim ." Enter
tmux split-window -h -t "$SESSION:editor"
tmux send-keys -t "$SESSION:editor.1" "npm test -- --watch" Enter
tmux select-pane -t "$SESSION:editor.0"

# Window 2: server logs
tmux new-window -t "$SESSION" -n "server"
tmux send-keys -t "$SESSION:server" "docker compose up" Enter
tmux split-window -v -t "$SESSION:server"
tmux send-keys -t "$SESSION:server.1" "tail -f logs/app.log" Enter

# Window 3: general shell
tmux new-window -t "$SESSION" -n "shell"

# Focus first window
tmux select-window -t "$SESSION:editor"

# Attach
tmux attach -t "$SESSION"

Configuration (~/.tmux.conf)

# Change prefix to Ctrl-a (screen-style)
unbind C-b
set -g prefix C-a
bind C-a send-prefix

# Enable mouse support
set -g mouse on

# Start window/pane numbering at 1
set -g base-index 1
setw -g pane-base-index 1

# Renumber windows when one is closed
set -g renumber-windows on

# Increase scrollback buffer
set -g history-limit 50000

# Use vi keys in copy mode
setw -g mode-keys vi

# Faster key repetition
set -s escape-time 0

# Reload config without restarting
bind r source-file ~/.tmux.conf \; display "Config reloaded"

# Intuitive splits: | and -
bind | split-window -h -c "#{pane_current_path}"
bind - split-window -v -c "#{pane_current_path}"

# New windows open in current directory
bind c new-window -c "#{pane_current_path}"

# Status bar
set -g status-right "#{session_name} | %H:%M %d-%b"
set -g status-interval 5

Copy Mode and Scrollback

# Enter copy mode (scroll up through output)
# Prefix + [

# In vi mode:
# / to search forward, ? to search backward
# Space to start selection, Enter to copy
# q to exit copy mode

# Paste the most recent buffer
# Prefix + ]

# List paste buffers
tmux list-buffers

# Show the most recent buffer
tmux show-buffer

# Save buffer to a file
tmux save-buffer /tmp/tmux-output.txt

# Load a file into a buffer
tmux load-buffer /tmp/data.txt

# Pipe pane output to a command
tmux pipe-pane -t work:1.0 "cat >> ~/session.log"

Practical Automation Patterns

# Idempotent session: create or attach
ensure_session() {
  local name="$1"
  tmux has-session -t "$name" 2>/dev/null \
    || tmux new-session -d -s "$name"
  tmux attach -t "$name"
}

# Run a command in a new background window and tail its output
run_bg() {
  local session="${1:-main}" cmd="${*:2}"
  tmux new-window -t "$session" -n "bg-$$"
  tmux send-keys -t "$session:bg-$$" "$cmd" Enter
}

# Wait for a pane to produce specific output (polling)
wait_for_output() {
  local target="$1" pattern="$2" timeout="${3:-30}"
  local elapsed=0
  while (( elapsed < timeout )); do
    tmux capture-pane -t "$target" -p | grep -q "$pattern" && return 0
    sleep 1
    (( elapsed++ ))
  done
  return 1
}

# Kill all background windows matching a name prefix
kill_bg_windows() {
  local session="$1" prefix="${2:-bg-}"
  tmux list-windows -t "$session" -F "#W" \
    | grep "^${prefix}" \
    | while read -r win; do
        tmux kill-window -t "${session}:${win}"
      done
}

Remote and SSH Workflows

# SSH and immediately attach to an existing session
ssh user@host -t "tmux attach -t work || tmux new-session -s work"

# Run a command on remote host inside a tmux session (fire and forget)
ssh user@host "tmux new-session -d -s deploy 'bash /opt/deploy.sh'"

# Watch the remote session output from another terminal
ssh user@host -t "tmux attach -t deploy -r"  # read-only attach

# Pair programming: share a session (both users attach to the same session)
# User 1:
tmux new-session -s shared
# User 2 (same server):
tmux attach -t shared

Best Practices

• Always name sessions (-s name) in scripts — unnamed sessions are hard to target reliably
• Use tmux has-session -t name 2>/dev/null before creating to make scripts idempotent
• Set -x and -y when creating detached sessions to give panes a proper size for commands that check terminal dimensions
• Use send-keys ... Enter for automation rather than piping stdin — it works even when the target pane is running an interactive program
• Keep ~/.tmux.conf in version control for reproducibility across machines
• Prefer bind -n for bindings that don't need the prefix, but only for keys that don't conflict with application shortcuts

Security & Safety Notes

• send-keys executes commands in a pane without confirmation — verify the target (-t session:window.pane) before use in scripts to avoid sending keystrokes to the wrong pane
• Read-only attach (-r) is appropriate when sharing sessions with others to prevent accidental input
• Avoid storing secrets in tmux window/pane titles or environment variables exported into sessions on shared machines

Common Pitfalls

• Problem: tmux commands from a script fail with "no server running" Solution: Start the server first with tmux start-server, or create a detached session before running other commands.

• Problem: Pane size is 0x0 when creating a detached session Solution: Pass explicit dimensions: `tmux new-session -d -s n

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