tmux

# tmux — Terminal Multiplexer ## 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 ```bash # 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 ```bash # 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 ```bash # 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 ```bash # 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. ```bash #!/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`) ```bash # 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 ```bash # 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 ```bash # 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 ```bash # 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 name -x 200 -y 50`. - **Problem:** `send-keys` types the text but doesn't run the command **Solution:** Ensure you pass `Enter` (capital E) as a second argument: `tmux send-keys -t target "cmd" Enter`. - **Problem:** Script creates a duplicate session each run **Solution:** Guard with `tmux has-session -t name 2>/dev/null || tmux new-session -d -s name`. - **Problem:** Copy-mode selection doesn't work as expected **Solution:** Confirm `mode-keys vi` or `mode-keys emacs` is set to match your preference in `~/.tmux.conf`. ## Related Skills - `@bash-pro` — Writing the shell scripts that orchestrate tmux sessions - `@bash-linux` — General Linux terminal patterns used inside tmux panes - `@ssh` — Combining tmux with SSH for persistent remote workflows ## Limitations - Use this skill only when the task clearly matches the scope described above. - Do not treat the output as a substitute for environment-specific validation, testing, or expert review. - Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.