Terminal Multiplexer

Terminal Multiplexer

Use tmux to manage background terminal sessions.

Prerequisites

Verify tmux is installed before use:

# Check if tmux is available
command -v tmux >/dev/null 2>&1 || {
    echo "Error: tmux is not installed"
    echo "Install with: brew install tmux (macOS) or apt install tmux (Linux)"
    exit 1
}

When to Use

• Long-running processes (servers, builds, downloads)
• Parallel execution of multiple commands
• Keeping tasks alive after SSH disconnect
• Capturing output from background jobs

When NOT to Use

• Simple one-off commands that complete quickly
• When user explicitly requests alternatives (screen, nohup)
• Interactive applications requiring full terminal features

Core Commands

Session Management

# Create and attach to a new session
tmux new-session -s <name>

# Create a detached session (background)
tmux new-session -d -s <name>

# List all sessions
tmux ls

# Attach to an existing session
tmux attach -t <name>

# Rename a session
tmux rename-session -t <old-name> <new-name>

# Kill a session
tmux kill-session -t <name>

Sending Commands

# Run a command in a detached session
tmux send-keys -t <name> "<command>" C-m

# Example: start a server in the background
tmux new-session -d -s api-server
tmux send-keys -t api-server "bun run dev" C-m

Capturing Output

# Capture the latest pane output
tmux capture-pane -p -t <name>

# Capture to a file
tmux capture-pane -t <name> && tmux save-buffer /tmp/output.txt

# Capture last N lines
tmux capture-pane -p -t <name> | tail -n 20

Common Workflows

Start a Background Server

tmux new-session -d -s server -n app
tmux send-keys -t server "npm start" C-m

Run Multiple Tasks in Parallel

tmux new-session -d -s jobs -n worker1
tmux send-keys -t jobs:worker1 "npm run build:client" C-m

tmux new-window -t jobs -n worker2
tmux send-keys -t jobs:worker2 "npm run build:server" C-m

Check if a Process Finished

tmux capture-pane -p -t <name> | tail -n 20

Monitoring a Background Process

# Start a build in background
tmux new-session -d -s build -n compile
tmux send-keys -t build:compile "npm run build 2>&1 | tee build.log" C-m

# Check progress
tmux capture-pane -p -t build:compile | tail -n 10

# When done, check exit code
tmux send-keys -t build:compile "echo $?" C-m
tmux capture-pane -p -t build:compile | tail -n 1

Detaching and Reattaching

# User is in a session, needs to disconnect
# Press: Ctrl-b d (detach)

# Later, reattach
tmux attach -t <name>

# Or attach to most recent session
tmux attach

Troubleshooting

Session Already Exists

# Check existing session
tmux ls | grep <name>

# Attach to existing session
tmux attach -t <name>

# Or kill and recreate
tmux kill-session -t <name>
tmux new-session -d -s <name>

Session Not Found

# List all sessions
tmux ls

# Common cause: session name typo
# Use tab completion or exact name from `tmux ls`

Command Not Executing in Session

# Verify session exists and is responsive
tmux list-panes -t <name>

# Send command with explicit enter
tmux send-keys -t <name> "<command>" C-m

# Wait and check output
sleep 2
tmux capture-pane -p -t <name>

Best Practices

• Name sessions descriptively (e.g., dev-server, test-runner)
• Kill sessions when done to free resources
• Use tmux ls to check existing sessions before creating new ones
• Prefer detached sessions (-d) for background tasks
• Use tmux send-keys over tmux new-session for existing sessions