tmux

tmux Skill

Use tmux as a programmable terminal for interactive CLIs that do not fit plain exec commands. This skill is for Linux, macOS, and WSL. Native Windows terminals are out of scope.

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Auth Approach

No authentication is required. Attempt the tmux command first. If it fails, diagnose missing tmux, missing WSL, a dead socket, or a stale session.

Tool Preference

Use the host shell tool to run tmux directly. Do not add helper scripts. Keep sessions on a private socket so agent-controlled panes stay separate from the user's personal tmux server.

Platform mapping:

• Claude Code: use the Bash tool for tmux commands.
• Codex: use exec_command for tmux commands and write_stdin only for host PTY sessions, not tmux panes.

Session Convention

Always create a socket directory and use tmux -S "$SOCKET":

TMUX_SOCKET_DIR="${CLAUDE_TMUX_SOCKET_DIR:-${TMPDIR:-/tmp}/agent-tmux-sockets}"
mkdir -p "$TMUX_SOCKET_DIR"
SOCKET="$TMUX_SOCKET_DIR/terminal.sock"
SESSION="agent-python"
tmux -S "$SOCKET" new-session -d -s "$SESSION" -n shell

After starting a session, tell the user how to monitor it:

tmux -S "$SOCKET" attach -t "$SESSION"
tmux -S "$SOCKET" capture-pane -p -J -t "$SESSION":. -S -200

Repeat the monitor command again when leaving a long-running session open.

Use "$SESSION":. for the active pane unless you have inspected pane indexes. This avoids failures on user configs that start window indexes at 1.

Operations: Tier 1 (Read)

List sessions on the private socket:

tmux -S "$SOCKET" list-sessions

List panes with targets:

tmux -S "$SOCKET" list-panes -a -F '#{session_name}:#{window_index}.#{pane_index} #{pane_current_command} #{pane_title}'

Capture recent output from a pane:

tmux -S "$SOCKET" capture-pane -p -J -t "$SESSION":. -S -200

For full-screen TUIs where style escape codes matter during diagnosis, add -e:

tmux -S "$SOCKET" capture-pane -p -e -J -t "$SESSION":. -S -200

Scan all known agent sockets:

find "${CLAUDE_TMUX_SOCKET_DIR:-${TMPDIR:-/tmp}/agent-tmux-sockets}" -type s -maxdepth 1 -print

Operations: Tier 2 (Write)

Start a new session:

tmux -S "$SOCKET" new-session -d -s "$SESSION" -n shell

Send literal text, then press Enter:

tmux -S "$SOCKET" send-keys -t "$SESSION":. -l -- 'python3 -q'
tmux -S "$SOCKET" send-keys -t "$SESSION":. Enter

Send control keys:

tmux -S "$SOCKET" send-keys -t "$SESSION":. C-c
tmux -S "$SOCKET" send-keys -t "$SESSION":. C-d

Poll for prompt text without a helper script:

deadline=$((SECONDS + 15))
while (( SECONDS < deadline )); do
  pane="$(tmux -S "$SOCKET" capture-pane -p -J -t "$SESSION":. -S -200)"
  printf '%s\n' "$pane" | grep -Eq '^>>>' && break
  sleep 0.5
done
printf '%s\n' "$pane" | grep -Eq '^>>>'

Operations: Tier 3 (Manage)

Kill one session when the interactive task is done:

tmux -S "$SOCKET" kill-session -t "$SESSION"

Kill the private server only after confirming no useful sessions remain:

tmux -S "$SOCKET" kill-server

Ask before killing sessions that the user may be monitoring.

Recipes

Python REPL:

tmux -S "$SOCKET" send-keys -t "$SESSION":. -l -- 'PYTHON_BASIC_REPL=1 python3 -q'
tmux -S "$SOCKET" send-keys -t "$SESSION":. Enter

Debugger:

tmux -S "$SOCKET" send-keys -t "$SESSION":. -l -- 'gdb --quiet ./a.out'
tmux -S "$SOCKET" send-keys -t "$SESSION":. Enter
tmux -S "$SOCKET" send-keys -t "$SESSION":. -l -- 'set pagination off'
tmux -S "$SOCKET" send-keys -t "$SESSION":. Enter

Generic TTY program:

tmux -S "$SOCKET" send-keys -t "$SESSION":. -l -- 'psql "$DATABASE_URL"'
tmux -S "$SOCKET" send-keys -t "$SESSION":. Enter

Steering Agent Sessions

Use tmux for nested agent CLIs only as an experiment. It can work for observing and steering codex or claude sessions, but it is more brittle than native subagent tools because prompts, permission flows, and screen updates are text scraped from a terminal pane.

Start a nested Codex session:

SESSION="agent-codex"
tmux -S "$SOCKET" new-session -d -s "$SESSION" -n codex
tmux -S "$SOCKET" send-keys -t "$SESSION":. -l -- 'codex'
tmux -S "$SOCKET" send-keys -t "$SESSION":. Enter

Start a nested Claude Code session:

SESSION="agent-claude"
tmux -S "$SOCKET" new-session -d -s "$SESSION" -n claude
tmux -S "$SOCKET" send-keys -t "$SESSION":. -l -- 'claude'
tmux -S "$SOCKET" send-keys -t "$SESSION":. Enter

Rules for nested agents:

• Keep each nested agent in its own session name and private socket.
• Capture before sending input so you know what state the agent is in.
• Wait several seconds before judging a blank pane. Agent CLIs may start MCP servers or render full-screen UI slowly.
• Prefer plain text prompts and explicit commands.
• Do not paste secrets into panes.
• Expect manual intervention for auth, trust, model selection, plugin prompts, and permission prompts.
• Prefer host-native subagent tools when the goal is normal delegation.

Self-Healing

If tmux is missing, tell the user to install it. On Windows, recommend WSL with tmux installed inside the Linux environment.

If a session is missing, run:

tmux -S "$SOCKET" list-sessions

If the pane target is wrong, run:

tmux -S "$SOCKET" list-panes -a

If a poll times out, capture the pane and reason from the visible state instead of blindly sending more input.

Behavioral Guidelines

• Use tmux only for programs that require a persistent TTY.
• Prefer simple shell commands for non-interactive work.
• Use slug-like session names without spaces.
• Always use send-keys -l -- for literal text.
• Use capture-pane -p -J before deciding the next keystroke.
• Clean up finished sessions.
• Leave monitor commands when a session remains open.