---
name: vellum-terminal-sessions
description: "Manage persistent tmux terminal sessions: create, read, write to, list, and close named shell sessions. For Claude Code or Codex, use the ACP skill instead."
license: "MIT"
compatibility: "Sandbox mode works without any host dependencies. Host mode requires tmux installed on the user's machine. Works on macOS and Linux."
metadata:
  decimalai-skill-id: "e11d7d91-056a-424e-ba58-bbeb35f24a55"
  decimalai-version-id: "1508702b-ac95-4ab8-88e3-e2da78109a61"
  decimalai-version: "2"
  decimalai-body-sha256: "6c6bdb3866e99a486586c29d525fc39180c9509d0045b79add4d1a68774bbbb5"
  decimalai-name: "vellum-terminal-sessions"
  decimalai-format: "1"
  decimalai-invocation: "model"
  decimalai-category: "devops"
  decimalai-source: "https://app.decimal.ai/s/vellum-terminal-sessions@2/SKILL.md"
---
## Overview

This skill manages **persistent terminal sessions** via tmux. Two modes:

|                       | Sandbox Mode                                  | Host Mode                                                           |
| --------------------- | --------------------------------------------- | ------------------------------------------------------------------- |
| **Where tmux runs**   | In the assistant's sandbox                    | On the user's host machine                                          |
| **How user connects** | `vellum terminal attach <session-name>`       | User opens their own terminal                                       |
| **Assistant access**  | Direct (`bash` tool)                          | Via `host_bash`                                                     |
| **Best for**          | Long-running builds, servers, always-on tasks | Work needing host access (e.g. SwiftUI builds, host-local services) |

**Default:** Use **Sandbox Mode** unless the task specifically requires host access. Details: [sandbox-sessions.md](references/sandbox-sessions.md) · [host-sessions.md](references/host-sessions.md) · [tmux-best-practices.md](references/tmux-best-practices.md)

## Prerequisites

**Sandbox Mode:** No setup needed — tmux is available in the sandbox.

**Host Mode:** Requires tmux on the host — see [host-sessions.md](references/host-sessions.md).

## Workflow: Orchestrating Multiple Sessions

- **List** all sessions: `tmux list-sessions` to get names and current commands
- **Read** each: `tmux capture-pane -t NAME -p -S -50` (30-50 lines is usually enough)
- **Summarize** before acting: "Build done, tests at 73%, deploy waiting for confirmation"
- **Act** on the user's instructions