---
summary: "Background exec execution and process management"
read_when:
  - Adding or modifying background exec behavior
  - Debugging long-running exec tasks
title: "Background Exec and Process Tool"
---

# Background Exec + Process Tool

SKYKOI runs shell commands through the `exec` tool and keeps long‑running tasks in memory. The `process` tool manages those background sessions.

## exec tool

Key parameters:

- `command` (required)
- `yieldMs` (default 10000): auto‑background after this delay
- `background` (bool): background immediately
- `timeout` (seconds, default 1800): kill the process after this timeout
- `elevated` (bool): run on host if elevated mode is enabled/allowed
- Need a real TTY? Set `pty: true`.
- `workdir`, `env`

Behavior:

- Foreground runs return output directly.
- When backgrounded (explicit or timeout), the tool returns `status: "running"` + `sessionId` and a short tail.
- Output is kept in memory until the session is polled or cleared.
- If the `process` tool is disallowed, `exec` runs synchronously and ignores `yieldMs`/`background`.

## Child process bridging

When spawning long-running child processes outside the exec/process tools (for example, CLI respawns or gateway helpers), attach the child-process bridge helper so termination signals are forwarded and listeners are detached on exit/error. This avoids orphaned processes on systemd and keeps shutdown behavior consistent across platforms.

Environment overrides:

- `PI_BASH_YIELD_MS`: default yield (ms)
- `PI_BASH_MAX_OUTPUT_CHARS`: in‑memory output cap (chars)
- `SKYKOI_BASH_PENDING_MAX_OUTPUT_CHARS`: pending stdout/stderr cap per stream (chars)
- `PI_BASH_JOB_TTL_MS`: TTL for finished sessions (ms, bounded to 1m–3h)

Config (preferred):

- `tools.exec.backgroundMs` (default 10000)
- `tools.exec.timeoutSec` (default 1800)
- `tools.exec.cleanupMs` (default 1800000)
- `tools.exec.notifyOnExit` (default true): enqueue a system event + request heartbeat when a backgrounded exec exits.

## process tool

Actions:

- `list`: running + finished sessions
- `poll`: drain new output for a session (also reports exit status)
- `log`: read the aggregated output (supports `offset` + `limit`)
- `write`: send stdin (`data`, optional `eof`)
- `kill`: terminate a background session
- `clear`: remove a finished session from memory
- `remove`: kill if running, otherwise clear if finished

Notes:

- Only backgrounded sessions are listed/persisted in memory.
- Sessions are lost on process restart (no disk persistence).
- Session logs are only saved to chat history if you run `process poll/log` and the tool result is recorded.
- `process` is scoped per koi; it only sees sessions started by that koi.
- `process list` includes a derived `name` (command verb + target) for quick scans.
- `process log` uses line-based `offset`/`limit` (omit `offset` to grab the last N lines).

## Examples

Run a long task and poll later:

```json
{ "tool": "exec", "command": "sleep 5 && echo done", "yieldMs": 1000 }
```

```json
{ "tool": "process", "action": "poll", "sessionId": "<id>" }
```

Start immediately in background:

```json
{ "tool": "exec", "command": "npm run build", "background": true }
```

Send stdin:

```json
{ "tool": "process", "action": "write", "sessionId": "<id>", "data": "y\n" }
```
