deepseek-harness/packages/shell/bash-local/README.md

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description: "The default POSIX Bash executor for deployments and maintainers choosing, configuring, or debugging unconfined command execution over the shell seam."

kind: "package-reference"

@deepseek-ai/dsh-bash-local

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Summary

dsh-bash-local is the default Bash executor for POSIX: every command runs as a fresh, non-login bash -c process with no rc files, so no shell state survives between calls. It applies configured budgets — working directory, timeout, output caps — to each command, classifies timeouts and cancellations, and returns bounded output with spill-file recovery when a stream overflows. Commands run with the harness process's own authority: this executor confines nothing, so compose dsh-bash-sandbox when commands need the sandbox capability. The model-facing bash tool talks to it once it is mounted.

Table of Contents

• Use this package
• Understand the implementation
• Further Exploration
• Model Experience
• Known Limitations and Deferred Work
• Dev Note

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Use this package

Mount this executor when a composition needs Bash command execution on POSIX without confinement. It registers as ctx.shell, and the model-facing bash tool works over it immediately: an agent calls the tool, and the command runs as a fresh bash -c process with the budgets below.

Minimal configuration

Load the executor with the budgets you want; every field has a default, so the smallest composition is the plugin entry alone. The settings provider (when composed) layers a user section over this entry, so budgets can change at runtime without a reload (see Adjusting budgets at runtime).

- id: bash
  name: '@deepseek-ai/dsh-bash-local'
  config:
    cwd: /path/to/workspace
    timeoutMs: 120000

Field	Default	Meaning
cwd	process.cwd()	Default working directory for commands
timeoutMs	120,000	Default foreground timeout, in milliseconds
maxTimeoutMs	600,000	Cap for per-call timeout overrides
maxOutputBytes	64,000	Per-stream in-memory output cap; overflow spills to a temp file
maxSpillBytes	67,108,864	Per-stream full-output spill cap
graceMs	3,000	Grace period for kill escalation and post-exit pipe draining

The generated configuration catalog is the exhaustive source for every accepted field and its JSDoc.

Running commands

Run a command with run and read its output from the result. A nonzero exit, a timeout, or a cancellation resolves with a descriptive result — only infrastructure failures reject. Per-call timeoutMs overrides are capped by the configuration, while workdir falls back to the configured default when unset; a trusted foreground caller can also raise the stdout capture budget for one call, while stderr and background runs keep maxOutputBytes. The environment is model-friendly by default: NO_COLOR=1 TERM=dumb PAGER=cat GIT_PAGER=cat keep pagers and ANSI colors from garbling output, and an explicit caller-provided entry still wins.

const result = await ctx.shell.run(ctx.shell.resolve({ command: 'ls -la' }))
if (result.timedOut) console.log('timed out after', result.timeoutMs)

Background processes

Call start to run a command in the background; it returns a handle immediately and no timeout applies. readOutput() merges the stream deltas into one consuming read, marking stderr under a [stderr] section; kill() terminates the provider-managed range; done settles when the direct command closes and never rejects. Job ids, ownership, polling, and notices belong to the generic ctx.jobs runtime, which the tool layer registers the handle with.

Adjusting budgets at runtime

When a settings provider is composed, this executor registers the capability's shared shell settings namespace with the composition entry as its base, so a user section in settings.yaml layers over it and the next command runs with the new budgets. Values the schema cannot judge — positive and finite numbers, and the graceMs timer bound — are refused at the write, leaving the running executor on its last good section; without a provider, the composition entry is what runs.

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Understand the implementation

Implementation internals — click to expand

This section explains the design of the executor and points at the code that realizes it; the observable behavior is fully covered in [Use this package](#use-this-package). ### Design concept The executor is a Service Provider for the `ctx.shell` seam built on the subprocess capability: it owns everything bash-shaped — command defaulting and caps, deadline fusion and cause classification, the model-friendly terminal environment, and the background read merge — while managed-range mechanics (bounded spill-backed output, credential scrub, termination escalation, quiescence, and disposal) belong to the subprocess service. Every call spawns a fresh non-login `bash -c` with no rc files, so commands are deterministic and shell state never leaks between calls. ### Source map | File | Role | |---|---| | [`src/index.ts`](src/index.ts) | Plugin entry: `LocalBashExecutor`, `Config`, settings-section wiring | | — | No runtime invariant companion is published; this package exposes no independent event sequence or mutable data relation beyond contracts enforced at its owning seam. | | `tests/executor.spec.ts` | Exercised behavior: budgets, classification, background handles, ownership | | `tests/settings.spec.ts` | Settings layering over the composition entry | ### Main flow A call runs through three steps: `resolve()` fills `workdir`/`timeoutMs`/`stdoutMaxBytes` from config (capping per-call overrides); `run` fuses the config-clamped timeout with the caller's abort signal into one deadline and spawns `['bash', '-c', command]` through `ctx.subprocess` with explicit byte caps and the `graceMs`; the settled subprocess outcome is classified — only the executor's own timeout reports `timedOut`, an upstream cancel reports `aborted`, a self-signaled command reports neither — and projected into a `ShellRunResult` with collected output. ### Invariants and ownership - The `graceMs` budget must be positive, finite, and no greater than `MAX_TIMER_DELAY_MS` so Node can represent it with one timer; invalid values are refused where they are written. - Environment layering is fixed: terminal overrides first, then the caller's `env`, then the trusted `dshEnv` snapshot last; the subprocess service scrubs ambient credentials and inherited `DSH_*` names independently. - A background process belongs to the subprocess service: it survives an executor-only reload and is killed and joined when the service disposes.

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Further Exploration

Read these pages when the executor contract is not enough. They move from the seam to the confining sibling and the mechanics underneath.

• shell seam — the executor contract this provider implements, including the request/spec split.
• bash-sandbox — the confining executor to compose instead when commands need the sandbox capability.
• tool-bash — the model-facing bash tool over this executor.
• Bash executor subsystem — request/spec vocabulary, results, and the service contract in full.
• subprocess-local — the managed-range mechanics behind this executor.

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Model Experience

Indirectly, through dsh-tool-bash, which renders this executor's bounded stdout/stderr tails, background-process deltas, spill-file paths, and infrastructure failures.

KV Cache effect

No direct invalidation; the named consumer owns any request-prefix changes.

Known Limitations and Deferred Work

These limits define when this executor is a poor fit. They are current package constraints, not a roadmap.

• Unconfined by itself — commands run with the harness process's authority; deployments needing confinement compose dsh-bash-sandbox, while per-call allow/deny/ask policy belongs on the tools' pre-execute waterfall.
• No persistent shell or PTY — every call starts a fresh non-login bash -c; cwd-only persistence and interactive terminal sessions remain deferred until a real workflow requires them.
• POSIX-only — the bash binary is hardcoded and the underlying service's group semantics are POSIX; Windows is unsupported.
• A background provider-failure note is single-delivery — SubprocessHandle.done can reject before or after target execution begins, so the executor injects the stage-neutral subprocess failed before reporting an outcome: … into exactly one readOutput() delta; a reader that discards that delta cannot recover it.

Dev Note

Working context for maintainers — click to expand

None.