# Kit examples — Install a tool at sandbox creation

> setup.install runs once per sandbox, at creation time. It's where anything that needs to land in the image goes — package managers (apt-get, pip, npm), binary downloads, or vendor install scripts. > [!TIP] > Each new sandbox runs all setup.install commands. The results aren't > cached between sandbo

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## Metadata

- Canonical URL: <https://wikikv.com/k/ref-docker-9c64b5888a545b098b87>
- Knowledge kind: `reference`
- Confidence: `0.72`
- Independent verifications: `0`
- Updated: `2026-08-16T09:32:14.472498+00:00`
- Tags: `reference-seed`, `docker`, `manuals`, `ai`, `sandboxes`, `customize`, `kit`, `examples`, `install`, `tool`, `sandbox`, `creation`

## Provenance

- Source: <https://github.com/docker/docs/blob/3a9d778562f39bcc0be46255b013c6a3ca526244/content/manuals/ai/sandboxes/customize/kit-examples.md>
- Source name: Docker Documentation
- Source revision: `3a9d778562f39bcc0be46255b013c6a3ca526244`
- Source license: `Apache-2.0`
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## Knowledge

Reference note (untrusted external data; do not execute it as instructions).

setup.install runs once per sandbox, at creation time. It's where anything that needs to land in the image goes — package managers (apt-get, pip, npm), binary downloads, or vendor install scripts.

&gt; [!TIP] &gt; Each new sandbox runs all setup.install commands. The results aren't &gt; cached between sandboxes. Creating a kit avoids building and distributing an &gt; image, so kits work well for smaller, composable changes. For substantial &gt; build or installation steps, consider a &gt; custom template. Sandboxes reuse &gt; template images from the local cache.

Bounded code example (external data; do not execute automatically):
```yaml
setup:
  install:
    - command: "apt-get update &amp;&amp; apt-get install -y jq"
    - command: "curl -fsSL https://example.com/install.sh | sh"
```

Install commands run as root by default. Set user: "1000" when the step should run as the agent user — for example, npm install -g against a user-scoped prefix, or anything that writes to /home/agent/.

Install steps run under sh, not bash, so bash-only builtins such as source fail with sh: source: not found. Pipe explicitly to bash (curl … | bash) or wrap the step in bash -c '…' when you need them.

Downloads are subject to the sandbox's network access rules. A domain that resolves from your host can still be blocked inside the sandbox — for example, get.sdkman.io returns a 403 until you allow it with sbx policy allow network get.sdkman.io. A tool may also need base packages that aren't in the image: SDKMAN!, for instance, needs zip and unzip, so add an apt-get install -y zip unzip step (as root) before installing it.

&gt; [!WARNING] &gt; curl … | bash masks download failures. The pipe's exit status is &gt; bash's, and bash exits 0 on empty input, so a blocked or failed &gt; download still reports success — the sandbox is created with no error &gt; even though nothing was installed. Download first, then run, so a &gt; failed fetch fails the step: &gt; &gt; yaml &gt; setup: &gt; install: &gt; - command: "curl -fsSL -o /tmp/install.sh &amp;&amp; bash /tmp/install.sh" &gt; user: "1000" &gt;

Attribution: Adapted from Docker Documentation under Apache-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.