containers-internals

containers-internals is a skill for Codex from OutlineDriven/outline-driven-development. It costs 52 tokens per session (2,095 once invoked), scanned A, original, Apache-2.0.

A guide to the Linux building blocks behind containers, including process isolation, resource limits, filesystems, permissions, and security filters. Containers are isolated processes that share the host system's kernel rather than running a full virtual machine.

In plain words
What is it for?
Use it to investigate container isolation, build a minimal container without a container daemon, write system-call security filters, or assess a container escape risk.
Why use it?
It helps explain or reproduce container failures and security problems at the operating-system level, including resource limits, permission errors, mount failures, and possible escapes.

Skill for Codex

Written for Codex: agents/openai.yaml present.

Good fit Use it to investigate container isolation, build a minimal container without a container daemon, write system-call security filters, or assess a container escape risk.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/outlinedriven/outline-driven-development/containers-internals
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add OutlineDriven/outline-driven-development --skill containers-internals
Clone the repo
git clone --depth 1 https://github.com/OutlineDriven/outline-driven-development

Made for: Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for containers-internals

README.md
[![agentmods](https://agentmods.dev/badge/skills/outlinedriven/outline-driven-development/containers-internals/github.svg)](https://agentmods.dev/skills/outlinedriven/outline-driven-development/containers-internals)
Your own site
<a href="https://agentmods.dev/skills/outlinedriven/outline-driven-development/containers-internals"><img src="https://agentmods.dev/badge/skills/outlinedriven/outline-driven-development/containers-internals/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for containers-internals

Your own site · 80×15
<a href="https://agentmods.dev/skills/outlinedriven/outline-driven-development/containers-internals"><img src="https://agentmods.dev/badge/skills/outlinedriven/outline-driven-development/containers-internals.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 52 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,095 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 3 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Privilege Escalation · line 29
    Potential security issue detected. Manual review is recommended.
    Fix: Review the flagged content for security risks. Ensure no credentials, secrets, or sensitive data are exposed.
  • high Privilege Escalation · line 30
    Potential security issue detected. Manual review is recommended.
    Fix: Review the flagged content for security risks. Ensure no credentials, secrets, or sensitive data are exposed.
  • medium MCP Rug Pull · line 136
    Docker image references without a specific tag (:latest is implicit) or digest (@sha256:...) can be silently replaced by a malicious image.
    Fix: Pin the image: image:tag or image@sha256:abc123
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00052 $0.02095
Opus 5 $0.00026 $0.01047
Sonnet 5 $0.00010 $0.00419
Haiku 4.5 $0.00005 $0.00210

Measured 3d ago against content hash 32ceb6b7165f, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

containers-internals scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.devin/skills/containers-internals/SKILL.md · 156 lines

How it starts

The opening of the file, as written. The whole thing — 156 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Containers internals

Contract

Field Bound contract
Trigger A container's isolation or resource limit needs explaining or debugging, a seccomp profile needs writing, a minimal container is being built without a daemon, or an escape vector needs assessing.
Authority Reversible local. The write set is namespaces and cgroups created for the session under /sys/fs/cgroup, overlay mounts on user-named directories, an OCI bundle directory, and seccomp filters applied to processes the skill starts. Rollback is stopping those processes, unmounting, and removing the cgroup directory. Most steps need root or a user namespace. No remote mutation.
Side effect Kernel namespaces, cgroups, and mounts exist while the experiment runs.
Done The isolation or limit in question is reproduced with the raw primitive, the observed behavior matches the explanation, and every created object has its teardown recorded.

Inputs

  • Question or symptom (required): an OOM kill, CPU throttling, a permission denial inside the container, a mount failure, or a concept.
  • Target (optional): a running container's PID, or a rootfs directory for a manual container.
  • Privilege (required to know): root, or an unprivileged user relying on user namespaces. Several steps differ.

Procedure

  1. Read and enter namespaces. Each namespace type isolates one resource. Done when: the target process's namespace inodes are listed and, when needed, a shell runs inside them.
ls -la /proc/self/ns/            # one link per namespace type
readlink /proc/1234/ns/net       # compare inodes to see who shares a namespace
nsenter -t <pid> -m -u -i -n -p bash
unshare --fork --mount-proc --pid --net --uts --ipc bash   # a manual container shell
Flag Isolates
CLONE_NEWNS Mount table
CLONE_NEWPID Process ids
CLONE_NEWNET Network stack
CLONE_NEWUTS Hostname and domain name
CLONE_NEWIPC System V IPC and POSIX message queues
CLONE_NEWUSER Uid and gid mappings
CLONE_NEWCGROUP The cgroup root the process sees
CLONE_NEWTIME Boot-time and monotonic clock offsets

Read the full file on GitHub · 156 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 156 lines · 52 tokens per session scan A 32ceb6b7165f

Subscribe to this mod's changes

containers-internals is a skill published in the GitHub repository OutlineDriven/outline-driven-development (52 stars, last pushed 3d ago), licensed Apache-2.0. It adds 52 tokens to every session and 2,095 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-06.

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