Source: ViewEdit

Isolation levels

Proposed vocabulary. These terms are a proposal from the essay Virtual environments are neither virtual nor temporary. They describe existing tools; they do not rename them.

Words like "virtual environment", "container" and "sandbox" do not say what is separated, how long it lasts, or what it applies to. This page gives each of those a small fixed vocabulary.

Three things, not one

Term Meaning Examples

Recipe

A description of what is wanted.

requirements.txt, pyproject.toml, Dockerfile, flake.nix, .nvmrc, .tool-versions

Artifact

What was built from a recipe and stored.

a venv folder, a Node version folder, a container image, a VM disk

Attachment

A process, session or folder currently using an artifact.

an activated venv, nvm use, a running container, a booted VM

Artifacts and attachments each have their own lifetime.

Isolation: what is separated

Level What changes Examples

overlay

Only name lookup: PATH, environment variables, import paths, command-namespace nodes. Files, processes, network and kernel are shared.

Python venv, nvm / nvm-windows, pyenv, asdf, mise, direnv, Nix dev shells, Volta

fence

Same view of the OS; permissions are reduced.

seccomp, Landlock, AppArmor, SELinux confinement, macOS sandbox, Windows AppContainer, Firejail profiles

partition

Own view of files, processes and network; shared kernel.

Docker / Podman containers, FreeBSD jails, systemd-nspawn, Linux namespaces, Windows Server containers (process isolation)

guest

Own kernel on virtual hardware.

Hyper-V, VirtualBox, QEMU/KVM VMs, Firecracker microVMs, WSL2, Windows Sandbox, Hyper-V-isolated containers

Plan 9 per-process namespaces sit between overlay and partition: each process gets its own file tree, built by binding, without a separate kernel.

Lifetime: how long it lasts

Term Ends when

run

the command or process exits

session

the shell session closes

kept

someone deletes it

Scope: what it applies to

process, session, folder (project), user, machine.

Writing a full name

<lifetime> <level>, optionally @<scope> for the attachment.

Thing Full name Why

Python venv, activated

kept overlay, attached @session

The folder persists; activate edits PATH, VIRTUAL_ENV and the prompt in one session. Calling .venv/bin/python directly needs no activation.

nvm use 22

kept overlay, attached @session

Versions are persistent folders; use edits PATH.

mise / asdf / direnv pin

kept overlay, attached @folder

A file in the project selects; the effect follows the current folder.

docker run --rm

run partition

The writable layer is removed on exit; the image stays.

Named container

kept partition

The writable layer lasts until docker rm.

Windows Sandbox

run guest

A lightweight VM discarded on close.

Hyper-V / VirtualBox VM

kept guest

Disk persists; snapshots allow rewinding.

Common misconceptions

  • "A venv dies with the shell." Only its activation does. The venv is a folder.

  • "Containers are persistent." Images are. A container lasts until removed, which with --rm is on exit.

  • "A container is a lightweight VM." On Linux it shares the host kernel; that is what separates a partition from a guest.

  • "A sandbox is a VM." Usually it is a fence. Windows Sandbox is the exception: it is a guest.

See also