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What is a Flox environment?

An environment is a shell that provides a collection of environment variables, software packages, and activation scripts that are run when entering the shell. Environments provide packages that take precedence over your existing packages without removing access to personalizations not provided by the environment. Flox environments layer on top of your system so that you can use the environment's software when it's active, while still using your personal shell aliases, IDE, tools, and kitted out text editor.

See the creating an environment guide to create your first environment.

Environment uses

  1. Path environment: An environment stored in a local directory. This environment is self contained in the .flox directory and can be reproduced by sharing the directory in version control or some other file sharing mechanism. Path environments are created with flox init, referred to with the --dir/-d option on most CLI commands, and are commonly used for self-contained projects or different subprojects within a monorepo.
  2. Centrally managed environment: An environment stored remotely on FloxHub. You can connect this to a project directory with flox pull ... or activate it directly with flox activate --remote ... for instant use. Centrally managed environments enable multiple projects or systems to consume a shared environment that is versioned with generations. Centrally managed environments are created by running flox push on a path environment and are referred to with the --remote/-r option on most commands. They are commonly used as base environments for projects of similar tech stacks, for reproducing issues on specific systems, or to quickly share tools.

See the sharing guide for a more thorough walk through about sharing and working with different types of environments.

Environment files

A Flox environment stores its metadata, declarative manifest, and manifest lock file in a .flox directory wherever the flox init command was run. Let's look closer at the files that were generated.

Environment manifest: .flox/env/manifest.toml

The manifest is a declarative specification for the environment and contains 5 parts:

  • Install: the packages installed to the environment.
  • Vars: environment variables for use in the activated environment.
  • Hook: Bash script executed before passing control to the user's shell.
  • Profile: Shell-specific scripts sourced by the user's shell.
  • Options: Environment-scoped options such as supported systems.

Read more about the manifest and consult the customizing environments guide to walk through examples.

Manifest lock: .flox/env/manifest.lock

The lock file serves as a snapshot of the specific versions of dependencies that were built and activated at a particular point in time.

manifest.lock
{
  "lockfile-version": 0,
 ...
        "input": {
          "attrs": {
            "lastModified": 1703581207,
            "narHash": "3ef...",
            "owner": "NixOS",
            "repo": "nixpkgs",
            "rev": "3ef...",
            "type": "github"
          },
          "fingerprint": "3ef...",
          "url": "github:NixOS/nixpkgs/3ef..."
        },
        "priority": 5
      },
      "nodejs": {    
}

Environment metadata: .flox/env.json

A metadata file that contains the name of the environment and the environment's version. Flox manages this file for you.

env.json
{
  "name": "example-project",
  "version": 1
}