ferroday-cage-cli 0.1.4

Run a command inside an unprivileged Linux sandbox from a shell prompt: fresh namespaces, a provided root filesystem, seccomp and Landlock hardening, and a clean environment. Installs the fcage binary
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# ferroday-cage

A pure-Rust library for running a command inside an unprivileged Linux sandbox: its
own root filesystem view, its own namespaces, and a clean environment, all established
by talking to the kernel directly.

Configure a sandbox with a typed builder, launch a command, and consume its streamed
output and a typed result. The command runs under a minimal init in its own PID
namespace, and a running sandbox is driven through a handle that can wait, set a
deadline, terminate, or kill. A companion command-line tool, `fcage`, offers the same
sandbox at a shell prompt.

The library issues the sandbox's syscalls itself, so a default build is
self-contained: pure Rust throughout, resting on the kernel alone. `unsafe` is
confined to the small kernel-facing core — namespaces, id maps, mounts, `pivot_root`,
`exec` — and everything above it, and every consumer, is safe Rust.

The sandbox rests on the same kernel primitives as bubblewrap — user and mount
namespaces, `pivot_root`, seccomp — and presents them as a library with a typed builder
and an in-process handle rather than a command to shell out to. `fcage` covers the
command-line case.

It is not a container runtime: there are no images, no registry, and no OCI runtime
specification. A root filesystem is a directory you supply or provision, and every
sandbox is rootless — built with the caller's own credentials, with no daemon involved.

## Features

A bare dependency gives the sandbox itself: namespaces, mounts, the root swap,
identity maps, the process model, output streaming, and resource limits. Each
capability below is opt-in, and every dependency it brings is pure Rust with C
backends off, so any combination keeps the build self-contained.

| Feature | What it adds |
| --- | --- |
| `hardening` | Landlock filesystem and network rules, seccomp syscall filters, and capability drops applied to the command — plus a restriction fallback for hosts that disable user namespaces, confining a plain process with the same primitives |
| `tarball` | Provision a rootfs atomically from a tar archive (uncompressed, gzip, xz, or zstd, detected by content) with kernel-enforced containment, and export one back with its ownership and extended attributes intact |
| `debian` | Bootstrap a Debian suite and architecture straight from the archive — a `debootstrap` replacement that verifies the release signature, resolves the dependency closure itself, and configures the root in a cage |
| `netstack` | A native userspace TCP/IP stack giving the isolated network outbound IPv4 and IPv6, terminated in-process and forwarded over ordinary host sockets |
| `serde` | The sandbox specification round-trips through profile files, including a restricted mode for profiles from an untrusted source |
| `subid` | uid/gid range maps through the shadow suite's `newuidmap`/`newgidmap`, so a userland needing more than one identity works inside |

```sh
cargo add ferroday-cage --features hardening,tarball
```

## Usage

```rust,no_run
use ferroday_cage::Cage;

fn main() -> ferroday_cage::Result<()> {
    let status = Cage::builder()
        .rootfs("/srv/rootfs/alpine")
        .command("/bin/sh")
        .args(["-c", "echo hello from the cage"])
        .build()?
        .run()?;
    assert!(status.success());
    Ok(())
}
```

Or at a shell prompt, through `fcage`:

```sh
cargo install ferroday-cage-cli
fcage --rootfs /srv/rootfs/alpine -- /bin/sh -c 'echo hello from the cage'
```

Requires Rust 1.91 or later, and Linux 5.6 or later with unprivileged user namespaces
enabled. A host that denies them is reported by name, with the blocking configuration
and its remedy. See the [guide](https://gregordinary.github.io/ferroday-cage/) for
details.

## Contributing and security

See [CONTRIBUTING.md](CONTRIBUTING.md) for how to build, test, and propose changes,
and [SECURITY.md](SECURITY.md) for how to report a containment bypass or another
security issue. Released changes are recorded in [CHANGELOG.md](CHANGELOG.md).

## Workspace

- `crates/ferroday-cage` — the library.
- `crates/ferroday-cage-cli` — the `fcage` binary, a thin consumer of the library's
  public API.
- `docs/` — the guide, an [mdBook](https://rust-lang.github.io/mdBook/).

## Status

The library is feature-complete for this release, and its public surface is
guarded by a committed API snapshot, `cargo-semver-checks`, and auto-trait
assertions. The API settles over the 0.x series: while the major version is 0,
a breaking change bumps the minor version. The [stability
chapter](https://gregordinary.github.io/ferroday-cage/stability.html) states
what each interface promises.

## License

Licensed under either of

- Apache License, Version 2.0
  ([LICENSE-APACHE](https://github.com/gregordinary/ferroday-cage/blob/main/LICENSE-APACHE)
  or <http://www.apache.org/licenses/LICENSE-2.0>)
- MIT license
  ([LICENSE-MIT](https://github.com/gregordinary/ferroday-cage/blob/main/LICENSE-MIT)
  or <http://opensource.org/licenses/MIT>)

at your option.

### Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.