isdocker

A tiny, zero-dependency Rust library that detects whether the current process is running inside a Docker container or a compatible OCI runtime.

What is isdocker?

isdocker exposes a single function:

pub fn is_docker() -> bool

Call it anywhere in your application to find out whether you are inside a container. That's it.

Why this crate exists

Many applications need to adapt their behaviour depending on their runtime environment — logging format, configuration paths, signal handling, and more. Checking for Docker is a common pattern, but writing the detection logic correctly (handling I/O errors, supporting multiple container runtimes, avoiding false positives) takes more care than it first appears.

isdocker packages that logic into a single well-tested function so you never have to think about it again.

Installation

Add the crate to your Cargo.toml:

[dependencies]
isdocker = "0.1"

Usage

use isdocker::is_docker;

fn main() {
    if is_docker() {
        println!("Running in Docker 🐳");
    } else {
        println!("Not running in Docker");
    }
}

Conditional logging configuration:

use isdocker::is_docker;

fn init_logging() {
    if is_docker() {
        // Emit structured JSON logs for log aggregators.
        init_json_logger();
    } else {
        // Pretty human-readable output for local development.
        init_pretty_logger();
    }
}

How detection works

On Linux, two checks are performed in sequence. The first positive result short-circuits further checks.

1. /.dockerenv

Docker creates the file /.dockerenv in the root of every container filesystem. Checking for its existence is fast (a single stat syscall) and reliable for Docker-managed containers.

2. /proc/self/cgroup

The Linux cgroup virtual filesystem exposes the cgroup hierarchy of the current process at /proc/self/cgroup. Docker, containerd, and Kubernetes all place containers in named cgroup paths that include recognisable substrings:

If any of these strings appear in the cgroup file, the function returns true.

Non-Linux platforms

On macOS, Windows, and other platforms the function always returns false without performing any I/O. Container detection is only meaningful on Linux.

Safety guarantees

• Never panics — all I/O is handled with match; errors silently return false.
• No unsafe code — enforced with #![forbid(unsafe_code)].
• No allocations on the fast path — the .dockerenv check is a single existence test with no heap allocation.
• Zero dependencies — nothing beyond std.

Minimum Supported Rust Version (MSRV)

Rust 1.56 (edition 2021). The crate is tested against stable Rust.

License

MIT — see LICENSE.