nix

Nix is the Rust crate that makes Unix system calls safe. Instead of writing unsafe libc bindings and manually checking errno, nix wraps POSIX APIs with proper Rust types, Result returns, and lifetime guarantees. Socket programming, signal handling, file operations, process management — all without the footguns of raw C FFI.

If you're writing systems-level Rust on Linux or macOS and touching POSIX APIs, nix saves you from entire categories of bugs. Rustix is the newer alternative with direct syscall support (bypassing libc entirely) and automatic 64-bit API selection — faster and more modern. The raw libc crate gives you unsafe bindings when you need exact C compatibility.

The catch: nix is safe wrappers, not zero-cost abstractions. Some operations are marginally slower than raw syscalls. The API surface is large and not everything is consistently documented. And if you're targeting WebAssembly, Windows, or non-POSIX systems, nix doesn't help — it's Unix-only by design. For new projects, evaluate rustix first.