tracel-ai/burn · error

unsupported TARGET_OS '{os}'

Error message

unsupported TARGET_OS '{os}'

What it means

burn-tch's build script recognizes only linux, windows, and macos as TARGET_OS values when locating libtorch and configuring the tch bindings. If the cargo-provided TARGET_OS environment variable holds anything else (or is malformed), the build script panics, failing compilation of the burn-tch crate.

Source

Thrown at crates/burn-tch/build.rs:53

    libtorch_include_dirs: Vec<PathBuf>,
    libtorch_lib_dir: PathBuf,
}

fn env_var_rerun(name: &str) -> Result<String, env::VarError> {
    println!("cargo:rerun-if-env-changed={name}");
    env::var(name)
}

impl SystemInfo {
    fn new() -> Option<Self> {
        let os = match env::var("CARGO_CFG_TARGET_OS")
            .expect("Unable to get TARGET_OS")
            .as_str()
        {
            "linux" => Os::Linux,
            "windows" => Os::Windows,
            "macos" => Os::Macos,
            os => panic!("unsupported TARGET_OS '{os}'"),
        };
        // Locate the currently active Python binary, similar to:
        // https://github.com/PyO3/maturin/blob/243b8ec91d07113f97a6fe74d9b2dcb88086e0eb/src/target.rs#L547
        let python_interpreter = match os {
            Os::Windows => PathBuf::from("python.exe"),
            Os::Linux | Os::Macos => {
                if env::var_os("VIRTUAL_ENV").is_some() {
                    PathBuf::from("python")
                } else {
                    PathBuf::from("python3")
                }
            }
        };
        let mut libtorch_include_dirs = vec![];
        let mut libtorch_lib_dir = None;
        let cxx11_abi = if env_var_rerun("LIBTORCH_USE_PYTORCH").is_ok() {
            let output = std::process::Command::new(&python_interpreter)
                .arg("-c")

View on GitHub (pinned to d16f7ba2ed)

Solutions

1. Build for a supported OS (linux, windows, macos); use another backend (libtorch via burn-core with a different backend, candle, ndarray) for unsupported targets.
2. Check `echo $TARGET_OS` in the failing build environment and remove any override of cargo's TARGET_OS.
3. If you must target another OS, patch the build script's match to add the Os variant and provide libtorch paths manually.

Example fix

// before
cargo build --target=x86_64-unknown-freebsd --features tch   // panics: unsupported TARGET_OS 'freebsd'
// after
cargo build --target=x86_64-unknown-linux-gnu --features tch  // or use the candle/ndarray backend

# fail fast before cargo build
import subprocess, os, sys
target_os = os.environ.get("CARGO_CFG_TARGET_OS", "")
if target_os not in ("linux", "windows", "macos") and "tch" in sys.argv:
    sys.exit(f"burn-tch does not support TARGET_OS '{target_os}'")

When it happens

Trigger: Building burn-tch for a target platform outside {linux, windows, macos} — e.g. freebsd, android, wasm, or a custom/nightly target triple whose OS string is unexpected; or an environment where TARGET_OS is unset/overridden by a wrapper script.

Common situations: Cross-compiling burn with the tch backend to embedded/mobile targets; building in nonstandard CI containers that clobber cargo metadata env vars; typos in `--target` triples via cargo build --target=<os-specific-string>.

Related errors

• no cxx11 abi returned by python {output:?}
• nearest exact interpolation is not supported by PyTorch/tch
• lanczos3 interpolation is not supported by PyTorch/tch backe
• nearest exact interpolation backward is not supported by PyT
• lanczos3 interpolation backward is not supported by PyTorch/

AI-assisted analysis of tracel-ai/burn@d16f7ba2ed (2026-09-05). Data as JSON: /api/errors/7f6f7578847b9d4b. Report an issue: GitHub.