firecracker-microvm/firecracker · error

Failed to clone API kill switch

Error message

Failed to clone API kill switch

What it means

Error "Failed to clone API kill switch" thrown in firecracker-microvm/firecracker.

Source

Thrown at src/firecracker/src/api_server_adapter.rs:197

    let api_seccomp_filter = seccomp_filters
        .remove("api")
        .expect("Missing seccomp filter for API thread.");

    let mut server = match HttpServer::new(&bind_path) {
        Ok(s) => s,
        Err(ServerError::IOError(inner)) if inner.kind() == std::io::ErrorKind::AddrInUse => {
            let sock_path = bind_path.display().to_string();
            return Err(ApiServerError::FailedToBindSocket(sock_path));
        }
        Err(err) => {
            return Err(ApiServerError::FailedToBindAndRunHttpServer(err));
        }
    };
    info_unrestricted!("Listening on API socket ({bind_path:?}).");

    let api_kill_switch_clone = api_kill_switch
        .try_clone()
        .expect("Failed to clone API kill switch");

    server
        .add_kill_switch(api_kill_switch_clone)
        .expect("Cannot add HTTP server kill switch");

    // Start the separate API thread.
    let api_thread = thread::Builder::new()
        .name("fc_api".to_owned())
        .spawn(move || {
            ApiServer::new(to_vmm, from_vmm, to_vmm_event_fd).run(
                server,
                process_time_reporter,
                &api_seccomp_filter,
                api_payload_limit,
            );
        })
        .expect("API thread spawn failed.");

View on GitHub (pinned to 0a745def42)

Solutions

1. Check the process file-descriptor limit; cloning the kill-switch fd fails on fd exhaustion.
2. Verify the kill-switch eventfd is still open when cloned.

When it happens

Trigger: Thrown at src/firecracker/src/api_server_adapter.rs:197 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of firecracker-microvm/firecracker@0a745def42 (2026-08-19). Data as JSON: /api/errors/53c801120149df7e. Report an issue: GitHub.