firecracker-microvm/firecracker · error

'mmds-size-limit' parameter expected to be of 'usize' type.

Error message

'mmds-size-limit' parameter expected to be of 'usize' type.

What it means

Error "'mmds-size-limit' parameter expected to be of 'usize' type." thrown in firecracker-microvm/firecracker.

Source

Thrown at src/firecracker/src/main.rs:417

    let api_enabled = !arguments.flag_present("no-api");
    let api_payload_limit = arg_parser
        .arguments()
        .single_value("http-api-max-payload-size")
        .map(|lim| {
            lim.parse::<usize>()
                .expect("'http-api-max-payload-size' parameter expected to be of 'usize' type.")
        })
        // Safe to unwrap as we provide a default value.
        .unwrap();

    // If the mmds size limit is not explicitly configured, default to using the
    // `http-api-max-payload-size` value.
    let mmds_size_limit = arg_parser
        .arguments()
        .single_value("mmds-size-limit")
        .map(|lim| {
            lim.parse::<usize>()
                .expect("'mmds-size-limit' parameter expected to be of 'usize' type.")
        })
        .unwrap_or_else(|| api_payload_limit);

    if api_enabled {
        let bind_path = arguments
            .single_value("api-sock")
            .map(PathBuf::from)
            .expect("Missing argument: api-sock");

        let start_time_us = arguments.single_value("start-time-us").map(|s| {
            s.parse::<u64>()
                .expect("'start-time-us' parameter expected to be of 'u64' type.")
        });

        let start_time_cpu_us = arguments.single_value("start-time-cpu-us").map(|s| {
            s.parse::<u64>()
                .expect("'start-time-cpu-us' parameter expected to be of 'u64' type.")
        });

View on GitHub (pinned to 0a745def42)

Solutions

1. Pass a non-negative integer for the mmds-size-limit metadata value.
2. Check the config file JSON types; the value must be a number, not a string.

When it happens

Trigger: Thrown at src/firecracker/src/main.rs:417 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/41e16499be2f909b. Report an issue: GitHub.