zeroclaw-labs/zeroclaw · error

setting default subscriber failed

Error message

setting default subscriber failed

What it means

Error "setting default subscriber failed" thrown in zeroclaw-labs/zeroclaw.

Source

Thrown at crates/zeroclaw-log/src/subscriber.rs:54

            None => {
                EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new(default_filter))
            }
        }
    } else {
        EnvFilter::new("off")
    };

    let fmt_layer = fmt::layer()
        .fmt_fields(RedactEphemeralFields)
        .with_writer(std::io::stderr)
        .event_format(AgentAliasFormatter::new())
        .with_filter(fmt_filter);

    let subscriber = tracing_subscriber::registry()
        .with(LogCaptureLayer.with_filter(recording_filter))
        .with(fmt_layer);

    tracing::subscriber::set_global_default(subscriber).expect("setting default subscriber failed");
}

#[doc(hidden)]
pub fn try_install_capture_subscriber() {
    use tracing_subscriber::Registry;
    let subscriber = Registry::default().with(LogCaptureLayer);
    let _ = tracing::subscriber::set_global_default(subscriber);
}

/// Test support: install a process-global subscriber that hands every
/// formatted event line to `sink`, exactly where the stderr fmt layer would
/// write. Lets an integration test in another crate observe, and deliberately
/// stall, the terminal write path without naming `tracing` types outside this
/// crate. The sink runs unlocked on whichever thread emits the event, so a
/// sink that blocks on one event models a wedged consumer of that event
/// without serializing every other thread's unrelated writes behind it.
/// Mirrors the production wiring by stacking [`LogCaptureLayer`] under the
/// terminal layer, so `attribution_span!` scopes carry their attribution

View on GitHub (pinned to 88bb9c8533)

Solutions

1. Ensure no other global tracing subscriber is set before zeroclaw-log initializes; initialize logging only once.
2. Check for conflicting logging setup in embedded usage and remove duplicate subscriber initialization.

When it happens

Trigger: Thrown at crates/zeroclaw-log/src/subscriber.rs:54 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of zeroclaw-labs/zeroclaw@88bb9c8533 (2026-08-23). Data as JSON: /api/errors/4eecc505a6882b80. Report an issue: GitHub.