What causes "Invalid scheduler, using default: %s\n" in mudler/LocalAI?

Correct the scheduler name to an exact enum string (e.g. discrete, karras, exponential, ays)

Invalid scheduler, using default: %s\n

Error message

Invalid scheduler, using default: %s\n

What it means

Warning during generation setup: the scheduler string failed to parse via str_to_scheduler(), so sd_get_default_scheduler(sd_ctx, sample_method) selects the default scheduler paired with the chosen sampler. Generation proceeds; the noise schedule differs from the requested one, which can shift output quality.

Source

Thrown at backend/go/stablediffusion-ggml/cpp/gosd.cpp:701

    sample_method_t sm = str_to_sample_method(sampler);
    if (sm != SAMPLE_METHOD_COUNT) {
        sample_method_found = (int)sm;
        fprintf(stderr, "Found sampler: %s\n", sampler);
    }
    if (sample_method_found == -1) {
        sample_method_found = sd_get_default_sample_method(sd_ctx);
        fprintf(stderr, "Invalid sample method, using default: %s\n", sd_sample_method_name((sample_method_t)sample_method_found));
    }
    sample_method = (sample_method_t)sample_method_found;

    scheduler_t sched = str_to_scheduler(scheduler_str);
    if (sched != SCHEDULER_COUNT) {
        scheduler = sched;
        fprintf(stderr, "Found scheduler: %s\n", scheduler_str);
    }
    if (scheduler == SCHEDULER_COUNT) {
        scheduler = sd_get_default_scheduler(sd_ctx, sample_method);
        fprintf(stderr, "Invalid scheduler, using default: %s\n", sd_scheduler_name(scheduler));
    }

    sd_c = sd_ctx;

    return 0;
}

void sd_tiling_params_set_enabled(sd_tiling_params_t *params, bool enabled) {
    params->enabled = enabled;
}

void sd_tiling_params_set_tile_sizes(sd_tiling_params_t *params, int tile_size_x, int tile_size_y) {
    params->tile_size_x = tile_size_x;
    params->tile_size_y = tile_size_y;
}

void sd_tiling_params_set_rel_sizes(sd_tiling_params_t *params, float rel_size_x, float rel_size_y) {
    params->rel_size_x = rel_size_x;

View on GitHub (pinned to 44413a9d06)

Solutions

Correct the scheduler name to an exact enum string (e.g. discrete, karras, exponential, ays)
Or omit it and accept the default pairing for the sampler
Verify via the 'Found scheduler:' log line

Example fix

// before
scheduler = "Karras";  // not matched

// after
scheduler = "karras";

Defensive patterns

Strategy: validation

Validate before calling

// Go caller: whitelist schedulers
validSchedulers := map[string]bool{"discrete": true, "karras": true, "exponential": true, "ays": true, "gits": true}
if req.Scheduler != "" && !validSchedulers[req.Scheduler] {
    return fmt.Errorf("unknown scheduler %q", req.Scheduler)
}

Prevention

Validate sampler and scheduler together at the request boundary
Lowercase/trim incoming strings before matching enum names

When it happens

Trigger: Passing scheduler with an unrecognized name (typo, wrong case, e.g. 'karras ' with trailing space or 'KARRAS' if the parser is case-sensitive); using a scheduler added after the vendored sd.cpp version.

Common situations: Sampler/scheduler pairs copied from other UIs; configs shared across LocalAI versions with different bundled sd libraries.

Related errors

AI-assisted analysis of mudler/LocalAI@44413a9d06 (2026-08-15). Data as JSON: /api/errors/a598d233f1558062. Report an issue: GitHub.