thanos-io/thanos · error

write file

Error message

write file

What it means

Wraps os.WriteFile of the .tmp staging file in Reloader.normalize: the normalized config could not be written next to the output path (permissions, full disk). Atomic replacement of the output file cannot proceed, so the reload cycle fails and retries.

Solutions

1. Check the output directory exists and is writable.
2. Free disk space if full.
3. Verify the cfg-output-file flag points to a valid path.

When it happens

Trigger: Thrown at pkg/reloader/reloader.go:391 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/4590bf9973e04289. Report an issue: GitHub.

Appendix: source

Thrown at pkg/reloader/reloader.go:391

		defer runutil.CloseWithLogOnErr(r.logger, zr, "gzip reader close")

		b, err = io.ReadAll(zr)
		if err != nil {
			return errors.Wrap(err, "read compressed config file")
		}
	}

	b, err = r.expandEnv(b)
	if err != nil {
		return errors.Wrap(err, "expand environment variables")
	}

	tmpFile := outputFile + ".tmp"
	defer func() {
		_ = os.Remove(tmpFile)
	}()
	if err := os.WriteFile(tmpFile, b, 0644); err != nil {
		return errors.Wrap(err, "write file")
	}
	if err := os.Rename(tmpFile, outputFile); err != nil {
		return errors.Wrap(err, "rename file")
	}
	return nil
}

// apply triggers Prometheus reload if rules or config changed. If cfgOutputFile is set, we also
// expand env vars into config file before reloading.
// Reload is retried in retryInterval until watchInterval.
func (r *Reloader) apply(ctx context.Context) error {
	var (
		cfgHash         []byte
		watchedDirsHash []byte
	)

	if r.cfgFile != "" {
		h := sha256.New()

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