hashicorp/packer · error

error creating %s writer: %s

Error message

error creating %s writer: %s

What it means

The bgzf compression writer could not be created. makeBGZFWriter returns ErrInvalidCompressionLevel (or a bgzf library error) when bgzf.NewWriterLevel rejects the configured compression level or writer parameters, and PostProcess wraps it via the errTmpl message naming the algorithm.

Source

Thrown at post-processor/compress/post-processor.go:164

	}
	outputFile, err := os.Create(target)
	if err != nil {
		return nil, false, false, fmt.Errorf(
			"Unable to create archive %s: %s", target, err)
	}
	defer outputFile.Close()

	// Setup output interface. If we're using compression, output is a
	// compression writer. Otherwise it's just a file.
	var output io.WriteCloser
	errTmpl := "error creating %s writer: %s"
	switch p.config.Algorithm {
	case "bgzf":
		ui.Say(fmt.Sprintf("Using bgzf compression with %d cores for %s",
			runtime.GOMAXPROCS(-1), target))
		output, err = makeBGZFWriter(outputFile, p.config.CompressionLevel)
		if err != nil {
			return nil, false, false, fmt.Errorf(errTmpl, p.config.Algorithm, err)
		}
		defer output.Close()
	case "bzip2":
		ui.Say(fmt.Sprintf("Using bzip2 compression with 1 core for %s (library does not support MT)",
			target))
		output, err = makeBZIP2Writer(outputFile, p.config.CompressionLevel)
		if err != nil {
			return nil, false, false, fmt.Errorf(errTmpl, p.config.Algorithm, err)
		}
		defer output.Close()
	case "lz4":
		ui.Say(fmt.Sprintf("Using lz4 compression with %d cores for %s",
			runtime.GOMAXPROCS(-1), target))
		output, err = makeLZ4Writer(outputFile, p.config.CompressionLevel)
		if err != nil {
			return nil, false, false, fmt.Errorf(errTmpl, p.config.Algorithm, err)
		}
		defer output.Close()

View on GitHub (pinned to eb36e3c3e4)

Solutions

1. Set compression_level to an integer in -1..9 (or remove it to use the default)
2. Run packer validate to catch the bad level before the build
3. If using bgzf, confirm no config override injects a level outside the flate range

Example fix

// before
algorithm = "bgzf"
compression_level = 12
// after
algorithm = "bgzf"
compression_level = 9

if cfg.CompressionLevel < -1 || cfg.CompressionLevel > 9 {
    return fmt.Errorf("bgzf requires compression_level in -1..9, got %d", cfg.CompressionLevel)
}

out, err := makeBGZFWriter(outputFile, cfg.CompressionLevel)
if errors.Is(err, compress.ErrInvalidCompressionLevel) {
    // retry with default level
    out, err = makeBGZFWriter(outputFile, -1)
}

When it happens

Trigger: Algorithm is "bgzf" and bgzf.NewWriterLevel(outputFile, p.config.CompressionLevel, runtime.GOMAXPROCS(-1)) returns an error — practically always an out-of-range compression_level (-2 or >9).

Common situations: Setting compression_level outside the gzip range for bgzf; passing a string/invalid value that survived config decoding as a bad integer; copy-pasted level from an lz4-specific config.

Related errors

• ErrInvalidCompressionLevel
• ErrWrongInputCount
• signing_mode %q requires signer
• build keyless identity policy: %w
• signing_mode %q requires keyless_identity and keyless_oidc_i

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/2f36e64d73e4264e. Report an issue: GitHub.