hashicorp/packer · error

ErrWrongInputCount

ErrWrongInputCount

Error message

Can only have 1 input file when not using tar/zip

What it means

ErrWrongInputCount is a sentinel error indicating the compress post-processor received more than one input artifact file while configured to write a single compressed file (no tar/zip). Without an archive format there is no way to bundle multiple files into one output.

Source

Thrown at post-processor/compress/post-processor.go:37

	"github.com/biogo/hts/bgzf"
	"github.com/dsnet/compress/bzip2"
	"github.com/hashicorp/hcl/v2/hcldec"
	"github.com/hashicorp/packer-plugin-sdk/common"
	packersdk "github.com/hashicorp/packer-plugin-sdk/packer"
	"github.com/hashicorp/packer-plugin-sdk/template/config"
	"github.com/hashicorp/packer-plugin-sdk/template/interpolate"
	"github.com/klauspost/pgzip"
	"github.com/pierrec/lz4/v4"
	"github.com/ulikunitz/xz"
)

var (
	// ErrInvalidCompressionLevel is returned when the compression level passed
	// to gzip is not in the expected range. See compress/flate for details.
	ErrInvalidCompressionLevel = fmt.Errorf(
		"Invalid compression level. Expected an integer from -1 to 9.")

	ErrWrongInputCount = fmt.Errorf(
		"Can only have 1 input file when not using tar/zip")

	filenamePattern = regexp.MustCompile(`(?:\.([a-z0-9]+))`)
)

type Config struct {
	common.PackerConfig `mapstructure:",squash"`

	// Fields from config file
	OutputPath       string `mapstructure:"output"`
	Format           string `mapstructure:"format"`
	CompressionLevel int    `mapstructure:"compression_level"`

	// Derived fields
	Archive   string
	Algorithm string

	ctx interpolate.Context

View on GitHub (pinned to eb36e3c3e4)

Solutions

1. Set compress to tar or zip mode so multiple inputs are archived (configure output with .tar/.zip extension or set the archive option)
2. Ensure only one artifact file reaches the post-processor (drop extra artifacts in prior post-processors or filter builds)
3. Split the build so each compression run handles one artifact

Example fix

// before: plain compression of multi-file artifact
{"type": "compress"}
// after: archive multiple inputs
{"type": "compress", "output": "output.tar.gz"}

if len(artifact.Files) > 1 && !strings.HasSuffix(cfg.OutputPath, ".tar") && !strings.Contains(cfg.OutputPath, ".tar.") && !strings.HasSuffix(cfg.OutputPath, ".zip") {
    return fmt.Errorf("multiple input files require tar/zip output")
}

_, _, _, err := pp.PostProcess(ctx, ui, artifact)
if errors.Is(err, compress.ErrWrongInputCount) {
    // re-run with a tar/zip output path or with a single-file artifact
}

When it happens

Trigger: PostProcess is given an artifact whose Files() list has more than one entry while algorithm output mode is a plain single-file compression (CompressionAlgorithm not tar/zip).

Common situations: Chaining the compress post-processor after a builder that produced multiple files (e.g. several disk images); using compress after an artifact that aggregates multiple outputs; forgetting to enable keep_input_artifact/tar when multiple artifacts are expected.

Related errors

• ErrInvalidCompressionLevel
• error creating %s writer: %s
• 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/e1ab7cacc9e6de96. Report an issue: GitHub.