hashicorp/packer · error

%s: %s

Error message

%s: %s

What it means

In main.go's config-loading path (decodeConfig of the JSON config in packer/config.go), if loading the external components (plugins) from the decoded config fails, the error is wrapped as "<configFilePath>: <err>". The message literally formats as "%s: %s" where the first %s is the template/config file path and the second is the underlying component-loading error.

Source

Thrown at main.go:385

	log.Printf("[INFO] PACKER_CONFIG env var set; attempting to open config file: %s", configFilePath)
	f, err := os.Open(configFilePath)
	if err != nil {
		if !os.IsNotExist(err) {
			return nil, err
		}

		log.Printf("[WARN] Config file doesn't exist: %s", configFilePath)
		return &config, nil
	}
	defer f.Close()

	// This loads a json config, defined in packer/config.go
	if err := decodeConfig(f, &config); err != nil {
		return nil, err
	}

	if err := config.LoadExternalComponentsFromConfig(); err != nil {
		return nil, fmt.Errorf("%s: %s", configFilePath, err)
	}

	return &config, nil
}

// copyOutput uses output prefixes to determine whether data on stdout
// should go to stdout or stderr. This is due to panicwrap using stderr
// as the log and error channel.
func copyOutput(r io.Reader, doneCh chan<- struct{}) {
	defer close(doneCh)

	pr, err := prefixedio.NewReader(r)
	if err != nil {
		panic(err)
	}

	stderrR, err := pr.Prefix(ErrorPrefix)
	if err != nil {

View on GitHub (pinned to eb36e3c3e4)

Solutions

1. Install the missing plugin with `packer plugins install <source>` and verify it appears in the plugin directory
2. Check the error after the file-path prefix — it names the component that failed to load
3. Verify plugin binaries are executable and follow the naming convention (packer-plugin-<name>_vX.Y.Z)
4. Validate the config file references only installed plugin types

Example fix

// before (shell)
packer build template.json
// after (shell)
packer plugins install github.com/hashicorp/amazon
packer build template.json

// Before running packer, verify required plugins are present:
//   packer init .
//   packer plugins installed
// and confirm each type referenced in the config exists in the output.

cfg, err := loadConfig(path)
if err != nil {
    // err is formatted as "<configFilePath>: <cause>" — split to inspect the cause
    parts := strings.SplitN(err.Error(), ": ", 2)
    return fmt.Errorf("config %s failed to load plugins: %v", path, parts)
}

When it happens

Trigger: Running any packer command that loads a JSON config file (legacy template or packer config) where config.LoadExternalComponentsFromConfig fails — typically a plugin named in the config cannot be found or initialized.

Common situations: Required plugin binaries missing from the plugin directory or PATH; misnamed plugin files that don't match the packer-plugin naming convention; corrupted or non-executable plugin binaries; referencing a plugin type that isn't installed.

Related errors

• The provisioner %s is unknown by Packer, and is likely part
• no such build found: %s

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/42767abfd6bfa069. Report an issue: GitHub.