What causes "readFileFromEnv: environment variable %s not found" in glanceapp/glance?

Export the environment variable pointing at the file: `export API_KEY_FILE=/etc/glance/api_key`.

readFileFromEnv: environment variable %s not found

Error message

readFileFromEnv: environment variable %s not found

What it means

Thrown by parseConfigVariableOfType for {{ file-from-env.NAME }} expressions: NAME is looked up as an environment variable whose VALUE is a file path, and this error means NAME itself is not set in the environment. It is the env-lookup stage of the two-step indirection (env var → path → read file).

Source

Thrown at internal/glance/config.go:218

		}

		return v, false, nil
	case configVarTypeSecret:
		secretPath := filepath.Join("/run/secrets", variableName)
		secret, err := os.ReadFile(secretPath)
		if err != nil {
			return "", false, fmt.Errorf("reading secret file: %v", err)
		}

		return strings.TrimSpace(string(secret)), false, nil
	case configVarTypeFileFromEnv:
		if !envVariableNamePattern.MatchString(variableName) {
			return "", true, nil
		}

		filePath, found := os.LookupEnv(variableName)
		if !found {
			return "", false, fmt.Errorf("readFileFromEnv: environment variable %s not found", variableName)
		}

		if !filepath.IsAbs(filePath) {
			return "", false, fmt.Errorf("readFileFromEnv: file path %s is not absolute", filePath)
		}

		fileContents, err := os.ReadFile(filePath)
		if err != nil {
			return "", false, fmt.Errorf("readFileFromEnv: reading file from %s: %v", variableName, err)
		}

		return strings.TrimSpace(string(fileContents)), false, nil
	default:
		return "", true, nil
	}
}

func formatWidgetInitError(err error, w widget) error {

View on GitHub (pinned to 91324e8de7)

Solutions

Export the environment variable pointing at the file: `export API_KEY_FILE=/etc/glance/api_key`.
Add it to the systemd unit Environment=, docker-compose environment:, or the container env.
Verify spelling/case of the variable name in {{ file-from-env.X }}.
Confirm the variable is set for the service user, not just your login shell (`systemctl show-environment`, `docker exec env`).

Example fix

# systemd unit (before)
[Service]
ExecStart=/usr/bin/glance --config /etc/glance/glance.yml

# after
[Service]
Environment=API_KEY_FILE=/etc/glance/api_key
ExecStart=/usr/bin/glance --config /etc/glance/glance.yml

Defensive patterns

Strategy: validation

Validate before calling

for var in $(grep -oE '\{\{ *file-from-env\.[A-Za-z_][A-Za-z0-9_]* *\}\}' glance.yml | sed -E 's/.*file-from-env\.([A-Za-z0-9_]+).*/\1/'); do
  printenv "$var" >/dev/null || { echo "file-from-env variable not set: $var"; exit 1; }
done

Prevention

Treat *_FILE variables as required service configuration; declare them in the unit/compose file.
Verify with `docker exec <ctr> env | grep _FILE=` that the indirection variable actually reached the process.

When it happens

Trigger: glance.yml contains {{ file-from-env.API_KEY_FILE }} and API_KEY_FILE is unset in the Glance process environment, even if the target file exists on disk.

Common situations: Using the file-from-env indirection for secret files at custom paths but forgetting to export the *_FILE variable in systemd/docker; env var set in the interactive shell but not in the service unit; typo in the variable name.

Related errors

AI-assisted analysis of glanceapp/glance@91324e8de7 (2026-08-15). Data as JSON: /api/errors/11877c8498249e32. Report an issue: GitHub.