.pkg File — macOS Installer Package

PKG files are macOS installer packages that contain software, configuration scripts, and metadata for automated installation on macOS systems. PKG files use a structured format based on XAR (eXtensible ARchive) that includes a Bill of Materials (BOM) listing all files to be installed, JavaScript or shell scripts for pre-installation and post-installation actions, installation check scripts, volume check scripts, and the payload files themselves compressed with gzip or bzip2. The macOS Installer application (installer CLI or Installer.app GUI) processes PKG files, presenting license agreements, destination selection, and installation progress. PKG files support component packages (individual installable units) and distribution packages (meta-packages that bundle multiple component packages with a custom installer UI defined by an XML distribution script). Enterprise deployment tools (Jamf, Munki, MDM solutions) use PKG files extensively for automated software distribution. PKG files are created using pkgbuild and productbuild command-line tools or third-party tools like Packages.app and Whitebox Packages. Apple Developer ID signing is required for PKG files to pass Gatekeeper verification on modern macOS versions.