What is the MPKG file format?
.mpkg is a macOS installer meta-package - a macOS bundle (a directory that Finder presents as a single file icon) containing multiple .pkg installer components so they can be installed together in one session. It was the standard format for distributing complex macOS software suites during the Mac OS X 10.0-10.5 era, including Apple's own developer tools and system updates.
An .mpkg bundle contains three main sections: a Packages/ folder holding the individual .pkg component files, a Resources/ folder with localized installer UI assets (license RTF, welcome HTML, background images), and an Info.plist that specifies the sub-packages, their installation order, and system requirements.
Unlike a flat .pkg, an .mpkg can be inspected in Finder by right-clicking and choosing Show Package Contents, revealing its full directory tree. The /usr/sbin/installer command-line tool or Installer.app handles installation. Integrity is verified per-package via a BOM (Bill of Materials) file; code signing is optional.
Apple deprecated PackageMaker - the tool that created .mpkg files - in 2012, replacing it with productbuild, which generates flat .pkg product archives (xar-based, introduced in macOS 10.5 Leopard). Legacy .mpkg files from older Xcode and QuickTime distributions still open in Installer.app on current macOS releases.
Security & safety
RISK: MEDIUMMPKG runs install scripts (preinstall, postinstall shell scripts inside each .pkg). A malicious MPKG can execute arbitrary code with root privileges during installation. Before installing unknown MPKG files, inspect with Suspicious Package to review all scripts. Only install from trusted, signed sources. Apple Gatekeeper checks code signatures on modern macOS; older unsigned MPKG files may be blocked by default.
Format details
in a nutshellFULL NAMEmacOS Meta-Package Installer Fileaka meta-package, Apple meta-package
DEVELOPERApple Inc.since Mac OS X 10.0 (2001); format established with Apple Installer
CATEGORYCompressed Files
MIME TYPEapplication/octet-stream
TYPEmacOS installer meta-package (directory bundle containing .pkg files)
This extension is also used by…
- Mono framework installer (cross-platform) - Mono project used .mpkg for multi-component installation on macOS (framework + tools + samples).
Programs that open MPKG files
macOS3 apps
Apple Installer (built-in)
Built-in Double-click the .mpkg file; Installer.app opens automatically and guides through installation.
Suspicious Package
Free Quick Look plugin + app; previews .mpkg contents (files, scripts, Info.plist) before installing. Technical details
deep spec| Bundle type | macOS directory bundle (presented as a single file icon by Finder) |
| Bundle contents | `Info.plist` + `Packages/` + `Resources/` directories |
| Payload compression | Gzip/cpio (legacy `.pkg` payload); zlib/xar (flat `.pkg` embedded) |
| Byte order | Big-endian (legacy PowerPC cpio/pax); little-endian (xar-based flat `.pkg`) |
| Integrity checking | BOM (Bill of Materials) file per component package tracks installed file checksums |
| Code signing | Optional Apple code signature; verifiable with `pkgutil --check-signature` |
| Installation tool | `/usr/sbin/installer` command-line or Installer.app GUI |
| Component ordering | Defined in `Info.plist`; sub-packages install sequentially |
| Creator tool | PackageMaker (deprecated by Apple 2012); replaced by `productbuild` |
| Successor format | Flat `.pkg` product archive (xar-based), introduced macOS 10.5 Leopard (2007) |
| Operating system | macOS (Mac OS X 10.0+); legacy `.mpkg` files still supported by Installer.app |
| Inspection method | Finder right-click → Show Package Contents reveals internal directory tree |
| Released | Mac OS X 10.0 (2001); format established with Apple Installer |
| Latest version | Superseded by flat .pkg (xar-based) for distribution since macOS 10.5 (2007); .mpkg still processable by Installer |
| Specification | developer.apple.com |
MPKG conversions
Community Q&A
asked by users
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Frequently asked questions
How do I open an MPKG file on macOS?
Double-click the .mpkg file; Apple Installer opens automatically. To inspect contents first, use Suspicious Package (free) or right-click → Show Package Contents in Finder.
Can I open an MPKG file on Windows?
No - MPKG is a macOS-only installer format. There is no Windows equivalent tool that runs MPKG installations.
Why is my MPKG blocked by macOS?
Unsigned MPKG files are blocked by Gatekeeper. Right-click → Open to bypass for trusted files, or check System Settings → Privacy & Security and click 'Open Anyway'.
What's the difference between .pkg and .mpkg?
.pkg is a single-component installer (flat file or bundle). .mpkg (meta-package) groups multiple .pkg files for a single multi-component installation session.
Is MPKG still used on modern macOS?
Rarely for new software. Apple's current standard is flat .pkg created with productbuild. MPKG is legacy but still opens in Installer.app on current macOS.
References
1Apple Developer - Software Distribution (archive)developer.apple.com
2FileFormat.com - MPKG formatdocs.fileformat.com
