As of summer 2011, Apple distributes operating systems only as downloads of installer Apps from the Mac App Store, or together with new Macs. This means there is no longer a tangible medium holding a copy of the operating system which could be used in case of emergency when the running copy of the OS on your computer was damaged or erased. There is only a small mini operating system for emergency cases stored in the recovery partition, which is usually installed for each operating system partition on your Mac and for each Time Machine destination disk. The recovery system allows you to download a copy of the full operating system from the Internet again when you have lost it. Depending on the speed of your Internet line, a full download may take more than 4 hours, however. In cases where all disk drives of your Mac have been erased or have become unusable, you can also start the recovery system by a NetBoot feature, so the emergency system is directly loaded from an Apple-provided Internet server.
All these emergency procedures won’t help if you need to install a new operating system on a Mac which has no Internet connection, or which should not have such a connection for security reasons. For such cases, all Mac operating systems as of OS X 10.9 or later support a feature to create standalone install media. Such a medium behaves like a classic operating system DVD: The computer can be started from it, and you can install a full copy of the operating system without the need for an Internet connection. The medium can also fully replace a recovery system: It contains all components of the recovery OS, so you can use Disk Utility, Terminal, or the “complete restore” feature of Time Machine for maintenance purposes if the main OS is no longer working correctly.
TinkerTool System can guide you through the process of creating macOS install media. A bootable installer can be created by a few mouse clicks.
You need additional software and hardware to create macOS install media. The following items are required:
If macOS or TinkerTool System have problems detecting an external storage device which should be used to create install media, erase the device first, creating an empty HFS+ file system:
After the device has been erased, macOS and TinkerTool System will accept it as destination medium.
To create the standalone installation disk, perform the following steps:
Warning: The storage device selected as install medium will be erased completely. You will lose all data in all volumes and partitions currently stored on the device.
If TinkerTool System doesn’t list a device you like to use, please read the instructions in the previous section.
Creating the installer disk is not directly managed by TinkerTool System, but by the installer App you downloaded from the App Store. For this reason, the procedure might slightly vary depending on what operating system version you are using.
As part of the creation process, macOS might open parts of the created system in a new Finder window which might appear at the end of the procedure. The window can be used to check successful creation of the disk. You can safely close the window and eject the disk.