To make a bootable macOS Sierra USB drive please follow the steps below. Assuming you have already downloaded the OS from app store.
Here is what you need to do:
- Connect the USB drive to your Mac.
- Using Disk Utility (it is typically found in the Other folder, under Launchpad), format the USB drive as Mac OS Extended (Journaled), using the GUID Partition Mac scheme, and name it macOSSierra. This can be done from the Erase tab within the app; make sure that there are no multiple partitions (turn to the Partition tab to verify and correct this).
- Open Terminal (it is found in the same folder as the Disk Utility app).
- Use (paste) the following command:
sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Sierra.app
- Type in your user password, when required, to start the process.
Based on my experience, this is the best method of creating a bootable macOS Sierra USB drive. It delivers consistent results every time, and does not cause any issues.