Apple on Monday told The Loop’s Jim Dalrymple that the free macOS Sierra software update will be available as an automatic download later today. This means that the software update will download in the background for Mac owners who have auto update downloads enabled in System Preferences.
Apple is being smart about the move and won’t download any files to your computer if it’s low on storage or does not meet the system requirements for macOS Sierra.
Apple will begin pushing macOS Sierra today, it’s a staggered release that will be gradually rolling out to all customers over the next week or so.
“If your computer is low on space, macOS Sierra will not download,” explained Dalrymple. “In addition, if it has downloaded and your computer starts to get low on space, the download will be automatically deleted”.
Once the software update has fully downloaded to your computer, it won’t install automatically as a prompt will go up asking if you wish to apply the update now, later or ignore the update. You will find the installer in your /Applications/ folder, named “Install macOS Sierra”.
To prevent software updates from downloading automatically in the background, open System Preferences → App Store and untick the boxes next to the options labeled “Download newly available updates in the background” and “Install OS X updates”.
If you use third-party software which requires custom kernel extensions—especially if your Mac Pro has an unsupported, non-flashed graphics card—be sure to uncheck the option to automatically install macOS updates until any custom kernel extensions have been updated to support Sierra.
Source: The Loop