Whenever Apple releases an update for High Sierra, many Mac users will rush to download it. Because of that, Apple’s servers slow down. Thus, your first course of action should be to check the System Status page of Apple and see macOS Software Update to find out if there are problems. In 2017, when Apple introduced MacOS High Sierra, the company removed Sierra from the Purchased list, which made it more difficult to revert to that earlier version, but it was still possible to.

How To Install Sierra Mac

These advanced steps are primarily for system administrators and others who are familiar with the command line. You don't need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful when you want to install on multiple computers without downloading the installer each time.

Download macOS

Find the appropriate download link in the upgrade instructions for each macOS version:

macOS Catalina, macOS Mojave, ormacOS High Sierra
Installers for each of these macOS versions download directly to your Applications folder as an app named Install macOS Catalina, Install macOS Mojave, or Install macOS High Sierra. If the installer opens after downloading, quit it without continuing installation. Important: To get the correct installer, download from a Mac that is using macOS Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators, please download from Apple, not a locally hosted software-update server.

OS X El Capitan
El Capitan downloads as a disk image. On a Mac that is compatible with El Capitan, open the disk image and run the installer within, named InstallMacOSX.pkg. It installs an app named Install OS X El Capitan into your Applications folder. You will create the bootable installer from this app, not from the disk image or .pkg installer.

Use the 'createinstallmedia' command in Terminal

Connect the USB flash drive or other volume that you're using for the bootable installer. Make sure that it has at least 12GB of available storage and is formatted as Mac OS Extended.
Open Terminal, which is in the Utilities folder of your Applications folder.
Type or paste one of the following commands in Terminal. These assume that the installer is still in your Applications folder, and MyVolume is the name of the USB flash drive or other volume you're using. If it has a different name, replace MyVolume in these commands with the name of your volume.
Catalina:*
Mojave:*

High Sierra:*
El Capitan:
Press Return after typing the command.
When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the bootable installer is created.
When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Catalina. You can now quit Terminal and eject the volume.

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument, similar to the way this argument is used in the command for El Capitan.

Use the bootable installer

Download Apple Mac Sierra Installer

After creating the bootable installer, follow these steps to use it:

Plug the bootable installer into a compatible Mac.
Use Startup Manager or Startup Disk preferences to select the bootable installer as the startup disk, then start up from it. Your Mac will start up to macOS Recovery.
Learn about selecting a startup disk, including what to do if your Mac doesn't start up from it.
Choose your language, if prompted.
A bootable installer doesn't download macOS from the Internet, but it does require the Internet to get information specific to your Mac model, such as firmware updates. If you need to connect to a Wi-Fi network, use the Wi-Fi menu in the menu bar.
Select Install macOS (or Install OS X) from the Utilities window, then click Continue and follow the onscreen instructions.

Learn more

For more information about the createinstallmedia command and the arguments that you can use with it, make sure that the macOS installer is in your Applications folder, then enter this path in Terminal:

Catalina:

Mojave:

High Sierra:

El Capitan:

Mac Os Sierra 10.12 Free Apple Download

Check compatibility

You can upgrade to macOS Sierra from OS X Lion or later on any of the following Mac models. Your Mac also needs at least 2GB of memory and 8.8GB of available storage space.

MacBook introduced in late 2009 or later
MacBook Air introduced in late 2010 or later
MacBook Pro introduced in mid 2010 or later
Mac mini introduced in mid 2010 or later
iMac introduced in late 2009 or later
Mac Pro introduced in mid 2010 or later

To find your Mac model, memory, storage space, and macOS version, choose About This Mac from the Apple menu . If your Mac isn't compatible with macOS Sierra, the installer will let you know.

Make a backup

Before installing any upgrade, it’s a good idea to back up your Mac. Time Machine makes it simple, and other backup methods are also available. Learn how to back up your Mac.

Get connected

It takes time to download and install macOS, so make sure that you have a reliable Internet connection. If you're using a Mac notebook computer, plug it into AC power.

Download High Sierra For Mac

Download macOS Sierra

For the strongest security and latest features, find out whether you can upgrade to macOS Catalina, the latest version of the Mac operating system.

If you still need macOS Sierra, use this link: Download macOS Sierra. A file named InstallOS.dmg will download to your Mac.

Install the macOS installer

Double-click the downloaded file to open a window showing its contents. Then double-click the file within, named InstallOS.pkg.

Follow the onscreen instructions, which will guide you through the steps necessary to install.

Begin installation

After installation of the installer is complete, open the Applications folder on your Mac, then double-click the file named Install macOS Sierra.

Click Continue and follow the onscreen instructions. You might find it easiest to begin installation in the evening so that it can complete overnight, if needed.

Allow installation to complete

Please allow installation to complete without putting your Mac to sleep or closing its lid. Your Mac might restart, show a progress bar, or show a blank screen several times as it installs both macOS and related updates to your Mac firmware.

Learn more

If you have hardware or software that isn't compatible with macOS Sierra, you might be able to install the previous version, OS X El Capitan.
macOS Sierra won't install on top of a later version of macOS, but you can erase your disk first or install on another disk.
You can use macOS Recovery to reinstall macOS.