SierraUSB (You can use any name, but matching this exactly makes the next command easier). Format: Mac OS Extended (Journaled) Scheme: GUID Partition Map Click Erase and wait for the process to finish. Run the Terminal Command
If you are running an older macOS version that supports the App Store: Open Safari. Click the official Mac App Store link for macOS Sierra. The App Store application will launch automatically.
The installation process can take anywhere from 20 minutes to an hour depending on your hard drive speed (SSDs are significantly faster than traditional HDDs). Your Mac will restart automatically during this process. Do not unplug the USB drive or close the laptop lid until the setup assistant screen appears. Troubleshooting Common Installation Errors
Double-click and follow the on-screen prompts.
Troubleshooting
If you are already running an older version of macOS (like OS X El Capitan), you can use the Terminal app to pull the installer. Open (found in Applications > Utilities). Type the following command and press Enter:
However, downloading older macOS deployment files can be challenging today because Apple hides outdated operating systems from the main Mac App Store search results. This comprehensive guide provides secure download links for the macOS Sierra 10.12 DMG file and a step-by-step walkthrough for creating a bootable installer. Prerequisites and System Compatibility
: Follow the on-screen prompts. This will not install the OS yet; instead, it places a file named "Install macOS Sierra.app" into your Applications folder.
: Enter your administrator password when prompted and wait for "Copy complete" to appear. 4. Install macOS Sierra download macos sierra 1012 dmg file install
A bootable USB drive is the most reliable way to install an older OS, especially for performing clean installations or troubleshooting.
8 GB+ USB flash drive, Sierra DMG mounted.
This is the most frequent issue encountered when installing older macOS versions. It occurs because Apple's security certificates embedded in the installer expired after the software's release.
Name the drive Macintosh HD , set the format to Mac OS Extended (Journaled) , and click . Close Disk Utility to return to the main menu. 3. Run the macOS Sierra Installer Select Install macOS from the utility menu. Click Continue and accept the license terms. SierraUSB (You can use any name, but matching
Also, make sure you have a backup of your important files and data, as installing a new operating system can potentially erase your existing data.
This occurs because the security certificates embedded inside older Apple installers have expired.
Once your flash drive is configured, you can proceed with the operating system installation. Shut down the target Mac completely. Insert the bootable USB installer into an available port.
Your Mac must already be running OS X 10.7.5 or later. Click the official Mac App Store link for macOS Sierra