Press , close Terminal, and attempt the installation process again. Error: "UNTRUSTED_CERT_TITLE"
Use Time Machine to back up all your files to an external drive.
The most reliable source for the macOS Sierra DMG is directly from Apple. download macos sierra 1012 dmg file install
This is the safest method as it downloads the official, unmodified installer directly from Apple's servers.
But there is one complication: Apple has officially removed Sierra from the Mac App Store. This means you can't just "re-download" it from your account's "Purchased" tab, as is still possible for many other versions. However, that does not mean all hope is lost. This guide will walk you through every legitimate method for finding, downloading, and creating a bootable installer for macOS Sierra. Press , close Terminal, and attempt the installation
Step 4 — Install macOS Sierra
If the App Store link is broken or you are on a newer Mac creating a boot drive for an older one, you often need a specific Install macOS Sierra.dmg file. This is the safest method as it downloads
When you download macOS Sierra from Apple, it arrives inside a disk image ( .dmg ) file, but it is not yet a runnable application. You must extract the underlying installation package first.
Scroll down to the "Use a web browser for older versions" section and click the link for Sierra 10.12 .
Now that your bootable media is ready, you can proceed with the installation. 1. Boot from the USB Drive Shut down the target Mac completely. Insert your bootable USB installer into the Mac.