Reinstalling MacOS Sierra

Internet Recovery is NOT available in ROM in most Macs before 2011 models. So you will need to explore this list of other possibilities.

When your computer was released, the way you launched the required Utilities (including Disk Utility and Installer) was to use the ones on the Release software DVD. if you have a model-specific version for your model (unlikely) or a Full Retail 10.6 DVD, you use its Utilities, boot and install that version, then use Software update to get to 10.6.8 with all updates, which is the version that can reach out to the Mac App store for the first time and download and install a later version.

10.11 El Capitan is a recommended waypoint, even if you expect to install a later version, because it has an improved Mac App Store that makes getting later versions much easier.

The next source of Utilities is the Recovery Partition on the boot drive. If your drive spins up, even if not MacOS bootable, it may still have a usable recovery partition. To get there, try invoking recovery with Command-R or hold Alt/Option at startup and see if the recovery partition shows as a potentially bootable drive.

Recovery Partitions up through 10.12 Sierra can be found with the Startup Manager (Alt/Option boot). At 10.13, if an SSD boot drive is used, the format is transitioned to APFS. The Recovery partition is present, but it is inside the APFS container, and the Startup Manager on an older Mac may not be able to find it.

The next source of Utilities to consider is any MacOS 10.6 or later versions on any additional drives or clones you may (or may not) have lying about, even if they are from another Mac. You can use those Utilities to ERASE a new drive, and start the installer to place MacOS on the new drive.

The next source to consider is a Time Machine backup drive. Versions from 10.7.3 or later are said to contain a Recovery Partition that could be used to ERASE a new drive and run Installer to place MacOS on a new drive. Time Machine backups created in MacOS 11 Big Sur or later are APFS format, and APFS format backup drives do NOT have a Recovery partition.

Two Mac solutions:

With certain combinations of new and old Mac, you can use Target Disk mode to repair, erase, and install on the drive of the old Mac, by treating it as a disk drive on the new Mac.

Transfer files between two Mac computers using target disk mode - Apple Support

IF you have a different Mac, you can use it to download MacOS install image, then interrupt the process and create a BOOTABLE USB-stick Installer/Utilities stick. BOOTABLE is key, because the way you will install from this USB-Stick is to BOOT the USB-stick, and use its Utilities to ERASE your drive and start the Installer. here is the article on bootable USB-Stick Utilities/Installer:

What you need to create a bootable installer

• A USB flash drive or other secondary volume formatted as GUID partition Map, Mac OS Extended, with at least 14GB of available storage

• A downloaded installer for macOS Big Sur, Catalina, Mojave, High Sierra, or El Capitan.

The Terminal command assumes that Installer in located in the /Applications folder.

from:

How to create a bootable installer for macOS

Create a bootable installer - Apple Support

NB>> if you name your incoming USB stick exactly MyVolume, you can copy and paste the very long Terminal command from the article directly into the Terminal window, without having to change anything.

exactly which model?

42 lb Mac Pro silver tower? what processor speed?

MacBook Pro notebook computer? what model, what model-year, and what screen size?

This is really annoying. But, after trying countless ways, I finally found one that resolved the macOS Sierra installation problem 100% (and without the need to create a bootable disk via USB).

The author suggests three alternatives - I used the third and it worked on the first try. Follow the instructions carefully and you will probably be successful too. The author generously created a very easy way to follow the instructions even if you don't have a 2nd Mac.

Here is the link to the original article. To make things easier, I'll reproduce the process that worked for me. I hope it works out for you too!

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At the main macOS Sierra menu, click on the Menu Bar and select the Terminal.app

Run this command in Terminal

curl -L https://archive.org/download/sierraurl/sierra.txt

This will give you a full list of instructions and commands on your screen. You can copy and paste directly into Terminal to avoid mistakes.

Change the directory to Macintosh HD

cd /Volumes/Macintosh\ HD

Download the macOS Sierra 10.12.6 InstallOS.dmg from Apple.com using curl. Note this is a 4.7GB file and might take a while or fail. If it fails run it again.

curl http://updates-http.cdn-apple.com/2019/cert/061-39476-20191023-48f365f4-0015-4c41-9f44-39d3d2aca067/InstallOS.dmg -o InstallOS.dmg

We need to mount the InstallOS.dmg

hdiutil attach InstallOS.dmg

Now we need to install the “Install macOS Sierra.app” from the InstallOS.dmg to Macintosh HD volume

installer -pkg /Volumes/Install\ macOS/InstallOS.pkg -target /Volumes/Macintosh\ HD

The Install macOS Sierra.app is now in the /Volumes/Macintosh\ HD/Applications folder. We can now start the Sierra installer

/Volumes/Macintosh\ HD/Applications/Install\ macOS\ Sierra.app/Contents/MacOS/Installassistant_springboard

In a few seconds the Sierra installer will start BEHIND the terminal window.

If you don’t see it make the terminal window but DON’T close it as it will stop the installer.

Done. Now step through the installer you are good to go now!

(Author: Mr.Macintosh)