Do you have access to a second mac which has a Thunderbolt connection and a Thunderbolt cable?
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I think you'll need to scratch the drive and re-install the OS. By leveraging the second Mac we can setup your system like a HD to it using [https://support.apple.com/en-us/HT201462|Target Disk Mode]. The other option here is to setup a USB thumb drive as a bootable drive using the other Mac system and installing on it the OS installer. Here's the steps for that:
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I think you'll need to scratch the drive and re-install the OS. By leveraging the second Mac we can setup your system like a HD to it using [https://support.apple.com/en-us/HT201462|Target Disk Mode].
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The other option here is to setup a USB thumb drive as a bootable drive using the other Mac system and installing on it the OS installer. Here's the steps for that:
* Get a USB thumb drive (16GB or larger)
* Download the OS installer from the App Store, make a backup copy
* Then create the GUID partition map on the thumb drive and format the partition with Mac OS Extended (Journaled) with '''Disk Utility'''.
* Run the OS installer and install the OS onto the thumb drive.
* Once done, copy to it the copy of the OS installer.
* Restart your system holding down the '''Option key''' so you gain access to the boot manager select the thumb drive.
* At this point you should be able to reformat the drive using '''Disk Utility''' on the thumb drive and using the OS installer on the thumb drive install a fresh copy of the OS.
Do make sure you are connected to the internet as there are some updates your system will need.
Do you have access to a second mac which has a Thunderbolt connection and a Thunderbolt cable?
I think you'll need to scratch the drive and re-install the OS. By leveraging the second Mac we can setup your system like a HD to it using [https://support.apple.com/en-us/HT201462|Target Disk Mode]. The other option here is to setup a USB thumb drive as a bootable drive using the other Mac system and installing on it the OS installer. Here's the steps for that:
* Get a USB thumb drive (16GB or larger)
* Download the OS installer from the App Store, make a backup copy
* Then create the GUID partition map on the thumb drive and format the partition with Mac OS Extended (Journaled) with '''Disk Utility'''.
* Run the OS installer and install the OS onto the thumb drive.
* Once done, copy to it the copy of the OS installer.
* Restart your system holding down the '''Option key''' so you gain access to the boot manager select the thumb drive.
* At this point you should be able to reformat the drive using '''Disk Utility''' on the thumb drive and using the OS installer on the thumb drive install a fresh copy of the OS.
Do make sure you are connected to the internet as there are some updates your system will need.