Will installing from a Bootable USB erase my hard drive?

BrandonW83 wrote:

My mid-2012 Pro will not boot correctly anymore.

I cannot boot to recovery mode or internet recovery mode.

If I create a bootable USB and reinstall Catalina from there, will it erase my hard drive or will it only replace the MacOS system files? Thanks.

Boot from your USBinstaller and from Disk Utility

the dropdown menu: Utilities>  Disk Utility> run the First Aid on your Macintosh HD (and the "Macintosh HD-Data" volume as well if Catalina/Big Sur) If errors are found and repaired, run again until no errors reported.

Disk Utility>View>Show All Devices The best sequence is —

• Volume level

• Container level

• Parent drive

You should still see your Disk structure on the internal—if it is still intact

How to repair a Mac disk with Disk Utility https://support.apple.com/en-us/HT210898

How to erase a disk for Mac - https://support.apple.com/en-us/HT208496

How to reinstall macOS from macOS Recovery - https://support.apple.com/en-us/HT204904

It will only erase your mac if you tell it to from Disk Utility.

If you choose Install OS from the Utilities panel when you

boot to the installer it will overwrite your system files your

personal files and apps etc will be fine.

But you must make a full back up before reinstalling.