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macOS recovery mode question

My 2013 MBP recently refused to boot up. I was able to boot from an external drive and retrieved my desktop and download folder files so i have those for sure. If i use Command-R and reinstall the OS, does it completely erase all of the files and programs, or does it only change/reload the operating system?

MacBook Pro 13″, macOS 10.15

Posted on Aug 23, 2020 4:59 PM

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Posted on Aug 23, 2020 5:22 PM

By design, a Re-Install without deliberately ERASE-ing the drive bulk-erases only certain System Folders, and does a file-by-file replacement on other parts of MacOS. It is intended to leave your Installed Applications and all your files and settings untouched.


That said, it does re-write over 350,000 files. If any problem develops, or if your drive is getting old, that could send your drive over the edge into failure.

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Aug 23, 2020 5:22 PM in response to stevefrombrooksville

By design, a Re-Install without deliberately ERASE-ing the drive bulk-erases only certain System Folders, and does a file-by-file replacement on other parts of MacOS. It is intended to leave your Installed Applications and all your files and settings untouched.


That said, it does re-write over 350,000 files. If any problem develops, or if your drive is getting old, that could send your drive over the edge into failure.

Aug 23, 2020 5:40 PM in response to stevefrombrooksville

stevefrombrooksville wrote:

My 2013 MBP recently refused to boot up. I was able to boot from an external drive and retrieved my desktop and download folder files so i have those for sure. If i use Command-R and reinstall the OS, does it completely erase all of the files and programs, or does it only change/reload the operating system?


And to add—


if you value your user data, do not wait for a catastrophic failure to get the back religion.


3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.


—Boot clone https://discussions.apple.com/docs/DOC-10081

—How to use Time Machine to back up or restore your Mac: https://support.apple.com/en-us/HT201250

—Use DiskUtility Restore feature https://support.apple.com/guide/disk-utility/restore-a-disk-dskutl14062/mac

note: >System Preferences>Security & Privacy >Privacy>Full Disk Access

unlock the padlock, press the + button and add Disk Utility



Aug 23, 2020 6:00 PM in response to stevefrombrooksville

stevefrombrooksville wrote:

Normally i do run Time Machine, but my work schedule hasn't really presented me the opportunity just yet.

Time machine is designed to run at low priority in the background, so as not to interfere with your important work.


That is NOT an excuse for not connecting your backup drive and letting it run -- it is hands-off, completely automatic operation.

Aug 23, 2020 6:03 PM in response to Grant Bennet-Alder

I know. I've just been traveling and don't like to carry it with me. I suppose two backup Time Machines are in order.


Someone on another forum said the reinstall could possibly clean the Keychain content. Is there a way to grab those files while I'm still booted from the external to re-populate those if that happens?

macOS recovery mode question

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