Patrick Angle – Restoring your Mac to a like-new state

These steps only apply to Mac computers with Intel processors.

Hello friend! If you are here, it’s because you’ve asked for help reinstalling macOS on your Mac, and want the computer to be like-new! Don’t worry, you aren’t the first person to ask me for help with this, as there are some parts of this process that are not necessarily intuitive at first. I’ve written these instructions up, borrowing from the relevant Apple support documents where necessary, to guide you through the process in one place.

These instructions assume you want to completely wipe your machine! This means that any and all information on your machine will be gone (kind of — data security is complicated, and if you need to delete incredibly sensitive private information or content please let me know so I can provide instructions on how to properly handle those situations).

What do I need to complete these steps?

About 15 minutes of direct attention, with about an hour of time in the middle where you can safely wander away.
A reliable internet connection that allows you to connect to *.apple.com domains. An internet connection is required for both parts 2 and 4.

1.

Backup your Machine

Before proceeding, it is highly advisable that you make a backup of your machine, unless you are truly okay with never seeing any of the data on the machine again. While many cloud services solve large portions of this problem (Photos in iCloud, Contacts in Google, etc.), it is best to not take for granted that all your information was in the correct place to be syncing to cloud in the first place. There are many ways to backup your Mac. The most common method is by using Time Machine, which is built into macOS and requires you have an external drive large enough to house your files. The may need to be erased to use it for Time Machine backups, so make sure you don’t need anything from the drive before setting up Time Machine. Be sure to allow the backup to complete before proceeding.

Learn More: Back up your Mac with Time Machine

2.

Boot your Mac into Internet Recovery

Shut down your computer, and then while turning the computer back on hold down

Option-Command-R

on the keyboard until you see a progress bar or Wi-Fi network dropdown appear. If prompted, select your Wi-Fi network and provide its password. Install media from Apple will be downloaded over the internet, and should be for the latest version of macOS available for your machine (there are some exceptions to this, so it’s good to make sure your Mac is up-to-date after installation as well). The initial install package will be around 2Gb, so it may take a few minutes to download depending on the speed of your internet connection.

After the download is complete, your Mac will boot into Internet Recovery. You may then be asked to select a user you know the password for. Select the user, then click Next and enter their administrator password.

3.

Erase your built-in disk

From the utilities window, select Disk Utility and click Continue.
In Disk Utility’s toolbar, click the View item and then select Show All Devices.
From the list of disks in the left of the window select the topmost item inside the Internal group. This should contain one or more disks named Macintosh HD (or whatever you may have previously named your disk).
Click the Erase item in the toolbar, and provide the following details:

Name: Macintosh HD
Format: APFS (only choose Mac OS Extended (Journaled) if you know that your computer has a mechanical hard drive)

Click the Erase button.
In some situations, you may be prompted to provide the Find My credentials previously used on the Mac. Provide that information if requested.
From the Disk Utility menu, select Quit Disk Utility.

If your get the error The volume "{volume name}" on {volume} couldn't be unmounted because it is in use by process ### (kextcache), you may need to forcibly unmount the volume. Quit Disk Utility. Once the utilities window has reappeared, select Terminal from the Utilities menu. Once in terminal, issue the following command: diskutil unmount force {volume} where {volume} should match the volume from the error message above. This will forcibly unmount the offending volume and allow you to format the disk using the above instructions. Quit Terminal and return to the first step in Erase your built-in disk above.

4.

Install macOS

After quitting Disk Utility, you should see the utilities window again. Select Reinstall macOS and click Continue. Follow the instructions provided by the installer. When selecting a disk, select your newly created Macintosh HD. You should observe the following guidelines during installation:

Do not unplug your computer during installation.
If your computer is a laptop, make sure it has as least 30% battery remaining and remains plugged into power for the duration of installation.
Do not close your computer’s lid or put it to sleep. The screen may go to sleep during installation, which is normal and can be awoken by moving your cursor on the screen.
If the installer offers you the choice between installing on Macintosh HD or Macintosh HD - Data, choose Macintosh HD.

Installation may take awhile. Your computer will reboot several times during the process, and there will be multiple progress bars that appears to start from zero. During some parts of the install, your screen may be entirely blank for multiple minutes. DO NOT FORCIBLY POWER OFF YOUR MACHINE DURING ANY PART OF THIS PROCESS.

5.

Welcome to your like-new Mac

After installation completes, your computer will boot up into the setup assistant, where you can configure your machine just like you did when you took it out of the box for the first time all those years (or months) ago. If left alone for long enough, the system voice, Samantha, will begin speaking out loud, telling you how to navigate the machine via the keyboard for users who are unable to see the screen.

Enjoy your like-new Mac!