There are a few reasons why you might want to reinstall macOS (or even Mac OS X). Perhaps your Mac is working erratically and you think that a clean install of the operating system might fix the issue.
Alternatively, you might be planning on selling your Mac, or passing it on to a member of the family (in which case, you need to wipe it first and return your Mac to factory settings).
It is even possible to reinstall the version of the macOS that your Mac shipped with - which might enable you to revert to an older version of the operating system if the latest version is upsetting you.
Whatever your reason to reinstall macOS, we will show you one of the simplest ways to do so below.
Our method involves using the Recovery partition via which you can reinstall the latest version of the macOS you installed on your Mac. Because macOS is normally installed via Software Update (or previously the Mac App Store) there are no physical installation disks, therefore Apple has made it possible to install the operating system over the internet using the Recovery HD.
An alternative option would be to create a bootable macOS install on an external drive. If your Mac doesn't boot in Recovery mode, read this: Mac can't access Recovery mode.
We also have this article about doing a clean install of macOS using a bootable drive.
What you need to reinstall macOS
A back up: If you are planning to wipe your Mac as part of this process (either because you think that a clean slate might fix issues you are having, or because you are selling the Mac) you may want to back up your important documents first. How you do this will depend on whether you want to recover your Mac into the same version of the Mac operating system, or if you were hoping to do a clean install. For more information read: Backing up a Mac.
Note, if you tend to use iCloud Drive to sync all your Documents and Desktop in the cloud you may find you don't need a backup, but make sure that everything is in iCloud before you delete!
An internet connection: You'll need an internet connection.
WEP/WPA: If you are using Internet recovery you'll need to be using a network with WEP or WPA security. This shouldn't be an issue as most home Wi-Fi networks do, but if you're on a proxy network or PPPoE then you will have problems.
How to reinstall macOS via Recovery
Entering Recovery mode was always a case of pressing and holding the Command and R buttons during start up until you hear the startup chime and see either a spinning globe or Apple logo.
However, this has changed for the Mac that use Apple's own processors, such as the M1 Macs introduced in November 2020.
If you want to enter recovery mode on an M1 Mac you need to press and hold the power button when you start up your Mac and continue to press and hold the button until you see a startup options window appear with an Options icon. Select Options and click Continue.
Follow these steps to reinstall the latest version of macOS installed on your Mac:
- Enter Recovery (either by pressing Command+R on an Intel Mac or by pressing and holding the power button on a M1 Mac)
- A macOS Utilities window will open, on which you will see the options to Restore From Time Machine Backup, Reinstall macOS [version], Safari (or Get Help Online in older versions) and Disk Utility. Your next step depends on whether you wish to wipe the Mac before reinstalling the operating system. If you want to wipe your disk click Disk Utility (otherwise you can jump ahead to step 8).
- Having selected Disk Utility, click Continue.
- Now select the volume you wish to Erase. You may need to click on View > Show All Drives before you can see the volume. Note that the process here is slightly different if you are running macOS Catalina or Big Sur. If you aren't running Catalina then you only need to delete the Macintosh HD volume. If you are running Catalina or later there will be two volumes probably called Macintosh HD and Macintosh HD-Data (or possibly Home and Home - Data). You'll need to delete the Data volume first and then Macintosh HD. We cover how to do this here: How to wipe and reformat your Mac. Remember this is going to delete all your data so make sure you have your important data backed up or stored in the cloud or on an external drive.
- The next step also depends on the version of macOS you are running. In Catalina, Mojave Big Sur, and potentially High Sierra (depending on your Mac) this will be APFS. But on older Macs running older macOS versions the format needs to be set to Mac OS Extended (Journaled). You will also need to have GUID Partition Table selected as the Scheme. (You won't see the Scheme option if you only have the volume selected).
- Click Erase and wait. (There are options under Security Options that allow you to erase the disk securely).
- Now choose Disk Utility > Quit Disk Utility. Or just Command + Q.
- If you are reformatting your drive, at this stage you will see the Utilities screen again. Alternatively you may have jumped here from above because you aren't erasing you hard drive first. Either way you now need to now choose Reinstall macOS from the options. If at this stage you find that Recovery Mode isn't available, perhaps because the startup volume has been erased, we have tips here: How to restore a Mac if Recovery isn't working.
- After clicking Reinstall macOS, click on Continue.
- Enter your Apple ID if required and wait while macOS is reinstalled. Expect this to take a while.
- When the setup wizard starts up quit if you are intending to sell or pass on the Mac so that the next owner can enter their own details. Otherwise continue setting up your Mac.
How to install an older version of macOS using Recovery mode
Alongside the Command + R key combination we mention above there are a couple of other key combinations you can use to reinstall macOS using Recovery mode. These will allow you to choose whether to install the latest version of macOS that is compatible with your Mac, or the version of macOS that came with your Mac.
Note you won't be able to use any of these options on an M1 Mac.
You can choose from:
- Command + R Will install the latest version installed on your Mac - won’t upgrade you to the latest version.
- Option/Alt + Command + R Will upgrade you to the latest macOS compatible with your Mac. Note: If you aren’t running Sierra 10.12.4 of later, this will install the version that came with your Mac; if your Mac has a T2 chip then Option/Alt + Command + R will install the latest macOS on your Mac.
- Shift + Option/Alt + Command R (if you are running Sierra 10.12.4 of later) will install the version of macOS that came with your Mac, or the one closest to it that is still available.
Follow the steps in the section above to reinstall macOS via recovery. It is only possible to run Big Sur on an M1 Mac - this may change in the future if Parallels or WMware come up with a solution for running older macOS in a virtual machine, but this doesn't yet exist.
If you wanted to revert to an older version of macOS - and your Mac shipped with that version - you will be able to reinstall it using the latter two choices. Alternatively, read: How to downgrade macOS to an older version.
How to connect to the internet in macOS Recovery mode
To reinstall macOS using Recovery mode you have to connect to the internet. Follow these steps to connect to the internet in Recovery mode if your Mac hasn't automatically connected:
- Click the Wi-Fi menu in the upper-right corner of the screen.
- Select a Wi-Fi network.
- Enter the Wi-Fi password (if required).
Recovery mode should now be connected to the internet and be able to download the macOS installation software.