To give your Mac a facelift or completely clean it up, nothing beats a clean and complete system reinstallation. A radical, yet simple solution thanks to the recovery features of macOS.
Your Mac has become too slow because its crowded drive is cluttered with files? Of course, you can clean it up to revive it a little (see our fact sheet Cleaning up a Mac that has become sluggish). Unfortunately, this is not always enough. And like on PC, it is sometimes faster and more efficient to reset it by erasing all its contents and reinstall the system cleanly to start from scratch, like the first day, when your Mac was new!
This method is also recommended if you want to sell your Mac with the confidence that none of your personal data goes with it. Conversely, if you’ve just bought a used Mac, you can do the same to make sure nothing is left of your seller’s data.
Not to mention that with a Mac, it’s easy: no need for CDs, DVDs or USB keys to reinstall the system. Indeed, since 2010 for some models and for all the others since, one can start a Mac in “recovery mode” to reinstall the system completely, thanks to a hidden partition on the internal storage space: it is a question of ‘a reserved area containing a complete installation version of the system, typically for these different cases.
Even stronger: you can even reinstall macOS on a Mac in the event of a major internal drive failure preventing the use of the hidden recovery partition. In this case, an internet connection is sufficient and your Mac is able to download a compatible version of macOS and install it. And this method also works if you changed your hard drive to an SSD, as older machines allowed. In this case, the storage space is necessarily empty and reinstallation via the Internet is required. And it works great!
What precautions should you take before reinstalling macOS?
Warning ! Before you start, be aware that this operation erases all content on a Mac before you reinstall the system. To avoid losing important data permanently, it is imperative to make a backup of your Mac beforehand. If you haven’t already, check out our Back up and recover Mac content with Time Machine article first.
Another important detail: if you intend to sell or give away your Mac, don’t forget to sign out of your iCloud account, from the System Preferences. This will allow you to make sure that the Mac is no longer linked to your account and in particular to the function Find my Mac. This is preferable for all Macs, but even absolutely essential for all Macs with a T2 protection chip. There are a large number of models, since 2018 (see the list here), to which must be added all Macs equipped with the “home” M1 chip. On all these models, the Find my Mac function is inseparable from the one called Activation lock, an anti-theft device that renders the Mac unusable without the original Apple account. It is therefore advisable to completely forget your Apple account on your Mac if you want to part with it.
If you ever forgot to do this before you part with your Mac, you can also turn off Activation Lock, by logging into your Apple account, via the site iCloud. Then click on Account settings. In the list of your devices, click Mac concerned, then on the cross to the right of his name. A window asks if you really want to remove this device from your account. A click on To delete, and your Mac is ready to join its new owner’s account.
No matter what model your Mac is, you need to restart it before you can enter macOS Recovery Mode. However, the operations to be carried out to access it depend on the model of your Mac.
- If you have any doubts, and you can start your Mac normally, click on the apple menu and choose About your Mac. The window that appears clearly indicates whether it is equipped with an Intel processor or an Apple chip (M1 or other).
- In any case, start by completely shutting down your Mac, either via the apple menu then the command Switch off, or by keeping the on-off button pressed.
- If you have a new model with an Apple processor (like the M1 chip), turn your Mac back on while keeping the power button pressed until you see the option to click the button. Options, which will give you access to the recovery mode menu.
- If you have an Intel-based Mac, restart it with a short press of the power button, then hold down the keys at the same time. Cmd (⌘) + R to boot to the recovery partition.
Regardless of the model of your Mac, M1 or Intel, the options presented by Recovery mode are the same:
- Restore from a Time Machine backup : to recover everything from a previous backup.
- Reinstall macOS : If you use this option at this point, your Mac will not be erased, but the system will be reinstalled on top of the data already stored. So you won’t lose anything, but you won’t get the benefits of really starting from scratch.
- Safari (Mac M1) or Get help online (Mac Intel): to open a browser and find information online.
- Disk Utility : This option launches the same application as the one in the Utilities folder of your Mac. It allows you to check the health of your storage space and also to format it, which interests us here.
- To format the internal drive before reinstalling the system, launch theDisk utility. A window displays by default the different data partitions created by the system. To completely reset the Mac, we first need to see the complete list of physical storage spaces inside or plugged into the Mac.
- To do this, expand the menu Presentation and choose Show all devices. In the window below, you will then see the list of all storage volumes. Notice the section Disk Images which shows the partition containing the rescue system which, in fact, allows it to be reinstalled on the internal disk of the Mac.
- Under section Internal from the left column of the window, select the name of the storage space built into your Mac (here APPLE SSD SM2…), then click on the button Wipe off up.
- In the window that appears above, start with give a name to the internal disk, then select APFS in the drop-down menu Format, and GUID Partition Table in the menu Diagram.
- Click on the button Wipe off. Please note that the formatting starts immediately without asking for confirmation!
- Once the Mac internal drive has been formatted, pull down the menu Disk Utility, at the top left of the screen, and choose To leave. You are returned to the Recovery mode screen.
- Click on Reinstall macOS, then on To continue, at the bottom of the window showing the version of the system that will be installed (here Catalina on a MacBook Air).
- If your Mac is not directly connected to your Internet box with a network cable, a message warns you that an Internet connection is necessary. Click on the Wi-Fi menu at the top right and connect your Mac to the Wi-Fi network of your box.
- Please note, it is not uncommon for the Mac’s keyboard to be automatically switched back to American mode at this stage (known as Qwerty). What does not help to type the password of the Wi-Fi network. To change it back to French, click on the little flag, at the top right of the screen, to choose French. If this icon does not appear, you can still type the password, being careful to replace for example the “a” by the “q”, the “m” by the comma and to type the numbers directly without holding down the button. shift key. Consult this page for a visual comparison of the two types of keyboard.
- After your Mac is connected to the Internet, select the internal disk that you have just formatted (see above) as the installation destination. Then click on To install.
- Hold on. When the installation is complete, the Mac will restart to be brand new, as if you just bought it and took it out of the box. All you have to do is follow the classic steps of the first start.
If you’ve changed your Mac’s original internal drive (for example to replace it with an SSD), you can no longer use its recovery partition to reinstall macOS. Never mind, you can ask your Mac to recover and reinstall the system directly through the Internet.
- As soon as the Mac starts up, hold down the keys at the same time. Option / Alt (⌥) + Cmd (⌘) + R. A message on the light gray background of the screen tells you that the Mac is in operating mode. Internet retrieval.
- If your Mac is not connected to your Internet box via a network cable, the next screen asks you to choose a wireless network, then enter the password. Please note, it is not uncommon for the Mac’s keyboard to be automatically switched back to American mode at this stage (known as Qwerty). If this is the case, you will not be able to switch the keyboard back to French. You will therefore have to type the password, being careful to replace, for example, the “a” by the “q”, the “m” by the comma and to type the numbers directly without holding down the Shift key. Consult this page for a visual comparison of the two types of keyboard.
- Once connected to the Internet, Ethernet or Wi-Fi, the Mac begins to download the latest version officially compatible with your model. Be patient: this is a file of several gigabytes, which may take several hours to download with an ADSL connection …
- When the download is complete, the Recovery mode window will appear with the same options as usual (see above). Choose Install macOS Where Reinstall Mac OS X depending on the version offered, and voila!
