There are a few different ways to force your Mac to reinstall the operating system. The easiest method is to erase the startup disk and reinstall macOS using Recovery Mode. This will completely wipe your Mac and install a fresh copy of the operating system.
Use Recovery Mode to Reinstall macOS
To reinstall macOS using Recovery Mode:
- Restart your Mac and immediately press and hold Command + R until you see the Apple logo or a spinning globe. This will boot you into Recovery Mode.
- If you are prompted to select a user account, choose your main admin account and enter the password.
- In the macOS Utilities window, select Reinstall macOS (or Reinstall OS X depending on your version) and click Continue.
- Follow the onscreen instructions to reinstall the latest macOS version that was previously installed on your Mac. All data and settings will be erased in the process.
This will completely erase your startup drive and do a clean install of macOS, essentially resetting your Mac to factory settings. It’s the most thorough way to reinstall the operating system.
Erase Startup Disk and Reinstall macOS
You can also erase your Mac’s startup disk first before reinstalling macOS. This serves the same purpose of wiping your Mac and doing a fresh OS install. To do this:
- Restart your Mac and boot into Recovery Mode as explained above.
- Open Disk Utility from the Utilities menu.
- Select your Mac’s startup disk (usually named “Macintosh HD”) and click Erase at the top.
- Choose a format (APFS is recommended) and Scheme (GUID Partition Map).
- Click Erase to wipe the disk – this will only take a few seconds.
- Quit Disk Utility and return to the main Utilities window.
- Select Reinstall macOS and click Continue to start the clean install process.
Erasing the disk first removes any files, settings or problems that could be carried over into the new OS install. It’s an extra step but ensures you have a completely clean slate.
How to Boot into Recovery Mode
Booting into Recovery Mode is required for the above steps. Here’s a quick rundown of how to enter Recovery Mode on different Macs:
- Macs with Apple silicon (M1/M2 chips): Press and hold the power button at startup until “Loading startup options” appears. Release the button and after a few seconds, Options will appear. Select Continue to boot into macOS Recovery.
- Intel-based Macs: Turn on your Mac and immediately press and hold Command + R after you hear the startup chime. Keep holding until the Apple logo or spinning globe appears.
- With macOS Monterey or later: Press and hold the power button at startup until “Loading startup options” appears. Release the button and after a few seconds, Options will appear. Select Recover from macOS and click Continue to enter Recovery Mode.
- With macOS Big Sur or earlier: Press and hold Option + Command + R at startup until you see the Apple logo or spinning globe.
This will boot your Mac directly into Recovery Mode so you can use the available tools like reinstalling macOS.
Erase and Reinstall macOS from macOS Itself
You don’t necessarily need Recovery Mode to erase your startup disk and reinstall the OS. This can be done directly from within macOS as well:
- Go to System Preferences > Software Update and install any available updates for macOS. This ensures the latest macOS version is ready to be installed.
- Restart your Mac and immediately press and hold Command + R to boot into Recovery Mode.
- Go to Disk Utility and select your startup disk. Click Erase to wipe it.
- Exit Disk Utility and return to the main Recovery Mode window.
- Instead of selecting Reinstall macOS, quit out of Recovery Mode and boot normally back into macOS.
- Once logged in, go to System Preferences > Software Update. The latest macOS installer should be there ready to download and install.
- Run the macOS installer to cleanly install the OS over your erased startup disk.
While this method takes a few more steps, it avoids having to re-download the full macOS installer in Recovery Mode which can be much slower. Instead, the latest installer is downloaded ahead of time over your usual Internet connection.
Use macOS Recovery Over the Internet
The above Recovery Mode methods require an existing macOS installation to recover from. If your Mac is completely unresponsive or lacks a recovery partition, you can still reinstall the OS over the Internet.
To start an Internet Recovery:
- Turn off your Mac and turn it on while holding Option + Command + R.
- Keep holding until you see a spinning globe. This indicates your Mac is starting up from Apple’s recovery servers.
- After a while, macOS Utilities will open. From here you can reinstall the OS, even if your startup disk has been erased.
Internet Recovery installs the latest compatible macOS version. The process is slower but useful for situations where local recovery partitions are unavailable.
Create a macOS Installer Drive
You can also prepare an external drive with a macOS installer, then boot from it to reinstall the operating system. Here’s how:
- Get an external drive with at least 12GB of available storage and format it for Mac OS Extended if needed.
- In System Preferences > Software Update, download the macOS installer for the version you want.
- Launch the installer once downloaded. Follow the steps until you reach the drive selection screen.
- Select the external drive rather than your startup disk. This will create the bootable installer drive.
- When done, reboot your Mac and hold the Option key at startup.
- Select the external drive to boot from the macOS installer.
- You can proceed with erasing your startup disk and reinstalling macOS cleanly from there.
This approach lets you download the OS installer ahead of time rather than having to get it over a slow Internet Recovery connection.
Reinstall macOS from Time Machine Backup
If you have a Time Machine backup available, you can use it to fully restore your Mac and OS after erasing your startup disk. To reinstall macOS from a Time Machine backup:
- Boot to Recovery Mode and erase your startup disk as explained earlier.
- Instead of reinstalling macOS right away, choose to Restore From Time Machine Backup.
- Select your Time Machine drive and a backup point to restore from.
- Follow the prompts to restore your entire Mac – OS, apps, data and settings – back to that previous state.
This way, you get a fresh macOS install from the backup rather than downloading the installer again. Plus all your data, apps and settings get restored.
Do a Clean Install of macOS
If you want to reinstall macOS but prefer not to erase your entire drive, you can do a clean install just of the system files:
- Start up in Recovery Mode as usual.
- Choose Reinstall macOS from the Utilities window.
- Rather than selecting your whole startup disk, click Show All Disks.
- Select the volume containing macOS (usually Macintosh HD).
- Click Reinstall to perform a clean install of just system files on that volume.
This will overwrite all system files and apps with a fresh macOS install, while retaining your user data and some settings.
Reset NVRAM Before Reinstalling macOS
Before reinstalling macOS, consider resetting your Mac’s NVRAM. This clears any potential issues that could be carried over into the new OS install.
To reset NVRAM, restart your Mac and immediately press these four keys together: Option, Command, P, R. Keep holding until you hear the startup chime again, then release.
NVRAM reset on Macs with Apple silicon (M1/M2 chips): Turn off your Mac completely. Turn it back on and immediately press and hold the power button until “Loading startup options” appears. Release the button, then press and hold Command + Option + P + R until you see the Apple logo.
Resetting NVRAM clears out any problematic settings that could affect your Mac during the OS reinstallation process.
Fix macOS Install Errors
In some cases, you may encounter errors while trying to reinstall macOS. Here are a few potential solutions:
- Use Disk Utility to check for and repair disk errors before reinstalling.
- Try installing macOS on an external drive first to isolate startup disk issues.
- Erase and format the startup disk again before retrying the install.
- Reset NVRAM again right before reinstalling macOS.
- Start up in Safe Mode and reinstall macOS from there.
- If using macOS Recovery over the Internet, try a different Wi-Fi network.
- Create a bootable macOS USB installer drive and install from that instead.
Persistent errors may indicate hardware problems or compatibility issues with the macOS version. If the error cannot be resolved, seek help from an Apple support advisor.
Tips for Reinstalling macOS
Here are some additional tips for smooth macOS reinstallation:
- Update existing macOS install first – This prepares the latest installer for Recovery Mode.
- Backup important data before erasing any disks.
- Make sure Mac is plugged into power during OS installation.
- Use wired ethernet for faster downloads if possible.
- Erase the startup disk using Disk Utility for a clean slate.
- Choose latest compatible macOS version when reinstalling.
- Restart to Recovery Mode immediately after backup to avoid issues.
- Be patient and let installer processes complete.
- Use dongle if you have trouble with Bluetooth keyboard in Recovery.
Following these best practices will help ensure the macOS reinstallation completes as smoothly as possible.
Frequently Asked Questions
Is my data erased when reinstalling macOS?
Yes, reinstalling macOS completely erases all data if you choose to wipe your startup disk first. Be sure to backup important files and data before proceeding.
Does reinstalling delete everything on my Mac?
Reinstalling the operating system only erases data on the startup disk you choose to install onto. Any other disks or drives connected to your Mac will not be affected.
Will apps be deleted when reinstalling macOS?
Yes, reinstalling macOS removes any apps that were installed on the startup disk. You’ll need to re-download apps afterwards. Your data in app sandboxes should remain intact.
Can I reinstall an older macOS version?
Recovery Mode allows you to reinstall the macOS version that came pre-installed on your Mac, or the closest still-compatible version.
Does reinstalling fix performance problems?
Often times yes – reinstalling macOS can resolve issues caused by outdated or corrupted system files after significant usage. A fresh OS install cleans the slate.
What data should I backup before reinstalling?
Important data to backup includes documents, photos, music, movies, app data, system settings, etc. Backing up the entire system with Time Machine is recommended.
Conclusion
Reinstalling the operating system is an effective troubleshooting step if your Mac is experiencing performance issues, glitches or outright crashes. Wiping the startup disk first provides the cleanest slate for macOS to be installed onto. Be sure to backup your data beforehand, then use Recovery Mode or an external installer drive to initiate the process. Take your time and follow all prompts carefully. For stubborn issues, a fresh OS install often gets a misbehaving Mac back up and running smoothly again.