How to Clean Install Mac OS Sierra and High Sierra: The Ultimate User Manual

Users choose Mac computers for their high proficiency and stability. But over time unused files, applications, system junk, and errors pile up, and this leads to Mac’s sluggish performance. And then, just when you least expect it, your Mac simply doesn't work the way you need it to. "I must write my research paper and turn it in tomorrow morning!" you shout in despair after emptying Trash and removing temporary files didn't help much. What to do when cleaning techniques don’t have a positive effect you were counting on? In this case, users resort to the ultimate troubleshooting technique – operating system reinstallation. The typical set of related questions includes: “Should I fresh-install my operating system?” and “How to do a macOS reinstall without losing data?”

Reinstall Mac OS

If the changes to the system have become irreversible, the first thing you should do is restore your Mac to the factory settings. Mind that reinstalling macOS Sierra / High Sierra from scratch requires using a recovery disk. Whether it’s an inbuilt recovery disk, or an external drive ensure you have it ready in case of emergency. Before making any serious system-wide changes, use Time Machine utility to back up the important user data. Also, macOS reinstallation is a procedure with several requirements to ensure its successful completion:

  • Ensure your Mac’s power adapter is plugged in;
  • Check, if the Internet connection is working.


And then, here it goes:

  1. Select Apple menu in the top menu bar -> select Restart.
  2. Press down the Command-R key combination while your Mac is restarting. Wait until the macOS Utilities window shows up.
  3. Select Disk Utility -> click
  4. On the left, choose your Startup Disk -> click Erase.
  5. In the Format drop-down menu, select Mac OS Extended -> enter the disk/volume name -> click Erase.


Mac OS Extended
Disk Utility

Note: Erasing the startup disk purges all the information stored on the disk.


6. When the Startup Disk erase is over, select Disk Utility -> Quit Disk Utility.
7. Choose Reinstall macOS -> Continue and follow the step-by-step onscreen instructions.

Apple recommends installing and upgrading to the latest macOS version for security reasons.

How to Make a Bootable Drive to Install OS X from USB?

Ensure you have a working external disc to reinstall macOS in the case of emergency. There are three ways to create a bootable USB drive similar for all Mac operating system versions:

Using Terminal commands

Manually (a combination of the Finder, Disk Utility, and Terminal)

Third-party apps


Note: experienced users insist on skipping the manual method for systems released after Mac OS X Mavericks. Also, mind that using third-party applications to create a bootable USB drive might not be safe. Using the Terminal $ createinstallmedia command turns out faster and safer.


Before making a bootable USB drive, make sure a macOS installer is in the Applications folder. Also, the USB drive should have at least 12 GB of storage. Follow these instructions to create a bootable macOS USB:


  1. Mount the USB flash drive on your Mac.
  2. Go to Applications -> Utilities -> launch Terminal.
  3. Enter the proper $ createinstallmedia command for a specific Mac OS version.
  4. Name the drive/volume used as the bootable installer.
  5. Press Enter (Return) to execute the command.
  6. Authenticate with your administrator password and press Enter (Return)
  7. Confirm the drive erase by typing Y and pressing Enter (Return).
  8. Wait until the bootable drive is ready, then quit the Terminal.

How to Install OSX on New Hard Drive?

If you choose to install Mac OS X to the brand new hard drive, follow these steps:

  1. Connect the new hard drive to your Mac’s hardware.
  2. Turn on your Apple device holding down the Option key -> select which drive to boot. If you still have your old hard drive connected, it will show as your default booting option.
  3. Select Disk Utility from the OS X Utilities
  4. Pick the new drive in the list -> click Verify Disk.
  5. Select Erase in the Disk Utility. Select the Mac OS Extended (Journaled) option in the Format drop-down menu to format the new drive.
  6. Optional: Use the Partition option in the Disk Utility to set the number and size of disk partitions.
  7. Quit the Disk Utility tool, then click Reinstall OS X in the recovery menu.
  8. Check if your Mac has an internet connection (plug in an Ethernet cord) to use the Mac OS X recovery options.
  9. Follow the instructions and login to your iTunes account.
  10. Select the new disk/partition to install Mac OS X on and follow the prompts to start the installation.

How to Reinstall Mac OS X Lion?

The OS X Lion installation procedure is pretty standard. Earlier Mac models running on Lion used to have DVD drives. A bootable OS X Lion DVD is one of the options to use for installation/reinstallation. The bootable DVD will let you erase a drive/partition as a part of the installation process.

  1. Insert the Lion installation DVD into the optical drive -> restart your Mac.
  2. Hold down the C key while restarting your Mac to boot from the DVD.
  3. When the boot process completes, the Mac OS X Utilities window will appear.
  4. Choose Disk Utility from the list -> click Continue.
  5. Select the target installation disk -> click the Erase
  6. Select Mac OS Extended (Journaled) from the Format drop-down menu.
  7. Name the disk -> click Erase. Confirm the target disk erase, then click Erase
  8. Choose Quit Disk Utility to exit Disk Utility when the erase is over.
  9. Next, the Mac OS X Utilities window will reappear.
  10. Select Re-install Mac OS X Lion from the list of options -> click Continue and follow the prompts on the screen.
Reinstall OS X Lion

How to Run a Mac OS X Mavericks Installer?

OS X Mavericks offers users a single installation option: choosing where to install the new system. Booting from a different disk/volume is unnecessary because the installer launches as a standard application.

Mavericks Installer
  1. Double-click the Install OS X Mavericks app -> click Continue -> click Agree (twice) to agree to the Mavericks terms and conditions.
  2. Leave the default installation target, or click Show All Disks to select a different installation target.
  3. Click Install -> authorize with an administrator username and password.
  4. Wait until the installer copies the files needed for Mavericks installation. It may take from 20 seconds to a minute.
  5. After that, your Mac will reboot, and the installation will launch. (In case you’re upgrading from Lion or Mountain Lion, you may need to authorize as an administrator to bypass the FileVault). Depending on the Mac model, the installation takes from 15 minutes to over an hour.
  6. Next, your Mac will restart to enter the final installation phase which lasts for five to ten minutes. Then, it will boot into Mavericks.

How to Install OS X Yosemite? 

The installation process of OS X Yosemite is a standard procedure. However, configuring the Mac OS Yosemite afterward is worth mentioning. Introduced in the earlier versions of Mac OS, the Migration Assistant utility can help transfer user data from the available sources. After the installation process finishes, follow these steps:

  1. Choose the keyboard layout -> click Continue.
  2. If you need to transfer personal data from your user account, another startup disk, or Time Machine backup, select Don’t transfer any information now. Use Migration Assistant to transfer the data to the new Yosemite installation later. Next, click Continue.
  3. Optional: authenticate with your Apple ID to pre-set the Mac App Store, iCloud, iTunes, and other Apple services. Next, click Continue.
  4. Enable Find My Mac; the service used to locate your lost Mac or to purge the data if it gets stolen.
  5. Click Agree (twice) to agree to the terms & conditions of OS X software license.
  6. To create an administrator profile, type in your full name and an account name. To login to your Mac using the details of your iCloud account, tick Use my iCloud account to log in and click
Install Yosemite

7. Yosemite uses iCloud Keychain, a system that stores an encrypted keychain data between several Macs containing your accounts. Select Set Up Later, and click Continue. It is possible to go back and make the needed settings later.

8. Important: don’t make settings for iCloud Drive in case you’re sharing the iCloud data with a Mac running an earlier OS X version/iOS 7 or earlier handheld devices. Switching the iCloud Drive on will convert all data kept in the cloud to the new data format. Earlier Mac OS X and iOS versions won’t be able to use the data. Skip the iCloud Drive settings, then click Continue.

How to Install OS X El Capitan?

If you’re installing El Capitan using the USB drive:

  1. Mount the USB drive and restart your Mac holding down the Option key.
  2. Choose to boot from USB that says Install OS X El Capitan.
  3. Choose Disk Utility -> select Startup drive, then press Erase.
  4. Return to the main menu, select Install OS X to proceed with the installation.

If you’re installing to a new/empty drive, ensure there is the El Capitan installer file in the Applications folder.

  1. Launch the El Capitan installer -> click Continue.
  2. Click Agree (twice) to confirm you agree to the terms & conditions.
  3. Change the default installation target to the correct one. Click Show All Disks and choose the target disk -> click Install.
  4. Skipping step 4 will install OS X El Capitan to the default installation target.
  5. Authenticate with your administrator password -> click OK.
  6. Wait until the installer copies the files to the selected drive, then restart your Mac.
  7. Once the installation process reaches its end, your Mac will restart. After that, follow the on-screen instructions to perform the initial Mac OS X setup.

Final Thoughts

Mac OS X / macOS installation procedure is pretty standard. To install or re-install operating system from scratch, one needs an external USB drive or an installation file located on another internal disk/volume. To create a bootable USB, use a special Terminal command for a particular Mac OS version. Mac users can also resort to a combination of manual methods (Disk Utility and Terminal), or third-party apps. It is possible to use a bootable DVD on older Macs with a DVD drive. Configuring Mac OS is no less important to ensure its stable performance. Ensure you have the latest software version installed on your Mac to prevent software issues.