Download the version of macOS you want to install. Unless you have a specific reason to install an older version of macOS, you can download the most recent installer from Apple.Look for the installers labeled “Combo Update” which contain the full installer. Nov 17, 2020 Creating the bootable OS X El Capitan installer will erase the USB flash drive you're using. Before you proceed, make sure you have a backup of the flash drive's contents or that you don’t care that the data will be erased. How To: Reformat Mac OS X Without a Recovery Disc or Drive How To: Create a Bootable Install USB Drive of Mac OS X 10.10 Yosemite How To: Close All Open Apps on Your Mac with a Single Click How To: Take Screenshots & Save as JPEG in Mac OS X 10.6 Snow Leopard or Lower. Free download Adobe Flash Player Adobe Flash Player for Mac OS X. Adobe Flash Player is a cross-platform, browser-based application runtime that provides uncompromised viewing of expressive applications, content, and videos across browsers.

Upgrading your Macbook is a very easy task if you are already running a previous version of Mac OS X. You just need to download the new OS Installer from the App Store and after that, it’s just like a normal installer setup. But the problem comes, when your Mac OS got corrupted and you need to install a clean setup without having to access the App Store.

Arguably, Mac OS is a more stable and reliable OS as compared to Windows. It crashes less and gets fewer malware attacks as compared to windows. Therefore there are very few documentations regarding clean installation for Mac OS relative to Windows Reinstallation.

In this tutorial, I would try to cover up as much detail I could to help you Reinstall a Clean Mac OS on to your Macbook or iMac. I recommend you to use 16GB or higher USB drive. Also, make sure to backup all your files and data before you initiate the setup.

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Step One: Download macOS Installer files

You can download the Mac OS Installer file from App Store. Or, if you don’t find the required OS on the App Store, then you can download the Mac OS Installer files from ISORIVER.

Step Two: Formatting Your USB Flash Drive

You can create a boot installer for macOS on Mac. If you are using a flash drive that already has data, be sure to back up all important files as you are about to erase everything in an instant.

Open search engine. Go to Applications > Utilities and open Disk Utility. You should see your flash drive in the External section of the left panel. After selecting it, click on the “Erase” button at the top.

Choose a descriptive name (which you will use later) and be sure to select Mac OS Extended (Journaled) for this format. Finally, click on Erase and you will be done with this step.

Step Three: Creating a Bootable USB Using DiskMaker X

DiskMaker X is a user-friendly and reliable software for creating a bootable macOS USB disk. You can download DiskMaker X for free.

After Installing DiskMaker X, you need to change security permissions for the app to work without breaking.

Navigate to System Preferences > Security & Privacy > Privacy > Accessibility. To make changes, click the lock icon at the bottom and enter your credentials.

Then click on the Plus button, navigate to the Applications folder, select DiskMaker X, and click open. DiskMaker X should now appear on the list.

As soon as you start DiskMaker X, you will be asked to confirm the download of the macOS installer.

The following message shows one of the advantages of DiskMaker X, as it is possible to create multiple installation disks. This means that you can create multiple partitions on the USB drive and have different macOS installers for each partition.

If you prefer to create an installation disk, select “Erase all disk“. Finally, confirm that you want to delete the entire contents of the USB drive.

DiskMaker will continue to create the disk in the background and update it while it works. After a few minutes, DiskMaker X will inform you that your startup disk is ready and will give you some instructions on how to use it.

Step Four: Booting Your Mac From a USB Drive

Simply connect the USB drive you created to an open USB port on your Mac. Turn on the system or restart it if it is already on. Immediately press and hold the Option (Alt) key on the keyboard when it starts.

You should now see an option to select the USB drive as a boot disk. Once selected, the system will start from the USB drive and will be directed to the macOS utility screen.

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That’s it for the tutorial If you face any issues or had any query then please let us know in the comment section below. You can also send us an email via the contact us page for personalized support.

I purchased a used 2018 Mac mini desktop and wanted to put a fresh installation of the latest macOS 10.15 Catalina on it. Below are the steps I took.

Note: The instructions below are the same for macOS 10.13 High Sierra and macOS 10.14 Mojave.

Download macOS Catalina

You will need a Mac to download macOS Catalina. (The Mac mini came with macOS 10.14 Mojave so I used it to download Catalina.)

Go to the Mac App Store, search for “macOS Catalina”, and download it. It will be saved to the “/Applications/Install macOS Catalina” location. If the installer automatically launches, just close it.

Note: If you plan to run the installer first to update your current macOS version to Catalina, you will want to move the “Install macOS Catalina” application out of the “/Applications” directory; otherwise, the installer will delete itself from the “/Applications” directory when the upgrade completes. For example, you can move the “Install macOS Catalina” application to the “~/Downloads” directory and run it from there.

Format USB Flash Drive

Because macOS Catalina is 8.4GB in size, you will need a 16GB USB flash drive. You don’t need to delete the existing content on the drive because we will blow it all away in a subsequent step.

If the USB flash drive is not already formatted as “Mac OS Extended (Journaled)”, format it like so:

1. Plug the USB flash drive into your Mac.
2. Launch the “Disk Utility” application.
3. On the left-hand pane, select the USB drive (not the partition under it, if any).
4. Click on the “Erase” tab (or button at the top).
   1. Input a name like “Catalina” (this name will be overwritten later).
   2. Select “Mac OS Extended (Journaled)” for “Format”.
   3. If available, select “Master Boot Record” for “Scheme”.
   4. Click the “Erase” button at the bottom. Click the “Erase” button in the warning popup dialog if you get one.
5. The format operation may take several minutes to complete. (USB 2.0 and large capacity drives may take longer.) After the format completes, the partition will be mounted under “/Volumes/Catalina” (or whatever name you selected above).
6. Close the “Disk Utility” application.

Write macOS Catalina to USB Flash Drive

To create a bootable USB macOS Catalina installer, run the “Terminal” application and this command:

Note: If the createinstallmedia command returns a “Failed to start erase of disk due to error (-9999, 0)” error, then your current Mac OS X version does not fully support the createinstallmedia tool. Use a more recent macOS version (at least Mac OS X 10.11 El Capitan) or manually create the USB installation drive using instructions from Bootable USB Flash Drive to Install Mac OS X 10.10 Yosemite.

The “createinstallmedia” program will erase the USB flash drive, create a new partition named “Install macOS Catalina”, and copy the installation files to that partition. The output will look like:

The above process took 20-30 minutes using my Kingston USB 2.0 flash drive.

Boot From USB Flash Drive

Note: Apple’s How to create a bootable installer for macOS page suggest using the “Startup Disk” configuration (under “System Preferences”) to select the USB flash drive as the startup drive. Then on restart, the Mac should boot from the USB flash drive. Unfortunately, the “Startup Disk” did not list my USB flash drive as a startup option, so I was not able to use this method.

To boot a Mac with the USB flash drive:

1. Insert the USB flash drive.
2. While holding the “option” key down, turn on the Mac to display the Startup Manager.
3. You should see one or more icons, one of which should be called “Install macOS Catalina” for the USB flash drive. (The internal hard drive may not be visible if it does not have a valid, bootable partition installed.)
   • Note: If you don’t see the USB flash drive’s “Install macOS Catalina”, try removing and re-inserting the USB flash drive while viewing the Startup Manager screen. The USB flash drive should then appear after a few seconds.
4. Select the “Install macOS Catalina” (with left/right arrow keys) and hit the “return/enter” key to boot from the USB flash drive.

It may take 5-10 minutes to load the installer from the USB flash drive. Sometimes the progress bar may appear to be frozen or the screen will go black for a minute or two. Be patient.

External Startup Disk Not Allowed

On a newer Mac with the T2 security chip, booting from an external drive may be disallowed by default. Attempting to boot from a USB flash drive will result in a “Security settings do not allow this Mac to use an external startup disk” warning message.

To allow booting from the USB flash drive, do the following:

1. Hold down “Command-R” (hold down both the “Command ⌘” and “R” keys) when you start the Mac to launch macOS Recovery. You can release the keys when you see the Apple logo.
   • Tip: An easier alternative is to hold the “Option/Alt” key on boot to launch the Startup Manager. Then just click and release “Command-R” keys to launch macOS Recovery.
2. The macOS Recovery screen contains a top-level “macOS Utilities” menu.
3. Click on the “Utilities” menu and select “Startup Security Utility”. Input your administrator password when prompted.
4. In the Startup Security Utility, under “Allowed Boot Media”, select the “Allow booting from external or removable media” option.
5. If the Mac won’t have access to the Internet (either by wire or wirelessly) when installing macOS Catalina, make sure to select either the “Medium Security” or “No Security” option under the “Secure Boot” section. (You can change the option back to the default “Full Security” afterwards.)
6. Quit the macOS Utilities to restart the Mac.
7. On restart, follow the directions in the previous section to boot from the USB flash drive.

Erase the Internal Hard Drive

When the installer finishes loading, you will see a “macOS Utilities” screen appear. It looks the same as the “macOS Recovery” screen with one difference. In the “macOS Utilities” window, the second option will say “Install macOS” instead of “Reinstall macOS”. In “macOS Recovery”, the “Reinstall macOS” option would just re-install the same version of macOS. The “Install macoS” option will install the macOS Catalina version on the USB flash drive.

Before installing macOS, I wanted a clean slate so I erased the internal hard drive like so:

1. Select the “Disk Utility” option and click the “Continue” button on the bottom to launch the “Disk Utility” application.
2. On the left-hand pane, select the internal hard drive (not the partition under it, if any).
3. Click on the “Erase” button at the top.
   1. Keep the default “Macintosh HD” name or input a new one.
   2. Select “APFS” for “Format”.
   3. Click the “Erase” button at the bottom. The SSD (Solid State Drive) format took less than a minute to complete.
4. Close the “Disk Utility” application.

Install macOS Catalina

Warning: If your Mac has a T2 security chip and you left the “Full Security” option configured in the Startup Security Utility, make sure that Internet access (wired or wireless) is available before starting the macOS Catalina installation. You can configure the wireless network by clicking on the wireless icon at the top-right corner of the macOS Utilities screen.

Back at the “macOS Utilities” window, do the following to start the macOS Catalina installation:

1. Click on the “Install macOS” option and click the “Continue” button.
2. The “macOS Catalina” installer’s splash screen will appear. Click the “Continue” button.
3. Click on the “Agree” button to agree to the license. A popup confirmation window will appear; click on the popup’s “Agree” button.
4. Select the internal hard drive and click the “Install” button.

My Mac mini took 20-30 minutes to complete the macOS Catalina installation. I think there were a couple of reboots in-between. And a few times, the screen would go black for a minute or two. Be patient and give the process an hour or more to complete.

If you run into problems installing macOS Catalina, check the “What Does Giving Up Mean?” section (at the bottom) of Install macOS Sierra Using Bootable USB Flash Drive for possible solutions.

Note: macOS Catalina seems to have an issue with my Dell 24in U2410 monitor. During the initial bootup screen, the monitor shows a blank screen with a message, “The current input timing is not supported by the monitor display”. Thankfully, the monitor works correctly after the bootup completes. And later, this warning message no longer appeared on bootup.

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Enjoy your fresh installation of macOS 10.15 Catalina.