After successfully created a macOS bootable USB, the next step is how to use it to install macOS from external USB drive. This is not normal case because macOS is very stable and have less bugs/virus than Windows PC. So many Mac users don't know how to perform a clean install of macOS on their Mac when the device was broken or could not boot into desktop.
- The key to reinstall mac OS Big Sur, Catalina or Mojave without losing data is the backup, since no one can guarantee all data will be perfectly maintained after macOS reinstallation. However, if we unfortunately lost files after macOS reinstallation, Time Machine or Cisdem Data Recovery is helpful to recover them back.
- Installing a new version of the Mac OS is generally a fairly pain-free process; this trend continues with macOS Catalina. Even so, it’s a good idea to review our Rocket Yard guides for a clean install of macOS Catalina as well as an upgrade install of Catalina.
Please don't worry. We will share detailed steps on how to install macOS/Mac OS X from an USB drive. Even you had issues during this process, it is not thing to be afriad as we have offered the troubleshooting guide as well.
If your Mac already runs macOS Big Sur, download the macOS Catalina here. Get an external hard drive that has at least 12 GB of available storage and plug it in your Mac. Launch the Disk Utility app and erase your hard drive selecting Mac OS Extended format. Now, it’s time to transfer your Catalina installer to your hard drive.
How to Install macOS on Mac from USB Drive (Normal Way)
If the target Mac computer already had a macOS or OS X on it, then installing macOS from USB is straightforward and this is called the normal way.
Step 1: Insert the macOS bootable USB drive on a USB port of Mac computer.
Step 2: Shut down the Mac and wait for 1-2 minutes. This will make sure the Mac is powered off.
Reinstall Mac Os X Catalina
Step 3: Hold the Power and Option key simultaneously for 15 seconds. This will bring up the Startup Manager on Mac.
Step 4: You will see all bootable devices attached to this Mac, including Macintosh HD and external USB or DVD. Click the drive name of your macOS bootable USB to start the installation process.
Step 5: Agree the terms and conditions and wait for the installation process to be done.
How to Install macOS on Mac from USB Drive (Advanced)
If the drive was not partitioned or the partition table was corrupted, then you can not install macOS on Mac with the normal way. You have to boot Mac into Recovery mode and format the hard drive or SSD to Apple file system first.
Step 1: Shut down your Mac and press the Power key to turn on the Mac; then immediately press Command and R keys.
Step 2: You will be directed to the macOS utility section and here you need to select 'Disk Utility' to format the USB drive. From the Disk Utility app, select Mac drive name under Internal section and then click on the 'Erase' button.
Step 3: You will get a couple of options from the Format. Pleasec choose APFS (macOS) or Mac OS Extended (Journaled) for old version Mac OS X.
Step 4: After the completion of the formatting process, go back to the macOS utility section and this time, select 'Reinstall macOS'.
Step 5: Further, go to the Startup Manager, move to the External drive section, and select your bootable macOS USB drive.
Step 6: Now, the configuration of MacOS will start. As soon as the process starts, it will provide Terms and Agreement page and your job is to agree with the same and then click on the continue button.
Step 7: After that, click on the 'Continue' button to start the installation process. This will take 30-45 minutes and once it gets completed, restart Mac.
Step 8: As you are using the fresh copy of MacOS on Mac machine, so you need to set up the OS and for that connect the Mac with the Wi-Fi and then sign in with the Apple account.
Step 9: After signing in, you can access the several products of Apple such as iCloud, DropBox and many more.
Reinstall Macos Catalina From Internet
Quick Troubleshooting Tips if You Got Stuck during MacOS Installation
Could not write installation information to disk
If you see the message like 'Could Not Write Installation Information to Disk' when you are trying to install the OS, it means, some important files are missing from the bootable USB device. Mostly, this error happens when you download Mac OS file from an unauthorized site.
You can fix this issue just by downloading the original OS file from the Apple store and then create a fresh bootable USB using the same.
Compatibility error
If you are upgrading the OS X after having an older version, you can get the compatibility error message. In such case, just cross-check the system requirement for the OS you want to install on your Mac system.
You can fix this issue just by downloading the original OS file from the Apple store and then create a fresh bootable USB using the same.
macOS could not be installed on your Computer
If you see the error message similar to 'macOS Could Not Be Installed on Your Computer' that means, either your system is not compatible or the Date and Time settings in your system is not up to date..
To resolve the problem, first, check the system combability for the OS X. If it's fine and still you are facing the error, then just update the system Time & Date with the option of 'Local Apple time server'.
Application is damaged, can't be used to install macOS
You the message 'application is damaged, can't be used to install macOS' appear on your screen, it means the OS certificated has been expired. And so, you won't be able to proceed further for installation.
The simple solution is; you need to create a fresh bootable USB by downloading the MacOS file from its official website.
MacOS couldn't install on this computer
Sometimes, the thirty-party tool which you use to create a bootable USB is the culprit. If the OS files will not be copied successfully using the bootable tool, then you may see the message like 'MacOS couldn't install on this computer'.
In this case, you should avoid using a third party bootable tool despite you should create a bootable USB with the help of command.
Conclusion
The above tutorial covers most of the issues you could come across during the installation process. If you had other issues not mentioned in this article, please contact us and our technical team will help you fix it.
Rachel is trying to sell her Mac, but…
My friend was wiping my Mac so I could sell it and I’m pretty sure they’ve deleted the start up disk? It’s not letting me reinstall the OS on a recovery startup.
She wonders about a fix. There are a couple of options with an erased partition.
Because Recovery didn’t work, the fastest way to install fresh is to make or borrow a macOS installer on a USB flash drive or a disk drive. We have instructions for making a bootable installer with macOS Sierra (as well as archived versions for several previous releases). You need at least an 8GB flash drive. The article includes instructions on obtaining the installer, which might involve you having to use someone’s else Mac to download it, if you don’t have a replacement Mac on hand yet.
But if you can’t get access to another Mac or the necessary drive, it’s still possible to use a different Recovery mode on all recent Macs, dating back to 2010. Normally, you can start up a Mac while holding down Command-R to boot into what Apple now calls macOS Recovery. That allows you to run Disk Utility, reinstall or wipe and install the system, access Terminal for command-line functions, and so on. In that mode, when you choose to reinstall without erasing the drive, my recollection is that Recovery looks for the current OS system installer on your startup disk in the Applications folder, and uses that. (Apple doesn’t document that, and I haven’t had to test that for years.)
Failing finding it, Recovery downloads the currently installed version of macOS (or OS X), which is about 5GB. When complete, it installs it and reboots, and places the installer in the Applications folder.
However, there’s yet another option: macOS Recovery over the Internet, which requires either a Mac model released in 2012 or later, or most 2010 and 2011 models with a firmware upgrade applied. There, the Mac reaches out over a Wi-Fi or ethernet connection to download the relatively modest Recovery software, which then bootstraps the download of the full macOS installer.
Apple says Internet-based Recovery should happen automatically on supported models, and you should see a spinning globe when that mode is invoked while the download occurs. However, if you have normal Recovery installed and it refuses to install macOS for some reason, you can manually invoke Internet Recovery.
While Command-R at startup always installs whatever the most recent version you installed on your Mac, holding down Command-Option-R brings down the very latest compatible version that can be installed. Apple also offers Shift-Command-Option-R, which installs the version of OS X or macOS with which your computer shipped, or the next oldest compatible system still available for download.
(Apple just changed this behavior with 10.12.4, but if you’re using Internet Recovery for a clean install on an erased drive, the new behavior should be active as it will be pulled from the version of Recovery that’s bootstrapped from Apple’s servers. The pre-10.12.4 option is simply Command-Option-R, but it acts like the new Shift-Command-Option-R, installing the shipped OS or the oldest compatible version.)
Apple recommends the Command-Option-R option as the only safe way to reinstall a Mac with El Capitan or earlier versions of macOS if you want to be sure your Apple ID doesn’t persist even after erasure.
Ask Mac 911
We’ve compiled a list of the questions we get asked most frequently along with answers and links to columns: read our super FAQ to see if your question is covered. If not, we’re always looking for new problems to solve! Email yours to mac911@macworld.com including screen captures as appropriate. Mac 911 can’t reply to—nor publish an answer to—every question, and we don’t provide direct troubleshooting advice.