How to create a bootable installer for macOS

You can use an external drive or secondary volume as a startup disk from which to install the Mac operating system.

These advanced steps are primarily for system administrators and others who are familiar with the command line. You don’t need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful when you want to install on multiple computers without downloading the installer each time.

What you need to create a bootable installer

• A USB flash drive or other secondary volume formatted as Mac OS Extended, with at least 14GB of available storage
• A downloaded installer for macOS Big Sur, Catalina, Mojave, High Sierra, or El Capitan

Download macOS

• Download: macOS Big Sur, macOS Catalina, macOS Mojave, or macOS High Sierra
  These download to your Applications folder as an app named Install macOS [ version name ]. If the installer opens after downloading, quit it without continuing installation. To get the correct installer, download from a Mac that is using macOS Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators, please download from Apple, not a locally hosted software-update server.
• Download: OS X El Capitan
  This downloads as a disk image named InstallMacOSX.dmg. On a Mac that is compatible with El Capitan, open the disk image and run the installer within, named InstallMacOSX.pkg. It installs an app named Install OS X El Capitan into your Applications folder. You will create the bootable installer from this app, not from the disk image or .pkg installer.

Use the ‘createinstallmedia’ command in Terminal

1. Connect the USB flash drive or other volume that you’re using for the bootable installer.
2. Open Terminal, which is in the Utilities folder of your Applications folder.
3. Type or paste one of the following commands in Terminal. These assume that the installer is in your Applications folder, and MyVolume is the name of the USB flash drive or other volume you’re using. If it has a different name, replace MyVolume in these commands with the name of your volume.

Big Sur:*

Catalina:*

Mojave:*

High Sierra:*

El Capitan:

* If your Mac is using macOS Sierra or earlier, include the —applicationpath argument and installer path, similar to the way this is done in the command for El Capitan.

After typing the command:

1. Press Return to enter the command.
2. When prompted, type your administrator password and press Return again. Terminal doesn’t show any characters as you type your password.
3. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the volume is erased.
4. After the volume is erased, you may see an alert that Terminal would like to access files on a removable volume. Click OK to allow the copy to proceed.
5. When Terminal says that it’s done, the volume will have the same name as the installer you downloaded, such as Install macOS Big Sur. You can now quit Terminal and eject the volume.
   

How to create a Windows 10 installer USB drive from a Mac

We previously showed you how to create a Windows 10 USB installation media when performing a clean install of Windows 10, but there might be an instance where the only machine you have available is a Mac. We’ll show you to create a bootable USB flash drive with the Windows 10 installer from a Mac. It’s easier than you think, thanks to the built-in Boot Camp Assistant from Apple.

Download Windows 10 Disc Image

First, you need to download the Windows 10 ISO file. Go to the download page and select the proper edition of Windows 10 in the dropdown menu. If you don’t know what K, KN, or Single Language edition stands for, just select Windows 10 in the list.

Create USB installer with Boot Camp Assistant

After downloading the ISO file, you’ll need to use Boot Camp Assistant to move it to a bootable USB drive.

1. Insert a USB flash drive to your Mac. Make sure it’s at least 8GB, which is usually marked on the USB stick. You can also check by right-clicking the USB drive on your desktop and clicking Get Info. Check if the number next to Capacity is at least 8GB. All the files in the drive will be deleted, so make sure there are no important documents inside.
2. Open Boot Camp Assistant. The easiest way to launch it is through Spotlight Search, which you can bring up by pressing Command and Spacebar. Press Enter to launch the app.
3. Check the box for «Create a Windows 7 or later version install disk» and deselect «Install Windows 7 or later version.»

Click Continue to proceed.

Boot Camp Assistant will automatically locate the ISO file from your downloads folder, but make sure it is the right file. Click the «Choose…» button and locate the ISO file. Make sure the destination disk is the USB thumb drive you’ve inserted.

Click Continue. It can take about 20 minutes to format and set up the USB installer on the Mac.

When Boot Camp Assistant is done, the USB drive will be renamed to WININSTALL. Click Quit to close the app and then Eject the USB drive.

That’s it! You now have a bootable USB drive with the Windows 10 installer. You can use it to configure new Windows 10 PCs from scratch. We told you it was easy!

Have you tried creating a Windows 10 installer USB drive from a Mac before? Did you encounter any issues? Let us know your experience in the comments!

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How to Make a Windows 10 USB Using Your Mac — Build a Bootable ISO From Your Mac’s Terminal

Quincy Larson

Most new PCs don’t come with DVD drives anymore. So it can be a pain to install Windows on a new computer.

Luckily, Microsoft makes a tool that you can use to install Windows from a USB storage drive (or «thumbdrive» as they are often called).

But what if you don’t have a second PC for setting up that USB storage drive in the first place?

In this tutorial we’ll show you how you can set this up from a Mac.

Step 1: Download the Windows 10 ISO file

You can download the ISO file straight from Windows. That’s right — everything we’re going to do here is 100% legal and sanctioned by Microsoft.

If you want an English-language version of the latest update of Windows 10, you can download the ISO here.

If you have a relatively new computer, you probably want the 64-bit version. If you’re not sure, go with the 32-bit version to be safe.

If you want a non-English-language version of Windows, or want to get an older update version, download the ISO here instead.

Step 2: Insert your USB storage drive into your Mac

The ISO file is only about 5 gigabytes, but I recommend you use a USB drive with at least 16 gigabytes of space just in case Windows needs more space during the installation process.

I bought a 32 gigabyte USB drive at Walmart for only $3, so this shouldn’t be very expensive.

Stick your USB drive into your Mac. Then open your terminal. You can do this using MacOS Spotlight by pressing both the ⌘ and Space bar at the same time, then typing «terminal» and hitting enter.

Don’t be intimidated by the command line interface. I’m going to tell you exactly which commands to enter.

Step 3: Use the diskutil command to identify which drive your USB is mounted on

Open Mac Spotlight using the ⌘ + space keyboard shortcut. Then type the word «terminal» and select Terminal from the dropdown list.

Paste the following command into your terminal and hit enter:

You will see output like this (note — your Mac’s terminal may be black text on a white background if you haven’t customized it).

Copy the text I point to here. It will probably be something like

Step 4: Format your USB Drive to work with Windows

Next format your USB drive to Windows FAT32 format. This is a format that Windows 10 will recognize.

Note that you should replace the disk2 with the name of the your drive from step 3 if it wasn’t disk2 . (It may be disk3 or disk4 ).

Run this command using the correct disk number for your USB:

diskutil eraseDisk MS-DOS «WIN10» GPT /dev/disk2

Then you’ll see terminal output like this.

This will probably only take about 20 seconds on a newer computer, but may take longer on an older computer.

Note that for some hardware, you may instead need to run this command, which uses the MBR format for partitioning instead of GPT. Come back and try this command if step 7 fails, then redo steps 5, 6, and 7:

Step 5: Use hdiutil to mount the Windows 10 folder and prepare it for transfer.

Now we’re going to prep our downloaded ISO file so we can copy it over to our USB drive.

You will need to check where your downloaded Windows 10 ISO file is and use that. But your file is probably located in your

/Downloads folder with a name of Win10_1903_V1_English_x64.iso .

Step 6: Copy the Windows 10 ISO over to your USB Drive

Update April 2020: One of the files in the Windows 10 ISO – install.wim – is now too large to copy over to a FAT-32 formatted USB drive. So I’ll show you how to copy it over separately.

Thank you to @alexlubbock for coming up with this workaround.

First run this command to copy over everything but that file:

rsync -vha —exclude=sources/install.wim /Volumes/CCCOMA_X64FRE_EN-US_DV9/* /Volumes/WIN10

Then run this command to install Homebrew (if you don’t have it installed on your Mac yet):

/usr/bin/ruby -e «$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)»

Then use Homebrew to install a tool called wimlib with this terminal command:

brew install wimlib

Then go ahead and create the directory that you’re going to write the files into:

Then run this command. Note that this process may take several hours, you may see 0% progress until it finishes. Don’t abort it. It will use wimlib to split the install.wim file into 2 files less than 4 GB each (I use 3.8 GB in the following command), then copy them over to your USB:

wimlib-imagex split /Volumes/CCCOMA_X64FRE_EN-US_DV9/sources/install.wim /Volumes/WIN10/sources/install.swm 3800

Once that’s done, you can eject your USB from your Mac inside Finder. Note that Windows will automatically rejoin these files later when you’re installing.

Step 7: Put your USB into your new PC and start loading Windows

Congratulations — your computer now should boot directly from your USB drive. If it doesn’t, you may need to check your new PC’s BIOS and change the boot order to boot from your USB drive.

Windows will pop up a screen and start the installation process.

Enjoy your new PC, and your newly-installed copy of Windows.

Quincy Larson

The teacher who founded freeCodeCamp.org.

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