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.

1. Boot Disk Utility Mac
2. Bootable Disk-utility Mac 10.13.6

• Mar 21, 2019 UNetbootin is a free, open source utility that allows you to create bootable USB drives on Windows, Linux, and Mac OS X. If you’ve downloaded Windows 10 ISO image, here is how you can create a bootable Windows installer USB on Mac using UNetbootin. Plug a USB drive into your Mac and open Disk Utility.
• Create bootable USB Mac disk utility. Download the MacOS High Sierra.dmg file, and extract that anywhere on your Running Mac Virtual Machine. After that open it and drag the Install MacOS High Sierra on Applications. When the Install MacOS High Sierra is copied, attached your USB Flash Drive.
• Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing. Turn on your Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes and a gear icon labled Options.

Create bootable USB Mac disk utility. Download the MacOS High Sierra.dmg file, and extract that anywhere on your Running Mac Virtual Machine. After that open it and drag the Install MacOS High Sierra on Applications. When the Install MacOS High Sierra is copied, attached your USB Flash Drive. Dec 31, 2020 Unfortunately, the Windows PE bootable disk only works to boot up an unbootable computer and temporarily access files on hard drive partitions. What about third-party formatting tools? Most formatting tools that support creating a bootable USB disk are not free. Some are even extremely complex. Bootable USB Hard Drive Format Utility Free Download.

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.

Boot Disk Utility Mac

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.
   

Use the bootable installer

Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

Apple silicon

1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
2. Turn on your Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes and a gear icon labled Options.
3. Select the volume containing the bootable installer, then click Continue.
4. When the macOS installer opens, follow the onscreen instructions.

Intel processor

1. Plug the bootable installer into a Mac that is connected to the internet and compatible with the version of macOS you're installing.
2. Press and hold the Option (Alt) ⌥ key immediately after turning on or restarting your Mac.
3. Release the Option key when you see a dark screen showing your bootable volumes.
4. Select the volume containing the bootable installer. Then click the up arrow or press Return.
   If you can't start up from the bootable installer, make sure that the External Boot setting in Startup Security Utility is set to allow booting from external media.
5. Choose your language, if prompted.
6. Select Install macOS (or Install OS X) from the Utilities window, then click Continue and follow the onscreen instructions.

Learn more

For more information about the createinstallmedia command and the arguments that you can use with it, make sure that the macOS installer is in your Applications folder, then enter the appropriate path in Terminal:

• Big Sur: /Applications/Install macOS Big Sur.app/Contents/Resources/createinstallmedia
• Catalina: /Applications/Install macOS Catalina.app/Contents/Resources/createinstallmedia
• Mojave: /Applications/Install macOS Mojave.app/Contents/Resources/createinstallmedia
• High Sierra: /Applications/Install macOS High Sierra.app/Contents/Resources/createinstallmedia
• El Capitan: /Applications/Install OS X El Capitan.app/Contents/Resources/createinstallmedia

A bootable installer doesn't download macOS from the internet, but it does require an internet connection to get firmware and other information specific to the Mac model.

How can I make a bootable Windows installation USB on Mac OS X? After upgrading to macOS Mojave, you may find that Boot Camp Assistant is no longer supported and thus creating a bootable USB turns out to be a little bit challenging. In this tutorial we’ll show you how to create Windows 10 bootable USB from ISO on Mac, by using the Terminal or third-party software like UNetbottin.

Method 1: Create Windows 10 Bootable USB on Mac Using UNetbottin

UNetbootin is a free, open source utility that allows you to create bootable USB drives on Windows, Linux, and Mac OS X. If you’ve downloaded Windows 10 ISO image, here is how you can create a bootable Windows installer USB on Mac using UNetbootin.

Bootable Disk-utility Mac 10.13.6

1. Plug a USB drive into your Mac and open Disk Utility. Select your USB drive from the left panel and click on Info button. Note down the device name since we will need that later.
2. Next, download and launch the UNetbottin utility. Select the “Diskimage” radio button, click “…” to select a bootable ISO image.
3. After locating your Windows 10 ISO file, click on Open.
4. Choose Type as USB Drive and select the device name of your USB drive (you probably would’ve noted it down earlier, so refer to that). Click OK to start installing to the USB drive.
5. This process takes several minutes or longer, depending on the size of your selected ISO image.

Method 2: Create Windows 10 Bootable USB on Mac Using Terminal

Of course, if you prefer not to use third-party software, you can still use the excellent Terminal app, which is a little bit more involved, but no additional software needs to be installed. Follow these steps:

1. After connecting a USB drive to your Mac, open a Terminal window and type diskutil list to display all the disks attached to your machine. You have to figure out the disk identifier of the USB drive you need to format. In my example, my USB drive is mounted as “disk2” and it’s about 32GB.
2. Next, run the following command to format your USB drive and name it “WIN10“, where # is a placeholder for the disk identifier of your USB drive.
   diskutil eraseDisk MS-DOS 'WIN10' GPT disk#
3. Now, mount your Windows 10 ISO image with the command below, assuming it’s saved the Downloads folder. In my case, it is mounted as a volume named “ESD-ISO“.
   hdiutil mount ~/Downloads/your_windows_10_image.iso
4. Finally, run the following command to copy all the files from the mounted ISO to your USB drive.
   cp -rp /Volumes/ESD-ISO/* /Volumes/WIN10/

   This command will take a while, and once it finishes, you can disconnect the mounted ISO with this command:
   hdiutil unmount /Volumes/ESD-ISO

5. Now you should be able to boot from the USB to install Windows 10 on your Mac or Windows machine.

Conclusion

These should be the easiest ways to create a Windows 10 bootable USB from ISO on Mac, without using Boot Camp Assistant. No matter which method you prefer, be sure that you backup any important data on your USB drive, as the procedure of creating bootable USB will delete everything on it.