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. Create A Bootable Usb Drive Mac Os
2. How To Make A Bootable Mac Usb

Download macOS

How to boot from the installer drive. Plug your external drive into your Mac. Power up (or restart) your Mac. Press down on the Option key while the Mac boots. After a few moments, your Mac should display the Startup Manager, which will show you the available boot drives. Click on the external drive. TransMac is Acute system in Windows operating system that can copy and paste and manage the files on Windows for Apple or Mac Systems, Including Mac-formatted USB drives, SSD drive, Hard drives, and any kind of storage devices, further, it can burn VMDK and dmg files of macOS Mojave, macOS High Sierra, macOS X El Capitan, macOS Sierra, macOS Yosemite, and any other operating system of. If you want to use your USB stick with an Apple Mac, you will need to restart or power-on the Mac with the USB stick inserted whilethe Option/alt(⌥)key is pressed. This will launch Apple’s ‘Startup Manager’ which shows bootable devices connected to the machine. Your USB stick should appear as gold/yellow and labelled ‘EFI Boot’. DMG Editor, a popular app developed by UUByte, is a multi-functional and cross-platform image burning tool that works on Windows, Linux and macOS. It supports creating bootable USB from popular image files, including dmg, iso, zip, img. Choose Mac OS Extended (Journaled) as the Format. Choose GUID Partition Map as the Scheme. Your drive will be called Untitled by default, you could give your drive a name such as 'macOS' or 'USB'. The easiest way to create a USB flash installer is with the free program, Disk Creator. Download the macOS Sierra installer and Disk Creator. Insert an 8GB (or larger) flash drive. If you have any.

Find the appropriate download link in the upgrade instructions for each macOS version:

macOS Catalina, macOS Mojave, ormacOS High Sierra
Installers for each of these macOS versions download directly to your Applications folder as an app named Install macOS Catalina, Install macOS Mojave, or Install macOS High Sierra. If the installer opens after downloading, quit it without continuing installation. Important: 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.

OS X El Capitan
El Capitan downloads as a disk image. 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. Make sure that it has at least 12GB of available storage and is formatted as Mac OS Extended.
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 still 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.
   Catalina:*
   Mojave:*
   
   High Sierra:*
   El Capitan:
   
4. Press Return after typing the command.
5. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
6. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the bootable installer is created.
7. When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Catalina. You can now quit Terminal and eject the volume.

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument, similar to the way this argument is used in the command for El Capitan.

Use the bootable installer

After creating the bootable installer, follow these steps to use it:

1. Plug the bootable installer into a compatible Mac.
2. Use Startup Manager or Startup Disk preferences to select the bootable installer as the startup disk, then start up from it. Your Mac will start up to macOS Recovery.
   Learn about selecting a startup disk, including what to do if your Mac doesn't start up from it.
3. Choose your language, if prompted.
4. A bootable installer doesn't download macOS from the Internet, but it does require the Internet to get information specific to your Mac model, such as firmware updates. If you need to connect to a Wi-Fi network, use the Wi-Fi menu in the menu bar.
5. 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 this path in Terminal:

Catalina:

Mojave:

Create A Bootable Usb Drive Mac Os

High Sierra:

How To Make A Bootable Mac Usb

El Capitan: