You don't need a bootable installer to upgrade macOS or reinstall macOS, but it can be useful if you want to install macOS on multiple computers without downloading the installer each time, or you're unable to install a compatible macOS from the Finder or macOS Recovery.
Use Terminal to create the bootable installer
- Plug in the USB flash drive or other volume that you're using for the bootable installer.
- Open Terminal, which is in the Utilities folder of your Applications folder.
- Paste the command below into Terminal, then press Return to enter the command. Each command assumes that the installer is in your Applications folder, and that MyVolume is the name of the USB flash drive or other volume that you're using. If the volume has a different name, replace MyVolume in the command with the name of your volume.
- When prompted, type your administrator password. Terminal doesn't show any characters as you type. Then press Return.
- 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.
- 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.
- When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Sonoma. You can now quit Terminal and eject the volume.
macOS Sonoma
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/UntitledmacOS Ventura
sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume