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These advanced steps are primarily for system administrators and people 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 it on multiple computers without having to download the installer each time.

What you need to create a bootable installer

Hit the return key on your keyboard and the process of creating the bootable USB will begin. This will take some time so please be patient. Once done, you'll be left with a USB flash drive from.

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

1. Banglazed said: For simplicity, download the El Capitan, rename flash drive to ElCapInstaller, enter that above into terminal and boom done. Don’t need to format the USB since the command used in the terminal will format and create the bootable USB.
2. Finally, I could boot up the Mac while holding 'option/alt' and my USB drive appeared as a bootable device! 17 minutes later I can startup OSX! I may go ahead and re-download the installer and create a new bootable USB using 'createinstallmedia', just in case there was a problem with the image I used, but at least now I can boot up the computer!

Download macOS

• Download: macOS Big Sur, macOS Catalina, macOS Mojave or macOS High Sierra
  These will be downloaded to your Applications folder as an app called Install macOS [version name]. If the installer opens after download, quit it without continuing the 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. For enterprise administrators, please download from Apple, not a locally hosted software update server.
• Download: OS X El Capitan
  This will be downloaded as a disk image called InstallMacOSX.dmg. On a Mac that is compatible with El Capitan, open the disk image and run the installer within, which has the name 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:*

Bootable Os X El Capitan

El Capitan:

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument and installer path, similar to the way this was 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 displays the progress as the volume is being erased.
4. After the volume has been erased, you may see an alert stating that Terminal would like to access files on a removable volume. Click OK to allow the copy to proceed.
5. When Terminal says it's finished, 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

Create Bootable Usb Mac Os El Capitan Iso

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.
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 displaying 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 the External Boot setting in Startup Security Utility has been 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.

Create Bootable Usb On Mac

Learn more

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.

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

It was 2009 when Apple last released a new operating system on physical media. Things have proceeded remarkably smoothly since version 10.7 switched to download-only installers, but there are still good reasons to want an old, reliable USB stick. For instance, if you find yourself doing multiple installs, a USB drive may be faster than multiple downloads (especially if you use a USB 3.0 drive). Or maybe you need a recovery disk for older Macs that don't support the Internet Recovery feature. Whatever the reason, you're in luck, because it's not hard to make one.

As with last year, there are two ways to get it done. There's the super easy way with the graphical user interface and the only slightly less easy way that requires some light Terminal use. Here's what you need to get started.

• A Mac that you have administrator access to, duh. We've created El Capitan USB stick from both Yosemite and El Capitan, but your experience with other versions may vary.
• An 8GB or larger USB flash drive or an 8GB or larger partition on some other kind of external drive. For newer Macs, use a USB 3.0 drive—it makes things significantly faster.
• The OS X 10.11 El Capitan installer from the Mac App Store in your Applications folder. The installer will delete itself when you install the operating system, but it can be re-downloaded if necessary.
• If you want a GUI, you need the latest version of Diskmaker X app. Version 5 is the one with official El Capitan support.
• Diskmaker X is free to download, but the creator accepts donations if you want to support his efforts.

The easy way

Once you've obtained all of the necessary materials, connect the USB drive to your Mac and run the Diskmaker X app. The app will offer to make installers for OS X 10.9, 10.10, and 10.11, and it should run on OS X versions all the way back to 10.7—support for 10.6 was dropped in the most recent release.

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Diskmaker X has actually been around since the days of OS X 10.7 (it was previously known as Lion Diskmaker), and it's still the easiest GUI-based way to go without intimidating newbies. If you're comfortable with the command line, it's still possible to create a disk manually using a Terminal command, which we'll cover momentarily.

Select OS X 10.11 in Diskmaker X, and the app should automatically find the copy you've downloaded to your Applications folder. It will then ask you where you want to copy the files—click 'An 8GB USB thumb drive' if you have a single drive to use or 'Another kind of disk' to use a partition on a larger drive or some other kind of external drive. Choose your disk (or partition) from the list that appears, verify that you'd like to have the disk (or partition) erased, and then wait for the files to copy over. The process is outlined in screenshots above.

The only slightly less-easy way

If you don't want to use Diskmaker X, Apple has actually included a terminal command that can create an install disk for you. Assuming that you have the OS X El Capitan installer in your Applications folder and you have a Mac OS X Extended (Journaled)-formatted USB drive named 'Untitled' mounted on the system, you can create an El Capitan install drive by typing the following command into the Terminal.

sudo /Applications/Install OS X El Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install OS X El Capitan.app --nointeraction

The command will erase the disk and copy the install files over. Give it some time, and your volume will soon be loaded up with not just the OS X installer but also an external recovery partition that may come in handy if your hard drive dies and you're away from an Internet connection.

How To Create Mac Os El Capitan Bootable Usb

Whichever method you use, you should be able to boot from your new USB drive either by changing the default Startup Disk in System Preferences or by holding down the Option key at boot and selecting the drive. Once booted, you'll be able to install or upgrade El Capitan as you normally would.