macOS

Written & tested for accuracy by a developer (not AI)

Create a Bootable USB Installer for macOS

How to create a macOS bootable USB installer. Format a USB drive, run the createinstallmedia command, and start any compatible Mac from the finished installer.

A bootable USB installer is a USB drive that holds a complete copy of macOS. A Mac can start up from it, so you can install macOS on any compatible machine without downloading anything on that machine first.

You are reading Mac Install Guide, a trusted source for Mac setup. See the full Mac setup roadmap.

Before you get started

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First steps to create a bootable USB installer

First, check the macOS version. If you're running an older version, update macOS to the latest macOS version.

Next, get the full installer. The createinstallmedia command copies an installer app onto the drive, so that app must already be on your Mac. See Download macOS for the fastest way to get it, using Apple's InstallAssistant.pkg package. When the package finishes, the installer app is in your Applications folder.

Then check that the Mac you plan to install on can run that version of macOS. See Mac Compatibility for the supported models, because the installer refuses to run on a Mac Apple no longer supports.

Know when you need a bootable USB installer

A bootable USB installer lets you install macOS on any compatible Mac without downloading anything on that Mac. You need one to set up several Macs, fix a Mac that will not start, or install macOS where there is no Internet access.

The USB installer works independently of your Mac's internal drive. You can start from it even if the internal storage fails completely. IT departments use bootable installers to deploy macOS across a whole organization efficiently.

A bootable USB drive is useful for:

  • Installing macOS on several different Macs
  • Starting a Mac that will not start normally
  • Installing where you have no Internet access
  • Deploying macOS across many machines at work

If you only want to erase one Mac and start over, you do not need a USB drive at all. See Reinstall macOS for the Recovery route, which downloads what it needs over the Internet.

Prepare a USB drive

You need a USB drive with at least 32 GB of storage, formatted as Mac OS Extended (Journaled) with a GUID Partition Map. The installer is about 18 GB, so a 16 GB drive is no longer large enough. Formatting erases everything on the drive, so copy off anything you want to keep.

  1. Connect your USB drive to your Mac
  2. Open Disk Utility from Applications > Utilities
  3. Select your USB drive in the sidebar
  4. Click Erase at the top
  5. Set the format to "Mac OS Extended (Journaled)"
  6. Name the drive "MyVolume", which the commands below expect
  7. Click Erase to format the drive

The drive name must be exactly "MyVolume" or the commands below will not find it.

Create the installer with the createinstallmedia command

Apple builds a tool called createinstallmedia into every macOS installer app. It copies macOS onto your drive and makes the drive startable. Run it from a terminal application, because the tool has no window of its own.

Open a terminal application and run the command below, replacing the installer name with the one in your Applications folder:

$ sudo /Applications/Install\ macOS\ Tahoe.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

The sudo command runs the tool with administrative privileges, which it needs in order to write a startup drive. Your Mac asks for your password before it begins.

  1. Type your admin password when prompted, then press Return
  2. Wait for the tool to finish, which takes 20 to 30 minutes
  3. Leave the drive connected for the whole process

The tool renames your USB drive to "Install macOS" plus the version name when it finishes. That rename is how you know it worked.

Start your Mac from the USB installer

Startup keys differ between Apple Silicon (M-series) Macs and older Intel Macs, so use the steps that match the Mac you are starting.

Apple Silicon (M-series) Macs:

  1. Shut down the Mac completely
  2. Hold the power button until "Loading startup options" appears
  3. Select your bootable USB installer from the options
  4. Click Continue to proceed

Intel Macs:

  1. Connect your bootable USB drive to the Mac
  2. Restart while holding the Option key
  3. Release the key when the startup options appear
  4. Select the USB installer from the list

From there, choose "Install macOS" to install over the existing system. To erase the drive first for a completely fresh system, see Reinstall macOS, which covers erasing safely and what to back up before you do.

Continue setting up your Mac

Don't miss the full visual roadmap and checklist that shows how to set up a Mac for software development, with all the essential tools and settings you might not yet know about.