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 starts the macOS installer on any compatible Mac. The drive holds the installer and its utilities, not a working copy of macOS. Creating an installer is not the same as installing macOS on an external drive to use as an everyday startup disk; that is a separate procedure with different steps.

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

Before you get started

Creating the installer requires a terminal command. Apple includes the Mac terminal but I prefer Warp Terminal. Warp is an easy-to-use terminal application, with AI assistance to help you learn and remember terminal commands. Download Warp Terminal now; it's FREE and worth a try.

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, download a full macOS installer app. See Download macOS for the fastest way to get it, using Apple's InstallAssistant.pkg package. The download is a package, not the installer app itself. Double-click the package and follow its instructions, and it places the installer app in your Applications folder. If the installer app opens on its own, quit it without installing anything.

Check that the Mac you plan to install on can run the macOS version supplied by the installer app. See Mac Compatibility for the supported models. On an incompatible Mac, installation may not complete, or the Mac may show a circle with a line through it at startup.

Know when you need a bootable USB installer

A bootable USB installer lets you install macOS on several Macs without downloading the full installer on each one. IT departments use bootable installers to deploy macOS across a whole organization efficiently. The same drive can start any Mac model that is compatible with the installer's macOS version, whether it has Apple Silicon or an Intel processor.

A bootable USB drive is useful for:

  • Installing macOS on several different Macs
  • Starting a Mac whose installed system will not start
  • Deploying macOS across many machines at work
  • Keeping a trusted installer on hand for repairs

A bootable installer does not give you fully offline installation without an internet connection. The target Mac still connects to the internet during installation, because the installer gets firmware and other information specific to that Mac model from Apple. You simply avoid downloading the full installer again on every machine.

A bootable installer also cannot fix broken hardware. It boots on a Mac whose installed system is damaged, but it cannot help when the internal storage or the firmware has failed.

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

Use a USB drive with at least 32 GB of storage. Apple says 32 GB is more than enough for any macOS installer, and 16 GB is enough for most older versions. Choose a fast drive with USB 3 or USB-C if you can, because a slow drive can stretch the process past an hour.

The steps below erase the drive completely, so copy off anything you want to keep. The createinstallmedia command erases the drive when it runs, so the goal here is the correct format and a predictable name.

  1. Connect your USB drive to your Mac
  2. Open Disk Utility from Applications > Utilities
  3. Choose View > Show All Devices, so the sidebar shows whole drives instead of only volumes
  4. Select the USB device itself, the top item in its sidebar group. Take care not to select your Mac's internal disk.
  5. Click Erase at the top
  6. Set the format to "Mac OS Extended (Journaled)". Disk Utility often suggests APFS, which the installer tool rejects, so check this menu carefully.
  7. Set the scheme to "GUID Partition Map"
  8. Name the drive "MyVolume", which the command below expects
  9. Click Erase to format the drive

The command below points at the path /Volumes/MyVolume. A drive with a different name works if you change that part of the command to match, with quotes around the path if the name contains spaces.

Create the installer with the createinstallmedia command

Apple builds a tool called createinstallmedia into each full macOS installer app it offers. The tool copies macOS onto your drive and makes the drive startable. You must run it from a terminal application, because the tool has no window of its own.

Open a terminal application and run the command below. It names the current macOS version, so replace 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 administrator privileges, which it needs in order to write a startup drive. The tool asks a few questions before it starts:

  1. Type your administrator password when prompted. The terminal application shows nothing as you type, so type carefully and press Return.
  2. Type Y to approve erasing the USB drive, then press Return
  3. Click OK if macOS asks to let the terminal application access files on a removable volume
  4. Leave the drive connected and wait. The tool shows little progress during long stretches. A fast drive finishes in minutes, while a slow drive can take an hour or more.

The terminal application reports that the install media is now available when the tool finishes. The tool also renames the drive to match the installer name, such as "Install macOS" plus the version. Quit the terminal application and eject the drive.

Some older installers need a different command. Apple publishes the exact command for each version it offers in Create a bootable installer for macOS. The OS X El Capitan installer takes an extra --applicationpath argument, and a Mac running macOS Sierra 10.12.6 or earlier adds that argument for any installer. To create an installer for a version older than macOS High Sierra, use an older Mac that can run that version.

Start your Mac from the USB installer

Startup steps differ between Macs with Apple Silicon and Intel-based Macs, so use the steps that match the Mac you are starting.

Macs with Apple Silicon:

  1. Shut down the Mac completely
  2. Connect the bootable USB drive directly to the Mac, not through a hub
  3. Press and hold the power button until "Loading startup options" appears
  4. Select your bootable USB installer from the options
  5. Click Continue to proceed

Intel-based Macs:

  1. Shut down the Mac completely, then connect the bootable USB drive directly
  2. Turn on the Mac and immediately hold the Option key
  3. Release the key when you see your bootable volumes
  4. Select the USB installer, then click the onscreen arrow or press Return

The Mac starts into the macOS installer. Choose "Install macOS" from the Utilities window 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.

Fix common bootable USB installer problems

The createinstallmedia tool reports problems as text messages in the terminal application. Here are the most common failures and the fix for each.

Fix "command not found"

The command cannot find the tool inside the installer app. Confirm the full installer app is in your Applications folder, and that the name in your command matches it exactly, including the version name. Also confirm the command ends with Contents/Resources/createinstallmedia. If you only downloaded InstallAssistant.pkg, open the package first, because the package puts the installer app in place.

Fix "not a valid volume mount point"

The path after --volume does not match a connected drive. Open a Finder window and check the drive's exact name, then make the path match it. Put quotes around the path if the name contains spaces. A drive that was ejected or never mounted has no path at all, so reconnect it.

Fix "APFS disks may not be used as bootable install media"

The drive is formatted as APFS, which the tool rejects. Erase the drive again in Disk Utility, and this time set the format to "Mac OS Extended (Journaled)" as shown above.

Fix "Operation not permitted"

macOS is blocking the terminal application from reading protected locations. Open System Settings > Privacy & Security > Full Disk Access, turn on your terminal application, and run the command again.

Fix a stalled createinstallmedia command

The tool can look frozen because it shows no progress bar during the long copy phase. Silence does not mean failure. Open Activity Monitor and click the Disk tab to confirm data is still being written. If the process truly never finishes, try a different USB drive, because worn-out or slow flash drives cause many failures.

Fix an invalid or damaged installer app

If the tool says the installer app is not valid, delete the app from your Applications folder and download it again. A download that was interrupted, or an installer copied from another Mac, often fails this check.

Fix a USB installer that does not appear at startup

Connect the drive directly to the Mac, not through a hub, and confirm the Mac can run the macOS version on the installer. On an Intel-based Mac with the Apple T2 Security Chip, the default security setting blocks starting from external drives. Restart into macOS Recovery, open Startup Security Utility, and allow booting from external or removable media.

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.