You can create a bootable macOS installer drive with a USB flash drive and Apple’s built-in createinstallmedia command. Download the macOS installer from Apple, erase and format a compatible USB drive in Disk Utility, then run the command for that installer in Terminal.
A bootable installer can help you install macOS on a compatible Mac, install macOS on multiple Macs without downloading it repeatedly, or troubleshoot a Mac that will not start normally.
Quick Answer
To create a bootable macOS USB installer:
- Download the full macOS installer from Apple.
- Connect a USB flash drive with at least 16GB of available capacity. A larger drive may be needed for some installers.
- Use Disk Utility to erase the drive as Mac OS Extended (Journaled) with the GUID Partition Map scheme.
- Open Terminal and run the matching
createinstallmediacommand. - Enter your administrator password when prompted.
- Start the target Mac from the installer drive.
Warning: Creating the installer erases the USB drive completely. Copy any files you want to keep to another location before continuing.
What You Need
Before you begin, prepare the following:
- A compatible Mac
- An internet connection
- A USB flash drive or external drive with enough storage
- The full macOS installer app
- An administrator account on the Mac
- A backup of important data
The USB drive does not need to be new, but everything on it will be erased. Do not use a drive containing files you need.
Choose the right installer
Download the installer for the macOS version you want to use, and make sure it is compatible with the Mac where you plan to install it. A bootable installer cannot make an incompatible Mac run an unsupported version of macOS.
Apple commonly provides macOS installers through the App Store or through support pages that link to the correct App Store download. After downloading, the installer usually appears in the Applications folder with a name similar to:
Install macOS [Name].app
Do not start the installation if you only want to create the USB drive. If the installer opens automatically, quit it with Install macOS [Name] > Quit Install macOS or press Command-Q.
If the installer is not in the Applications folder, search for it in Finder. The createinstallmedia command depends on the installer app being complete and stored in its expected location.
Prepare the USB Drive in Disk Utility
Warning: The following steps permanently erase the selected drive. Carefully confirm that you have selected the USB drive, not your Mac’s internal storage.
- Connect the USB drive to your Mac.
- Open Disk Utility. You can find it in Applications > Utilities or by searching with Spotlight.
- In the menu bar, select View > Show All Devices.
- In the sidebar, select the physical USB device at the top level, not only a volume indented beneath it.
- Click Erase.
- Enter a temporary name, such as
MyVolume. - Set Format to Mac OS Extended (Journaled).
- Set Scheme to GUID Partition Map.
- Click Erase, then click Done when the process finishes.
- Quit Disk Utility.
The temporary volume name matters because it appears in the Terminal command. Using a simple name such as MyVolume reduces the chance of typing errors.
If Scheme is not available, you may have selected a volume instead of the physical device. Select the device at the top of the sidebar and try again.
Create the Bootable macOS USB in Terminal
Apple includes createinstallmedia inside the macOS installer app. This tool copies the installer files to the USB drive and configures the drive to start the macOS installation environment.
Warning: The command below erases the volume named MyVolume. If your USB drive has a different name, replace MyVolume in the command with the exact name of your drive. Do not run the command until you have confirmed the drive name and backed up its contents.
1. Open Terminal
Open Terminal from Applications > Utilities, or search for it with Spotlight.
2. Run the matching command
Use the command that matches the installer app in your Applications folder. Replace [Name] with the exact name of the macOS release, and replace MyVolume if you used a different USB volume name.
sudo "/Applications/Install macOS [Name].app/Contents/Resources/createinstallmedia" --volume "/Volumes/MyVolume"
For example, if the installer is named Install macOS Example.app, the command would be:
sudo "/Applications/Install macOS Example.app/Contents/Resources/createinstallmedia" --volume "/Volumes/MyVolume"
The quotation marks are important when the installer name or volume name contains spaces.
3. Confirm the erase operation
Terminal may ask you to confirm that the volume should be erased. Type Y and press Return only after checking that the displayed volume is the USB drive.
4. Enter your administrator password
When Terminal requests your password, type the password for an administrator account and press Return. Nothing appears on screen while you type—not even dots. This is normal.
5. Wait for the process to finish
The command erases the USB volume, copies the installer, and makes the drive bootable. The process can take some time, especially with a slower USB drive.
Do not disconnect the drive or close Terminal while the command is running. When it finishes, Terminal should report that the install media is available at the selected volume.
What the command changes
The command has three important parts:
sudoruns the tool with administrator privileges.- The path ending in
createinstallmediaselects Apple’s installer-creation utility inside the macOS installer app. --volume "/Volumes/MyVolume"identifies the USB volume that will be erased and used as the installer.
The command does not erase your Mac’s internal drive unless you accidentally select an internal volume as the target. Always verify the volume path before confirming.
Start a Mac From the Installer Drive
After creating the drive, you can use it to install macOS or access installation tools. The startup procedure depends on whether the Mac has Apple silicon or an Intel processor.
Apple silicon Mac
Apple silicon Macs include models with Apple-designed processors. To start one from a bootable installer:
- Shut down the Mac.
- Connect the bootable USB installer.
- Press and hold the power button.
- Keep holding the button until Loading startup options appears.
- When the startup options screen appears, select the installer volume.
- Click Continue.
If prompted, choose a user account and enter its password. The macOS Recovery or installer environment should then open.
Intel-based Mac
For an Intel-based Mac:
- Shut down the Mac.
- Connect the bootable USB installer.
- Turn on the Mac and immediately hold the Option key.
- Release the key when the startup manager appears.
- Select the installer volume.
- Click the arrow or press Return.
On some Macs with a T2 Security Chip, external startup may be restricted by the Startup Security Utility. If the installer does not appear, you may need to allow external or removable media startup from macOS Recovery. Security settings vary by Mac, so change them only when necessary and restore stricter settings afterward if appropriate.
Install macOS from the drive
When the installer environment opens:
- Select Install macOS.
- Click Continue.
- Follow the onscreen instructions.
If you want a clean installation, use Disk Utility from the installer’s Utilities menu to erase the Mac’s internal storage first.
Warning: Erasing the internal drive permanently removes the Mac’s files, apps, accounts, and settings. Make a current backup before choosing an erase option. A clean installation is not required for a normal macOS upgrade.
Alternative Method: Use the Installer Without a USB Drive
A bootable USB is useful when you need offline installation media or a separate startup environment, but it is not always necessary.
If the Mac starts normally, you can usually install macOS directly from the installer app:
- Download the full installer.
- Open it from the Applications folder.
- Follow the onscreen instructions.
You can also use macOS Recovery to reinstall macOS without creating a USB installer. On an Apple silicon Mac, hold the power button while starting up until startup options appear, then choose Options. On an Intel-based Mac, start the Mac while holding Command-R.
Recovery may download installation files from Apple, so it requires a working internet connection. It is often simpler than creating a USB drive, while a bootable installer is more useful when internet access is limited or several Macs need the same installer.
Troubleshooting
The installer app is missing
Check the Applications folder and confirm that the full installer app downloaded successfully. A small installation helper or an incomplete download will not contain the required createinstallmedia tool.
If the installer opened and was deleted after quitting, download it again from Apple.
Terminal says the command cannot be found
Check all of the following:
- The installer app is in
/Applications. - The installer name in the command matches the app name exactly.
- The command includes
Contents/Resources/createinstallmedia. - The quotation marks surround paths containing spaces.
You can type the beginning of a path in Terminal and drag the installer app from Finder into the Terminal window to insert its exact path.
Terminal says the volume cannot be found
The USB drive may have a different name than the command expects. In Finder, check the name shown in the sidebar, or enter this command:
ls /Volumes
This lists mounted volumes. Replace MyVolume with the exact USB volume name in the createinstallmedia command.
If the name contains spaces, keep the path inside quotation marks. For example:
sudo "/Applications/Install macOS [Name].app/Contents/Resources/createinstallmedia" --volume "/Volumes/My USB"
The USB drive does not appear at startup
Try these steps:
- Shut down the Mac completely.
- Reconnect the USB drive directly to the Mac rather than through a hub or adapter.
- Try another USB port.
- Recreate the installer using a different compatible drive.
- On an Intel-based Mac, hold Option immediately after turning on the Mac.
- On an Apple silicon Mac, hold the power button until startup options appear.
On some Intel Macs, review the external startup setting in Startup Security Utility from macOS Recovery.
The Mac says the installer cannot be verified
Confirm that the installer is compatible with the Mac and that the Mac’s date and time are correct. An incorrect system date can interfere with certificate validation. If necessary, connect to the internet and use the installer’s recovery environment to check the date and time before trying again.
The process stops or reports an erase error
The USB drive may be damaged, incorrectly formatted, write-protected, or too small. Reopen Disk Utility, select View > Show All Devices, and erase the physical device using Mac OS Extended (Journaled) and GUID Partition Map.
If the error continues, try another USB drive. Avoid disconnecting the drive while it is being erased or written.
How to safely stop or undo the process
If you have not confirmed the erase prompt, press Control-C in Terminal to cancel the command.
If the command has already erased or started writing to the USB drive, do not interrupt it unless it appears completely unresponsive for an extended period. Interrupting it may leave the drive incomplete, but it does not normally affect the Mac’s internal storage when the correct USB volume was selected.
There is no “undo” command for an erased USB drive. To reuse it as ordinary storage, open Disk Utility, select the physical USB device, click Erase, choose a suitable format such as APFS or ExFAT, choose GUID Partition Map when available, and click Erase. This removes the installer and any remaining data on the USB drive.
Frequently Asked Questions
Can I use any USB flash drive?
Use a reliable USB drive with enough available capacity for the installer. A drive with at least 16GB is commonly sufficient for many installers, but some macOS installers require more space. If the installer creation tool reports that the drive is too small, use a larger drive.
Does creating a bootable installer erase the Mac?
No. The createinstallmedia command is intended to erase the selected target volume, which should be the USB drive. It does not erase the Mac’s internal storage unless you select the wrong target in Disk Utility or Terminal.
Can I store other files on the installer drive?
It is best to use the drive only for the installer. The creation process erases the drive and configures it as startup media. Adding files afterward may reduce available space or interfere with its use.
Can I use the installer on any Mac?
No. The Mac must support the macOS version in the installer. A bootable drive does not bypass hardware compatibility requirements.
Can I create the installer on a Windows PC?
Apple’s createinstallmedia tool runs in macOS and is designed to be used from a Mac. The most reliable approach is to create the installer on a compatible Mac using the official installer app and Terminal.
Will the installer work without an internet connection?
The bootable installer contains the files needed to begin installation, but some Mac models, firmware updates, activation steps, or installation situations may still require internet access. Connect to the internet when possible.
Can I reuse the USB drive afterward?
Yes. Reformat it in Disk Utility. Reformatting erases the installer and all other contents on the drive.
Final Thoughts
A bootable macOS installer is straightforward to create: download the full installer, erase a suitable USB drive, and run Apple’s createinstallmedia command in Terminal. The most important precautions are selecting the correct installer, confirming that the USB drive is the target, and backing up data before erasing any storage. Once created, the drive provides a practical way to install or troubleshoot macOS on compatible Macs.