How to create a bootable macOS installer on a USB drive and reinstall macOS
Creating a bootable macOS installer on a USB drive gives you a reliable way to install or reinstall macOS, recover a Mac, or install the OS on multiple machines without re-downloading each time. This guide walks through preparing a USB stick, downloading the installer, making the bootable media, and reinstalling macOS step by step. Follow the steps carefully and allow 30–90 minutes depending on download speed and Mac model.
Step 1: Check Mac compatibility and backup
Confirm the macOS version you intend to install supports your Mac model by checking Apple's compatibility list or system model year. Create a full backup with Time Machine or clone your drive using Carbon Copy Cloner; backups typically take 15–60 minutes depending on data size and connection speed. Backing up prevents data loss if you erase the drive during reinstall.
[Illustration: Mac screen showing About This Mac and an external drive with backup progress]
Step 2: Get a USB drive of at least 16GB
Use a USB flash drive or SSD with at least 16 GB free and preferably USB 3.0 for faster write speeds; label it for easy identification. Copy any files off it first because the process will erase the entire drive, and test it in a spare port to ensure it mounts reliably for about 1–2 minutes.
[Illustration: USB flash drive labeled 'macOS Installer' beside MacBook with Finder window open]
Step 3: Download macOS installer from App Store or Settings
On a compatible Mac, open the App Store or System Settings > Software Update to download the full macOS installer; expect 5–20 GB and 10–60 minutes depending on network speed. Do not run the installer when it finishes—quit it so the installer app remains in the Applications folder for making the USB media.
[Illustration: Mac App Store showing macOS installer download progress on screen]
Step 4: Format the USB drive as macOS Extended (Journaled) or APFS
Open Disk Utility, select the USB drive (not a partition), choose Erase, set the format to APFS for macOS 10.13+ or Mac OS Extended (Journaled) for older installers, and use GUID Partition Map as the scheme; this takes 1–2 minutes. Correct formatting ensures the createinstallmedia tool can write a bootable volume.
[Illustration: Disk Utility window with erase dialog and format options displayed]
Step 5: Create the bootable installer with Terminal
Open Terminal and run the createinstallmedia command included in the installer app; for example, paste: sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia --volume /Volumes/YourUSB. Enter your admin password and confirm when prompted; the process typically takes 10–30 minutes depending on drive speed. Wait for the 'Install media now available' message before ejecting.
[Illustration: Terminal window showing createinstallmedia command and progress text on screen]
Step 6: Boot the Mac from the USB installer
Shut down the Mac, plug in the USB drive, then hold Option (Alt) while powering on to access the Startup Manager. Select the USB installer (usually named 'Install macOS') and press Return; boot time to the installer UI is usually 30–120 seconds. If using Apple silicon, hold the power button until startup options appear, then choose the USB volume.
[Illustration: Startup Manager screen showing bootable volumes including a USB installer]
Step 7: Erase or reinstall macOS from Utilities
In the installer, choose Disk Utility to erase the internal drive if doing a clean install: select the internal drive, Erase with APFS and GUID, then quit Disk Utility. Choose Reinstall macOS, follow on-screen prompts, select the target drive, and allow 20–60 minutes for installation and automatic restarts. After setup, restore your files from the Time Machine backup or copy data manually.
[Illustration: Erase or reinstall macOS from Utilities]
- Keep the Mac connected to power during download and install to avoid interruptions.
- Use a high-quality USB 3.0 drive or external SSD for faster create and install times; this can cut write time by 50% or more.
- If createinstallmedia returns 'not found', ensure the installer is in the /Applications folder and the path matches exactly.
- Label the USB drive with a unique name before creating the installer to avoid selecting the wrong volume in Terminal.
- If you need to install on multiple Macs, verify each machine's firmware and apply macOS combo updates after installing to reduce compatibility issues.
- Test the bootable USB on one Mac before using it for critical reinstall so you can confirm it works and troubleshoot if needed.
- Keep the macOS installer app after creating the USB—having it saved avoids re-downloading large files later.
- Creating the bootable USB erases all data on that drive; double-check the selected USB volume to avoid accidental data loss.
- Erasing the internal drive will remove all user files and applications; confirm your backup is complete and restorable before proceeding.
- Do not interrupt the macOS installer once it starts writing to the internal drive or the system may become unbootable; allow 20–90 minutes for the process to finish.
- Third-party tools that promise to create installers may be insecure; prefer Apple's official createinstallmedia command or Disk Utility for best results.
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