For some Mac users, downloading a macOS installer (whether a new macOS version or the latest updates) on an external drive can be a convenient way to create a portable system, run multiple systems, or perform troubleshooting.
As we know, just following the steps to install macOS on an external drive or create a macOS bootable installer is enough. However, several users encounter a roadblock when they can't install macOS updates on the external drive.
I am stuck on macOS Ventura on a Samsung SSD, and macOS updates appear successful but fail to install on the drive. How can I deal with the issue? -Apple.Community
I installed macOS Sequoia on my external NVMe SSD which is used as my startup disk. But after I tried to apply the latest update from macOS 15.3 to 15.4 on my external SSD, it couldn't finish. Any fix? The update worked fine on my internal SSD. -discussion.apple.com
If you are facing this issue, you're not alone. We will walk you through why this happens and how to fix it, so you can successfully update macOS on your external drive without hassle.
How to fix the issue that I can't install macOS updates on external SSD?
Follow these step-by-step solutions to identify and resolve the issue that you can't install macOS updates on external drives.
# 1 Make sure the drive is set as the Startup disk
If you're trying to update a macOS installation on an external drive, your Mac needs to boot from it first.
- Apple menu > System Settings > General > Startup Disk.
- Select your external macOS volume.
- Click Restart.
Booting from the correct disk ensures the system targets the right volume during updates.
# 2 Ensure sufficient free space
macOS updates usually require 20-30 GB of free space on the target drive. If your external disk (set as the start-up disk) is nearly full, the update will fail. Or you find it too slow to install the updates on the drive, it due to the slow performance of your Mac's hard drive.
Removing unwanted files from both the startup disk and external drives will enhance the success rate, especially if you can install the updates before, but now you can't. iBoysoft DiskGeeker for Mac is a macOS cleaner for you to clean up junk data from startup drives.
Its AI analysis can scan disk space visually, and helps you to know whether the folder/file can be deleted directly. And the unnecessary will be deleted forever, unable to be recovered.
Let's clear more space for the startup disk with iBoysoft DiskGeeker for Mac:
- Free download, open, and install iBoysoft DiskGeeker for Mac.
- Select your drive on the left.
- Click Space Analyze from the right toolbar.
- After scanning, preview the files.
(You can move your cursor on the specific one to know whether it can be removed or not.) - Drag and drop the junk files to the circle and click Delete to permanently remove them.
This tool simplifies space management and helps ensure your startup external drive is ready for macOS updates.
# 3 Verify drive format and partition scheme
macOS requires specific formats for installations and updates, so please check it in Disk Utility.
- Finder > Applications > Utilities > Disk Utility.
- Select your external drive and click Erase at the top. (Remember to do a backup first!)
- Choose the Format: APFS (for macOS High Sierra or later); Scheme: GUID Partition Map, then click Erase.
Note that: Avoid using Mac OS Extended (Journaled), which may cause update failures on newer macOS versions.
# 4 Check drive permissions
Incorrect permissions can block macOS from writing update files, like this issue, you are unable to update the operating system on an external SSD.
- Open Finder, right-click the external drive, and select Get Info.
- Scroll to the bottom and ensure Ignore ownership on this volume is unchecked.
- Click the lock icon to make changes and enter your password if needed.
If you succeed here, please share our post.
# 5 Update using macOS installer app
Instead of using System Settings > Software Update, you can download the full macOS installer from the official website or App Store.
- Visit Apple's macOS download page or search in the App Store.
- Download the installer.
- Run the installer and choose the external drive as the destination.
- Open Apple menu > System Settings > General > Software Update, find and click Update Now. (The version is the latest one.)
# 6 Run First Aid in Disk Utility
If there are disk errors, the update might fail. Use First Aid to detect and fix issues.
- Finder > Applications > Utilities > Disk Utility.
- Select the external drive on the left.
- Click First Aid > Run > Run and wait for the process to complete.
- If any errors are found and repaired, retry the update.
# 7 Adjust Security Settings
For Apple Silicon Macs or T2 chip Macs, startup security settings may block booting from or updating external drives.
- Restart your Mac into macOS Recovery Mode.
- Click Utilities > Startup Security Utility.
- Select your external disk and set [Secure Boot: Medium or No Security; External Boot: Allow booting from external media].
After adjusting, restart your Mac and attempt the update again. For Intel Macs, ensure no firmware passwords block external booting.
# 8 Disable System Integrity Protection (SIP)
SIP prevents certain modifications to macOS, including some that updates may require.
- Restart your Mac and hold Command + R to enter macOS Recovery.
- In the menu bar, go to Utilities > Terminal. Enter: csrutil disable and press the Enter key.
- Restart your Mac
Warning: Disabling SIP reduces system security. Re-enable it after the update by running csrutil enable in Recovery mode.
Being unable to install macOS updates on an external drive can be frustrating, but it's often due to: Insufficient storage space, incorrect drive format or partition scheme, startup disk not correctly set, inadequate security settings, SIP blocking, corrupted disk or update file, and so on...
Tools like iBoysoft DiskGeeker for Mac can help ensure your drive has enough space, and following the steps above will resolve most installation issues.
With the right setup, you can keep your external macOS installation secure, updated, and ready for future work. Please share our post if you feel it is useful.