macOS Update Error -1 — Installation Failed Fix

What Does This Error Mean?

macOS Update Error -1 is a generic failure code that appears when the Software Update process hits an unexpected problem. It typically means the update download was interrupted, the installer is corrupted, or your Mac does not have enough free disk space to complete the installation. Clearing the cached download and retrying usually fixes it.

Affected Models

MacBook Air
MacBook Pro
iMac
Mac Mini
Mac Studio

Common Causes

The downloaded update file is corrupted or incomplete due to a network interruption
Not enough free disk space to extract and install the update
The Mac was on battery and went to sleep mid-download
A firewall or security software blocked part of the update download
The Software Update system cache is in a bad state

How to Fix It

Plug in your Mac and retry. If you are on a MacBook, connect the power adapter. Updates require the Mac to stay on and connected throughout the process.

macOS pauses downloads when on battery in some configurations. Being plugged in ensures the download completes without interruption.
Free up disk space. Go to Apple menu > About This Mac > More Info > Storage. Make sure you have at least 25 GB free. Delete large files or empty the Trash to make room.

macOS needs free space for both the downloaded installer file and the working space the installer needs during installation.
Delete the cached update. Open Terminal (Applications > Utilities) and type: sudo rm -rf /Library/Updates/* then press Enter. Enter your password, restart your Mac, then try updating again.

This removes any partially downloaded update files. macOS will re-download a fresh copy.
Try Software Update from System Settings. Go to System Settings > General > Software Update. Sometimes using the System Settings route works when the notification-based update does not.

There are two ways to trigger a macOS update — via a notification and via System Settings. They use slightly different processes.
Download the update manually from Apple. Visit support.apple.com/downloads and search for your macOS version. Download and run the full installer directly.

Manual installers bypass the Software Update system and often work when the built-in updater fails.

When to Call a Professional

Error -1 is almost always fixable at home. If the error keeps happening across multiple update attempts and different networks, visit an Apple Store. They can run diagnostics to rule out a hardware problem affecting the update process.

Frequently Asked Questions

Is it safe to keep using macOS if I cannot install an update?

Yes for a short time, but updates include important security patches. The longer you stay on an old version, the more security vulnerabilities your Mac is exposed to. Try to get the update installed within a week or two.

Can a slow internet connection cause Error -1?

Yes — a slow or unstable connection can interrupt the download and leave a corrupted file. If your internet is very slow, consider downloading the update overnight or using a faster network. The macOS installer can be 3 to 12 GB depending on the version.

My Mac says 'Update downloaded. Restart to install' but after restarting I get Error -1. What now?

This means the download succeeded but the installation itself failed. Delete the cached update files using Terminal (Step 3), restart, and try downloading again. If the problem persists, try downloading the full installer from Apple's website.