The error: A macOS update repeatedly fails to install, showing the same generic error ("An error occurred installing the selected updates" or similar) regardless of how many times it's retried.
Environment: Any current macOS version.
Why this happens: A repeatable identical failure, rather than an intermittent one, usually points to either a corrupted downloaded update package, insufficient free disk space for the installer to actually complete its work, or (for managed/MDM-enrolled Macs specifically) a configuration profile actively restricting the update from completing.
The fix:
- Confirm genuinely adequate free disk space — major macOS updates need significantly more headroom than their download size alone suggests, to accommodate the installer's own temporary files.
- Delete the cached update installer and force a fresh download: for App Store-delivered updates, this is typically in
/Library/Updates; for full installer apps, just delete the installer from Applications and re-download. - Check Console.app for the specific installer log around the failure time — the on-screen error is generic, but the underlying installer log almost always names the actual blocking issue.
- On an MDM-managed Mac, check with whoever manages the device fleet for a software update deferral or restriction policy before assuming it's a local fault at all.
One thing worth knowing: on a managed fleet, this is worth checking the MDM policy for before spending time on local troubleshooting — a deferral policy silently blocking an update looks identical to a genuine local failure from the end user's side.