Preparing to Update
For Mac Computers – Laptops and Desktops
Your Mac should be properly prepared before installing or running any System Update on it.
OS Upgrades — even small system updates — cause the rewriting or overwriting of portions of the code which runs your Mac. A glitch during the software download, including flaky network connections or power fluctuations, can result in a computer which no longer works as expected. Sometimes they won't even reboot.
And sometimes the Software Update itself is so buggy that Apple withdraws it, trying to quickly replace it with a fixed version after it's been installed on enough Macs to reveal the glitch. It has happened.
Properly preparing for the update process can avoid some problems while keeping you prepared to recover your Mac so you can use it fully once again in case of disaster.
The Checklist — in order, please
- Backup!
Back up your computer. Ideally you should make a bootable clone so your Mac can be restarted in original pre-update working order from that backup disk in an emergency. - Unmount then disconnect your backup drive(s). You don't want them accidentally affected by an update.
- Check Available Free Space
To be safe, you should have at least several times as much free space on your startup disk as the updater says it will require. This allows the software to download, then to uncompress files it needs to use, and then to rewrite parts of the operating system before removing older versions. If an update says it will require 3 Gigs of disk space, make sure you have more than 10 Gigs free before proceeding to install the update. (In practice, you also should have at least 20% of your internal drive as free space for the efficient running of your Mac.) If you are short of space, use About This Mac > Storage (tab) > Manage (button) to locate and remove anything you don't still need. - Pick Your Time
Do not start updates during "prime time" when all of your neighbors are using broadband in your area for streaming TV. A slow internet connection means a longer and riskier download of your updates. You also need to allow lots of time for the Update to run after the download (see Do Not Interrupt, below). - Check Power Settings
Be sure your computer is plugged in, not running on battery power even if fully charged. Go to System Preferences > Energy Saver and disable Sleep for both the Disk and the Screen while powered. You should also disable any timed screen saver. It can be useful to see that your system is busy working during the update process. - Quit All Applications
You don't want any apps running during an upgrade. - Restart the Computer
This loads all current system software into the running processes afresh. This can be especially important if you tend to Sleep your computer and it hasn't been rebooted in days. Glitches happen while computers are running, and you don't want any problems in place during an upgrade. - Open System Preferences > Software Update
There you will see not only what update is waiting, but if there is more than one update, you can click the list to see the available items. This will usually tell you which of them will require a Restart during the installation. - Selecting Installation Items
If there are multiple items, uncheck any that require a restart, and then run the non-restarting updates first. After those have run, go back and run those requiring a Restart. Restarts tend to increase both the time required and potential problems during updates. - Restart When Prompted
There is no reason to wait for any countdown to run before restarting, which can be lengthy process. A full OS Upgrade may require several Gigs of download and take an hour or more to install. The Restart process itself may appear to stall for most of an hour without even showing a progress bar as the system rewrites that OS extensively. - Do Not Interrupt!
Your computer is rewriting its operating system, and if you force restart it or use the Power button to interrupt the installation, don't count on that disk being able to boot your computer later. Let the update do it's job. I have heard reports from techies who have had to let system updates run overnight, taking many hours. My own experience has never run over 3 hours, usually less than 1 hour, but do not start any update on a tight schedule. Plan to let your computer do it's own thing without needing to use it. - Success
Eventually your computer will finishing restarting, although it may appear to start over multiple times during the installation process. In fact, any progress bars which might appear (much of the time they don't) may vanish and then restart again. You'll know it's done when you see the login screen. Then login and see About This Mac in the Apple Menu to check the new version information. - Or Failure
If you've let your update run overnight and the computer is not running the next morning, try restarting it. That may kick back into it's Restart/installation mode if it's not done yet (let it run), or you may see the login screen if it completed. However, sometimes we see a disk error message — a question mark or an unknown disk image. If you have a disk error message, something went so wrong during the update that you may need to boot from your backup. This is rare, but most of the techies I know, including me, have experienced it. It's the reason we all have Backups. (Restoring from a Backup is a separate topic.) - Recovery
We have added a Recovery Webpage with information about how to get a "bricked" Apple computing device restarted. If you have followed the preparatory checklist above before updating, you will have the necessary backups to get up and running after a Recovery process.
This checklist will help minimize the risk of something going wrong.
Updated February 13, 2024