Is it a disaster if my Mac doesn't finish installing an update? Will anything be lost? What should I do?

As you use Mac OS X, you'll find updates to both apps, and the operating system, routinely crop up. Sooner or later you'll find an update gets interrupted.

The first time your Mac doesn't finish installing an update can be a bit harrowing. After all, you think that interrupting a Mac when it's updating would be a disaster. Fortunately, it's pretty easy to get your Mac to finish installing its update.

See also:

Run El Capitan on your Mac at the same time as Yosemite

How to update to the new Mac software, how to download OS X El Capitan

Run El Capitan on a hard drive attached to your Mac

How to force quit on a Mac, close programs that aren't responding

What not to do if your Mac doesn't finish installing an update

Don't panic! If you're using your Mac and updating either software, or OS X, and the process is interrupted (say due to a power shortcut), then it's usually okay.

We've pulled the plug on a Mac several times during a Software Update (even during the upgrade from Yosemite to El Capitan), and it bounces back just fine and completes the installation. Mac OS X is an extremely robust operating system, so the chances of the installation going wrong are slim.

In either case start your Mac back up and see what happens. If you were installing an app from the App Store, then open the App Store and click Updates. You should find that the update/installation process carries on. If you were installing an OS X update, you should find Mac OS X picks back up where it left off and continues.

What to do if your Mac doesn't finish installing OS X

The solution to a frozen update is easier than you'd ever imagine: just wait it out.

Sometimes people who are updating OS X Yosemite (or moving from OS X Yosemite to El Capitan) find that progress seems to halt during the update. Users report being faced with a stuck progress bar or, even worse, with a blank grey screen.

Sometimes it takes a long time to update the operating system, and the progress bar in installation is at best a guess. In some cases OS X is taking a while to install one file behind the scenes, in others it's busy but the progress bar seems still.

How to tell if your Mac is still installing OS X

OS X install log

Just because the progress bar hasn't moved for a while, doesn't mean that OS X has stopped doing things. There is still installation taking place in the background.

Press Command + L. This brings up more information, such as the amount of time waiting to install. This is easier to view than the progress bar and may give you a better indication of the amount of time left.

How to speed up the OS X installation

The fact that some people suffer from very slow installations, updates, and migrations when installing OS X is good knowledge to have in advance. There are several reasons why OS X may be taking a long time to install, but usually it's because you don't have much free disk space.

When OS X has limited disk space free (typically less than 10GB), it struggles with installation. It may also run more slowly during use. Some users have reported updates taking up to 16 hours, so we'd just leave it overnight and see what happens.

This advice may be of little comfort if you're already watching a progress bar crawl across the screen. In future be sure to check the amount of free disk space you have left, and clear out some files prior to performing a system update.

What to do if you're positive OS X hasn't finished installing the update

We can't stress enough that you should wait before deciding that OS X isn't finishing your update. It can sometimes just take a while. But if you're sure that OS X has frozen during an update, there are some steps you can take.

  1. Press Command + L to bring up the Log. Double-check that files are not being installed.
  2. Hold down the power button to shut off the Mac.
  3. Press the power button to start up the Mac.
  4. Wait again to see if the bar progresses. Press Command + L to check the Log screen and ensure files are being installed.
  5. If that doesn't work, hold the power button to force the Mac to switch off.
  6. Press the power button and hold down the Shift key. See if the Mac will start up in Safe Mode. Open App Store and update your apps while in Safe mode. Reboot.
  7. If Safe Mode doesn't work, restart the Mac and hold down Command, Option, P and R. This will reset the NVRAM. Wait until the computer restart and wait to see if it starts updating.

As a final measure, restart the Mac and hold down Command + R to enter recovery mode. This enables you to start the installation process again from scratch.