When you turn on your Mac, it should display a gray screen as it searches for your startup drive. Once the drive is detected, you will see a blue screen as your Mac loads the boot information from your startup drive and then displays the desktop.

That’s the normal chain of events, and something most of us don't even think about. When I start my Mac each morning, I push the power button, then head to the kitchen to make coffee, fully expecting everything to work as it should.

When I get back to my Mac, the desktop is waiting for me; I hardly ever see the gray screen or the blue screen. If either screen is waiting for me, then I know something is wrong. The Mac should always be ready before the coffee.

In this tip, we look at why a Mac may get stuck at the blue screen, and how to fix the problem.

The Mac's Blue Screen of Death

Okay, it's not really the same blue screen of death that strikes fear into the heart of Windows users, but it's not exactly a welcome sight, either.

If your Mac has made it to the blue screen, we can rule out some possible problems right off the bat. To get to the blue screen, your Mac has to power up, run its basic self-test, check to ensure that the expected startup drive is available, and then start to load data from the startup drive. This is where it got stuck, which means your Mac is in pretty good shape overall, but your startup drive may have some problems.

Repairing the Startup Drive

Your startup drive may be suffering from one or more issues, many of which you can fix using Apple's Disk Utility.

You can also use a third-party app, such as Drive Genius, TechTool Pro, or DiskWarrior, to repair drive damage. Because you can't start your Mac up successfully, you'll have to boot from another drive that has a system on it, or from a DVD install disk. If you're using OS X Lion or later, you can boot from the recovery disk; if you're not sure how to do that, you'll find instructions in the guide at the link below.

If you don't have a startup option other than your usual startup drive, you can still try to repair the drive by starting your Mac in single-user mode. This is a special startup environment that allows you to work with your Mac using commands that you type into a Terminal-like display. (Terminal is a text-based app that is included with OS X.) Because single-user mode doesn't require the startup drive to be completely functional, we can use some of the commands to perform drive repairs.

No matter which method you're going to try - another startup drive, a DVD, the recovery disk, or single-user mode - you will find step-by-step instructions in the How Can I Repair My Hard Drive If My Mac Won’t Start? guide.

In most cases, repairing the drive will get your Mac working again, but be aware that a drive that has exhibited this type of problem is likely do it again. Take this as an early warning that your startup drive is having issues, and consider replacing the drive soon. Be proactive and make sure you have backups or clones of your startup drive available.

Fixing Startup Permissions

While repairing the startup drive should solve the blue screen problem for most users, there's another less common drive issue that can cause a Mac to freeze at the blue screen, and that's a startup drive that has its permissions set incorrectly.

This can happen as the result of a power outage or power surge, or turning off your Mac without going through the proper shutdown process. It can also happen to those of us who like to experiment with Terminal commands, and accidentally change the startup drive's permissions to not allow any access. Yes, it is possible to set a drive to deny all access. And if you happen to do that to your startup drive, your Mac won't boot.

We're going to show you two ways to fix a drive that was set to no access. The first method assumes you're able to start your Mac using another startup drive or an install DVD. You can use the second method if you don't have access to another startup device.

How to Change Startup Drive Permissions by Booting From Another Device

1. Boot your Mac from another startup device. You can do this by starting your Mac and holding down the option key. A list of available startup devices will display. Select a device and your Mac will use it to finish booting.
2. Once your Mac displays the desktop, we're ready to correct the permissions problem. Launch Terminal, located in the /Applications/Utilities folder.
3. Enter the following command in Terminal. Note that there are quotes around the startup drive's path name. This is necessary to ensure that if the drive name contains any special characters, including a space, that it will work with the command. Be sure to replace startupdrive with the name of the startup drive that is having problems:

   sudo chown root "/Volumes/startupdrive/"

4. Press enter or return.
5. You will be asked to provide your administrator password. Enter the information and press enter or return.
6. Enter the following command (again, replace startupdrive with the name of your startup drive

   sudo chmod 1775 "/Volumes/startupdrive/"

7. Press enter or return.

Your startup drive should now have the correct permissions and be able to boot your Mac.

How to Change Startup Drive Permissions If You Don't Have Another Startup Device Available

1. If you don't have another startup device to use, you can still change the startup drive's permissions by using the special single-user startup mode.
2. Start your Mac while holding down the command and s keys.
3. Continue to hold both keys down until you see a few lines of scrolling text on your display. It will look like an old-fashioned computer terminal.
4. At the command prompt that appears once the text has stopped scrolling, enter the following:

   mount -uw /

5. Press enter or return. Enter the following text:

   chown root /

6. Press enter or return. Enter the following text:

   chmod 1775 /

7. Press enter or return. Enter the following text:

   Exit

8. Press enter or return.
9. Your Mac will now boot from the startup drive.

If you still have problems, try repairing the startup drive using the methods described earlier in this article.

Reference

chown man page

chmod man page

mount man page

Published: 10/16/2012

Updated: 5/19/2015