When you start up your Mac, OS X will display a progress indicator on a background with an Apple symbol, right before loading the OS X interface. In versions of OS X prior to Yosemite this was a spinning wheel, and in Yosemite it is an iOS-like progress bar. This indicator should only display for a few moments before you see your login screen; however, if something goes wrong during startup then you might see your Mac pause either for a long time or indefinitely at this loading point.
If this happens, then the first step is to try rebooting with the Shift key held down at the startup chimes, to load your Mac in Safe Mode. If this works, then you need to test your Mac’s software setup by updating third-party drivers, checking any attached hardware devices, or even reinstalling OS X (see below, or see this article).
Unfortunately, in some instances this issue will require you format your drive, so hopefully you have a recent and full backup of your data that you can restore. To check your drive’s formatting when your Mac cannot boot fully, you have two approaches: use another Mac, or use your Mac’s built-in recovery options.
Using Built-In Recovery Options
Since it is the most convenient, using built-in options for recovery are the first to try; however, there may be times when OS X will not boot to the recovery partition, in which case alternative approaches will need to be used:
- Reboot your Mac and hold Command-R at startup to enter Recovery Mode.
- Open Disk Utility at the OS X Tools window.
- Select your boot drive and boot disk on the sidebar.
- Click Disk Utility’s “Repair Disk” button in the First Aid tab.
After performing these routines to fix your drive’s partition scheme and formatting, use Disk Utility to perform a permissions fix on your boot volume (this is in the same First Aid tab). Then shut down your Mac (do not reboot it), and perform an SMC reset (see here) and PRAM reset (see here) for good measure.
Using Another Mac
This approach is likely more thorough, since you can use any disk management tools on another Mac (third-party ones included) to help address the problem at hand:
- Reboot your Mac and hold the T key down when you hear the boot chimes to get to Target Disk mode.
- Attach your Mac to another one using a FireWire or Thunderbolt cable.
- Open Disk Utility on your second Mac.
- Hold the Command key and click both the boot volume and drive device on your first Mac to select them.
- Click Disk Utility’s “Repair Disk” button in the First Aid tab.
If you have third-party utilities like DiskWarrior or DriveGenius, then you can use these to check your drive’s partition health and volume formatting, and similarly repair any problems you find.
Using Another Hard Drive
If you have a spare USB, Firewire, or Thunderbolt hard drive available, then you can also use this to hopefully fix the problem at hand, by first installing a fresh copy of OS X to the drive, and then booting off of it to perform the repair on your Mac’s internal drive:
- Boot your Mac into Recovery Mode by holding Command-R at the boot chimes (hold Option-Command-R to load Internet Recovery, if needed).
- Open Disk Utility at the OS X Tools menu, and select your external drive device (not the drive itself).
- Use the Partition tab that appears, and choose “1 Partition” from the drop-down menu, followed by selecting GUID as the partition scheme from the Options button, and then clicking Apply to format the drive.
- Quit Disk Utility and then select the option to install OS X.
- Follow the on-screen instructions to install OS X, and be sure you select your external drive as the destination.
With this done, your Mac will now boot to this external drive, where you will see your internal one appear as a secondary volume. You can now install third-party disk utilities, and/or use Apple’s Disk Utility program to attempt a repair on your drive.
What Next? Reinstallation!
Following this, try booting your Mac normally, and your OS X should now load properly; however, if not, then your next step is to attempt an OS X reinstallation. There are a couple of approaches here: reinstalling OS X over your current OS installation, and performing a clean OS installation.
For the first option, you simply need to reboot your Mac into Recovery Mode, and then run the OS X installation tool. This routine will not touch your personal data and account settings, and will simply replace all of your operating system files to ensure they are set up properly. If this does not work, or cannot be done, then your next option is to perform a clean install. Hopefully you have a full and recent backup of your files at this point, because doing this will erase all files on your hard drive. If you do not have a backup, you can at least try using Target Disk mode to copy your user account folder from your old hard drive to another computer:
- Boot to Target Disk mode and attach your Mac to another one.
- Go to the Users folder on the Target Disk drive.
- Copy all folders from this location to another backup drive (note this may take some time to complete).
Note that this same routine for backing up your data can be done if you install OS X to an external drive. Once you have booted off of it, you can then copy the contents of the Users directory to the external boot drive (or to another USB or Firewire drive of your choosing) before restarting and performing the reinstallation of OS X.
Once your data is secured, perform the following steps to erase your Mac’s boot drive and reinstall OS X:
- Restart your Mac in Internet Recovery Mode by holding Option-Command-R at startup.
- Open Disk Utility at the OS X Tools panel.
- Select your boot drive device in the sidebar.
- Go to the Partition tab that appears, and then choose “1 Partition” from the drop-down menu.
- Name the drive, and then click Apply to format it.
- Quit Disk Utility when formatting is complete.
At this point, you can choose the option to restore from a Time Machine backup, if you have one, or if not, then use the Install OS X option to install a fresh copy of OS X from scratch.
DiskWarrior or DriveGenius? In my experience with hundreds of Macs:
BEST is DiskWarrior.
LESS USEFUL are TechTool Pro & [DiskTools Pro (80 USD) ≈ SpeedTools Utilities Pro (30 USD)].
USELESS are Drive Genius & diglloydTools.
At one time I would have agreed with you about DiskWarrior. However, in the last few months I’ve encountered problems that DiskWarrior 4.x could not solve, rendering it unable to replace a disk’s directory. I ran TechTool Pro 7 on the same drive and partitions and it did fix the problem(s). When I used DiskWarrior again on the same drives it ran cleanly. I recently upgraded to DiskWarrior 5, but it’s too soon to tell if it will have the same issues. I suspect not, but time will tell. The upshot is that if you are serious about Mac maintenance it’s a good idea to have more than one heavy duty repair utility on hand.
By the way, Drive Genius has also had a substantial upgrade just this week. I’ve used it a few times to learn the new interface, but have not tested it extensively. It has an ancillary function called Drive Pulse which I’ve found throws up frequent false positives so I’ve turned it off.
Max, I ran Disk Warrior 4 to fix a corrupted file system due to improper shutdown on OS X 10.6 , it recovered the file system, but a few weeks later it did it again, and again disk warrior fixed the issue, but stated that I should back up, and reformat the partition, which I did, and have seen the problem since doing so.
That is why an application like the great Conflict Catcher by Casady & Greene would be great also for Mac with OS X
Don’t you think if it were possible to build a Conflict Catcher-like app for OS X, someone would have done it by now?
Just yesterday my 2014 27″ iMac shut down when I connected an additional external hard drive and refused to start up. I unplugged it to reset the SMC (but was too impatient to disconnect peripherals so it may not have worked properly); then I reset the PRAM and this did the trick, thankfully. My iMac has had problems before with external drives. Apparently its power settings are rather fragile.
Guess nobody knows whats happening with mail then?
all my emails are just disappearing and re appearing as they see fit. tried things suggested in earlier posts but no success. I have to shut down mail and re open it on a very regular basis just to see who’s mailed me, bit of a pain running a business that way I imagine. Bring back Apple of the past when things just worked. NOT HAPPY