If your Mac is having trouble running, one way to figure out what’s wrong is to boot it into Safe Mode, which is a restricted environment that only loads Apple-supplied software for basic functions. To enter Safe Mode, simply restart your Mac while holding down the Shift key; however, in rare circumstances, this will not work, and the machine will either load properly or hang without booting at all.
It’s possible that you won’t be able to boot into Safe Mode because your system is set up with encryption or other security settings that restrict you from doing so, because of peculiarities in how wireless keyboards deliver startup arguments to the system, or because of file system issues.
The Security Settings Can Be Adjusted
The inability to boot into Safe Mode may be due to several security settings in OS X. FileVault or a firmware password will prevent your machine from booting into Safe Mode, even if you’ve disabled the feature. Before entering Safe Mode, these options must be disabled.The firmware password must be disabled using the Firmware Password utility, which is available in the Utilities menu in the OS X installer. The firmware password must be disabled using the Firmware Password utility, which is available in the Utilities menu in the OS X installer. Using the FileVault tab in the Security system options, FileVault can be disabled, however the firmware must be updated. password must be disabled using the Firmware Password utility, which is available in the OS X installer’s Utilities menu (You can get to this in OS X Lion and later by holding Command-R at startup).
Keyboards With No Wires
If you use a wireless keyboard, another possible issue that prevents Safe Mode from operating is that you use a wireless keyboard. While many tutorials recommend holding the Shift key at startup to enter Safe Mode, the system’s Bluetooth controllers will not activate until after the starting chimes have played, so if the key is held before then, the key press will be ignored. Instead, if you have a wireless keyboard, hold down the Shift key after the boot chimes play.
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In addition to checking the battery level of your keyboard, you should also check the timing of the key press.
Errors In The File System
Finally, faults with the file system structure of the boot drive may prohibit you from booting into Safe Mode. The HFS+ file system includes a number of indexing databases that store information about where files are located on the disc as well as numerous properties about them. You’ll find them listed as the Catalog file, Extents file, and Extended Attributes file, among other things, when you conduct a file system check using Disk Utility.
As soon as Safe Mode is activated, a grey progress bar appears to show that the system is performing various maintenance tasks. A filesystem check on a file system’s structure using the utility “fsck hfs” is one of these jobs, however if a problem stops the tool from checking, it may hang, resulting in the system only loading to the grey screen with the Apple and a progress bar below it.
Unfortunately, while the system is just displaying a grey progress bar, it’s difficult to tell if this is the case; however, you may compel the system to show you what’s going on by booting to both Safe and Verbose modes at the same time. To do so, open up the Terminal program and input the command below into the text field. I’ve used “Safe-Verbose” mode in this command, but you may use “Single User” mode instead by replacing the “v” with a “s” (they should be comparable for this purpose):
Reboot the system after running this command, and you’ll see the system load into a text environment with the most recent occurrences at the bottom and the history of events scrolling upward. Look for a function called “fsck_hfs” that the system should load at some time (this should happen quickly, and then pause for a few seconds) while it performs the above-mentioned file system structure tests).This process should only take a few minutes, but if it does not progress after a long time, it is unable to inspect the disc for faults and becomes stuck, resulting in the inability to boot to Safe Mode.
If this is the case, hard-reset the system by pressing and holding the power button, then pressing and holding the Command-Option-P-R keys at startup (immediately after the boot chimes) to restore the system.
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clear the PRAM and allow the system to load normally rather than in Safe-Verbose mode Releasing these keys once the system has completed a full reset and the boot chime has played once more Resolving the issues with the filesystem structure can now solve the problem. While third-party tools such as DiskWarrior have been known to discover and cure faults that Disk Utility cannot, reformatting the hard disc is another option.
First, make sure you have a completely restorable backup of your system, which you can do with Time Machine or a file-level clone of your drive with Carbon Copy Cloner. After that, use Disk Utility to partition and format the disc from the OS X installer (the Recovery HD drive in OS X Lion or later).Choose “1 Partition” from the drop-down option in the Partition tab that appears after selecting the drive device (above the volume names like “Macintosh HD”). After naming the drive and applying the formatting modifications, close Disk Utility and restore your backup to the drive.