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Most of the time, your Mac just works after restarting.

But there will be times when a rogue app, a misbehaving service, outdated caches and other issue will cause your Mac to slow, stop starting up or exhibit other unwanted symptoms. Thankfully, Apple has provided a way to boot OS X in Safe Mode.

Although booting in Safe Mode on a daily basis?or whenever an insignificant problem arises? isn?t recommended, there are definitely instances when starting up in Safe Mode could be your last resort.

If your Mac doesn?t finish starting up?Certain issues might keep your Mac from completely starting up and using Safe Mode can help you resolve them.

If an app is causing issues? An app you recently installed might be the culprit, especially if it came outside the Mac App Store. Starting up in Safe Mode might help isolate the misbehaving app as it prevents certain software from automatically loading or opening.

If your Mac is running slow? Just like Windows, your Mac also creates temporary files and various caches over time which might slow down the overall performance of the operating system and apps. These unnecessary files are safely cleaned from Mac when started in safe Mode.

If your Mac has directory issues?Many, but not all issues with your Mac?s startup disk can be resolved using the built-in Disk Utility application. If you?re plagued with an issue that cannot be reproduced in Safe Mode but appears to be resolved when you start up normally, chances are it was caused by a cache or a directory issue with your startup disk that Safe Mode fixed.

If your startup disk is encrypted with FileVault, you can still hold down the Shift key immediately after powering on your Mac to start up in safe mode. You might be prompted to log in twice as part of this process ? first to unlock the startup disk, and a second time to log into the Finder. You can let go of the Shift key after you see the first login screen.

If an issue doesnt happen when your Mac is started in safe mode, try restarting again without pressing any keys at startup. If the issue appears to be resolved when you start up normally, it was possibly caused by a cache or a directory issue with your startup disk that safe mode fixed.

If you restart your Mac normally and an issue comes back when you reach your desktop, try disabling any login items that automatically open when you log in.

If your Mac automatically restarts in safe mode, OS X might have found an issue that its trying to fix. 

Safe mode performs a directory check of your startup disk, similar to what happens when you choose to verify or repair a disk using Disk Utility. If OS X finds an issue, the directory on your startup disk is repaired and your Mac restarts. 

If your Mac turns itself off when you start up in safe mode, check the power connection on your Mac to make sure its plugged in securely at both your Mac and the power outlet. If youre using a MagSafe power adapter, make sure the LED on your power adapter is yellow or green. Then, try starting up in safe mode again.

This is normal.Your Mac performs a directory check of your startup disk as part of Safe Mode so it will take a significantly longer time than usual to reach the login screen or the desktop

If you?re unsure as to whether or not you?re in Safe Mode, take note of the following signs that give it away.

The first indication that you?re starting up in Safe Mode appears when you land on the login screen. If you?re in Safe Mode, the words ?Safe Boot? in red letters will appear in the menu bar in the upper right corner of the screen.

Past the login screen, you?ll notice slower overall performance. Graphics will no longer be accelerated as default drivers are loaded. The OS X menus, windows and the Dock appear solid even if Translucent Menu Bar is selected in System Preferences.

Your screen might blink or tear during the login process. OS X menus, the Dock, your desktop and other aspects of the user interface won?t have as many visual effects and translucency will be disabled.

And as mentioned further below, several OS X features might be unavailable to you in Safe Mode, like watching movies in the DVD Player app, capturing video, connecting to Wi-Fi networks and more.

Another method of determining the status of your boot mode involves using the System Information application.

Step 1: Open System Information from Applications > Utilities. You can also choose About This Mac from the Apple menu and then click the System Report button in the Overview section.

Step 2: In the lefthand column, locate and click the Software section. You should see a couple related items listed on the right side of the System Information window.

If the Boot Mode is listed as ?Safe? you?re started in Safe Mode. If it reads ?Normal,? you?re in OS X?s normal-boot mode.

Some features of your Mac arent available when its started in safe mode, so after youre done using safe mode you should restart your computer normally.

For example, these features dont work in safe mode:

Safe mode in OS X v10.5 or later also disables accelerated graphics. This makes the OS X menu bar appear solid even if "Translucent Menu Bar" is selected in System Preferences. Your screen might also "blink" or "tear" during login when your Mac is started in safe mode.

Safe mode in OS X v10.6 or later also disables File Sharing.

If your Mac doesnt have a keyboard available to start in safe mode but you have remote access to it, you can configure the Mac to startup in safe mode using the command line.

Access the command line by either opening Terminal remotely, or by logging into the computer using SSH.

Unfortunately it is a bit difficult to see if this is the case when the system is only displaying a gray progress bar; however, you can force the system to show you what is going on by having it boot to both Safe and Verbose modes at the same time.If you want to start in verbose mode as well, use this instead:

To restart your Mac normally from Safe Mode.After using safe mode, use this Terminal command to return to a normal startup: