Start your Mac in safe mode to troubleshoot and solve problems

If you have problems with your Mac, identifying the cause is a problem in itself. One way to try to find the cause is to start the Mac in safe mode. It's a bare bones boot without extras.

Computers are complex machines and this can sometimes make problems very hard to solve unless you are an expert. Although some faults have an obvious cause and are thus easy to fix, this is not always the case. What can you do? Starting the Mac in safe mode can sometimes help you to solve certain faults.

Problems are foten infuriating, especially when nothing you do seems to cure them. However, there are techniques that experts use to help identify the cause of problems and one of these is to use the many different ways of booting up an Apple Mac.

You may not be aware that there is in fact, more than one way to start it. You press the power button and it comes on. What else is there to the process? Quite a lot actually.

Stop login items

When macOS starts, some apps and services are automatically loaded in the background. You can see some of these by going to the Apple menu, System Preferences, Users & Groups, Login Items. An item listed here could be the cause of the problem you have with your Mac.

If you suspect that one of the login items is causing problems, select it in the list and click the minus button below. The entry for the item is deleted and it will not automatically start when you log into your Mac. This does not delete the app from the disk, it just prevents it from automatically starting.

Stop launch agents and startup items

There are other startup items that are hidden unless you know how to find them. Hold down the Option key, click the Go menu and select Library. Open LaunchAgents and the items listed here also load automatically when macOS starts.

Command click the LaunchAgents name in Finder title bar and select the Mac's disk from the menu to go to the root of the drive. Open the Library (/Macintosh HD/Library) and there is another LaunchAgents folder and just below it is LaunchDaemons. Both of these can contain more apps and services that are started automatically with macOS. Here is an exxample.

Start in safe mode

As you will discover if you start exploring LaunchAgents, LaunchDaemons, and Startupitems (also in your personal and system Library folders), there can be a lot of background items starting with macOS and when you have a problem with no obvious cause, one useful tool for identifying the cause is to start in safe mode. This starts the Mac with the absolute minimum of extras and startup items, which are not core functions of the operating system, are ignored.

If the Mac starts up in safe mode and does not exhibit the problem you have been having, it narrows down the cause to software that is loading with macOS. More than likely, it is software you have added rather than macOS system apps and services. Knowing this, you can then look at the startup items, see what is running, and remove or update them.

If the problem persists even in safe mode, then it probably is not any of the apps you have installed and it is a more fundamental problem with the Mac’s hardware or macOS itself. Bug fixe releases are common.

Starting in safe mode does more than just prevent unnecessary extras from loading automatically and during the boot procedure, a check is made of the disk drive contents. The startup disk is verified and problems are automatically repaired in a similar way to the functions that are available in Disk Utility (in the Applications/Utilities folder). It takes a bit longer to start up, so be patient.

Any font that you have added yourself is disabled in safe mode, leaving only the system fonts that come with macOS. This means that if the problem is solved by safe mode, the cause could be corrupted third party fonts. Fonts are loaded again when you restart in normal mode. Fonts are cached (placed in a temporary store where they can be quickly accessed), and starting in safe mode moves the font caches to the Trash. Other caches are cleared too and this may solve certain types of problems.

It is possible that simply starting up in safe mode and then restarting normally will fix whatever problem you are having. It depends on the cause, but repairing the disk and clearing the various caches will cure certain problems. It is certainly worth trying.

How do you start in safe mode?

If the Mac is currently running, go to the Apple menu and select Shut down. When this has been done, wait a few seconds and then press the power button. As soon as the Mac starts, hold down the Shift key on the keyboard. Release the Shift key only when the login screen appears. If FileVault is active, you may get a double startup, once to unlock the disk and once to log in.

Start in safe mode from the command prompt

If there is a problem with starting in safe mode using the Shoft key, there is a way to tell the Mac to start in safe mode next time and this does not require you to hold down any keys. Go to the Applications folder, open the Utilities folder and start Terminal. At the command prompt, enter:

sudo nvram boot-args="-x"

Close the Terminal window and restart the Mac to start in safe mode.

A lots of things happen when the Mac starts up, but everything is hidden. This may include error messages too. To start in safe mode and display all startup messages, use this command instead in the Terminal window:

sudo nvram boot-args="-x -v"

The -x means start in Safe Mode and -v stands for verbose, in other words show every status message on the screen.

This startup settings are stored and the command is permanent until it is cancelled. To start the Mac in normal mode you must enter this command into the Terminal window:

sudo nvram boot-args=""