You can boot your Mac in different modes or reset different parameters with keyboard shortcuts.
Sometimes your Mac isn't running correctly, so you need to reset the NVRAM and PRAM. Sometimes you need to boot in Recovery Mode to reinstall an OS or recover your hard drive via the internet. Whatever your needs, you can boot your Mac in a variety of modes to complete a task before startup; all you need to do is press some keys down and wait for the chime (unless you have a newer MacBook Pro, sorry).
Safe mode: shift
Safe mode is a way of starting up your Mac that makes sure it performs certain checks and prevents specific software from loading or opening automatically. Here's what it does according to Apple:
- Verifies startup disk and tries to repair directory issues if needed
- Loads only required kernel extensions
- Prevents Startup Items and Login items from opening automatically
- Disables user-installed fonts
- Deletes font caches, kernel cache, and other system cache files
How to start in Safe Mode
- Start or restart your Mac and immediately press and hold shift on your keyboard.
- Release the shift key when you see the login window.
You can leave safe mode by restarting your Mac without pressing any keys during startup.
Startup Manager: option (alt)
The Startup Manager lets you choose a different startup disk during boot. So if you have your Mac partitioned to run Windows or a macOS beta, for example, you can select that startup disk instead of the default disk.
How to start the Startup Manager
- Start or restart your Mac and immediately press and hold the option key on your keyboard.
- Release the option key when you see the Startup Manager window.
- Select a startup disk.
- Click the arrow or press return on your keyboard.
Start up from Apple Hardware Test or Apple Diagnostics: D
If there are issues with your Mac that you think may be related to the hardware, you can run the Apple Hardware Test. You can run Apple Diagnostics once you think you've isolated the issue to a possible hardware issue.
How to start up from the Apple Hardware Test or Apple Diagnostics
- Start or restart your Mac and immediately press and hold the D key on your keyboard.
- Release the D key when you see the choices appear.
- Select Apple Hardware Test or Apple Diagnostics.
You can also hold option-D to start up from either utility over the internet.
Start up from a NetBoot server: N
Booting from a NetBoot server allows you to boot from a network, rather than a local hard disk or optical disk drive. Your Mac must have capable firmware to boot from a system.
How to start up from a NetBoot server
- Start or restart your Mac and immediately press and hold the N key on your keyboard.
- Release the N key when you see the choices appear.
- Select a network.
Reset the NVRAM and PRAM: option-command-P-R
Sometimes specific processes on your Mac just don't work. It can be any random issue from iCloud not allowing you to sign in to certain apps just not opening. One of the first fixes you'll find on any forum is resetting the NVRAM (nonvolatile random-access memory). This is a small amount of memory that your Mac uses to store settings that it wants to access quickly.
If you're having a complicated issue with your Mac, this is an excellent place to start.
How to reset the NVRAM and PRAM on your Mac
- Start or restart your Mac and immediately press and hold command-option-P-R on your keyboard. You'll probably have to use both hands.
- Release the keys after about 20 seconds. If you have a Mac that plays a startup chime, you can release the keys after you heard it a second time.
You may have to go back into System Preferences and adjust settings like volume and display resolution to your liking since they get reset when you reset the NVRAM.
Boot in Recovery Mode: command-R
Sometimes, as a last-ditch effort, you need to boot in Recovery Mode, and either repair a disk or (NOOOOO!) reinstall macOS. You may also need to restore from a Time Machine backup. If any of that is the case, then here's what to do:
How to boot up your Mac in Recovery Mode
- Startup or restart your Mac and immediately press and hold command-R on your keyboard.
- Release the keys when you see the Apple logo or a spinning globe.
- Click an option.
- Click Continue.
Start up in single-user mode: command-S
If you're comfortable with UNIX, sometimes you may want to boot your Mac in single-user mode, which lets you try and isolate startup-related issues. You'll want to be an advanced user if you're considering this move.
How to boot up in the single-user mode
- Start or restart your Mac and immediately press and hold command-S on your keyboard.
- Release the keys when you see white text on the screen.
Start up in target disk mode: T
Target disk files allow you to share files between two Macs that are connected via FireWire, Thunderbolt 2, USB-C, or Thunderbolt 3. One Mac shows up as an external disk on the other Mac, so you can browse and copy files over like you would from a hard drive.
How to start up in target disk mode
- Start or restart your Mac and immediately press and hold T on your keyboard.
- Release T after about 20 seconds.
After your Mac starts in target disk mode, you'll see it as a desktop icon on the other Mac. You can treat it just like an external hard drive and drag it to the trash when you want to "eject" it.
Start up in verbose mode: command-V
Verbose mode is another startup mode for advanced users, which allows you to enter UNIX commands to try and isolate startup-related issues.
How to start-up in the verbose mode
- Start or restart your Mac and immediately press and hold Command-V on your keyboard.
- Release the keys when you see the white text on the screen.
Eject removable media on startup: ⏏, F12, mouse button, or trackpad button
If you don't want an external hard drive to mount on startup or you simply want your CD or flash drive out as quickly as possible when you turn on your Mac, you can eject it right on startup.
How to eject removable media on startup
- Start or restart your Mac and immediately press and hold the eject button (⏏), F12, your mouse button, or your trackpad button. Press and hold one of these.
- Release when your removable media is ejected.
Reset the SMC in MacBooks: shift-control-option
The SMC (system management controller) is a system that controls the hardware in your MacBook, including components like cooling fan speeds, power, display management, port illumination, and more. There are many things you should try before resetting the SMC, but if you're at the end of your rope, then reset it.
How to reset the SMC in your MacBook
Note:If the battery in your MacBook is removable (older MacBooks), then just take it out, press the power button for 5 seconds, and put the battery back in and turn it on again.
- Start or restart your Mac and immediately press and hold shift-control-option on the left side of your keyboard and then press and hold the power button at the same time. Hold the three keys and the power button for 10 seconds.
- Release all the keys.
- Press the power button to turn your MacBook on.
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