Booting up your Mac is usually a matter of pressing the power button and waiting for the login screen or desktop to appear, but every now and then you might want something different to happen when you start your Mac. Maybe you use one of the troubleshooting modes or take advantage of the Recovery HD.
45 Simple Mac Keyboard Shortcuts You Should Know
Startup shortcuts change the default behavior of your Mac when it starts up. You can enter special modes, such as Safe Mode or Single-User Mode, which are both troubleshooting environments, or you can use startup shortcuts to select a startup device other than the default startup disk you normally use. The many startup shortcuts are collected here.
When using a wired keyboard, enter the keyboard shortcuts immediately after pressing your Mac's power button. When using the Restart command, enter them after your Mac's power light goes out or the screen goes black.
If you're having trouble with your Mac and are using the startup keyboard shortcuts to help with troubleshooting, try using a wired keyboard to eliminate Bluetooth issues that can prevent your Mac from recognizing the use of keyboard shortcuts. Any USB keyboard will work in this role; it doesn't have to be an Apple keyboard. If you're using a Windows keyboard, read up on the Windows keyboard equivalents for Mac special keys to learn which keys to use.