With the release of the macOS High Sierra operating system, Cupertino ditched its venerable Mac OS Extended file system, commonly abbreviated as HFS+, and switched to an entirely new file system.
- If you succeed in downloading the OS installation, your next step is to create a bootable USB or DVD and then reinstall the OS on your computer. How to download older Mac OS X versions via the App Store. If you once had purchased an old version of Mac OS X from the App Store, open it and go to the Purchased tab.
- Open your Mac or restart the device if you were already using it. When the startup music is playing press and hold the “C” key from the keyboard. This will start the OS X installer from the CD/DVD on your Mac. So, it is not too complicated to Mac boot from CD/DVD. You can easily burn a bootable image of OS X on a DVD by using Disk.
- Click ‘Install’ and select your hard drive as the destination. Your Mac downloads the latest compatible version of macOS or OS X over the Internet and installs it on your hard drive. It may take some time. Follow the onscreen prompts to complete your macOS or OS X installation.
- How can I create a hard link to a directory in Mac OS X? This feature has been added to their file system in Mac OS X v10.5 (Leopard) (for time machine), but I could not find any information on actually using it from the command line.
These key combinations apply only to Mac computers with an Intel processor, not Mac computers with Apple silicon.
To use any of these key combinations, press and hold the keys immediately after pressing the power button to turn on your Mac, or after your Mac begins to restart. Keep holding until the described behavior occurs.
- Command (⌘)-R: Start up from the built-in macOS Recovery system. Or use Option-Command-R or Shift-Option-Command-R to start up from macOS Recovery over the Internet. macOS Recovery installs different versions of macOS, depending on the key combination you use while starting up. If your Mac is using a firmware password, you're prompted to enter the password.
- Option (⌥) or Alt: Start up to Startup Manager, which allows you to choose other available startup disks or volumes. If your Mac is using a firmware password, you're prompted to enter the password.
- Option-Command-P-R:Reset NVRAM or PRAM. If your Mac is using a firmware password, it ignores this key combination or starts up from macOS Recovery.
- Shift (⇧): Start up in safe mode. Disabled when using a firmware password.
- D: Start up to the Apple Diagnostics utility. Or use Option-Dto start up to this utility over the Internet. Disabled when using a firmware password.
- N: Start up from a NetBoot server, if your Mac supports network startup volumes. To use the default boot image on the server, hold down Option-N instead. Disabled when using a firmware password.
- Command-S: Start up in single-user mode. Disabled in macOS Mojave or later, or when using a firmware password.
- T: Start up in target disk mode. Disabled when using a firmware password.
- Command-V: Start up in verbose mode. Disabled when using a firmware password.
- Eject (⏏) or F12 or mouse button or trackpad button: Eject removable media, such as an optical disc. Disabled when using a firmware password.
If a key combination doesn't work
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If a key combination doesn't work at startup, one of these solutions might help:
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- Press and hold all keys in the combination together, not one at a time.
- Shut down your Mac. Then press the power button to turn on your Mac. Then press and hold the keys as your Mac starts up.
- Wait a few seconds before pressing the keys, to give your Mac more time to recognize the keyboard as it starts up. Some keyboards have a light that flashes briefly at startup, indicating that the keyboard is recognized and ready for use.
- If you're using a wireless keyboard, plug it into your Mac, if possible. Or use your built-in keyboard or a wired keyboard. If you're using a keyboard made for a PC, such as a keyboard with a Windows logo, try a keyboard made for Mac.
- If you're using Boot Camp to start up from Microsoft Windows, set Startup Disk preferences to start up from macOS instead. Then shut down or restart and try again.
Remember that some key combinations are disabled when your Mac is using a firmware password.
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- Keyboard shortcuts that you can use after your Mac has started up.
To quit (close) a Mac app normally, choose Quit from the app's menu in the menu bar, or press Command (⌘)-Q. If the app doesn't quit, follow these steps to force the app to quit.
How to force an app to quit
Press these three keys together: Option, Command, and Esc (Escape). Or choose Force Quit from the Apple menu in the upper-left corner of your screen. (This is similar to pressing Control-Alt-Delete on a PC.)
Then select the app in the Force Quit window and click Force Quit.
You can even force the Finder to quit, if it stops responding: Select Finder in the Force Quit window, then click Relaunch.
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Learn more
How to force an app to close on your iPhone, iPad, or iPod touch.