Boot from your Recovery HD partition by restarting your Mac while holding down the Command+R keys. The OS X Utilities window appears. Select Reinstall OS X, and click Continue. The OS X Yosemite splash screen appears. A sheet appears informing you that your computer’s eligibility needs to be verified by Apple.
Boot to OS X, using whatever means are available to you. Holding Option (or Alt) while powering up will normally give you Apple's own boot manager, which should enable you to boot to OS X. If your rEFInd installation is currently starting but is not showing an OS X option, skip to step #7; but if rEFInd isn't starting, follow steps #2–7. If interested in going that route, you can learn about clean installing OS X Yosemite, or clean installing OS X Mavericks, both of which are best performed from a separate boot drive or bootable USB installer. You can also use Command+R to boot into Recovery mode, older Mac models that do not support Internet Recovery will need to do that. There seems to be a bug in Yosemite Recovery Update 1.0 which no longer allows the recovery hd to boot from the startup manager available when booting up by holding down the option key. Command R and Command Option R may still work though. If this is affecting you, here is a workaround to get your old recovery hd back. Insert an external drive, launch the OS X Recovery Disk Assistant, select the drive where you would like to install, and follow the on screen instructions. When the OS X Recovery Disk Assistant completes, the new partition will not be visible in the Finder or Disk Utility. To access OS X Recovery, reboot the computer while holding the Option key.
Want to learn how to create a bootable USB installer for OS X Yosemite?. Here is the complete step by step guide which you can follow on your MAC create the bootable USB disc. We all know that Yosemite OS X is the latest operating system form Apple, which comes with lots of new features and improvement. If you are interested in new OS and want to try it then sign up for the OS X Beta Program here, which will allow them to test the new OS, if selected.
Once you have the installation app for Yosemite (Install OS X 10.10 Developer Preview), don’t install it directly, other wise you will lose the file and can’t make the USB disc. To get started all you nee a *GB or above USB drive, Apple computer with Mac App Store (10.6.8+) and OS X Yosemite installer.
Create OS X Yosemite Bootable USB Drive
Step 1. Insert the USB drive or Disc on youir MAC and run the Disk Utility app from the Applications > Utilities folder.
Step 2. Now in the app select the USB drive and Selct the Partition Tab.
Step 3. Under Partition Layout, select 1 Partition from the drop-down menu. And enter the Partition information Name: ”yosemite”, Format: “Mac OS Extended (Journaled)”.
Step 4. Click the Options... button and Select GUID Partition Table. After that hit the “Ok” button then “Partition” button.
Step 5. Now the partition process will start and this will take some time to format and making USB drive as a 1 partition
Now the USB part is over and lets move to the OS X Yosemite installer package.
Step 6. Go to Applications again and find the Install OS X 10.10 Developer Preview app that you downloaded.
Step 7. Right-click the installer and select Show Package Contents from the context menu. See the Screenshot below:-
Step 8. Now navigate to Contents -> SharedSupport and open InstallESD.dmg
Step 9. This will start the verify process on your MAC. Wait for some time…….
Step 10. Once the verify process is done you will see the Package Folder.
Step 11. Don’t do anything with this Packages folder just yet. First, we need to unhide the files located in this newly mounted OS X Install ESD image.
Step 12. Launch Terminal.app to enter a command to unhide the file and folder on your MAC.
Step 13. Enter the below mention two commands one by one:-
defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder
Install Os X Yosemite Download
Step 14. Now you will see three more files next to the Package folder (Step 10)
Step 15. Switch back to Disk Utility.app to select the partition name created in step 3.
Step 16. Now drag the partition from the device list to the Destination box. Also, drag the BaseSystem.dmg to the Source path
Hit the Restore button.
Step 17. Now a new popup screen appears. From here click on Erase to start the restore process, then enter in your admin password and hit OK to proceed.
Step 18. Once the restore process is done, you will see a new window son your screen. Like the screen below:-
Step 19. Here, open the “System” > “Installation” folders and move the Packages file to trash.
Step 20. Now copy the Packages folder from Step 10 and paste it into the Installation folder that you just opened in previous step.
Step 21. Now Hide the system files again using this command on terminal window
defaults write com.apple.finder AppleShowAllFiles NO
That’s it!. To perform a clean install on your MAC, simply insert the USB drive that you created, power on the computer, and hold down the [option] key to access the boot selection menu. From there, select the USB drive partition, and follow the prompts to install OSX 10.10 on your Mac.
These key combinations apply only to Mac computers with an Intel processor.
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
If a key combination doesn't work at startup, one of these these solutions might help:
- 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.
Os X Yosemite Recovery Boot Mac
Learn more
Os X Yosemite Update
- Learn what to do if your Mac doesn't turn on.
- Learn about Mac keyboard shortcuts that you can use after your Mac has started up.