Open the Terminal app (in ApplicationUtilities), then type (or copy and paste) the following command, and then press Return.

Modern, downloadable versions of OS X create a recovery partition on your drive, but its always a smart idea to make your own bootable installer drive too.

I recommend making one for Yosemite, on an external hard drive or USB thumb drive, for many of the same reasons I recommend making a bootable Mavericks installer drive: If you want to install Yosemite on multiple Macs, using a bootable installer drive can be more convenient than downloading or copying the entire installer to each computer.

If you want to erase the drive on a Mac before installing Yosemite, or start over at any time, you can use a dedicated installer drive to boot that Mac, erase its drive, and then install the OS clean and restore whatever data you need from a backup.

And if your Mac is experiencing problems, a bootable installer drive makes a handy emergency disk.

As with the Mavericks installer, if you leave the Yosemite beta installer in its default location (in the main Applications folder) when you install OS X 10.10, the installer will delete itself after the installation finishes.

If you plan to use that installer on other Macs, orin this caseto create a bootable drive, be sure to copy the installer to another drive, or at least move it out of the Applications folder, before you install.

If you dont, youll have to redownload the installer from the Mac App Store before you can create a bootable installer drive.

Create the Yosemite install drive: The options Ive come up with three ways you can create a bootable OS X install drive for the Yosemite: using the installers built-in createinstallmedia tool; using Disk Utility; or performing the Disk Utility procedure using Terminal.

The createinstallmedia method is the easiest; if youre at all comfortable using Terminal, its the approach that I recommend you try first.

Note that the createinstallmedia tool doesnt work under OS X 10.6 Snow Leopardit requires OS X 10.7 Lion or later.) The Disk Utility method is the way to go for people who are more comfortable in the Finder (though it does require a couple Terminal commands), and it works under Snow Leopard, Lion, Mountain Lion, Mavericks, and Yosemite.

The Disk Utility-via-Terminal approach is for the shell junkies out there.

Whichever method you use, you need a Mac-formatted drive (a hard drive, solid-state drive, thumb drive, or USB stick) thats big enough to hold the installer and all its dataI recommend at least an 8GB flash drive.

That drive must also be formatted with a GUID Partition Table.

Follow this tutorial to properly format the drive.) Your OS X user account must also have administrator privileges.

Option 1: Use createinstallmedia Starting with Mavericks, hidden inside the OS X installer is a Unix program called createinstallmedia, provided by Apple specifically for creating a bootable installer drive.

If youre comfortable using Terminal, createinstallmedia is a relatively simple tool to use.

As mentioned above, the createinstallmedia tool works only in Lion, Mountain Lion, Mavericks, or Yosemiteyou cant create an installer drive this way while booted into Snow Leopard.

If you need to create a Yosemite beta install drive while booted into Snow Leopard, you should use the Disk Utility instructions, below.

Wait until you see the text Copy Complete.

Done. (see the screenshot above), which could take as long as 20 or 30 minutes, depending on how fast your Mac can copy data to your destination drive.

If you like, you can rename the drive from its default name of Install OS X Yosemite, though I think its kind of a catchy name.

Option 2: Use Disk Utility Youll find Disk Utility, a handy app that ships with OS X, in ApplicationsUtilities.

The procedure is a bit more involved with Yosemite than it was for Mavericks (which was itself a bit more involved than under Mountain Lion and Lion).

IDG.

Its called Install OS X Yosemite.app and it should have been downloaded to your main Applications folder (Applications).

That volume will appear in the Finder as OS X Install ESD; open it to view its contents.

How To Make Boot Disk For Mac Os X