Once you download it, the installer will start up automatically.
What if you want to perform a clean install, completely erasing your startup drive?
The problem is you cannot upgrade another Mac without downloading the installer all over again.
Lifewire / Alex Dos Diaz
The workaround is to create a bootableUSB flash drivecontaining the OS X Yosemite installer.
The first is touse a hidden Terminal commandthat can handle all of the heavy lifting for you.
The second is more manual and time-intensive.
bluehill75 / Getty Images
It uses the Finder and Disk Utility apps.
The first step is to gain access to this file.
Open a Finder windowand navigate to /Applications/.
Locate the file namedInstall OS X Yosemite, and then right-opt for file and selectShow Package Contents.
Open theContentsfolder, then open theShared Supportfolder.
Here you will find the disk image that contains the files you better create a bootable installer.
You may notice that the mounted image seems to contain only a single folder, namedPackages.
In actuality, the image file contains an entire bootable system that is hidden.
You’ll need touseTerminalto make the system files visible.
Connect the target USB drive to your Mac.
LaunchDisk Utility, located at /Applications/Utilities/.
Select theBaseSystem.dmgitem listed in the left-hand pane of the Disk Utility window.
It may be listed near the bottom, after your Mac’s internal and external drives.
ensure you selectBaseSystem.dmg, notInstallESD.dmg, which will also appear in the list.
In the Restore tab, you will seeBaseSystem.dmglisted in the Source field.
If not, drag theBaseSystem.dmgitem from the left-hand pane to the Source field.
Drag theUSB flash drivefrom the left-hand pane to theDestinationfield.
If requested, supply your administrative password and selectOK.
The restore process will take some time.
Keep this Finder window open, because we’ll be making use of it in subsequent steps.
In the Finder window namedOS X Base System, open theSystemfolder, and then open theInstallationfolder.
Within the Installation folder, you will find an alias namedPackages.
Leave the Installation window open, because we’ll use it below.
From the OS X Install ESD window, drag thePackagesfolder to theInstallationwindow you left open in the previous step.
Close all of the Finder windows once your rig finishes copying the files over.
Your USB flash drive is now ready to be used as a bootable OS X Yosemite installer.
To keep your Finder as usable as possible,make the files you unhid invisibleagain.
