How to Create a Bootable Flash Drive in OS X

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Flash drives are one of the most common forms of storage media. Chances are you’d have one lying around just now!

They are small, fast and most importantly portable. Now if you’re someone who has to reinstall OS’s often, you’d know how problematic it is to carry a bunch of DVD drives around.

Even if you’re a home user, it’s incredibly difficult to keep track of a DVD. Besides as time goes on, DVD’s are prone to get scratched and that means that it will be no longer usable.

To save you from the hassle of all of that, we will show you how the common flash drive can become an OS installer.

To make this tutorial a little bit easier we will first divide it into the three parts. These are according to the most common Operating systems in use today.

And we will show you how to make a bootable USB in Windows, Mac OSX and Linux ( We’ll be using Ubuntu, but you could replicate this with most GUI based distros )

Pre-Requisites

  • 8 GB Pen drive.
  • A working computer and an internet connection.
  • You will also need Admin privileges on the computer.
  • An ISO file of the operating system that has to be made into a bootable disc.
  • The disc needs to be formatted before loading the operating system into it, so if you have any files you’d like to keep that are in this Flash drive then be sure to back them up before you begin with the process!

That’s all you need except for a spattering of common sense which I’m sure you’d have! So let’s get on with it, shall we?

Creating a bootable USB in Mac

Skip Step 1 if you already have the Mac OS X installer downloaded

Step 1

First up we will go to the App Store > Purchases and click Download next Mac OS X 10.10 Yosemite. This will download Yosemite to the Applications folder. Do not install from here as this will delete the downloaded file!

Step 2

For this procedure, we need to unhide the hidden folders. Open the Terminal app (found in Utilities) and copy the text written below! It will relaunch finder with all files made visible.

defaults write com.apple.finder AppleShowAllFiles 1 && killall Finder

Some files that weren’t previously there, will appear on the desktop such as.DS_Store

Step 3

Now open a Finder window and locate the file you just downloaded from the store, Right-click on Install OS X Yosemite (the file name may vary depending on the version of OS X you’re running) and choose Show Package Contents.

Step 4

Navigate to Contents > Shared Support and then browse to the file called installESD.dmg.

Step 5

Double-clicking on InstallESD.dmg will mount the volume in Mac OS X. A Finder window should open. There will be a file inside called BaseSystem.dmg.

Step 6

Next up, we open Disk Utility (you can find it by clicking Go > Utilities).

Step 7

Dragging the BaseSystem.dmg file from Finder to the Source sidebar will make it appear in the Disk Utility as shown below (the list of volumes on the left-hand side).

Step 8

Click on BaseSystem.dmg in the sidebar and the Restore tab. Then browse the USB Flash drive in the Source sidebar, below it there should be the Volume for it. Click and drag this volume from the sidebar to the Destination field in the Disk Utility window.

Step 9

Now we click on Restore and Erase. You have to provide your Admin password to authenticate the action and then click OK.

Important: This erases all the data on the USB Stick.

Step 10

A progress bar is displayed at the bottom of the window. It should typically take between 5-10 minutes to complete.

Step 11

Once that is done, the USB drive will mount on the Finder. Open the volume (it should be called OS X Base System) and open System > Installation. Browse to an alias file called Packages and delete it.

Step 12

Open the mounted OS X Install ESD volume, and you’ll see only a folder called Packages. Drag that folder into the Installation folder on the USB drive. (You’re basically replacing the deleted Packages alias with this Packages folder.)

The folder is about 4.8GB in size, so the copy might take a bit of time, especially if you’re copying to a slow thumb drive.

Step 13

Next, from the same OS X Install ESD volume, find the files BaseSystem.chunklist and BaseSystem.dmg. Drag these to the root (base) level of the OS X Base System (Do not place them inside any one of the folders).

Step 14

Eject the OS X Install ESD Volume.

Optional Step

 You might now want to hide the files that were previously hidden as these are system files and important for the OS to function properly. If you do want to do so, paste the following line in Terminal and press enter.

defaults write com.apple.finder AppleShowAllFiles 0 && killall Finder

Congratulations! You now have a Yosemite boot drive with which you can install Mac OS X Yosemite onto a Mac.

Insert the boot drive into a USB port on a Mac and start it up while holding down the Alt key to access it. This will enable you to install Mac OS onto a Mac without having to download the Install file each time!

While this tutorial was done keeping Yosemite in mind, this should work with all versions of OS X.

If you have any questions or queries, do leave a comment down below and we will try to answer them for you. And stay tuned for the next two parts of this series, how to make a bootable USB drive in Windows and Linux!

Amartya

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