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Boot your Mac from CD, DVD, external drive, or USB flash drive

Boot your Mac from CD, DVD, external drive, or USB flash drive

At some point, you may find a need to boot your Mac from a disc or a drive other than the primary Mac OS X startup volume. Apple made it easy so all you need to know is just a simple keyboard command.

Let’s say you need to use the Mac OS X installation disc that came with your computer to reformat the hard drive and put it back to factory settings. Or maybe you’re trying to boot from a USB flash drive that has a clean install of OS X on it for troubleshooting purposes. Perhaps you’ve got a cloned backup of your entire Mac on an external hard drive and you want to make sure it’s bootable. These are all potential reasons for booting to an external device, among many others.

There easiest way to boot to any device other than a Mac’s internal hard drive is to press and hold the Option key immediately after hearing the Mac startup chime. Continuing to hold this button down will bring up a menu where you can select a disc or drive to boot from. Use the keyboard arrows to choose your boot device, then press the Enter key. The computer will start up from the chosen volume, but bear in mind performance will likely be much slower than when you normally operate your Mac. This is especially true of USB flash drives.

Rather than hold the Option key, you could instead just press & hold the C key if you’re booting from a CD or DVD disc. This will bypass the selection menu and immediately start from the disc. It won’t work for USB and FireWire drives, though.

Booting to another volume using either of these methods is a one-time temporary change, so you don’t have to worry about altering any settings to reverse it. Your Mac will go back to booting to it’s primary startup disk next time you reboot.

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16 Comments Have Been Posted (Leave Your Response)

Thank you! I have been searching forever for a solution, and holding down the option key to boot from an external dvd was the answer!

I don’t totally agree with the above assertion of being able to boot from any drive when holding down the “option” key. I’ve tried this several times and when I get the menu, the drive I am attempting to boot from (which does have an operating system on it) does NOT appear as one of the bootable drives.

Collin Westgard
March 6th, 2013, 6:06 AM

Anyone else using this to get rid of OSX and out Linux on? Anyone?

When i try to boot from my Memory stick (16gb) it doesnt show up next to the hard drive? any solutions?

My old mac booted from a 1TB Newertech MiniStack via Firewire 800. It was much faster than the 5400 speed 2.5″ internal drive in the mac mini.

Recently, I got a new iMac with 3TB fusion drive. I did a nice clean install and didn’t bother to import my old settings, preferences, software.

But there are things I would like to do with my old lion drive. Unfortunately, even though it seems to be available in target disk mode, the system won’t boot. On the new mac there is no firewire so I had to hook it up with USB 2.

I suppose there could be 2 problems…
1. it can’t boot from USB 2
2. it can’t boot since the OS was installed on the mini and not from the iMac.

I hope it is the latter. I am getting another 3 TB drive to mirror my 3 TB fusion drive so that I have a bootable copy of my current setup so if something goes wrong I can plug in and go. I would like to boot from USB3 if possible.

I am not sure that the Mac can boot from USB3 and fear that I may have to boot from firewire which means buying an adapter that converts from thunderbolt to firewire.

thanks for your aid…

hi have some prob. with my macg4 9.1
downloaded the mac os 9.2.1 and saved it int he memory stick placed on the mac rebooted and pressed the option key .. the memory stick did not show up and the cd also …. only the hard drive showed up. ANY HELP PLEASE

I used a program to clean my poermac g5 non intel power pc now when i type my pass word at log in some of the keyboard keys dont work so i can not log in and guest is turned off also this program let me boot up in safe mode and now is stuck in that .my mac did not come with a lapord dvd and i dont have a restore disc tryed to get one fro amazon but is was not a real one. so i can not log in can any one help. please

command s dont work eather

I already pressed Alt key and connected with WIFI but I can’t download direct from net as I did befour

I made a clone for my Mac already but am confuse on one part.
When I boot from an external hard drive, how do I copy the system from the clone to my actual MAC HD. Do I need to erase my whole MAC HD before I do the installation of the Clone or how do I proceed? Thanks in advance.

Same here… secondary drive won’t boot.

Bought my first Intel iMac from a friend… used 10.6.3 Installer DVD to wipe the drive, create 2 partitions, & install 10.6.3 on both partitions.
(aka “2 HDs”)
Used Apple’s 10.6.8 Combo upgrader to raise both HDs to 10.6.8.
Installer & Upgrader both reported successful installation on both HDs.
Startup Disc shows both HDs… which usually means both are bootable… & at that point I can choose either one.
This has always been my method, from System 6 thru OSX 10.5.8, so that I have a B/U “Disc Tools” HD onboard if my main drive develops problems. It has always worked like a charm… until now.
Loaded all my goodies onto the bigger HD & went to work.
Now I find my B/U boot drive won’t boot… it hangs at grey screen.
Tried Safe Mode, same result.
Disk Utility reports the drive is OK.

Why is this method not working? – OR –
Why does it work for some but not for others?

Why are these questions going unanswered?

It is most useful and informative post for us and I hope it also for others. Thanks

I have iMac and created usb as well as dvd both are bootable.. I reformatted machd drive, it shows only the recovery options.. I want to clean install using usb or dvd.. But, both didn’t show up in startup menu and holding c does nothing… All I can get is recovery partition in startup menu and is osc utilities menu once I select recovery option…. How to get dvd or usb options when they are not listed?

[…] Boot your Mac from CD, DVD, external drive, or USB flash … – At some point, you may find a need to boot your Mac from a disc or a drive other than the primary Mac OS X startup volume. Apple made it easy so all you need to know … […]

I have a imac and i cant get passed the blue and gray screen ..

I now have disk warrior but load on thumb-drive and when I boot up using command+c or the option key on boot it will not show up.

I even tried command+R (RECOVERY) it wont take me to the recovery section it just blue gray screen..

the other option i went into was the command line section …and ran the fix and nothing.

Hardware is fine..

Please help anyone

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