What can I download/install onto a USB drive, have it boot off that USB drive and then copy the files I need to another USB flash drive?

The error message I get when booting is "Missing Operating system". I cannot reinstall OSX currently (no media for it).

The Mac in question is an iMac so I cannot easily take out the hard drive.

  • 1
    Please add your iMac model.
    – klanomath
    Sep 2, 2015 at 19:24

4 Answers 4


Did you try...
Internet Recovery ?
before resorting to
Target Disk Mode or
How to install OS X on an external drive connected to your Mac or
Create a bootable installer for OS X Mavericks or Yosemite
- which, as already mentioned, needs another Mac


The best thing is to have a bootable backup of your iMac drive, such as one created by Carbon Copy Cloner or SuperDuper. You do have one of those, right?

A Mac can be started via a USB port, as a USB key or drive, but that device needs to have Mac OSX on it to boot, as well as other requirements. Best bet is to always backup your iMac hard drive with a bootable image created by those two tools mentioned above. For more info on usb boot, see:


If you don't have a bootable backup, or a way to get a Mac drive, things get very complicated.

First, try to boot your iMac in Recovery mode, holding down Cmd-r on restart. If that doesn't work, try for Internet Recovery, which is restart and hold down Cmd-Opt-R.

If neither of those work, find another Mac, connect it to the iMac with Firewire or Thunderbolt cable. Then reboot the iMac holding down the 't' key, which puts it in Target Disk Mode. If this works, the iMac hard drive will appear as a mounted drive on the other Mac.

If none of those work, you are going to need to take the drive out of the iMac, so be sure to read thru the iFixit guides.


You can do it, but you'll need access to a working Mac to create a bootable USB drive. Apple's instructions for doing so in Mavericks or Yosemite are here.


It might be possible to do this transfer if you start up Internet Recovery, but at that point, you might as well reinstall OS X.

OS X Recovery includes a built in set of utilities as part of the Recovery System. To start your computer from Recovery, restart your Mac and hold down the Command key and the R key (Command-R). Press and hold these keys until the Apple logo appears.

Using this will allow you to reinstall OS X without a separate bootable disk or device.

If you absolutely want a copy of your OS X partition exactly as it is, you'll have to use third party software or dd.

Hope this helps!

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