Few days ago, the guys at the Apple store had to reinstall my OS and they have installed OS X 10.10. Is there a simple and easy way to create a copy of this to an external hard drive to use it in the future if I need to boot it from an external source?

Carbon Copy is a tool I use in my data center to clone macs.... there may be a free trail. The external disk that is used as the backup target can be used as the boot device in a pinch.

Other options are
CloneZilla - Requires some setup
Boot a linux live disk and DD the entire drive - be careful with this one to not erase your disk.

Thanks

Actually, you can use the built in Disk Utility (Shift+Cmd+U from Finder).

  1. Create a recovery partition.
  2. Resize your current HDD to the same size as your clone drive so as to not run into size issues.
  3. Create a single partition on your clone drive.
  4. Restart system, hold down option key as it's booting, select the recovery partition and go to the Disk Utility again.
  5. Select your HDD, click the Restore tab.
  6. Click+drag your HDD to the Source input box.
  7. Click+drag your clone drive to the Destination input box.
  8. Select Erase Destination check box (if available) then click Restore button.
  9. Once copying is complete, restart system same as before to confirm successful cloning. If it's successful, you should be able to boot into your clone drive with no problems.

Carbon Copy Cloner or SuperDuper! (the former is freeware, the latter is shareware) can both make full-disk bootable backups. I use SuperDuper! every night (at around 2 AM) to makle a bootable backup of my system, to go with my local Time Machine incremental backup and my offsite CrashPlan backups.

This is actually quite simple. Boot from a Linux DVD/CD drive. Use the dd command to copy the system disc image to an external drive, such as: dd if=/dev/sda of=/externaldrive/osx-image bs=1M. This says, copy /dev/sda to /externaldrive/osx-image in 1MB chunks. You can also pipe that through a compression tool such as gzip or bzip2 to take less space on the target drive. I do this all the time to keep a recent image of my OS available in case I have to reinstall it without too much pain and suffering. It has "saved my bacon" on many occasions!

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