My MBP Retina 13″ late 2012 is showing the stop sign and I know that I need to reinstall my OS. I have not got my hard drive backed up with Time Machine. Is there a way in which I can backup my hard drive to an external drive using Disk Utility and then restore it back once I have reinstalled the OS (I have to restore as for some reason I don't have enough space or something)?
Absolutely - this is a good plan in general - having a bootable backup in addition to a Time Machine interval backup.
I like to get a SD card / micro SD card and install an emergency boot OS with just enough tools to fix any situation.
I would do that before making any changes. Next, you will want to measure how large your drive is - open Apple Menu - about this Mac and look in storage:
For this Mac, you would need 185 GB of space.
- Connect a USB drive and partition it to have one free partition that's at least 5 GB larger than the space needed. (I would go 15GB or more larger if you care about speed or ever booting from that partition)
- Erase the partition you will be using and format it as OS X Extended and name it "target" or something unmistakable.
- Shut down the Mac and hold R when booting to boot to Recovery HD
- Use Disk Utility from Recovery to restore data from Macintosh HD to target
- Wait - enjoy some tea or coffee or whatever
- When things are done, power off and boot holding option - you should see two boot drives with different icons on the grey screen and can test booting from the clone.