Installing mac from a External Drive

[brissens]

Hello, I've been strugglin lately with El Capitan OS system. My problem is that I erased the Macintosh HD Drive and every time I boot on Recovery Mode I can't re-install the new OS because I dont have the Apple ID from this particular machine. I tried all the key board compbinations and none of them worked (still ask for an Apple ID). I even tried with a USB but stills ask me for a apple ID. So, there's no system now, just RECOVERY MODE OS.
My question is, Can I install another OS in a external hard drive and the boot it from this computer so I can reinstall it from there?

 

[Weaselboy]

You should be able to boot to Internet recovery with command-option-r at startup and install the OS that ay without needing an AppleID.

 

[brissens]

It should, but somehow when I press command-option-r at startup and then click on re-installing it keeps asking me for a AppleID. Dont really know why. It's driving me crazy. That's why I though that I may be able to install an OS in a external drive and then boot it from there.

 

[Weaselboy]

That's why I though that I may be able to install an OS in a external drive and then boot it from there.

You mean on another Mac then copy it over? Yes, that would work.

What year model Mac are we talking about here. Older ones don't have Internet recovery.

 

[brissens]

Its a Mac Pro from Middle 2010. It came with Snow Leopard OS but then I installed El Capitan. I wasn't sure that I could still boot an external OS even if I had erased the Macintosh HD disk.

 

[Weaselboy]

Its a Mac Pro from Middle 2010. It came with Snow Leopard OS but then I installed El Capitan. I wasn't sure that I could still boot an external OS even if I had erased the Macintosh HD disk.

Yeah... no Internet recovery on that model. Buy yes, if you have say El Capitan on installed on an external drive, you can option key boot to it.

 

[Fishrrman]

OP:

As Weaselboy mentioned...
Do you have a bootable copy of El Cap -already installed- on an external drive?

If the answer is yes...
Is it a relatively clean copy, working as you like?

If the answer is yes...
I suggest you do this:
1. Boot from the external drive.
2. Download CarbonCopyCloner (it's FREE to download and use for 30 days):
http://www.bombich.com/download.html
3. Open Disk Utility and ERASE the INTERNAL drive. NUKE IT BACK TO ZERO (HFS+ with journaling enabled).
4. Once that's done, open CCC.
5. On the left, pick the external as your "source" drive
6. To the right, choose the internal as the "target"
7. You can accept all of CCC's defaults.
8. If CCC asks if you wish to clone over the recovery partition, YES, you want to do this.
9. Let CCC do its thing.
10. When done, the Mac should have an exact copy of what was on the external drive, now on the INTERNAL drive.
11. See if you can boot now.