A true clean install of OS X. Dealing with previous EFI and OS X Base System disk image

[1976pianoman]

I would like to do a true clean install of OS X El Capitain on a real Apple iMac. This mean two things have to go, or at least be replaced with generic alternatives that do not contain data pertaining to the previous system/user. The EFI, which can I can access and delete, using Terminal - yet I'm afraid to as I do not know what the consequeces might be (if it's true that new Apple computers come with a blank EFI, then I would assume I can simply just delete it). The second and more pesky bastard is the "OS X Base System" disk image (disk1s1) which for some reason is being labeled as an external physical volume by Disk Utility. I get the build philosphy as to it's purpose, however it contains a plethora of exotic shenenagins and data pertaining to the previous system/user. It does not get to stay and will face the Dewalt power drill if refuses to go.

Much ot this motivation is simply a matter of principle that I would rather not go into. This is not the place for a discourse on my Libertarian ideals. I figured this realm with you guys would be the place to go for this kind of help. I hope it is. Thank you for any guidance you could offer me. I am planning a custom build for my next computer, so I'll be visinting you all quite often very soon. This here, that I'm dealing with now will be a good learning exprerience for the futrue. Thanks!

 

[WonkeyDonkey]

What you are seeing is 100% correct. An EFI partition, the original system partition (If not already deleted) and an OSX Recovery partition.

You can easily zap all 3 of these forever but how you do that depends on the exact mac model, whether the mass storage is SSD or HDD and whether or not you have an optical drive available, either built-in or of the USB variety.

A few more details of the hardware would be helpful at this point.

 

[1976pianoman]

Hi. Thanks for this. The computer is an Apple 24" iMac (intel) 2.4 Ghz Dual Core (I think the call it a Core 2 Duo?) from late 2007. It has a built in optical drive. The internal HD is not solid state. If you need more detailed info about this beast, let me know and I will boot her into OS X and get it for you.

 

[1976pianoman]

Here is more than enough info about this particular iMac. This on is the 24" on the far right.

https://support.apple.com/kb/SP16?locale=en_US&viewlocale=en_US

 

[WonkeyDonkey]

For that system, it is very straight forward. You have a mechanical HDD and an optical drive available. So I would use a linux boot cd and the tools available from it.

The one I use right now is called Parted Magic. This has a small cost associated with it but has excellent tools available to erase the disk entirely.

Otherwise you can download a free linux boot cd and use the 'dd' command to overwrite every block on the disk. You can see a simple example here.

There are many disk erase tools available out there, see here for a few other examples.

No specific tool is recommended over another, you should research the options I have given you above and decide which is best for you.

If you want to take a 'paranoid' approach to it then you can download more than one and run them in succession, or run the same tool multiple times.

 

[1976pianoman]

Thank you! Now once I have a blank HD, how do I proceed with installing OS X? Doesn't the installation require a base system and possibly an EFI? I would also love to learn Linux. I've been having some fun with Tails but I'm wondering what might be a good Linux build that won't throw
me to the wolves- something with a GUI that is not 100% command line. Something for beginners? Maybe there is no such thing. My primary goal with this computer is to destroy its past and get a fresh OS X on it.

 

[WonkeyDonkey]

Thank you! Now once I have a blank HD, how do I proceed with installing OS X? Doesn't the installation require a base system and possibly an EFI? I would also love to learn Linux. I've been having some fun with Tails but I'm wondering what might be a good Linux build that won't throw
me to the wolves- something with a GUI that is not 100% command line. Something for beginners? Maybe there is no such thing. My primary goal with this computer is to destroy its past and get a fresh OS X on it.

The EFI stuff is setup as part of the OSX installation. This site does not specifically cover installing OSX on a real mac, but there are plenty of guides out there which describe it in enough detail. It is all GUI based as with most operating systems these days. Do a google search.

Linux has not been 100% command line for some time now unless you choose to do it that way. Most of the modern distros are point and click. A lot of folks swear by Ubuntu, which is easy to navigate and use. I personally use Mint Linux, which is based on Ubuntu but has a more polished interface and a good support forum.

Since you are in the beginners camp, stick with one OS for the time being until you get comfortable with it, and then venture out further down the line. If you have successfully zapped the HDD in the mac, then you have a good clean starting point.

 

[1976pianoman]

I found Diskmaker X which might work. I'm wondering if I could use the methods you guys use here on a real iMac. I know, this sounds backwards - just wondering why it would not work. I've already messed around with the clover boot loader and it works great.

 

[WonkeyDonkey]

I found Diskmaker X which might work. I'm wondering if I could use the methods you guys use here on a real iMac. I know, this sounds backwards - just wondering why it would not work. I've already messed around with the clover boot loader and it works great.

There is no need to use the methods described here to install a real mac. Your mac will have its own install media to get a base installation, at which point you can upgrade to the latest version that it supports.

DiskMakerX will allow you to create a USB installer for the latest version, which means you wouldn't need the base installation beforehand. But check and make sure your mac will boot from that USB installer.

If you plan to dual boot, then Clover may or may not be of benefit. You will have to research using Clover on a real mac to find out.