Xserve + OS X Yosemite 10.10.5

This year I aquired a 2006 Xserve for relatively cheap. Unfortunately I hadn't realized that in order to bring it up to date in terms of putting a later version of OS X on it I would need a new graphics card that was supported by the later versions of OS X.

Just this last week I also managed to get my hands on a 2009 MacPro which came with two NVIDIA GT 120 video cards. I pulled one and placed it into the Xserve. After a few hours of hacking apart the OS X installer, I finally had OS X 10.10.5 running on it!

Requirements

8GB+ USB Flash Drive
Copy of OS X Yosemite installer app
2GBs of RAM on destination Mac
Flat Package Editor
Pacifist

Creating Modified OS X Yosemite Installer

Open Disk Utility and format your flash key. Ensure to set the Scheme as GUID and format as OS X Extended (Journaled) / HFS+.
Download the OS X Yosemite installer from the App Store.
Once the installer has finished downloading it, I recommend making a copy of it. I placed my copy into ~/Downloads/tmp/. Right click on the copy you've made, and select, Show Package Contents. Go to /Contents/Resources/SharedSupport and open the .dmg file.
You will now need to show hidden files which can easily be done with a Terminal command: defaults write com.apple.Finder AppleShowAllFiles YES && killall -9 Finder
Now navigate to the .dmg file you've just mounted. Locate the BaseSystem.dmg file. This part may be a bit tricky depending on the system you're working on. I did this on OS X El Capitan where the Disk Utility app got quite the overhaul. Previous to this you were able to just drag an image file into the sidebar however in El Capitan it seems to be a bit of a different process. I first went to Images >> Scan Image for Restore and selected the BaseSystem.dmg. Once the scanning is done, then click on the partion (not the root device) and go again to Image from the menu bar but this time choose the Restore option. Select the BaseSystem.dmg file. I believe it took about 5-10 minutes to complete.
Once the restore is done, go back over the .dmg you originally mounted and and copy the Packages folder. Paste this folder into your flash key to the directory, /System/Installation/. This will take a bit longer as it's about 5.5GBs in size. It took about 30-45 minutes when I did this.
You will now need to start editing some of the installer files. It's very important these files do not get corrupted or edited incorrectly. You must be very careful to ensure you're replacing the right things else your installer won't work. You may want to create copies of the files you're editing before you do so, just in case something goes wrong.
First you'll need to obtain your Mac's Board-ID value. If you have OS X already running on the Mac you're wanting to upgrade you should be able to use an app, IORegistryExplorer.app, which can provide this ID to you. If you don't, there's a fantastic list of IDs here. Once you have your ID, go to your flash key and open the following file in a text editor (I recommend Atom), /System/Installation/Packages/InstallableMachines.plist. Go to the last ID and replace it with your own. I have my .plist file here if you want to reference or even use it. It's been modified for the Xserve 1,1 model.
Next you'll want to open and edit /System/Library/CoreServices/PlatformSupport.plist. You can reference or use mine, it is pre-edited for the Xserve 1,1 model. You'll want to again put in the board ID as well as the model.
On your flash drive, make a copy of the following file, /System/Installation/Packages/OSInstall.mpkg. I put mine into ~/Downloads/tmp/. Open your copy of the OSInstall.mpkg in the Flat Package Editor. Extract the Distribution file and open it in your text editor. Locate the var platformSupportValues=[" ... "]; section and add your board ID value here. You can see my edited file here. Save and then replace the original file inside the OSInstall.mpkg. You'll want to delete the original from the .mpkg file and the insert your edited file. Save the OSInstall.mpkg file and replace it into the flash drive at /System/Installation/Packages/.
Again, go to the .dmg you originally mounted and copy the BaseSystem.dmg and BaseSystem.chunklist and paste them into the root of your flash drive.
Using Pacifist open the following file from the original .dmg that was mounted - Packages >> Essentials.pkg. Once this is opened up navigate to /System/Library/Kernels and extract the kernel file.
Go to your flash key, and navigate to /System/Library. Create a new directory in here called, Kernels. Take your extracted kernel file and place it into this new directory.
This step is somewhat optional, but very important if your system has 32-bit EFI. You will need to download a modified boot.efi file. I used the one here, and it seemed to have no issues. You'll want to copy this boot.efi into the following two locations on your flash drive, /System/Library/CoreServices/ and /usr/standalone/i386/.
At this point your installer should be all ready to rock and roll. Moment of trust, you'll attach it to your Mac and boot from it. You can hold the Alt key to get to a list of bootable drives connected to the Mac if it doesnt automatically boot from it.
Hopefully your install has gone without a hitch. Once you've installed and rebooted into OS X Yosemite, I highly recommend installing the PikeYoseFix script. This will allow you to install any OS updates without issue. Normally during an OS update some files will get replaced which can prevent the system from booting.

Resources

Well this is definitely awesome.