Upgrading from 10.5 to 10.10

[Agincourt]

Okay I've got two iMacs dating back to ~2010 and presently have OS 10.5 and 10.6. I'm completely unable to connect to the internet because the OS systems are too old, so no means to upgrade via internet. I'm trying to create a bootable 10.10 OS on an external drive, but everything I've download onto the drives are not bootable. Claiming that it 'cannot download Mac OS X onto selected drive because it doesn't have Mac OS X installed.'

I got the files from official Apple site sources and all of these (10.8 - 10.10) simply don't work. I completely erased the HD from one and it's become completely screwed up. It won't upload from the internet and it won't even boot up from my 10.5 DVD. It starts up and restarts every 30 seconds now without booting up from the DVD. I can't download new OS via firewire disk mode because of the above 'cannot download Mac OS X onto selected drive because it doesn't have Mac OS X installed' message.

Create a bootable installer for macOS - Apple Support (HK)

Use an external drive or secondary volume as a startup disk from which to install macOS.

support.apple.com

I am growing insane with rage because the software that's supposed to be bootable from a USB are all failing to do anything. The best I've been able to do was boot up via firewire disk mode, but cannot clone or upload new OS through the good computer. Please help.

 

[Agincourt]

I presently have a Mac mini with 10.10 already and would settle for a means to clone it onto the now blank drive on one of the iMacs. Each time I try and do that via disk recovery it refuses unless I restart and go into disk recovery. Again I pressed 'command' 'option' and 'r' at startup and the computer simply boots up normally. I'm confused because I just uploaded an OS from this source on another computer and everything worked properly. 'Command' + 'R' isn't working and these are not showing up when I press 'option' upon startup. The keys are working so that's not the problem.

I cannot understand why having the 'install OS 10.8' on an external drive cannot boot up either of these iMacs. Can someone link me to a complete step by step process in creating a bootable drive complete with operating systems that I can download and format? The above link seems to only point me to upgrades which are not themselves complete operating systems.

 

[MrCheeto]

I've used this and it is plenty fast on old systems. It doesn't do anything like modify your EFI etc, it really just bypasses system checks and not much else. You can't install this directly within Leopard. You must create the boot drive with a later system, which will certainly work on your 10.10 machine.

macOS High Sierra Patcher