Trying to revert to Yosemite from el cap on a macbook. Anyone have any bright ideas on how to do this w/out buying a usb connector? Can I boot from another computer on my network? I tried to reinstall from the internet (cmd opt R), no love there.
Any help would be appreciated, thanks.
So long as your MacBook is relatively new (last 5 years or so) then it can be put into Target Mode by connecting it (physically, not over the network) to another Mac with a FireWire or Thunderbolt cable.
Then boot the MacBook holding the T key until the screen shows a big connector icon in the middle of the screen.
On the other Mac, your MacBook's internal drive will now appear as an external drive and, once you've downloaded the Yosemite Installer on the other Mac (If you've downloaded it before you'll have to hold the alt/option key while you click on your Purchases tab in the App Store), then you should have no difficulty selecting the MacBook's intenal drive to install to.
You will have to erase the El Capitan install before being able to install Yoseemite though because the installer prevents installing an older version of itself over a newer version. So, of course, anything you need from MacBook needs to be copied over to somewhere safe before you erase. This should be easy because of your MacBook being in Target Mode.
Post back if you run into any trouble...
Speculation on my part but I think illusiondweller may have a 2015 MacBook which only has a USB C port.
Thanks, re-reading the question with that in mind leads me to think you're right.
I appreciate your input.
I'm going to assume that dialabrain is correct and that you've got a 2015 MacBook.
I appreciate that connectivity for that model is difficult/non-existant without paying for adaptors or cables etc.
However, if you already have a USB 3.0 or USB 3.1 USB-A to USB-C Cable (not an adaptor - I'm guessing you don't have one of those) then you can use target mode as described above.
Internet Recovery Mode (which you've already attempted, I know), should work for you. In instances where it should but doesn't, the problem is typically the nature of the internet connection. See here for a chart of what won't work: https://support.apple.com/en-ie/HT201314
If IRM really is a dead duck, and you've no way to physically connect to an external installer (bar IRM you can't install OS X remotely without a physical connection), you're going to run up against OS X refusing to install a version of itself that is lower than the one already installed.
I can think of a couple of hacky command-line-from-Recovery-Mode based solutions, but I've not tested either of them and you'd be taking the chance that you could end up with no functioning OS X on your MacBook at all if it goes badly wrong. At that point, you would need an adaptor or cable to get back to Yosemite.