I've acquired four older intel based iMacs from a school, i've been collecting older computers and installing Edubuntu on them for lower income families. But I can't seem to figure out this iMac. I think because it was from a school they have a lot of the options locked down. I've tried holding down the option key to get it to show the startup manager but nothing is working. Apologize in advance but I'm not very knowledgeable when it comes to the mac OS.
Any ideas on how to get this machine booting from USB?