Unable to properly boot Power Mac G5 running Debian without a screen connected
The server is ping-able the entire time, but startup utilities such as
  SSH and other are never started; or at least they aren’t reachable.


That happens because while a system might be pingable, that only happens at the most “embryonic” levels of any system booting into existence. This is why simply pinging a server is not the best way to determine overall system service state. And the reason services—such as SSH—are not starting is because the system is hanging due to it not knowing how to deal with being without a monitor attached; the keyboard should not play any factor in things. 

What you are looking for is a way to run that Power Mac G5 as a headless system. To my knowledge, this can be done if Mac OS X is installed, but this cannot be done if another OS—such as Linux—is running.

That said, you can “trick” the Power Mac G5 to believe a display is installed by using a “headless dongle” which is a fairly common/simple hardware item in the server world. Most of these devices are based on VGA display settings and if you look at instructions—like these for a Mac Mini server—the concept is quite simple. By placing a 75-85ohm resistor between pin 1 and pin 6 on a VGA connecter on a machine you can “trick” the machine into believing a display is connected.



In your case, unclear on whether your Power Mac G5 has native VGA output or not, but if it does, then just find a 75-85ohm resistor, stick it between pin 1 and pin 6, and you should be good to go.

If your Power Mac G5 has a DVI connector, then you’ll need to get a DVI-to-VGA adapter and then set the 75-85ohm resistor on that. But the overall concept is the same.

There are also some online tutorials—such as this one for a “VGA dummy”, this one on Instructables and this one as well—that are a bit more elaborate. Heck, look at these instructions here from a user running Ubuntu on a Mac Mini who faced similar issues as you describe; note he used the three resistor setup:



Why do all of those tutorials require three 75-85ohm resistors for pins 1 &amp; 6, 2 &amp; 7 and 3 &amp; 8 instead of just one for 1 &amp; 6? Not clear myself. But the general concept of these devices are the same: A simple piece of hardware that “tricks” your computer—regardless of OS—to believe a display is attached to it.

Also, if you are running a server on hardware that uses an HDMI connector, you can use one of these similar dongles which runs around $15-20 (U.S.) a piece and works great. Allows you to have true HD resolution on a headless machine when you remote into it. Pretty sure your Power Mac G5 does not have an HDMI connector, but worth mentioning here for reference.