(Sorry for the incredibly noob question. I’m trying to figure what is possible before buying some parts, which is why I’m asking instead of just trying it out myself.)

I am planning to make a server out of a few old PC parts. I’ll mostly be using it for two purposes:

(1) Serving media, cloud storage and a few other services to my devices.

(2) As a media center for a home cinema setup.

Of course, since (1) implies it will be running 24/7, I’m trying to be mindful about power consumption. One of the ways I’ve planned to do that is by keeping the setup headless until I actually want to use it as in (2), when I’d like to be able to launch a graphical session (for the sake of the argument, let’s say in Ubuntu).

Now my question is: is there any way to launch an X session (again, simplicity, let’s say I plug in a keyboard and type a command) and exit it without needing to restart the server? For example, if someone else is using the server to watch something in their own laptop, I wouldn’t want to restart the server just to watch something in the home cinema.

My intuition tells me that simply running startx should not kill the existent session, is this correct?