I've been looking around for this and I can't seem to find the answer.

I have a long running process that I send into the background when I start it with the &

I close my session and the process continues running the way I want it to. However, when I log in again the process is now an orphan. How do I regain control of that process again so I can have access to it again?

I checked all the manuals I can find on process management. I even found a command that forces a process to be disowned from... me. But there's nothing on regaining control of such a process.

Is this done to protect running processes started by other users from being meddled with? That's the only reason I can think of for not being able to find any commands to regain control of an orphan process.