Inspired by one of the previously answered questions, I tried executing a program by a user who was not its owner -- and the process's RUID and EUID remained the same. (Unless I read the answer wrong and that's not how you can achieve the difference.)
Then I tried opening a program as another user via
sudo -- and still nothing.
I've scanned through all already-existing processes (I think) via
ps axo euid,ruid,comm -e g, and none of them had different RUIDs and EUIDs.
How can I achieve (or find the processes with) the difference? Some specific commands would help, because I could have possibly made some mistakes in some steps.