Process prioritisation

                                                           User IDs                   Group IDs

Process starter (Real)                          RUID                        GUID

Right controller (Effective)                EUID                         EGID

$ ps -lf
To see the processes with their PRiority and NIce

NICE
-20 highest priority
+20 lowest priority

$ renice +x/-x <ppid>
To increase/decrease the nice of a process.
Child processes inherit the nice of the parent ones.

PRIORITY
Priorities are 0 to 139 in which 0 to 99 for real time and 100 to 139 for users.
Deepening: https://askubuntu.com/questions/656771/process-niceness-vs-priority