renice

Set the absolute priority of a running process

$ renice --priority [3] -p [pid]

$ sudo renice --relative [-4] -p [pid]

$ renice --relative [4] -u [user]

$ sudo renice [-5] -g [process_group]

renice [-n] priority [-g|-p|-u] identifier...

renice alters the scheduling priority (niceness) of running processes. Niceness values range from -20 (highest priority, most favorable to the process) to 19 (lowest priority, least favorable).
Regular users can only increase niceness (lower priority) of their own processes. The superuser can decrease niceness (raise priority) and modify any process.

-n, --priority _priority_

Specify the scheduling priority to set

Change priority relative to current value

Interpret arguments as process IDs (default)

Interpret arguments as usernames or UIDs

Interpret arguments as process group IDs

Lowering niceness (increasing priority) requires root privileges. The actual scheduling effect depends on the system's scheduler and load. Setting extreme priorities can impact system responsiveness.

The renice command originated in 4.0BSD and has been a standard Unix utility since. It complements the nice command, which sets priority when launching new processes.

nice(1), top(1), ps(1), ionice(1)