When we work with the nice command, it's clear that it can't change the scheduling priority of running processes. As we've just seen, we would need to stop and then start the process in this case. This is where the renice command shines. We can leverage the renice command to change the niceness while the process is running. To see the syntax, we would pass the --help option:
root@ubuntu:/home/philip# renice --help
Usage:
renice [-n] <priority> [-p|--pid] <pid>...
renice [-n] <priority> -g|--pgrp <pgid>...
renice [-n] <priority> -u|--user <user>...
Alter the priority of running processes.
Options:
-n, --priority <num> specify the nice increment value
-p, --pid <id> interpret argument as process ID (default)
-g, --pgrp <id> interpret argument as process group ID
-u, --user <...