How to alter the priority of running processes

Answer:

The basic syntax is as the following

renice {priority} pid

Where priority range from -20 to 19 (lowest priority)

For example, to set the priority of pid 755 to -19, try

sudo renice 19 755

If you want to set by process name instead of pid, you can use

sudo renice 19 `pgrep apache2`

Where apache2 is the process name you want to set.