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This thorn tries to renice all processes of Cactus to a given nice level.
To renice a process means to change its nice level after the start. The nice level is a way to control the priority of processes for cpu power. It is always a good idea to give cpu-intensive jobs (like Cactus runs) a low priority if you are using desktop machines, especially if other people are using them too.

The nice level has a range of $-20$ to $19$. A higher number means less priority. Mostly, normal processes will get $0$ and only the superuser (root) can use negative values. Also only root can lower the nice level of a process, so if you nice your Cactus Run to 19, you cannot renice it later to an lower nice-level. The nice level of single processes can be controled by the system commands $nice$ and/or $renice$. In the case of Cactus and Lamd this is not possible at startup. Therefore this thorn will set the nice level of your processes at CCTK_PARAMCHECK (in the beginning of the calculation).
This thorn has only one parameter: