Unix systems (and thus Linux) are multi-tasking and multi-user systems. Indeed, several processes can run in parallel, and be owned by different users: the kernel mediates access to the resources between the different processes. As a part of this task, it has a concept of priority, which allows it to favor certain processes over others, as needed. When you know that a process can run in low priority, you can indicate so by running it with nice program. The program will then have a smaller share of the CPU, and will have a smaller impact on other running processes. Of course, if no other process needs to run, the program will not be artificially held back.

nice 会给优先级添加“niceness”：正值优先级（从1到19）逐渐降低优先级，而负值（从 -1 到 -20）增加优先级－但是仅有超级用户可以使用负值优先级。除非特别指明（参看 nice(1) 手册）， nice 将当前优先级加10。

若发现已运行的工作应以 nice 启动，修正它并不算太迟；renice 命令可改变运行中进程的优先序，增加或减少均可 (但减少 “niceness” 是超级用户的权限)。