运行级别（Runlevel）指的是Unix或者Linux等类Unix操作系统下不同的运行模式。运行级别通常分为7等，分别是从0到6，但如果必要的话也可以更多。

例如在大多数linux操作系统下一共有如下6个典型的运行级别：

在Debian Linux中2－5这四个运行级别都集中在级别2上。这个级别也是系统预设的正常运行级别。

Runlevel is a mode of operation in one of the computer operating systems that implement Unix System V-style initialization. Conventionally, seven runlevels exist, numbered from zero to six; though up to ten, from zero to nine, may be used. S is sometimes used as a synonym for one of the levels. Only one runlevel is executed on startup; run levels are not executed one after another, i.e. either the runlevel 2, 3 or 4 is executed, not more of them sequentially or in any other order.