Programming

Different systems use priority differently and this results in the contradictory information. A bit of standardization comes from the parameters to nice and renice: a positive parameter makes the process less important (is nice to other processes). Negative niceness makes the process more important. But what values show up in the kernel depends of who wrote the kernel.

Somewhat universally, there must be two forms of priorities. The first, a scheduling priority helps decide the relative importance of processes on the run queue. This kind of priority is affected by nice and by how much cpu the process tries to use.

The second kind of priority is based on any in-progress system call. When a process, regardless of its first type of priority, issues, for example, a mkdir() system call, it suddenly gets a very high "second kind" priority. Once a mkdir() starts, it must be allowed to complete, or the file system will be damaged. The priority must be so high that the process is unkillable during the system call. Ideally this should last only a fraction of a second.

Users cannot affect the second type of priority. So you can't issue a nice() system call to render your particular mkdir() unimportant and interruptible. (And I'm using mkdir() simply as an example.)

These two types of priorities have varying names on different OS's and many times it seems to me that the names should be switched. So, yeah, some confusion exists here...