nice [ -increment ] command [ argument ... ]
The preferred syntax for invoking nice is to use the -n option to specify the increment. The older form (using -increment) is obsolete but still supported. Using the older form of the command, root can run commands with priority higher than normal by specifying a negative increment. For example, an argument of --10 would decrement the default nice value of 20 by 10 to produce a nice value of 10. This nice value will give a process a higher scheduling priority than the default nice value of 20. Using the new form of the syntax, the increment to the nice value would be specified as -n -10.
Only root may specify a negative value for increment.
You can use the -l and -o nice options to the ps(C) command to display the nice value of a process.
Note also that this description of nice applies only to programs run under the Bourne Shell. The C-Shell has its own nice command, which is documented in csh(C).
By default, background jobs run by the Bourne and Korn shells are assigned a nice value four greater than that of the parent shell. The ksh(C) option +o bgnice disables this behavior, causing background processes to run with the same nice value as the parent shell.
ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992);
AT&T SVID Issue 2;
X/Open CAE Specification, Commands and Utilities, Issue 4, 1992.