The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


nice - change the nice value of a process


[XSI] [Option Start] #include <unistd.h>

int nice(int
incr); [Option End]


The nice() function shall add the value of incr to the nice value of the calling process. A process' nice value is a non-negative number for which a more positive value shall result in less favorable scheduling.

A maximum nice value of 2*{NZERO}-1 and a minimum nice value of 0 shall be imposed by the system. Requests for values above or below these limits shall result in the nice value being set to the corresponding limit. Only a process with appropriate privileges can lower the nice value.

[PS|TPS] [Option Start] Calling the nice() function has no effect on the priority of processes or threads with policy SCHED_FIFO or SCHED_RR. The effect on processes or threads with other scheduling policies is implementation-defined. [Option End]

The nice value set with nice() shall be applied to the process. If the process is multi-threaded, the nice value shall affect all system scope threads in the process.

As -1 is a permissible return value in a successful situation, an application wishing to check for error situations should set errno to 0, then call nice(), and if it returns -1, check to see whether errno is non-zero.


Upon successful completion, nice() shall return the new nice value -{NZERO}. Otherwise, -1 shall be returned, the process' nice value shall not be changed, and errno shall be set to indicate the error.


The nice() function shall fail if:

The incr argument is negative and the calling process does not have appropriate privileges.

The following sections are informative.


Changing the Nice Value

The following example adds the value of the incr argument, -20, to the nice value of the calling process.

#include <unistd.h>
int incr = -20;
int ret;

ret = nice(incr);








getpriority(), setpriority(), the Base Definitions volume of IEEE Std 1003.1-2001, <limits.h>, <unistd.h>


First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

A statement is added to the description indicating the effects of this function on the different scheduling policies and multi-threaded processes.

End of informative text.

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