This manual page is part of the POSIX Programmer’s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


nice — change the nice value of a process


#include <unistd.h>

int nice(int incr);


The nice() function shall add the value of incr to the nice value of the calling process. A nice value of a process 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.

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.

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 nice value of the process 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);








exec, getpriority()

The Base Definitions volume of POSIX.1-2008, <limits.h>, <unistd.h>


Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at .

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