NICE(3) Library Functions Manual NICE(3)

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 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);

None.

None.

None.

exec(3), getpriority(3)

XBD <limits.h>, <unistd.h>

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

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

June 14, 2024 posix.fail