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nice - change the nice value of a process
#include <unistd.h>
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.
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 process' nice value shall not be changed, and errno shall be set to indicate the error.
The nice() function shall fail if:
The following sections are informative.
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>
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