NAME
nice - change the nice value of a process
SYNOPSIS
#include <unistd.h>
int nice(int incr);
DESCRIPTION
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.
RETURN VALUE
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.
ERRORS
The nice() function shall fail if:
EPERM The incr argument is negative and the calling process does not
have appropriate privileges.
The following sections are informative.
EXAMPLES
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);
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
getpriority() , setpriority() , the Base Definitions volume of
IEEE Std 1003.1-2001, <limits.h>, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. 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 http://www.opengroup.org/unix/online.html .