nice(2) System Calls nice(2)NAMEnice - change priority of a process
SYNOPSIS
#include <unistd.h>
int nice(int incr);
DESCRIPTION
The nice() function allows a process to change its priority. The
invoking process must be in a scheduling class that supports the
nice().
The nice() function adds the value of incr to the nice value of the
calling process. A process's nice value is a non-negative number for
which a greater positive value results in lower CPU priority.
A maximum nice value of (2 * NZERO) −1 and a minimum nice value of 0
are imposed by the system. NZERO is defined in <limits.h> with a
default value of 20. Requests for values above or below these limits
result in the nice value being set to the corresponding limit. A nice
value of 40 is treated as 39.
Calling the nice() function has no effect on the priority of processes
or threads with policy SCHED_FIFO or SCHED_RR.
Only a process with the {PRIV_PROC_PRIOCNTL} privilege can lower the
nice value.
RETURN VALUES
Upon successful completion, nice() returns the new nice value minus
NZERO. Otherwise, −1 is returned, the process's nice value is not
changed, and errno is set to indicate the error.
ERRORS
The nice() function will fail if:
EINVAL The nice() function is called by a process in a scheduling
class other than time-sharing or fixed-priority.
EPERM The incr argument is negative or greater than 40 and the
{PRIV_PROC_PRIOCNTL} privilege is not asserted in the effec‐
tive set of the calling process.
USAGE
The priocntl(2) function is a more general interface to scheduler func‐
tions.
Since −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 if errno is
non-zero.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │Async-Signal-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOnice(1), exec(2), priocntl(2), getpriority(3C), attributes(5), privi‐
leges(5), standards(5)SunOS 5.10 1 Apr 2004 nice(2)