nice(2)
NAME
nice - 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 superuser privileges 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 effective user ID of the calling process is not
superuser.
USAGE
The priocntl(2) function is a more general interface to
scheduler functions.
Since -1 is a permissible return value in a successful
situation, an application wishing to check for error situa-
tions 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 attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
| MT-Level | Async-Signal-Safe |
|_____________________________|_____________________________|
SEE ALSO
nice(1), exec(2), priocntl(2), getpriority(3C), attri-
butes(5), standards(5)
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