nice(2) - osol9

1nice(2)                          System Calls                          nice(2)
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NAME

6       nice - change priority of a process
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SYNOPSIS

9       #include <unistd.h>
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11       int nice(int incr);
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DESCRIPTION

15       The  nice()  function  allows  a  process  to change its priority.  The
16       invoking  process must be in  a  scheduling  class  that  supports  the
17       nice().
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20       The  nice()  function  adds the value of  incr to the nice value of the
21       calling process. A process's nice value is a  non-negative  number  for
22       which a greater positive value results in lower CPU priority.
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25       A  maximum  nice  value of (2 * NZERO) −1 and a minimum nice value of 0
26       are imposed by the system.  NZERO  is  defined  in  <limits.h>  with  a
27       default  value  of  20. Requests for values above or below these limits
28       result in the nice value being set to the corresponding limit.  A  nice
29       value of 40 is treated as 39.
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32       Calling  the nice() function has no effect on the priority of processes
33       or threads with policy SCHED_FIFO or SCHED_RR.
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36       Only a process with the {PRIV_PROC_PRIOCNTL} privilege  can  lower  the
37       nice value.
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RETURN VALUES

40       Upon  successful  completion,  nice()  returns the new nice value minus
41       NZERO. Otherwise, −1 is returned,  the  process's  nice  value  is  not
42       changed, and errno is set to indicate the error.
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ERRORS

45       The nice() function will fail if:
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47       EINVAL    The  nice()  function  is called by a process in a scheduling
48                 class other than time-sharing or fixed-priority.
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51       EPERM     The incr argument is negative or  greater  than  40  and  the
52                 {PRIV_PROC_PRIOCNTL}  privilege is not asserted in the effec‐
53                 tive set of the calling process.
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USAGE

57       The priocntl(2) function is a more general interface to scheduler func‐
58       tions.
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61       Since  −1  is  a permissible return value in a successful situation, an
62       application wishing to check for error situations should set  errno  to
63       0,  then  call  nice(),  and if it returns −1, check to see if errno is
64       non-zero.
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ATTRIBUTES

67       See attributes(5) for descriptions of the following attributes:
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72       ┌─────────────────────────────┬─────────────────────────────┐
73       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
74       ├─────────────────────────────┼─────────────────────────────┤
75       │Interface Stability          │Standard                     │
76       ├─────────────────────────────┼─────────────────────────────┤
77       │MT-Level                     │Async-Signal-Safe            │
78       └─────────────────────────────┴─────────────────────────────┘
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