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30.Dd $Mdocdate: July 18 2013 $
31.Dt NICE 3
32.Os
33.Sh NAME
34.Nm nice
35.Nd change process scheduling priority
36.Sh SYNOPSIS
37.In unistd.h
38.Ft int
39.Fn nice "int incr"
40.Sh DESCRIPTION
41.Bf -symbolic
42This interface is obsoleted by
43.Xr setpriority 2 .
44.Ef
45.Pp
46The
47.Fn nice
48function adds the value specified in
49.Fa incr
50to the scheduling priority of the invoking process.
51.Pp
52.Fa incr
53is an integer such that the resulting scheduling priority
54is within the range \-20 to 20.
55Priority values outside this range are truncated to the appropriate limit.
56The default priority is 0; lower priorities cause more favorable scheduling.
57Only the superuser may lower priorities.
58.Pp
59Children inherit the priority of their parent processes via
60.Xr fork 2 .
61.Sh RETURN VALUES
62On success,
63.Fn nice
64returns the new priority.
65On error, it returns -1.
66.Pp
67Since
68.Fn nice
69can legitimately return the value -1, it is necessary
70to clear the external variable
71.Va errno
72prior to the
73call, then check it afterward to determine
74if a -1 is an error or a legitimate value.
75.Sh ERRORS
76.Fn nice
77has the same failure conditions as
78.Xr setpriority 2 .
79.Sh SEE ALSO
80.Xr nice 1 ,
81.Xr fork 2 ,
82.Xr setpriority 2 ,
83.Xr renice 8
84.Sh HISTORY
85A
86.Fn nice
87system call first appeared in
88.At v3 .
89It has accepted an
90.Fa incr
91argument since
92.At v4 .
93