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34.Dd $Mdocdate: December 11 2021 $
35.Dt TIME 3
36.Os
37.Sh NAME
38.Nm time
39.Nd get time of day
40.Sh SYNOPSIS
41.In time.h
42.Ft time_t
43.Fn time "time_t *now"
44.Sh DESCRIPTION
45The
46.Fn time
47function returns the number of seconds elapsed since
48Jan 1 1970 00:00:00 UTC.
49This value is also written to
50.Fa now
51unless
52.Fa now
53is
54.Dv NULL .
55.Sh RETURN VALUES
56The
57.Fn time
58function is always successful,
59and no return value is reserved to indicate an error.
60.Sh SEE ALSO
61.Xr clock_gettime 2 ,
62.Xr gettimeofday 2 ,
63.Xr ctime 3
64.Sh STANDARDS
65The
66.Fn time
67function conforms to
68.St -p1003.1-2008 .
69.Sh HISTORY
70A
71.Fn time
72system call first appeared in
73.At v1 .
74That version counted time in sixtieths of a second with a 32-bit return value,
75ensuring an integer overflow crisis every 2.26 years.
76In
77.At v6
78the granularity of the return value was reduced to whole seconds,
79delaying the aforementioned crisis until 2038.
80In
81.Bx 4.1c
82the function was moved out of the kernel into the C standard library and
83reimplemented with
84.Xr gettimeofday 2 .
85