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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified Sat Jul 24 14:13:40 1993 by Rik Faith <faith@cs.unc.edu>
.\" Additions by Joseph S. Myers <jsm28@cam.ac.uk>, 970909
.\"
.TH time 2 2024-05-02 "Linux man-pages (unreleased)"
.SH NAME
time \- get time in seconds
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <time.h>
.P
.BI "time_t time(time_t *_Nullable " tloc );
.fi
.SH DESCRIPTION
.BR time ()
returns the time as the number of seconds since the
Epoch, 1970-01-01 00:00:00 +0000 (UTC).
.P
If
.I tloc
is non-NULL,
the return value is also stored in the memory pointed to by
.IR tloc .
.SH RETURN VALUE
On success, the value of time in seconds since the Epoch is returned.
On error, \fI((time_t)\ \-1)\fP is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EOVERFLOW
The time cannot be represented as a
.I time_t
value.
This can happen if an executable with 32-bit
.I time_t
is run on a 64-bit kernel when the time is 2038-01-19 03:14:08 UTC or later.
However, when the system time is out of
.I time_t
range in other situations, the behavior is undefined.
.TP
.B EFAULT
.I tloc
points outside your accessible address space (but see BUGS).
.IP
On systems where the C library
.BR time ()
wrapper function invokes an implementation provided by the
.BR vdso (7)
(so that there is no trap into the kernel),
an invalid address may instead trigger a
.B SIGSEGV
signal.
.SH VERSIONS
POSIX.1 defines
.I seconds since the Epoch
using a formula that approximates the number of seconds between a
specified time and the Epoch.
This formula takes account of the facts that
all years that are evenly divisible by 4 are leap years,
but years that are evenly divisible by 100 are not leap years
unless they are also evenly divisible by 400,
in which case they are leap years.
This value is not the same as the actual number of seconds between the time
and the Epoch, because of leap seconds and because system clocks are not
required to be synchronized to a standard reference.
Linux systems normally follow the POSIX requirement
that this value ignore leap seconds,
so that conforming systems interpret it consistently;
see POSIX.1-2018 Rationale A.4.16.
.P
Applications intended to run after 2038 should use ABIs with
.I time_t
wider than 32 bits; see
.BR time_t (3type).
.SS C library/kernel differences
On some architectures, an implementation of
.BR time ()
is provided in the
.BR vdso (7).
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
SVr4, 4.3BSD, C89, POSIX.1-2001.
.\" Under 4.3BSD, this call is obsoleted by
.\" .BR gettimeofday (2).
.SH BUGS
Error returns from this system call are indistinguishable from
successful reports that the time is a few seconds
.I before
the Epoch, so the C library wrapper function never sets
.I errno
as a result of this call.
.P
The
.I tloc
argument is obsolescent and should always be NULL in new code.
When
.I tloc
is NULL, the call cannot fail.
.SH SEE ALSO
.BR date (1),
.BR gettimeofday (2),
.BR ctime (3),
.BR ftime (3),
.BR time (7),
.BR vdso (7)
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