.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992

.\"

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.\" 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 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

time \- get time in seconds

.SH SYNOPSIS

.B #include <time.h>

.PP

.BI "time_t time(time_t *" tloc );

.SH DESCRIPTION

.BR time ()

returns the time as the number of seconds since the

Epoch, 1970-01-01 00:00:00 +0000 (UTC).

.PP

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 \fIerrno\fP is set

appropriately.

.SH ERRORS

.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 CONFORMING TO

SVr4, 4.3BSD, C89, C99, POSIX.1-2001.

.\" Under 4.3BSD, this call is obsoleted by

.\" .BR gettimeofday (2).

POSIX does not specify any error conditions.

.SH NOTES

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.

The intention is that the interpretation of seconds since the Epoch values be

consistent; see POSIX.1-2008 Rationale A.4.15 for further rationale.

.PP

On Linux, a call to

.BR time ()

with

.I tloc

specified as NULL cannot fail with the error

.BR EOVERFLOW ,

even on ABIs where

.I time_t

is a signed 32-bit integer and the clock ticks past the time 2**31

(2038-01-19 03:14:08 UTC, ignoring leap seconds).

(POSIX.1 permits, but does not require, the

.B EOVERFLOW

error in the case where the seconds since the Epoch will not fit in

.IR time_t .)

Instead, the behavior on Linux is undefined when the system time is out of the

.I time_t

range.

Applications intended to run after 2038 should use ABIs with

.I time_t

wider than 32 bits.

.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.

.PP

The

.I tloc

argument is obsolescent and should always be NULL in new code.

When

.I tloc

is NULL, the call cannot fail.

.\"

.SS C library/kernel differences

On some architectures, an implementation of

.BR time ()

is provided in the

.BR vdso (7).

.SH SEE ALSO

.BR date (1),

.BR gettimeofday (2),

.BR ctime (3),

.BR ftime (3),

.BR time (7),

.BR vdso (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.