time(2) System Calls Manual time(2)
NAME
time - get time in seconds
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <time.h>
time_t time(time_t *_Nullable tloc);
DESCRIPTION
time() returns the time as the number of seconds since the Epoch,
1970-01-01 00:00:00 +0000 (UTC).
If tloc is non-NULL, the return value is also stored in the memory
pointed to by tloc.
RETURN VALUE
On success, the value of time in seconds since the Epoch is returned.
On error, ((time_t) -1) is returned, and errno is set to indicate the
error.
ERRORS
EOVERFLOW
The time cannot be represented as a time_t value. This can hap-
pen if an executable with 32-bit 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 time_t range in other situations, the
behavior is undefined.
EFAULT tloc points outside your accessible address space (but see BUGS).
On systems where the C library time() wrapper function invokes an
implementation provided by the vdso(7) (so that there is no trap
into the kernel), an invalid address may instead trigger a
SIGSEGV signal.
VERSIONS
POSIX.1 defines seconds since the Epoch using a formula that approxi-
mates 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 ac-
tual 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 require-
ment that this value ignore leap seconds, so that conforming systems in-
terpret it consistently; see POSIX.1-2018 Rationale A.4.16.
Applications intended to run after 2038 should use ABIs with time_t
wider than 32 bits; see time_t(3type).
C library/kernel differences
On some architectures, an implementation of time() is provided in the
vdso(7).
STANDARDS
C11, POSIX.1-2008.
HISTORY
SVr4, 4.3BSD, C89, POSIX.1-2001.
BUGS
Error returns from this system call are indistinguishable from success-
ful reports that the time is a few seconds before the Epoch, so the C
library wrapper function never sets errno as a result of this call.
The tloc argument is obsolescent and should always be NULL in new code.
When tloc is NULL, the call cannot fail.
SEE ALSO
date(1), gettimeofday(2), ctime(3), ftime(3), time(7), vdso(7)
Linux man-pages 6.9.1 2024-05-02 time(2)
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