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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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time(2) System Calls Manual time(2)
time - get time in seconds
Standard C library (libc, -lc)
#include <time.h>
time_t time(time_t *_Nullable tloc);
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.
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.
EOVERFLOW
The time cannot be represented as a time_t value. This can
happen 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.
POSIX.1 defines 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.
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).
C11, POSIX.1-2008.
SVr4, 4.3BSD, C89, POSIX.1-2001.
Error returns from this system call are indistinguishable from
successful 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.
date(1), gettimeofday(2), ctime(3), ftime(3), time(7), vdso(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 time(2)
Pages that refer to this page: clock_getres(2), gettimeofday(2), seccomp(2), syscalls(2), ctime(3), difftime(3), ftime(3), getdate(3), misc_conv(3), pmtimeval(3), __ppc_get_timebase(3), pthread_cond_init(3), pthread_tryjoin_np(3), strftime(3), strptime(3), time_t(3type), tzset(3), uuid_time(3), rtc(4), tzfile(5), utmp(5), signal-safety(7), time(7), lsof(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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