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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)
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Linux man-pages 6.9.1 2024-05-02 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 2024-06-26 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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