time(2) — Linux manual page


time(2)                    System Calls Manual                   time(2)

NAME         top

       time - get time in seconds

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <time.h>

       time_t time(time_t *_Nullable tloc);

DESCRIPTION         top

       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         top

       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         top

       EFAULT tloc points outside your accessible address space (but see

              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         top

       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.  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.

       On Linux, a call to time() with tloc specified as NULL cannot
       fail with the error EOVERFLOW, even on ABIs where time_t is a
       signed 32-bit integer and the clock reaches or exceeds 2**31
       seconds (2038-01-19 03:14:08 UTC, ignoring leap seconds).
       (POSIX.1 permits, but does not require, the EOVERFLOW error in
       the case where the seconds since the Epoch will not fit in
       time_t.)  Instead, the behavior on Linux is undefined when the
       system time is out of the time_t range.  Applications intended to
       run after 2038 should use ABIs with time_t wider than 32 bits.

   C library/kernel differences
       On some architectures, an implementation of time() is provided in
       the vdso(7).

STANDARDS         top

       C11, POSIX.1-2008.

HISTORY         top

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

BUGS         top

       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.

SEE ALSO         top

       date(1), gettimeofday(2), ctime(3), ftime(3), time(7), vdso(7)

Linux man-pages (unreleased)     (date)                          time(2)

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