time(2) — Linux manual page

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 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.

VERSIONS

       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).

STANDARDS

       C11, POSIX.1-2008.

HISTORY

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

BUGS

       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

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

COLOPHON

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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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