time(2) — Linux manual page


TIME(2)                   Linux Programmer's Manual                  TIME(2)

NAME         top

       time - get time in seconds

SYNOPSIS         top

       #include <time.h>

       time_t time(time_t *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 appropriately.

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.

CONFORMING TO         top

       SVr4, 4.3BSD, C89, C99, POSIX.1-2001.  POSIX does not specify any
       error conditions.

NOTES         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 ticks past the time 2**31 (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.

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.

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.09 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2017-09-15                          TIME(2)

Pages that refer to this page: clock_getres(2)clock_gettime(2)clock_settime(2)gettimeofday(2)seccomp(2)settimeofday(2)syscalls(2)aiocb(3)asctime(3)asctime_r(3)clockid_t(3)clock_t(3)ctime(3)ctime_r(3)daylight(3)dev_t(3)difftime(3)div_t(3)double_t(3)fenv_t(3)fexcept_t(3)file(3)FILE(3)float_t(3)ftime(3)getdate(3)getdate_err(3)getdate_r(3)gid_t(3)gmtime(3)gmtime_r(3)id_t(3)imaxdiv_t(3)int16_t(3)int32_t(3)int64_t(3)int8_t(3)intmax_t(3)intn_t(3)intN_t(3)intptr_t(3)lconv(3)ldiv_t(3)lldiv_t(3)localtime(3)localtime_r(3)misc_conv(3)mktime(3)off_t(3)pid_t(3)pmPrintHighResStamp(3)pmPrintStamp(3)pmtimeval(3)pmtimevalAdd(3)pmtimevalDec(3)pmtimevalFromReal(3)pmtimevalInc(3)pmtimevalNow(3)pmtimevalSub(3)pmtimevalToReal(3)__ppc_get_timebase(3)__ppc_get_timebase_freq(3)pthread_timedjoin_np(3)pthread_tryjoin_np(3)ptrdiff_t(3)regex_t(3)regmatch_t(3)regoff_t(3)siginfo_t(3)sigset_t(3)sigval(3)size_t(3)ssize_t(3)strftime(3)strptime(3)suseconds_t(3)timer_t(3)timespec(3)time_t(3)timeval(3)timezone(3)tzname(3)tzset(3)uid_t(3)uint16_t(3)uint32_t(3)uint64_t(3)uint8_t(3)uintmax_t(3)uintn_t(3)uintN_t(3)uintptr_t(3)uuid_time(3)va_list(3)void(3)rtc(4)tzfile(5)utmp(5)utmpx(5)wtmp(5)signal-safety(7)system_data_types(7)time(7)lsof(8)