Movatterモバイル変換

gettimeofday(2) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|VERSIONS \|STANDARDS \|HISTORY \|NOTES \|SEE ALSO \|COLOPHON

gettimeofday(2)            System Calls Manualgettimeofday(2)

NAME top

       gettimeofday, settimeofday - get / set time

LIBRARY top

       Standard C library (libc,-lc)

SYNOPSIS top

#include <sys/time.h>int gettimeofday(struct timeval *restricttv,struct timezone *_Nullable restricttz);int settimeofday(const struct timeval *tv,const struct timezone *_Nullabletz);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):settimeofday():           Since glibc 2.19:               _DEFAULT_SOURCE           glibc 2.19 and earlier:               _BSD_SOURCE

DESCRIPTION top

       The functionsgettimeofday() andsettimeofday() can get and set       the time as well as a timezone.       Thetv argument is astruct timeval (as specified in<sys/time.h>):           struct timeval {               time_t      tv_sec;     /* seconds */               suseconds_t tv_usec;    /* microseconds */           };       and gives the number of seconds and microseconds since the Epoch       (seetime(2)).       Thetz argument is astruct timezone:           struct timezone {               int tz_minuteswest;     /* minutes west of Greenwich */               int tz_dsttime;         /* type of DST correction */           };       If eithertv ortz is NULL, the corresponding structure is not set       or returned.  (However, compilation warnings will result iftv is       NULL.)       The use of thetimezone structure is obsolete; thetz argument       should normally be specified as NULL.  See VERSIONS.       Under Linux, there are some peculiar "warp clock" semantics       associated with thesettimeofday() system call if on the very       first call (after booting) that has a non-NULLtz argument, thetv       argument is NULL and thetz_minuteswest field is nonzero.  (Thetz_dsttime field should be zero for this case.)  In such a case it       is assumed that the CMOS clock is on local time, and that it has       to be incremented by this amount to get UTC system time.  No doubt       it is a bad idea to use this feature.

RETURN VALUE top

gettimeofday() andsettimeofday() return 0 for success.  On error,       -1 is returned anderrno is set to indicate the error.

ERRORS top

EFAULTOne oftv ortz pointed outside the accessible address              space.EINVAL(settimeofday()):timezone is invalid.EINVAL(settimeofday()):tv.tv_sec is negative ortv.tv_usec is              outside the range [0, 999,999].EINVAL(since Linux 4.3)              (settimeofday()): An attempt was made to set the time to a              value less than the current value of theCLOCK_MONOTONIC              clock (seeclock_gettime(2)).EPERMThe calling process has insufficient privilege to callsettimeofday(); under Linux theCAP_SYS_TIMEcapability is              required.

VERSIONS top

C library/kernel differences       On some architectures, an implementation ofgettimeofday() is       provided in thevdso(7).       The kernel accepts NULL for bothtv andtz.  The timezone argument       is ignored by glibc and musl, and not passed to/from the kernel.       Android's bionic passes the timezone argument to/from the kernel,       but Android does not update the kernel timezone based on the       device timezone in Settings, so the kernel's timezone is typically       UTC.

STANDARDS top

gettimeofday()              POSIX.1-2008 (obsolete).settimeofday()              None.

HISTORY top

SVr4, 4.3BSD. POSIX.1-2001 describesgettimeofday() but notsettimeofday(). POSIX.1-2008 marksgettimeofday() as obsolete, recommending the use ofclock_gettime(2) instead. Traditionally, the fields ofstruct timeval were of typelong.The tz_dsttime field On a non-Linux kernel, with glibc, thetz_dsttime field ofstructtimezone will be set to a nonzero value bygettimeofday() if the current timezone has ever had or will have a daylight saving rule applied. In this sense it exactly mirrors the meaning ofdaylight(3) for the current zone. On Linux, with glibc, the setting of thetz_dsttime field ofstruct timezone has never been used bysettimeofday() orgettimeofday(). Thus, the following is purely of historical interest. On old systems, the fieldtz_dsttime contains a symbolic constant (values are given below) that indicates in which part of the year Daylight Saving Time is in force. (Note: this value is constant throughout the year: it does not indicate that DST is in force, it just selects an algorithm.) The daylight saving time algorithms defined are as follows:DST_NONE/* not on DST */DST_USA/* USA style DST */DST_AUST/* Australian style DST */DST_WET/* Western European DST */DST_MET/* Middle European DST */DST_EET/* Eastern European DST */DST_CAN/* Canada */DST_GB/* Great Britain and Eire */DST_RUM/* Romania */DST_TUR/* Turkey */DST_AUSTALT/* Australian style with shift in 1986 */ Of course it turned out that the period in which Daylight Saving Time is in force cannot be given by a simple algorithm, one per country; indeed, this period is determined by unpredictable political decisions. So this method of representing timezones has been abandoned.

NOTES top

       The time returned bygettimeofday()is affected by discontinuous       jumps in the system time (e.g., if the system administrator       manually changes the system time).  If you need a monotonically       increasing clock, seeclock_gettime(2).       Macros for operating ontimeval structures are described intimeradd(3).

COLOPHON top

       This page is part of theman-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 isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17gettimeofday(2)

Pages that refer to this page:adjtimex(2), alarm(2), clock_getres(2), getitimer(2), seccomp(2), stime(2), syscalls(2), time(2), timerfd_create(2), adjtime(3), ctime(3), difftime(3), ftime(3), pmdaeventarray(3), pmtimeval(3), pthread_cond_init(3), timeradd(3), timeval(3type), tzset(3), uuid_time(3), rtc(4), systemd.exec(5), capabilities(7), time(7), vdso(7), hwclock(8), mount(8)