Provided by: manpages-dev_3.35-0.1ubuntu1_all bug


       gettimeofday, settimeofday - get / set time


       #include <sys/time.h>

       int gettimeofday(struct timeval *tv, struct timezone *tz);
       int settimeofday(const struct timeval *tv, const struct timezone *tz);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       settimeofday(): _BSD_SOURCE


       The  functions  gettimeofday()  and  settimeofday() can get and set the
       time as well as a timezone.  The tv argument is a  struct  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 (see
       time(2)).  The tz argument is a struct timezone:

           struct timezone {
               int tz_minuteswest;     /* minutes west of Greenwich */
               int tz_dsttime;         /* type of DST correction */

       If either tv or tz is NULL, the corresponding structure is not  set  or

       The  use  of the timezone structure is obsolete; the tz argument should
       normally be specified as NULL.  The tz_dsttime  field  has  never  been
       used  under Linux; it has not been and will not be supported by libc or
       glibc.  Each and every occurrence of this field in  the  kernel  source
       (other  than  the declaration) is a bug.  Thus, the following is purely
       of historic interest.

       The field tz_dsttime contains a symbolic  constant  (values  are  given
       below) that indicates in which part of the year Daylight Saving Time is
       in force.  (Note: its 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      /* Rumania */
           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.  Under
       Linux, in a call to settimeofday() the tz_dsttime field should be zero.

       Under Linux there are some peculiar "warp clock"  semantics  associated
       with  the  settimeofday()  system call if on the very first call (after
       booting) that has a non-NULL tz argument, the tv argument is  NULL  and
       the tz_minuteswest field is nonzero.  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.

       Macros  for  operating  on  timeval   structures   are   described   in


       gettimeofday()  and  settimeofday()  return  0  for  success, or -1 for
       failure (in which case errno is set appropriately).


       EFAULT One of tv or tz pointed outside the accessible address space.

       EINVAL Timezone (or something else) is invalid.

       EPERM  The  calling  process  has  insufficient   privilege   to   call
              settimeofday();  under  Linux  the  CAP_SYS_TIME  capability  is


       SVr4,  4.3BSD.    POSIX.1-2001   describes   gettimeofday()   but   not
       settimeofday().    POSIX.1-2008   marks   gettimeofday()  as  obsolete,
       recommending the use of clock_gettime(2) instead.


       Traditionally, the fields of struct timeval were of type long.


       date(1), adjtimex(2),  time(2),  ctime(3),  ftime(3),  capabilities(7),


       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at