GETTIMEOFDAY(2)                      BSD                       GETTIMEOFDAY(2)



NAME
     gettimeofday, settimeofday - get/set date and time

SYNOPSIS
     #include <sys/time.h>

     gettimeofday(tp, tzp)
     struct timeval *tp;
     struct timezone *tzp;

     settimeofday(tp, tzp)
     struct timeval *tp;
     struct timezone *tzp;

DESCRIPTION
     The system's notion of the current Greenwich time and the current time
     zone is obtained with the gettimeofday call and set with the settimeofday
     call.  The time is expressed in seconds and microseconds since midnight
     (0 hour), January 1, 1970.  The resolution of the system clock is
     hardware dependent, and the time may be updated continuously or in
     "ticks." If tzp is 0, the time zone information will not be returned or
     set.

     The structures pointed to by tp and tzp are defined in <sys/time.h> as
     follows:

          struct timeval {
               long tv_sec;        /* seconds */
               long tv_usec;       /* and microseconds */
          };

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

     The timezone structure indicates the local time zone (measured in minutes
     of time westward from Greenwich), and a flag that, if nonzero, indicates
     that daylight-saving time applies locally during the appropriate part of
     the year.

     Only the super-user may set the time of day or time zone.

ERRORS
     The following error codes may be set in errno:

     [EFAULT]   An argument address referenced invalid memory.

     [EPERM]    A user other than the super-user attempted to set the time.

SEE ALSO
     date(1), ctime(3), timed(8)

DIAGNOSTICS
     A 0 return value indicates that the call succeeded.  A -1 return value
     indicates an error occurred, and in this case an error code is stored
     into the global variable errno.

NOTES
     Domain/OS uses timeval to seed the algorithm by which it computes UIDs
     (unique identifiers).  The UID generator is seeded when the system is

     booted.  Setting timeval backwards, therefore, incurs the risk that
     objects created during the interval of time starting after the
     workstation is shut down and lasting for as long as timeval was set
     backwards will be assigned the same UIDs as existing objects.  The only
     way to eliminate this risk entirely is not to create any objects during
     this time:  when shutting down, wait for as much time as timeval was set
     backwards before rebooting.