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     gettimeofday, settimeofday — get/set date and time


     Standard C Library (libc, -lc)


     #include <sys/time.h>

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

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


     Note: timezone is no longer used; this information is kept outside the kernel.

     The system's notion of the current Greenwich time and the current time zone is obtained with
     the gettimeofday() system call, and set with the settimeofday() system 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 tp or tzp is NULL, the associated time information will not
     be returned or set.

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

     struct timeval {
             time_t          tv_sec;         /* seconds */
             suseconds_t     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.  If the system is running at
     securelevel >= 2 (see init(8)), the time may only be advanced or retarded by a maximum of
     one second.  This limitation is imposed to prevent a malicious super-user from setting
     arbitrary time stamps on files.  The system time can be adjusted backwards without
     restriction using the adjtime(2) system call even when the system is secure.


     Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and
     the global variable errno is set to indicate the error.


     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.


     date(1), adjtime(2), clock_gettime(2), ctime(3), timeradd(3), clocks(7), timed(8)


     The gettimeofday() system call appeared in 4.2BSD.