NAME

       gettimeofday, settimeofday — get/set date and time

LIBRARY

       Standard C Library (libc, -lc)

SYNOPSIS

       #include <sys/time.h>

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

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

DESCRIPTION

       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.

RETURN VALUES

       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.

ERRORS

       The following error codes may be set in errno:

       [EINVAL]           The supplied timeval value is invalid.

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

SEE ALSO

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

HISTORY

       The gettimeofday() system call appeared in 4.2BSD.

Debian                                           August 4, 2018                                  GETTIMEOFDAY(2)