freebsd-dev/lib/libc/sys/gettimeofday.2

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.\"     @(#)gettimeofday.2	8.2 (Berkeley) 5/26/95
.\" $FreeBSD$
.\"
.Dd May 26, 1995
.Dt GETTIMEOFDAY 2
.Os BSD 4
.Sh NAME
.Nm gettimeofday ,
.Nm settimeofday
.Nd get/set date and time
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include <sys/time.h>
.Ft int
.Fn gettimeofday "struct timeval *tp" "struct timezone *tzp"
.Ft int
.Fn settimeofday "const struct timeval *tp" "const struct timezone *tzp"
.Sh DESCRIPTION
.Bf -symbolic
Note: timezone is no longer used; this information is kept outside
the kernel.
.Ef
.Pp
The system's notion of the current Greenwich time and the current time
zone is obtained with the
.Fn gettimeofday
call, and set with the
.Fn 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
.Dq ticks .
If
.Fa tp
or
.Fa tzp
is NULL, the associated time
information will not be returned or set.
.Pp
The structures pointed to by
.Fa tp
and
.Fa tzp
are defined in 
.Ao Pa sys/time.h Ac
as:
.Pp
.Bd -literal
struct timeval {
	long	tv_sec;		/* seconds since Jan. 1, 1970 */
	long	tv_usec;	/* and microseconds */
};

struct timezone {
	int	tz_minuteswest; /* minutes west of Greenwich */
	int	tz_dsttime;	/* type of dst correction */
};
.Ed
.Pp
The 
.Fa 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.
.Pp
Only the super-user may set the time of day or time zone.
If the system is running in secure mode (see
.Xr init 8 ),
the time may only be advanced.
This limitation is imposed to prevent a malicious super-user
from setting arbitrary time stamps on files.
The system time can still be adjusted backwards using the
.Xr adjtime 2
system call even when the system is secure.
.Sh RETURN VALUES
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
.Va errno .
.Sh ERRORS
The following error codes may be set in
.Va errno :
.Bl -tag -width Er
.It Bq Er EFAULT
An argument address referenced invalid memory.
.It Bq Er EPERM
A user other than the super-user attempted to set the time.
.El
.Sh SEE ALSO
.Xr date 1 ,
.Xr adjtime 2 ,
.Xr ctime 3 ,
.Xr clocks 7 ,
.Xr timed 8
.Sh HISTORY
The
.Fn gettimeofday
function call appeared in
.Bx 4.2 .