:man| Alphabetical   Categories   About us 
 
GETTIMEOFDAY (2) | System calls | Unix Manual Pages | :man

NAME

gettimeofday, settimeofday - get/set date and time

CONTENTS

Library
Synopsis
Description
Return Values
Errors
See Also
History

LIBRARY


.Lb libc

SYNOPSIS


.In sys/time.h int gettimeofday "struct timeval *tp" "struct timezone *tzp" int settimeofday "const struct timeval *tp" "const struct timezone *tzp"

DESCRIPTION


.Bf -symbolic Note: timezone is no longer used; this information is kept outside the kernel.
.Ef

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
.In sys/time.h as:


struct timeval {
long tv_sec; /* seconds since Jan. 1, 1970 */
long tv_usec; /* and microseconds */
};


struct timezone {
inttz_minuteswest; /* minutes west of Greenwich */
inttz_dsttime;/* type of dst correction */
};

The
.Vt 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


.Rv -std

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

HISTORY


Share this page

     Follow us

Facebook Twitter Google+ LinkedIn


 
Created by Blin Media, 2008-2013