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'\" te
.\" Copyright 1989 AT&T Copyright (c) 1980 Regents of the University of California. All rights reserved. The Berkeley software License Agreement specifies the terms and conditions for redistribution. Copyright (c) 2003, Sun Microsystems, Inc. All Rights Reserved
.TH ADJTIME 2 "Sep 19, 2022"
.SH NAME
adjtime \- correct the time to allow synchronization of the system clock
.SH SYNOPSIS
.nf
#include <sys/time.h>
\fBint\fR \fBadjtime\fR(\fBconst struct timeval *\fR\fIdelta\fR, \fBstruct timeval *\fR\fIolddelta\fR);
.fi
.SH DESCRIPTION
The \fBadjtime()\fR function adjusts the system's notion of the current time as
returned by \fBgettimeofday\fR(3C), advancing or retarding it by the amount of
time specified in the \fBstruct\fR \fBtimeval\fR pointed to by \fIdelta\fR.
.sp
.LP
The adjustment is effected by speeding up (if that amount of time is positive)
or slowing down (if that amount of time is negative) the system's clock by some
small percentage, generally a fraction of one percent. The time is always a
monotonically increasing function. A time correction from an earlier call to
\fBadjtime()\fR may not be finished when \fBadjtime()\fR is called again.
.sp
.LP
If \fIdelta\fR is 0, then \fIolddelta\fR returns the status of the effects of
the previous \fBadjtime()\fR call with no effect on the time correction as a
result of this call. If \fIolddelta\fR is not a null pointer, then the
structure it points to will contain, upon successful return, the number of
seconds and/or microseconds still to be corrected from the earlier call. If
\fIolddelta\fR is a null pointer, the corresponding information will not be
returned.
.sp
.LP
This call may be used in time servers that synchronize the clocks of computers
in a local area network. Such time servers would slow down the clocks of some
machines and speed up the clocks of others to bring them to the average network
time.
.sp
.LP
Only a processes with appropriate privileges can adjust the time of day.
.sp
.LP
The adjustment value will be silently rounded to the resolution of the system
clock.
.SH RETURN VALUES
Upon successful completion, \fBadjtime()\fR returns \fB0\fR. Otherwise, it
returns \fB\(mi1\fR and sets \fBerrno\fR to indicate the error.
.SH ERRORS
The \fBadjtime()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 10n
The \fIdelta\fR or \fIolddelta\fR argument points outside the process's
allocated address space, or \fIolddelta\fR points to a region of the process's
allocated address space that is not writable.
.RE
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The \fBtv_usec\fR member of \fIdelta\fR is not within valid range (\(mi1000000
to 1000000).
.RE
.sp
.ne 2
.na
\fB\fBEPERM\fR\fR
.ad
.RS 10n
The {\fBPRIV_SYS_TIME\fR} privilege is not asserted in the effective set of the
calling process.
.RE
.sp
.LP
Additionally, the \fBadjtime()\fR function will fail for 32-bit interfaces if:
.sp
.ne 2
.na
\fB\fBEOVERFLOW\fR\fR
.ad
.RS 13n
The size of the \fBtv_sec\fR member of the \fBtimeval\fR structure pointed to
by \fIolddelta\fR is too small to contain the correct number of seconds.
.RE
.SH SEE ALSO
.BR date (1),
.BR gettimeofday (3C),
.BR privileges (7)
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