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.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\"
.\" The GNU General Public License's references to "object code"
.\" and "executables" are to be interpreted as the output of any
.\" document formatting or typesetting system, including
.\" intermediate and printed output.
.\"
.\" This manual is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
.\" License along with this manual; if not, write to the Free
.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
.\" USA.
.\"
.\" 2002-02-16, joey: Converted from glibc.info
.\"
.TH ADJTIME 2 2002-02-16 "Linux 2.0" "Linux Programmer's Manual"
.SH NAME
adjtime \- smoothly tune kernel clock
.SH SYNOPSIS
.B #include <sys/time.h>
.sp
.BI "int adjtime(const struct timeval *" delta ", struct timeval *" olddelta );
.SH DESCRIPTION
This function speeds up or slows down the system clock in order to
make a gradual adjustment. This ensures that the calendar time
reported by the system clock is always monotonically increasing, which
might not happen if you simply set the clock.
The
.I delta
argument specifies a relative adjustment to be made to the clock time.
If negative, the system clock is slowed down fora while until it has
lost this much elapsed time. If positive, the system clock is speeded
up for a while.
If the
.I olddelta
argument is not a null pointer, the
.B adjtime
function returns information about any previous time adjustment that
has not yet completed.
This function is typically used to synchronize the clocks of computers
in a local network. You must be a privileged user to use it.
.SH "RETURN VALUE"
The
.B adjtime
function returns 0 on success and -1 on failure and sets the external
variable
.I errno
accordingly.
.SH ERRORS
.TP
.B EPERM
The calling process does not have enough privileges to access the clock.
.SH NOTE
With a Linux kernel, you can use the
.BR adjtimex (2)
function to permanently change the system clock speed.
.SH "CONFORMING TO"
This function is derived from 4.3 BSD and SVr4.
.SH "SEE ALSO"
.BR adjtimex (2),
.BR settimeofday (2)
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