[unix-history] / usr / src / lib / libc / sys / adjtime.2

.\" Copyright (c) 1980, 1991 Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)adjtime.2	1.7 (Berkeley) %G%
.\"
.Dd 
.Dt ADJTIME 2
.Os BSD 4.3
.Sh NAME
.Nm adjtime
.Nd "correct the time to allow synchronization of the system clock"
.Sh SYNOPSIS
.Fd #include <sys/time.h>
.Ft int
.Fn adjtime "struct timeval *delta" "struct timeval *olddelta"
.Sh DESCRIPTION
.Fn Adjtime
makes small adjustments to the system time, as returned by
.Xr gettimeofday 2 ,
advancing or retarding it
by the time specified by the timeval
.Fa delta .
If
.Fa delta
is negative, the clock is
slowed down by incrementing it more slowly than normal until
the correction is complete.
If
.Fa delta
is positive, a larger increment than normal
is used.
The skew used to perform the correction is generally a fraction of one percent.
Thus, the time is always
a monotonically increasing function.
A time correction from an earlier call to
.Fn adjtime
may not be finished when
.Fn adjtime
is called again.
If
.Fa olddelta
is non-nil,
the structure pointed to will contain, upon return, the
number of microseconds still to be corrected
from the earlier call.
.Pp
This call may be used by 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.
.Pp
The call 
.Fn adjtime
is restricted to the super-user.
.Sh RETURN VALUES
A return value of 0 indicates that the call succeeded.
A return value of -1 indicates that an error occurred, and in this
case an error code is stored in the global variable
.Va errno .
.Sh ERRORS
.Fn Adjtime
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
An argument points outside the process's allocated address space.
.It Bq Er EPERM
The process's effective user ID is not that of the super-user.
.El
.Sh SEE ALSO
.Xr date 1 ,
.Xr gettimeofday 2 ,
.Xr timed 8 ,
.Xr timedc 8 ,
.Rs
.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
.%A R. Gusella
.%A S. Zatti
.Re
.Sh HISTORY
The
.Nm
function call appeared in
.Bx 4.3 .
Commit	Line	Data
931b8415	1	.\" Copyright (c) 1980, 1991 Regents of the University of California.
d4a07fef	2	.\" All rights reserved.
ab34755c	3	.\"
91cff1e1	4	.\" %sccs.include.redist.man%
d4a07fef	5	.\"
931b8415	6	.\" @(#)adjtime.2 1.7 (Berkeley) %G%
ab34755c	7	.\"
931b8415 CL	8	.Dd
	9	.Dt ADJTIME 2
	10	.Os BSD 4.3
	11	.Sh NAME
	12	.Nm adjtime
	13	.Nd "correct the time to allow synchronization of the system clock"
	14	.Sh SYNOPSIS
	15	.Fd #include <sys/time.h>
	16	.Ft int
	17	.Fn adjtime "struct timeval delta" "struct timeval olddelta"
	18	.Sh DESCRIPTION
	19	.Fn Adjtime
9d26ec35	20	makes small adjustments to the system time, as returned by
931b8415	21	.Xr gettimeofday 2 ,
9d26ec35	22	advancing or retarding it
09cfce6f	23	by the time specified by the timeval
931b8415 CL	24	.Fa delta .
	25	If
	26	.Fa delta
	27	is negative, the clock is
9d26ec35 MK	28	slowed down by incrementing it more slowly than normal until
9d26ec35 MK	29	the correction is complete.
931b8415 CL	30	If
	31	.Fa delta
	32	is positive, a larger increment than normal
ab34755c	33	is used.
9d26ec35	34	The skew used to perform the correction is generally a fraction of one percent.
ab34755c RG	35	Thus, the time is always
ab34755c RG	36	a monotonically increasing function.
931b8415 CL	37	A time correction from an earlier call to
	38	.Fn adjtime
	39	may not be finished when
	40	.Fn adjtime
	41	is called again.
	42	If
	43	.Fa olddelta
	44	is non-nil,
	45	the structure pointed to will contain, upon return, the
ab34755c RG	46	number of microseconds still to be corrected
ab34755c RG	47	from the earlier call.
931b8415	48	.Pp
9d26ec35	49	This call may be used by time servers that synchronize the clocks
ab34755c RG	50	of computers in a local area network.
	51	Such time servers would slow down the clocks of some machines
	52	and speed up the clocks of others to bring them to the average network time.
931b8415	53	.Pp
ab34755c	54	The call
931b8415	55	.Fn adjtime
ab34755c	56	is restricted to the super-user.
931b8415	57	.Sh RETURN VALUES
ab34755c	58	A return value of 0 indicates that the call succeeded.
931b8415 CL	59	A return value of -1 indicates that an error occurred, and in this
	60	case an error code is stored in the global variable
	61	.Va errno .
	62	.Sh ERRORS
	63	.Fn Adjtime
	64	will fail if:
	65	.Bl -tag -width Er
	66	.It Bq Er EFAULT
ab34755c	67	An argument points outside the process's allocated address space.
931b8415	68	.It Bq Er EPERM
ab34755c	69	The process's effective user ID is not that of the super-user.
931b8415 CL	70	.El
	71	.Sh SEE ALSO
	72	.Xr date 1 ,
	73	.Xr gettimeofday 2 ,
	74	.Xr timed 8 ,
	75	.Xr timedc 8 ,
	76	.Rs
	77	.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
	78	.%A R. Gusella
	79	.%A S. Zatti
	80	.Re
	81	.Sh HISTORY
	82	The
	83	.Nm
	84	function call appeared in
	85	.Bx 4.3 .