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|---|---|---|
| ab34755c RG |
1 | .\" Copyright (c) 1980 Regents of the University of California. |
| 2 | .\" All rights reserved. The Berkeley software License Agreement | |
| 3 | .\" specifies the terms and conditions for redistribution. | |
| 4 | .\" | |
| 5 | .\" @(#)adjtime.2 1.1 (Berkeley) %G% | |
| 6 | .\" | |
| 7 | .TH ADJTIME 2 "" | |
| 8 | .UC 6 | |
| 9 | .SH NAME | |
| 10 | adjtime \- correct the time to allow synchronization of the system clock | |
| 11 | .SH SYNOPSIS | |
| 12 | .nf | |
| 13 | .ft B | |
| 14 | #include <sys/time.h> | |
| 15 | .PP | |
| 16 | .ft B | |
| 17 | adjtime(delta, olddelta) | |
| 18 | struct timeval *delta; | |
| 19 | struct timeval *olddelta; | |
| 20 | .fi | |
| 21 | .SH DESCRIPTION | |
| 22 | .I Adjtime | |
| 23 | changes the system time, as returned by | |
| 24 | .IR gettimeofday (2), | |
| 25 | moving it backward or forward | |
| 26 | by the number of microseconds corresponding to the timeval | |
| 27 | \fIdelta\fP. | |
| 28 | .PP | |
| 29 | The time is maintained by incrementing it with a machine-dependent tick | |
| 30 | every clock interrupt. | |
| 31 | If \fIdelta\fP is negative, the clock is | |
| 32 | slowed down by incrementing it in smaller ticks until | |
| 33 | the correction is made. | |
| 34 | If \fIdelta\fP is positive, a larger tick | |
| 35 | is used. | |
| 36 | Thus, the time is always | |
| 37 | a monotonically increasing function. | |
| 38 | A time correction from an earlier call to \fIadjtime\fP | |
| 39 | may not be finished when \fIadjtime\fP is called again. | |
| 40 | If \fIolddelta\fP is non-zero, | |
| 41 | then the structure pointed to will contain, upon return, the | |
| 42 | number of microseconds still to be corrected | |
| 43 | from the earlier call. | |
| 44 | .PP | |
| 45 | This call can be used in time servers that synchronize the clocks | |
| 46 | of computers in a local area network. | |
| 47 | Such time servers would slow down the clocks of some machines | |
| 48 | and speed up the clocks of others to bring them to the average network time. | |
| 49 | .PP | |
| 50 | The call | |
| 51 | .IR adjtime (2) | |
| 52 | is restricted to the super-user. | |
| 53 | .SH NOTES | |
| 54 | On a VAX the time is incremented | |
| 55 | in 10ms ticks. | |
| 56 | When \fIadjtime\fP is called with an argument other than zero, | |
| 57 | ticks of 9ms or 11ms are used until the time is corrected. | |
| 58 | A \fIdelta\fP of less than 1ms would have no effect. | |
| 59 | .SH "RETURN VALUE | |
| 60 | A return value of 0 indicates that the call succeeded. | |
| 61 | A return value of \-1 indicates that an error occurred, and in this | |
| 62 | case an error code is stored in the global variable \fIerrno\fP. | |
| 63 | .SH "ERRORS | |
| 64 | The following error codes may be set in \fIerrno\fP: | |
| 65 | .TP 15 | |
| 66 | [EFAULT] | |
| 67 | An argument points outside the process's allocated address space. | |
| 68 | .TP 15 | |
| 69 | [EPERM] | |
| 70 | The process's effective user ID is not that of the super-user. | |
| 71 | .SH "SEE ALSO" | |
| 72 | date(1), gettimeofday(2), timed(8), timedc(8), | |
| 73 | .br | |
| 74 | \fITSP: The Time Synchronization Protocol for UNIX 4.3BSD\fP, | |
| 75 | R. Gusella and S. Zatti |