1.\" Copyright (C) 1993-1998 by Andrey A. Chernov, Moscow, Russia. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD: src/sbin/adjkerntz/adjkerntz.8,v 1.18.2.5 2002/08/21 18:58:00 trhodes Exp $ 26.\" $DragonFly: src/sbin/adjkerntz/adjkerntz.8,v 1.6 2008/05/09 20:31:04 swildner Exp $ 27.\" 28.Dd April 4, 1996 29.Dt ADJKERNTZ 8 30.Os 31.Sh NAME 32.Nm adjkerntz 33.Nd "adjust local time CMOS clock to reflect time zone changes and keep current timezone offset for the kernel" 34.Sh SYNOPSIS 35.Nm 36.Fl i 37.Nm 38.Fl a Op Fl s 39.Sh DESCRIPTION 40The 41.Nm 42utility maintains the proper relationship between the kernel clock, which 43is always set to UTC, and the CMOS clock, which may be set to local 44time. 45The 46.Nm 47utility also informs the kernel about machine timezone shifts to 48maintain proper timestamps for local time file systems such as the MS-DOS 49file system. 50The main purpose of this thing is not general fixing of 51initially broken MS-DOS file timestamp idea but keeping 52the same timestamps between 53.Dx 54MS-DOS file system 55and MS-DOS operating system installed on the same 56machine. 57If the file 58.Pa /etc/wall_cmos_clock 59exists, it means that CMOS clock keeps local time (MS-DOS and MS-Windows 60compatible mode). 61If that file does not exist, it means that the CMOS clock keeps UTC time. 62The 63.Nm 64utility passes this state to the 65.Va machdep.wall_cmos_clock 66kernel variable. 67.Pp 68Adjustments may be needed at system startup and shutdown, and 69whenever a time zone change occurs. 70To handle these different situations, 71.Nm 72is invoked in two ways: 73.Bl -tag -width 4n 74.It Fl i 75This form handles system startups and shutdowns. 76The 77.Nm 78utility is invoked with this option from 79.Pa /etc/rc 80on entry to multi-user mode, before any other daemons have been started. 81The 82.Nm 83utility puts itself into the background. 84Then, for a local time CMOS clock, 85.Nm 86reads the local time from it 87and sets the kernel clock to the corresponding UTC time. 88The 89.Nm 90utility also stores the local time zone offset into the 91.Va machdep.adjkerntz 92kernel variable, for use by subsequent invocations of 93.Em "'adjkerntz -a'" 94and by local time file systems. 95.Pp 96For a local time CMOS clock 97.Em "'adjkerntz -i'" 98pauses, and remains inactive as a background daemon until it 99receives a 100.Dv SIGTERM . 101The 102.Dv SIGTERM 103will normally be sent by 104.Xr init 8 105when the system leaves multi-user mode (usually, because the system 106is being shut down). 107After receiving the 108.Dv SIGTERM , 109.Nm 110reads the UTC kernel clock and updates the CMOS clock, if necessary, 111to ensure that it reflects the current local time zone. 112Then 113.Nm 114exits. 115.It Fl a Op Fl s 116This form is used to update the local time CMOS clock and kernel 117.Va machdep.adjkerntz 118variable when time zone changes occur, 119e.g., when entering or leaving daylight savings time. 120The 121.Nm 122utility uses the kernel clock's UTC time, 123the previously stored 124time zone offset, and the changed time zone rule to 125calculate a new time zone offset. 126It stores the new offset into the 127.Va machdep.adjkerntz 128kernel variable, and updates the wall CMOS clock to the new local time. 129If 130.Em "'adjkerntz -a'" 131was started at a nonexistent time (during a timezone change), it exits 132with a warning diagnostic unless the 133.Fl s 134option was used, in which case 135.Nm 136sleeps 30 minutes and tries again. 137.Pp 138This form should be invoked from root's 139.Xr crontab 5 140every half hour between midnight and 5am, when most modern time 141zone changes occur. 142Warning: don't use the 143.Fl s 144option in a 145.Xr crontab 5 146command line, or multiple 147.Em "'adjkerntz -a'" 148instances could conflict with each other. 149.El 150.Pp 151The 152.Nm 153utility clears the kernel timezone structure and makes the kernel clock run 154in the UTC time zone. 155Super-user privileges are required for all operations. 156.Sh ENVIRONMENT 157.Bl -tag -width Fl 158.It Ev TZ 159Time zone change rule, see 160.Xr tzset 3 ; 161not needed when 162.Xr tzsetup 8 163or 164.Xr zic 8 165is used. 166.El 167.Sh FILES 168.Bl -tag -width /etc/wall_cmos_clock -compact 169.It Pa /etc/localtime 170Current zoneinfo file, see 171.Xr tzsetup 8 172and 173.Xr zic 8 . 174.It Pa /etc/wall_cmos_clock 175Empty file. 176Its presence indicates that the machine's CMOS clock is set to local 177time, while its absence indicates a UTC CMOS clock. 178.El 179.Sh DIAGNOSTICS 180No diagnostics. 181If an error occurs, 182.Nm 183logs an error message via 184.Xr syslog 3 185and exits with a nonzero return code. 186.Sh SEE ALSO 187.Xr tzset 3 , 188.Xr crontab 5 , 189.Xr mount_msdos 8 , 190.Xr rc 8 , 191.Xr sysctl 8 , 192.Xr tzsetup 8 , 193.Xr zic 8 194.Sh HISTORY 195The 196.Nm 197utility appeared in 198.Fx 1.0 . 199.Sh AUTHORS 200.An Andrey A. Chernov Aq ache@astral.msk.su 201