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.\" $FreeBSD$ 26.\" 27.Dd April 4, 1996 28.Dt ADJKERNTZ 8 29.Os 30.Sh NAME 31.Nm adjkerntz 32.Nd "adjust local time CMOS clock to reflect time zone changes and keep current timezone offset for the kernel" 33.Sh SYNOPSIS 34.Nm 35.Fl i 36.Nm 37.Fl a Op Fl s 38.Sh DESCRIPTION 39The 40.Nm 41utility maintains the proper relationship between the kernel clock, which 42is always set to UTC, and the CMOS clock, which may be set to local 43time. 44The 45.Nm 46utility also informs the kernel about machine timezone shifts to 47maintain proper timestamps for local time file systems such as the MS-DOS 48file system. 49The main purpose of this thing is not general fixing of 50initially broken MS-DOS file timestamp idea but keeping 51the same timestamps between 52.Fx 53MS-DOS file system 54and MS-DOS operating system installed on the same 55machine. 56If the file 57.Pa /etc/wall_cmos_clock 58exists, it means that CMOS clock keeps local time (MS-DOS and MS-Windows 59compatible mode). 60If that file does not exist, it means that the CMOS clock keeps UTC time. 61The 62.Nm 63utility passes this state to the 64.Pa machdep.wall_cmos_clock 65kernel variable. 66.Pp 67Adjustments may be needed at system startup and shutdown, and 68whenever a time zone change occurs. 69To handle these different situations, 70.Nm 71is invoked in two ways: 72.Bl -tag -width 4n 73.It Fl i 74This form handles system startups and shutdowns. 75The 76.Nm 77utility is invoked with this option from 78.Pa /etc/rc 79on entry to multi-user mode, before any other daemons have been started. 80The 81.Nm 82utility puts itself into the background. 83Then, for a local time CMOS clock, 84.Nm 85reads the local time from it 86and sets the kernel clock to the corresponding UTC time. 87The 88.Nm 89utility also stores the local time zone offset into the 90.Pa machdep.adjkerntz 91kernel variable, for use by subsequent invocations of 92.Em "'adjkerntz -a'" 93and by local time file systems. 94.Pp 95For a local time CMOS clock 96.Em "'adjkerntz -i'" 97pauses, and remains inactive as a background daemon until it 98receives a SIGTERM. 99The SIGTERM will normally be sent by 100.Xr init 8 101when the system leaves multi-user mode (usually, because the system 102is being shut down). 103After receiving the SIGTERM, 104.Nm 105reads the UTC kernel clock and updates the CMOS clock, if necessary, 106to ensure that it reflects the current local time zone. 107Then 108.Nm 109exits. 110.It Fl a Op Fl s 111This form is used to update the local time CMOS clock and kernel 112.Pa machdep.adjkerntz 113variable when time zone changes occur, 114e.g., when entering or leaving daylight savings time. 115The 116.Nm 117utility uses the kernel clock's UTC time, 118the previously stored 119time zone offset, and the changed time zone rule to 120calculate a new time zone offset. 121It stores the new offset into the 122.Pa machdep.adjkerntz 123kernel variable, and updates the wall CMOS clock to the new local time. 124If 125.Em "'adjkerntz -a'" 126was started at a nonexistent time (during a timezone change), it exits 127with a warning diagnostic unless the 128.Fl s 129option was used, in which case 130.Nm 131sleeps 30 minutes and tries again. 132.Pp 133This form should be invoked from root's 134.Xr crontab 5 135every half hour between midnight and 5am, when most modern time 136zone changes occur. 137Warning: do not use the 138.Fl s 139option in a 140.Xr crontab 5 141command line, or multiple 142.Em "'adjkerntz -a'" 143instances could conflict with each other. 144.El 145.Pp 146The 147.Nm 148utility clears the kernel timezone structure and makes the kernel clock run 149in the UTC time zone. 150Super-user privileges are required for all operations. 151.Sh ENVIRONMENT 152.Bl -tag -width Fl 153.It Ev TZ 154Time zone change rule, see 155.Xr tzset 3 ; 156not needed when 157.Xr tzsetup 8 158or 159.Xr zic 8 160is used. 161.El 162.Sh FILES 163.Bl -tag -width /etc/wall_cmos_clock -compact 164.It Pa /etc/localtime 165Current zoneinfo file, see 166.Xr tzsetup 8 167and 168.Xr zic 8 . 169.It Pa /etc/wall_cmos_clock 170Empty file. 171Its presence indicates that the machine's CMOS clock is set to local 172time, while its absence indicates a UTC CMOS clock. 173.El 174.Sh DIAGNOSTICS 175No diagnostics. 176If an error occurs, 177.Nm 178logs an error message via 179.Xr syslog 3 180and exits with a nonzero return code. 181.Sh SEE ALSO 182.Xr tzset 3 , 183.Xr crontab 5 , 184.Xr mount_msdosfs 8 , 185.Xr rc 8 , 186.Xr sysctl 8 , 187.Xr tzsetup 8 , 188.Xr zic 8 189.Sh HISTORY 190The 191.Nm 192utility appeared in 193.Fx 1.0 . 194.Sh AUTHORS 195.An Andrey A. Chernov Aq ache@astral.msk.su 196