1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
182 lines
5.5 KiB
Groff
182 lines
5.5 KiB
Groff
.\" Copyright (C) 1993-1996 by Andrey A. Chernov, Moscow, Russia.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 4, 1996
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.Dt ADJKERNTZ 8
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.Os FreeBSD
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.Sh NAME
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.Nm adjkerntz
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.Nd "adjust local time CMOS clock to reflect time zone changes and keep current timezone offset for the kernel"
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.Sh SYNOPSIS
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.Nm adjkerntz
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.Fl i
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.Nm adjkerntz
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.Fl a Op Fl s
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.Sh DESCRIPTION
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.Nm Adjkerntz
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maintains the proper relationship between the kernel clock, which
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is always set to UTC, and the CMOS clock, which may be set to local
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time.
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.Nm Adjkerntz
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also informs the kernel about machine timezone shifts to
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maintain proper timestamps for local time file systems such as the MS-DOS
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file system. The main purpose of this thing is not general fixing of
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initially broken MS-DOS file timestamp idea but keeping
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the same timestamps between FreeBSD MS-DOS file system
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and MS-DOS operating system installed on the same
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machine.
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If the file
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.Pa /etc/wall_cmos_clock
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exists, it means that CMOS clock keeps local time (MS-DOS and MS-Windows
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compatible mode).
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If that file does not exist, it means that the CMOS clock keeps UTC time.
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.Nm Adjkerntz
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passes this state to the
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.Pa machdep.wall_cmos_clock
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kernel variable.
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.Pp
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Adjustments may be needed at system startup and shutdown, and
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whenever a time zone change occurs.
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To handle these different situations,
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.Nm adjkerntz
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is invoked in two ways:
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.Bl -tag -width 4n
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.It Cm Fl i
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This form handles system startups and shutdowns.
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.Nm Adjkerntz
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is invoked with this option from
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.Pa /etc/rc
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on entry to multi-user mode, before any other daemons have been started.
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.Nm Adjkerntz
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puts itself into the background.
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Then, for a local time CMOS clock,
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.Nm adjkerntz
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reads the local time from it
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and sets the kernel clock to the corresponding UTC time.
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.Nm Adjkerntz
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also stores the local time zone offset into the
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.Pa machdep.adjkerntz
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kernel variable, for use by subsequent invocations of
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.Nm "'adjkerntz -a'"
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and by local time file systems.
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.Pp
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For a local time CMOS clock
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.Nm "'adjkerntz -i'"
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pauses, and remains inactive as a background daemon until it
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receives a SIGTERM.
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The SIGTERM will normally be sent by
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.Xr init 8
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when the system leaves multi-user mode (usually, because the system
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is being shut down).
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After receiving the SIGTERM,
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.Nm adjkerntz
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reads the UTC kernel clock and updates the CMOS clock, if necessary,
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to ensure that it reflects the current local time zone.
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Then
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.Nm adjkerntz
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exits.
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.It Cm Fl a Op Fl s
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This form is used to update the local time CMOS clock and kernel
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.Pa machdep.adjkerntz
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variable when time zone changes occur,
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e.g., when entering or leaving daylight savings time.
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.Nm Adjkerntz
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uses the kernel clock's UTC time,
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the previously stored
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time zone offset, and the changed time zone rule to
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calculate a new time zone offset.
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It stores the new offset into the
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.Pa machdep.adjkerntz
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kernel variable, and updates the wall CMOS clock to the new local time.
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If
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.Nm "'adjkerntz -a'"
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was started at a nonexistent time (during a timezone change), it exits
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with a warning diagnostic unless the
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.Fl s
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option was used, in which case
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.Nm adjkerntz
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sleeps 30 minutes and tries again.
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.Pp
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This form should be invoked from root's
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.Xr crontab 5
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every half hour between midnight and 4am, when most modern time
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zone changes occur.
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Warning: don't use the
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.Fl s
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option in a
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.Xr crontab 5
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command line, or multiple
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.Nm "'adjkerntz -a'"
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instances could conflict with each other.
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.El
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.Pp
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.Nm Adjkerntz
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clears the kernel timezone structure and makes the kernel clock run
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in the UTC time zone.
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Super-user privileges are required for all operations.
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.Sh ENVIRONMENT
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.Bl -tag -width Fl
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.It Ev TZ
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Time zone change rule, see
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.Xr tzset 3 ;
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not needed when
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.Xr tzsetup 8
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or
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.Xr zic 8
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is used.
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.Sh FILES
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.Bl -tag -width /etc/wall_cmos_clock -compact
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.It Pa /etc/localtime
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Current zoneinfo file, see
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.Xr tzsetup 8
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and
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.Xr zic 8 .
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.It Pa /etc/wall_cmos_clock
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Empty file.
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Its presence indicates that the machine's CMOS clock is set to local
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time, while its absence indicates a UTC CMOS clock.
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.Sh SEE ALSO
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.Xr tzset 3 ,
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.Xr crontab 5 ,
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.Xr mount_msdos 8 ,
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.Xr rc 8 ,
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.Xr sysctl 8 ,
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.Xr tzsetup 8 ,
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.Xr zic 8 .
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.Sh DIAGNOSTICS
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No diagnostics.
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If an error occurs,
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.Nm adjkerntz
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logs an error message via
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.Xr syslog 3
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and exits with a nonzero return code.
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.Sh AUTHOR
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Andrey A. Chernov <ache@astral.msk.su>
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.Sh HISTORY
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The
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.Nm adjkerntz
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command appeared in FreeBSD 1.0.1.
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