194 lines
5.5 KiB
Groff
194 lines
5.5 KiB
Groff
.\" Copyright (C) 1993-1998 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 March 8, 2012
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.Dt ADJKERNTZ 8
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.Os
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.Sh NAME
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.Nm adjkerntz
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.Nd adjust the local time CMOS clock to reflect time zone changes and keep the current timezone offset for the kernel
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.Sh SYNOPSIS
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.Nm
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.Fl i
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.Nm
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.Fl a Op Fl s
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.Sh DESCRIPTION
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The
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.Nm
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utility 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 time.
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The
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.Nm
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utility also informs the kernel about machine timezone shifts in order to
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maintain proper timestamps for local time file systems such as the MS-DOS
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file system.
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The main purpose of maintaining these timestamps properly is to keep the
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timestamps of a
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.Fx
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MS-DOS file system and an MS-DOS operating system synchronized when they are
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installed on the same system rather than fixing broken MS-DOS file
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timestamps.
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If the file
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.Pa /etc/wall_cmos_clock
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exists, it means that the 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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The
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.Nm
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utility 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
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is invoked in two ways:
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.Bl -tag -width 4n
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.It Fl i
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This form handles system startups and shutdowns.
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The
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.Nm
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utility 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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The
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.Nm
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utility puts itself into the background.
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Then, for a local time CMOS clock,
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.Nm
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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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The
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.Nm
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utility also stores the local time zone offset in the
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.Pa machdep.adjkerntz
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kernel variable, for use by subsequent invocations of
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.Em "'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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.Em "'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
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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
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exits.
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.It 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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The
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.Nm
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utility 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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.Em "'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
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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 5am, when most modern time
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zone changes occur.
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Warning: do not 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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.Em "'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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The
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.Nm
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utility 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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.El
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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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.El
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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
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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 SEE ALSO
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.Xr tzset 3 ,
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.Xr crontab 5 ,
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.Xr mount_msdosfs 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 HISTORY
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The
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.Nm
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utility appeared in
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.Fx 1.0 .
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.Sh AUTHORS
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.An Andrey A. Chernov Aq Mt ache@astral.msk.su
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