123 lines
4.1 KiB
Groff
123 lines
4.1 KiB
Groff
.\" $NetBSD: dmesg.8,v 1.26 2018/10/30 19:40:36 kre Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. 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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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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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.\" @(#)dmesg.8 8.1 (Berkeley) 6/5/93
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.\"
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.Dd October 30, 2018
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.Dt DMESG 8
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.Os
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.Sh NAME
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.Nm dmesg
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.Nd display the system message buffer
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.Sh SYNOPSIS
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.Nm
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.Op Fl dTt
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.Op Fl M Ar core
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.Op Fl N Ar system
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.Sh DESCRIPTION
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.Nm
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displays the contents of the system message buffer.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl d
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Show the timestamp deltas.
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Used together with
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.Fl t
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only the deltas are shown.
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.It Fl M
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Extract values associated with the name list from the specified core
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instead of the default ``/dev/mem''.
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.It Fl N
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Extract the name list from the specified system instead of the default
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``/netbsd''.
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.It Fl T
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Format uptime timestamps in a human readable form (using
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.Xr ctime 3 )
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using output suitable for the local locale as set in the environment.
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Repeating this option prints the uptime in ISO 8601 duration form,
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giving the duration since boot, in hours, minutes, and seconds (to
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millisecond resolution).
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A third occurrence causes the duration to always be represented
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to millisecond precision, even where that means trailing zeroes
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appear.
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.It Fl t
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Quiet printing, don't print timestamps.
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.El
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.Pp
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The system message buffer is a circular buffer of a fixed size.
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If the buffer has been filled, the first line of the
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.Nm
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output may not be complete.
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The size of the message buffer is configurable at compile-time on
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most systems with the
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.Dv MSGBUFSIZE
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kernel option.
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Look for
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.Dv MSGBUFSIZE
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in
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.Xr options 4
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for details.
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.Sh FILES
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.Bl -tag -width /var/run/dmesg.boot -compact
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.It Pa /var/run/dmesg.boot
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copy of dmesg at the time of last boot.
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.El
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.Sh SEE ALSO
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.Xr options 4 ,
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.Xr syslogd 8
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.Sh HISTORY
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The
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.Nm
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command appeared in
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.Bx 3.0 .
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.Sh BUGS
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The
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.Fl T
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option will report nonsense when displaying lines from
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the message buffer that were not added by the current
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running kernel.
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.Pp
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When
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.Fl TT
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is used, the duration is always given with maximum units of hours,
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even when the number of hours is in the hundreds, thousands, or more.
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This is because converting hours to days, over periods when
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.Dq time skips
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occur, such as summer time beginning or ending, is not trivial.
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A duration of 26 hours might be 1D3H or 1D1H at such events,
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rather than the usual 1D2H,
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and when a time zone alters its offset,
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even more complex calculations are needed.
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None of those calculations are done
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.Pq even to account for sub-hour time zone shifts ,
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the duration indicated is always calculated by simple division of
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seconds by 60 to produce minutes, and again to produce hours.
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Most of the time\ [!] this is correct.
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