1.\" $NetBSD: dmesg.8,v 1.26 2018/10/30 19:40:36 kre Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)dmesg.8 8.1 (Berkeley) 6/5/93 31.\" 32.Dd October 30, 2018 33.Dt DMESG 8 34.Os 35.Sh NAME 36.Nm dmesg 37.Nd display the system message buffer 38.Sh SYNOPSIS 39.Nm 40.Op Fl dTt 41.Op Fl M Ar core 42.Op Fl N Ar system 43.Sh DESCRIPTION 44.Nm 45displays the contents of the system message buffer. 46.Pp 47The options are as follows: 48.Bl -tag -width Ds 49.It Fl d 50Show the timestamp deltas. 51Used together with 52.Fl t 53only the deltas are shown. 54.It Fl M 55Extract values associated with the name list from the specified core 56instead of the default ``/dev/mem''. 57.It Fl N 58Extract the name list from the specified system instead of the default 59``/netbsd''. 60.It Fl T 61Format uptime timestamps in a human readable form (using 62.Xr ctime 3 ) 63using output suitable for the local locale as set in the environment. 64Repeating this option prints the uptime in ISO 8601 duration form, 65giving the duration since boot, in hours, minutes, and seconds (to 66millisecond resolution). 67A third occurrence causes the duration to always be represented 68to millisecond precision, even where that means trailing zeroes 69appear. 70.It Fl t 71Quiet printing, don't print timestamps. 72.El 73.Pp 74The system message buffer is a circular buffer of a fixed size. 75If the buffer has been filled, the first line of the 76.Nm 77output may not be complete. 78The size of the message buffer is configurable at compile-time on 79most systems with the 80.Dv MSGBUFSIZE 81kernel option. 82Look for 83.Dv MSGBUFSIZE 84in 85.Xr options 4 86for details. 87.Sh FILES 88.Bl -tag -width /var/run/dmesg.boot -compact 89.It Pa /var/run/dmesg.boot 90copy of dmesg at the time of last boot. 91.El 92.Sh SEE ALSO 93.Xr options 4 , 94.Xr syslogd 8 95.Sh HISTORY 96The 97.Nm 98command appeared in 99.Bx 3.0 . 100.Sh BUGS 101The 102.Fl T 103option will report nonsense when displaying lines from 104the message buffer that were not added by the current 105running kernel. 106.Pp 107When 108.Fl TT 109is used, the duration is always given with maximum units of hours, 110even when the number of hours is in the hundreds, thousands, or more. 111This is because converting hours to days, over periods when 112.Dq time skips 113occur, such as summer time beginning or ending, is not trivial. 114A duration of 26 hours might be 1D3H or 1D1H at such events, 115rather than the usual 1D2H, 116and when a time zone alters its offset, 117even more complex calculations are needed. 118None of those calculations are done 119.Pq even to account for sub-hour time zone shifts , 120the duration indicated is always calculated by simple division of 121seconds by 60 to produce minutes, and again to produce hours. 122Most of the time\ [!] this is correct. 123