1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. 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.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)dmesg.8 8.1 (Berkeley) 6/5/93 29.\" $FreeBSD: src/sbin/dmesg/dmesg.8,v 1.5.2.5 2002/08/21 18:58:17 trhodes Exp $ 30.\" 31.Dd September 29, 2016 32.Dt DMESG 8 33.Os 34.Sh NAME 35.Nm dmesg 36.Nd "display the system message buffer" 37.Sh SYNOPSIS 38.Nm 39.Op Fl a 40.Op Fl c 41.Op Fl f[f] 42.Op Fl M Ar core 43.Op Fl N Ar system 44.Op Fl n Ar dumpnr 45.Sh DESCRIPTION 46The 47.Nm 48utility displays the contents of the system message buffer. 49If neither the 50.Fl N 51nor the 52.Fl M 53option is specified, the buffer is read from the currently running kernel 54via the 55.Xr sysctl 3 56interface. 57Otherwise, the buffer is read from the specified core file (or from the 58default one), using the name list from the specified kernel image (or from 59the default image). 60.Pp 61The options are as follows: 62.Bl -tag -width indent 63.It Fl a 64Show all data in the message buffer. 65This includes any syslog records and 66.Pa /dev/console 67output. 68.It Fl c 69Clear the kernel buffer after printing. 70.It Fl f[f] 71After the initial message buffer dump 72.Nm 73monitors the kernel for additional data and displays it as it arrives. 74.Nm 75will not terminate until killed in this mode. 76If this option is specified twice, 77.Nm 78will live loop (using the CPU heavily) to obtain updates as quickly as 79possible. 80This second mode should only be used when trying to debug a kernel crashing 81situation. 82.It Fl M Ar core 83Extract values associated with the name list from the specified 84.Ar core 85instead of the default 86.Pa /dev/kmem . 87.It Fl N Ar system 88Extract the name list from the specified 89.Ar system 90instead of the default, which is the kernel image the system has booted from. 91.It Fl n Ar dumpnr 92Use the kernel core dump file numbered 93.Ar dumpnr 94for debugging. 95If not found in the current directory, 96.Pa /var/crash 97is checked. 98.El 99.Sh FILES 100.Bl -tag -width ".Pa /var/run/dmesg.boot" -compact 101.It Pa /var/run/dmesg.boot 102usually a snapshot of the buffer contents 103taken soon after file systems are mounted 104at startup time 105.El 106.Sh SEE ALSO 107.Xr sysctl 3 , 108.Xr syslogd 8 109.Sh HISTORY 110The 111.Nm 112utility appeared in 113.Bx 3.0 . 114