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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgment: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)dmesg.8 8.1 (Berkeley) 6/5/93 33.\" $FreeBSD: src/sbin/dmesg/dmesg.8,v 1.5.2.5 2002/08/21 18:58:17 trhodes Exp $ 34.\" 35.Dd May 10, 2013 36.Dt DMESG 8 37.Os 38.Sh NAME 39.Nm dmesg 40.Nd "display the system message buffer" 41.Sh SYNOPSIS 42.Nm 43.Op Fl a 44.Op Fl c 45.Op Fl f[f] 46.Op Fl M Ar core 47.Op Fl N Ar system 48.Op Fl n Ar dumpnr 49.Sh DESCRIPTION 50The 51.Nm 52utility displays the contents of the system message buffer. 53If neither the 54.Fl N 55nor the 56.Fl M 57option is specified, the buffer is read from the currently running kernel 58via the 59.Xr sysctl 3 60interface. 61Otherwise, the buffer is read from the specified core file (or from the 62default one), using the name list from the specified kernel image (or from 63the default image). 64.Pp 65The options are as follows: 66.Bl -tag -width indent 67.It Fl a 68Show all data in the message buffer. 69This includes any syslog records and 70.Pa /dev/console 71output. 72.It Fl c 73Clear the kernel buffer after printing. 74.It Fl f[f] 75After the initial message buffer dump 76.Nm 77monitors the kernel for additional data and displays it as it arrives. 78.Nm 79will not terminate until killed in this mode. 80If this option is specified twice, 81.Nm 82will live loop (use the cpu heavily) to obtain updates as quickly as 83possible. 84This second mode should only be used when trying to debug a kernel crashing 85situation. 86.It Fl M 87Extract values associated with the name list from the specified core 88instead of the default 89.Pa /dev/kmem . 90.It Fl N 91Extract the name list from the specified system instead of the default, 92which is the kernel image the system has booted from. 93.It Fl n Ar dumnr 94Use the kernel core dump file numbered dumpnr for debugging. 95.El 96.Sh FILES 97.Bl -tag -width ".Pa /var/run/dmesg.boot" -compact 98.It Pa /var/run/dmesg.boot 99usually a snapshot of the buffer contents 100taken soon after file systems are mounted 101at startup time 102.El 103.Sh SEE ALSO 104.Xr sysctl 3 , 105.Xr syslogd 8 106.Sh HISTORY 107The 108.Nm 109utility appeared in 110.Bx 4.0 . 111