.\" Copyright (c) 1980, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)dmesg.8 8.1 (Berkeley) 6/5/93 .\" $FreeBSD: src/sbin/dmesg/dmesg.8,v 1.5.2.5 2002/08/21 18:58:17 trhodes Exp $ .\" .Dd September 29, 2016 .Dt DMESG 8 .Os .Sh NAME .Nm dmesg .Nd "display the system message buffer" .Sh SYNOPSIS .Nm .Op Fl a .Op Fl c .Op Fl f[f] .Op Fl M Ar core .Op Fl N Ar system .Op Fl n Ar dumpnr .Sh DESCRIPTION The .Nm utility displays the contents of the system message buffer. If neither the .Fl N nor the .Fl M option is specified, the buffer is read from the currently running kernel via the .Xr sysctl 3 interface. Otherwise, the buffer is read from the specified core file (or from the default one), using the name list from the specified kernel image (or from the default image). .Pp The options are as follows: .Bl -tag -width indent .It Fl a Show all data in the message buffer. This includes any syslog records and .Pa /dev/console output. .It Fl c Clear the kernel buffer after printing. .It Fl f[f] After the initial message buffer dump .Nm monitors the kernel for additional data and displays it as it arrives. .Nm will not terminate until killed in this mode. If this option is specified twice, .Nm will live loop (using the CPU heavily) to obtain updates as quickly as possible. This second mode should only be used when trying to debug a kernel crashing situation. .It Fl M Ar core Extract values associated with the name list from the specified .Ar core instead of the default .Pa /dev/kmem . .It Fl N Ar system Extract the name list from the specified .Ar system instead of the default, which is the kernel image the system has booted from. .It Fl n Ar dumpnr Use the kernel core dump file numbered .Ar dumpnr for debugging. If not found in the current directory, .Pa /var/crash is checked. .El .Sh FILES .Bl -tag -width ".Pa /var/run/dmesg.boot" -compact .It Pa /var/run/dmesg.boot usually a snapshot of the buffer contents taken soon after file systems are mounted at startup time .El .Sh SEE ALSO .Xr sysctl 3 , .Xr syslogd 8 .Sh HISTORY The .Nm utility appeared in .Bx 3.0 .