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.\" $FreeBSD$ 30.\" 31.Dd May 7, 2022 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 ac 40.Op Fl M Ar core Op Fl N Ar system 41.Sh DESCRIPTION 42The 43.Nm 44utility displays the contents of the system message buffer. 45If the 46.Fl M 47option is not specified, the buffer is read from the currently running kernel 48via the 49.Xr sysctl 3 50interface. 51Otherwise, the buffer is read from the specified core file, 52using the name list from the specified kernel image (or from 53the default image). 54.Pp 55The options are as follows: 56.Bl -tag -width indent 57.It Fl a 58Show all data in the message buffer. 59This includes any syslog records and 60.Pa /dev/console 61output. 62.It Fl c 63Clear the kernel buffer after printing. 64.It Fl M 65Extract values associated with the name list from the specified core. 66.It Fl N 67If 68.Fl M 69is also specified, 70extract the name list from the specified system instead of the default, 71which is the kernel image the system has booted from. 72.El 73.Sh SYSCTL VARIABLES 74The following 75.Xr sysctl 8 76variables control how the kernel timestamps entries in the message buffer: 77The default value is shown next to each variable. 78.Bl -tag -width indent 79.It kern.msgbuf_show_timestamp : No 0 80If set to 0, no timetamps are added. 81If set to 1, then a 1-second granularity timestamp will be added to most lines 82in the message buffer. 83If set to 2, then a microsecond granularity timestamp will be added. 84This may also be set as a boot 85.Xr loader 8 86tunable. 87The timestamps are placed at the start of most lines that the kernel generates. 88Some multi-line messages will have only the first line tagged with a timestamp. 89.El 90.Sh FILES 91.Bl -tag -width ".Pa /var/run/dmesg.boot" -compact 92.It Pa /var/run/dmesg.boot 93usually a snapshot of the buffer contents 94taken soon after file systems are mounted 95at startup time 96.El 97.Sh SEE ALSO 98.Xr sysctl 3 , 99.Xr syslogd 8 100.Sh HISTORY 101The 102.Nm 103utility appeared in 104.Bx 3 . 105