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.\" 30.Dd May 7, 2022 31.Dt DMESG 8 32.Os 33.Sh NAME 34.Nm dmesg 35.Nd "display the system message buffer" 36.Sh SYNOPSIS 37.Nm 38.Op Fl ac 39.Op Fl M Ar core Op Fl N Ar system 40.Sh DESCRIPTION 41The 42.Nm 43utility displays the contents of the system message buffer. 44If the 45.Fl M 46option is not specified, the buffer is read from the currently running kernel 47via the 48.Xr sysctl 3 49interface. 50Otherwise, the buffer is read from the specified core file, 51using the name list from the specified kernel image (or from 52the default image). 53.Pp 54The options are as follows: 55.Bl -tag -width indent 56.It Fl a 57Show all data in the message buffer. 58This includes any syslog records and 59.Pa /dev/console 60output. 61.It Fl c 62Clear the kernel buffer after printing. 63.It Fl M 64Extract values associated with the name list from the specified core. 65.It Fl N 66If 67.Fl M 68is also specified, 69extract the name list from the specified system instead of the default, 70which is the kernel image the system has booted from. 71.El 72.Sh SYSCTL VARIABLES 73The following 74.Xr sysctl 8 75variables control how the kernel timestamps entries in the message buffer: 76The default value is shown next to each variable. 77.Bl -tag -width indent 78.It kern.msgbuf_show_timestamp : No 0 79If set to 0, no timetamps are added. 80If set to 1, then a 1-second granularity timestamp will be added to most lines 81in the message buffer. 82If set to 2, then a microsecond granularity timestamp will be added. 83This may also be set as a boot 84.Xr loader 8 85tunable. 86The timestamps are placed at the start of most lines that the kernel generates. 87Some multi-line messages will have only the first line tagged with a timestamp. 88.El 89.Sh FILES 90.Bl -tag -width ".Pa /var/run/dmesg.boot" -compact 91.It Pa /var/run/dmesg.boot 92usually a snapshot of the buffer contents 93taken soon after file systems are mounted 94at startup time 95.El 96.Sh SEE ALSO 97.Xr sysctl 3 , 98.Xr syslogd 8 99.Sh HISTORY 100The 101.Nm 102utility appeared in 103.Bx 3 . 104