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.Dd May 7, 2022 29.Dt DMESG 8 30.Os 31.Sh NAME 32.Nm dmesg 33.Nd "display the system message buffer" 34.Sh SYNOPSIS 35.Nm 36.Op Fl ac 37.Op Fl M Ar core Op Fl N Ar system 38.Sh DESCRIPTION 39The 40.Nm 41utility displays the contents of the system message buffer. 42If the 43.Fl M 44option is not specified, the buffer is read from the currently running kernel 45via the 46.Xr sysctl 3 47interface. 48Otherwise, the buffer is read from the specified core file, 49using the name list from the specified kernel image (or from 50the default image). 51.Pp 52The options are as follows: 53.Bl -tag -width indent 54.It Fl a 55Show all data in the message buffer. 56This includes any syslog records and 57.Pa /dev/console 58output. 59.It Fl c 60Clear the kernel buffer after printing. 61.It Fl M 62Extract values associated with the name list from the specified core. 63.It Fl N 64If 65.Fl M 66is also specified, 67extract the name list from the specified system instead of the default, 68which is the kernel image the system has booted from. 69.El 70.Sh SYSCTL VARIABLES 71The following 72.Xr sysctl 8 73variables control how the kernel timestamps entries in the message buffer: 74The default value is shown next to each variable. 75.Bl -tag -width indent 76.It kern.msgbuf_show_timestamp : No 0 77If set to 0, no timestamps are added. 78If set to 1, then a 1-second granularity timestamp will be added to most lines 79in the message buffer. 80If set to 2, then a microsecond granularity timestamp will be added. 81This may also be set as a boot 82.Xr loader 8 83tunable. 84The timestamps are placed at the start of most lines that the kernel generates. 85Some multi-line messages will have only the first line tagged with a timestamp. 86.El 87.Sh FILES 88.Bl -tag -width ".Pa /var/run/dmesg.boot" -compact 89.It Pa /var/run/dmesg.boot 90usually a snapshot of the buffer contents 91taken soon after file systems are mounted 92at startup time 93.El 94.Sh SEE ALSO 95.Xr sysctl 3 , 96.Xr syslogd 8 97.Sh HISTORY 98The 99.Nm 100utility appeared in 101.Bx 3 . 102