1.\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org> 2.\" 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.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $ 26.\" $DragonFly: src/share/man/man4/ktr.4,v 1.3 2006/05/26 19:39:39 swildner Exp $ 27.\" 28.Dd February 16, 2001 29.Dt KTR 4 30.Os 31.Sh NAME 32.Nm ktr 33.Nd kernel tracing facility 34.Sh SYNOPSIS 35.Cd options KTR 36.Cd options KTR_COMPILE=(KTR_LOCK|KTR_INTR|KTR_PROC) 37.Cd options KTR_CPUMASK=0x3 38.Cd options KTR_ENTRIES=8192 39.Cd options KTR_MASK=(KTR_INTR|KTR_PROC) 40.Cd options KTR_VERBOSE 41.Sh DESCRIPTION 42The 43.Nm 44facility allows kernel events to be logged while the kernel executes so that 45they can be examined later when debugging. 46The only mandatory option to enable 47.Nm 48is 49.Dq Li options KTR . 50.Pp 51The 52.Dv KTR_ENTRIES 53option sets the size of the buffer of events. 54It should be a power of two. 55The size of the buffer in the currently running kernel can be found via the 56read-only sysctl 57.Va debug.ktr.entries . 58By default the buffer contains 1024 entries. 59.Ss Event Masking 60Event levels can be enabled or disabled to trim excessive and overly verbose 61logging. 62First, a mask of events is specified at compile time via the 63.Dv KTR_COMPILE 64option to limit which events are actually compiled into the kernel. 65The default value for this option is for all events to be enabled. 66.Pp 67Secondly, the actual events logged while the kernel runs can be further 68masked via the run time event mask. 69The 70.Dv KTR_MASK 71option sets the default value of the run time event mask. 72The runtime event mask can also be set by the 73.Xr loader 8 74via the 75.Va debug.ktr.mask 76environment variable. 77It can also be examined and set after booting via the 78.Va debug.ktr.mask 79sysctl. 80By default the run time mask is set to log only 81.Dv KTR_GEN 82events. 83The definitions of the event mask bits can be found in 84.In sys/ktr.h . 85.Pp 86Furthermore, there is a CPU event mask whose default value can be changed via 87the 88.Dv KTR_CPUMASK 89option. 90A CPU must have the bit corresponding to its logical id set in this bitmask 91for events that occur on it to be logged. 92This mask can be set by the 93.Xr loader 8 94via the 95.Va debug.ktr.cpumask 96environment variable. 97It can also be examined and set after booting via the 98.Va debug.ktr.cpumask 99sysctl. 100By default events on all CPUs are enabled. 101.Ss Verbose Mode 102By default, events are only logged to the internal buffer for examination 103later, but if the verbose flag is set then they are dumped to the kernel 104console as well. 105This flag can also be set from the loader via the 106.Va debug.ktr.verbose 107environment variable, or it can be examined and set after booting via the 108.Va debug.ktr.verbose 109sysctl. 110If the flag is set to zero, which is the default, then verbose output is 111disabled. 112If the flag is set to one, then the contents of the log message and the CPU 113number are printed to the kernel console. 114If the flag is greater than one, then the filename and line number of the 115event are output to the console in addition to the log message and the CPU 116number. 117The 118.Dv KTR_VERBOSE 119option sets the flag to one. 120.Ss Examining the Events 121The KTR buffer can be examined from within 122.Xr ddb 4 123via the 124.Ic show ktr Op Cm /v 125command. 126This command displays the contents of the trace buffer one page at a time. 127At the 128.Dq Li --more-- 129prompt, the Enter key displays one more entry and prompts again. 130The spacebar displays another page of entries. 131Any other key quits. 132By default the timestamp, filename, and line number are not displayed with 133each log entry. 134If the 135.Cm /v 136modifier is specified, then they are displayed in addition to the normal 137output. 138Note that the events are displayed in reverse chronological order. 139That is, the most recent events are displayed first. 140.Sh SEE ALSO 141.Xr ktr 9 142.Sh HISTORY 143The KTR kernel tracing facility first appeared in 144.Bsx 3.0 145and was imported into 146.Fx 5.0 147and 148.Dx 1.1 . 149