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.\" $FreeBSD$ 26.\" 27.Dd October 20, 2012 28.Dt KTR 4 29.Os 30.Sh NAME 31.Nm ktr 32.Nd kernel tracing facility 33.Sh SYNOPSIS 34.Cd options KTR 35.Cd options ALQ 36.Cd options KTR_ALQ 37.Cd options KTR_COMPILE=(KTR_LOCK|KTR_INTR|KTR_PROC) 38.Cd options KTR_CPUMASK=0x3 39.Cd options KTR_ENTRIES=8192 40.Cd options KTR_MASK=(KTR_INTR|KTR_PROC) 41.Cd options KTR_VERBOSE 42.Sh DESCRIPTION 43The 44.Nm 45facility allows kernel events to be logged while the kernel executes so that 46they can be examined later when debugging. 47The only mandatory option to enable 48.Nm 49is 50.Dq Li options KTR . 51.Pp 52The 53.Dv KTR_ENTRIES 54option sets the size of the buffer of events. 55The size of the buffer in the currently running kernel can be found via the 56sysctl 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 block any tracing. 81The definitions of the event mask bits can be found in 82.In sys/ktr.h . 83.Pp 84Furthermore, there is a CPU event mask whose default value can be changed via 85the 86.Dv KTR_CPUMASK 87option. 88When two or more parameters to 89.Dv KTR_CPUMASK , 90are used, it is important they are not separated by whitespace. 91A CPU must have the bit corresponding to its logical id set in this bitmask 92for events that occur on it to be logged. 93This mask can be set by the 94.Xr loader 8 95via the 96.Va debug.ktr.cpumask 97environment variable. 98It can also be examined and set after booting via the 99.Va debug.ktr.cpumask 100sysctl. 101By default, only CPUs specified in 102.Dv KTR_CPUMASK 103will log events. 104See 105.Pa sys/conf/NOTES 106for more information. 107.Ss Verbose Mode 108By default, events are only logged to the internal buffer for examination 109later, but if the verbose flag is set then they are dumped to the kernel 110console as well. 111This flag can also be set from the loader via the 112.Va debug.ktr.verbose 113environment variable, or it can be examined and set after booting via the 114.Va debug.ktr.verbose 115sysctl. 116If the flag is set to zero, which is the default, then verbose output is 117disabled. 118If the flag is set to one, then the contents of the log message and the CPU 119number are printed to the kernel console. 120If the flag is greater than one, then the filename and line number of the 121event are output to the console in addition to the log message and the CPU 122number. 123The 124.Dv KTR_VERBOSE 125option sets the flag to one. 126.Ss Examining the Events 127The KTR buffer can be examined from within 128.Xr ddb 4 129via the 130.Ic show ktr Op Cm /vV 131command. 132This command displays the contents of the trace buffer one page at a time. 133At the 134.Dq Li --more-- 135prompt, the Enter key displays one more entry and prompts again. 136The spacebar displays another page of entries. 137Any other key quits. 138By default the timestamp, filename, and line number are not displayed with 139each log entry. 140If the 141.Cm /v 142modifier is specified, then they are displayed in addition to the normal 143output. 144If the 145.Cm /V 146modifier is specified, then just the timestamp is displayed in 147addition to the normal output. 148Note that the events are displayed in reverse chronological order. 149That is, the most recent events are displayed first. 150.Ss Logging ktr to Disk 151The 152.Dv KTR_ALQ 153option can be used to log 154.Nm 155entries to disk for post analysis using the 156.Xr ktrdump 8 157utility. 158This option depends on the 159.Dv ALQ 160option. 161Due to the potentially high volume of trace messages the trace mask should be 162selected carefully. 163This feature is configured through a group of sysctls. 164.Bl -tag -width ".Va debug.ktr.alq_enable" 165.It Va debug.ktr.alq_file 166displays or sets the file that 167.Nm 168will log to. 169By default its value is 170.Pa /tmp/ktr.out . 171If the file name is changed while 172.Nm 173is enabled it will not take effect until 174the next invocation. 175.It Va debug.ktr.alq_enable 176enables logging of 177.Nm 178entries to disk if it is set to one. 179Setting this to 0 will terminate logging to disk and revert to 180logging to the normal ktr ring buffer. 181Data is not sent to the ring buffer while logging to disk. 182.It Va debug.ktr.alq_max 183is the maximum number of entries that will be recorded to disk, or 0 for 184infinite. 185This is helpful for limiting the number of particularly high frequency entries 186that are recorded. 187.It Va debug.ktr.alq_depth 188determines the number of entries in the write buffer. 189This is the buffer that holds entries before they are written to disk and 190defaults to the value of the 191.Dv KTR_ENTRIES 192option. 193.It Va debug.ktr.alq_failed 194records the number of times we failed to write an entry due to overflowing the 195write buffer. 196This may happen if the frequency of the logged 197.Nm 198messages outpaces the depth 199of the queue. 200.It Va debug.ktr.alq_cnt 201records the number of entries that have currently been written to disk. 202.El 203.Sh SEE ALSO 204.Xr ktrdump 8 , 205.Xr alq 9 , 206.Xr ktr 9 207.Sh HISTORY 208The KTR kernel tracing facility first appeared in 209.Bsx 3.0 210and was imported into 211.Fx 5.0 . 212