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 January 25, 2005 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. 55It must be a power of two. 56The size of the buffer in the currently running kernel can be found via the 57read-only sysctl 58.Va debug.ktr.entries . 59By default the buffer contains 1024 entries. 60.Ss Event Masking 61Event levels can be enabled or disabled to trim excessive and overly verbose 62logging. 63First, a mask of events is specified at compile time via the 64.Dv KTR_COMPILE 65option to limit which events are actually compiled into the kernel. 66The default value for this option is for all events to be enabled. 67.Pp 68Secondly, the actual events logged while the kernel runs can be further 69masked via the run time event mask. 70The 71.Dv KTR_MASK 72option sets the default value of the run time event mask. 73The runtime event mask can also be set by the 74.Xr loader 8 75via the 76.Va debug.ktr.mask 77environment variable. 78It can also be examined and set after booting via the 79.Va debug.ktr.mask 80sysctl. 81By default the run time mask is set to log only 82.Dv KTR_GEN 83events. 84The definitions of the event mask bits can be found in 85.In sys/ktr.h . 86.Pp 87Furthermore, there is a CPU event mask whose default value can be changed via 88the 89.Dv KTR_CPUMASK 90option. 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 events on all CPUs are enabled. 102.Ss Verbose Mode 103By default, events are only logged to the internal buffer for examination 104later, but if the verbose flag is set then they are dumped to the kernel 105console as well. 106This flag can also be set from the loader via the 107.Va debug.ktr.verbose 108environment variable, or it can be examined and set after booting via the 109.Va debug.ktr.verbose 110sysctl. 111If the flag is set to zero, which is the default, then verbose output is 112disabled. 113If the flag is set to one, then the contents of the log message and the CPU 114number are printed to the kernel console. 115If the flag is greater than one, then the filename and line number of the 116event are output to the console in addition to the log message and the CPU 117number. 118The 119.Dv KTR_VERBOSE 120option sets the flag to one. 121.Ss Examining the Events 122The KTR buffer can be examined from within 123.Xr ddb 4 124via the 125.Ic show ktr Op Cm /v 126command. 127This command displays the contents of the trace buffer one page at a time. 128At the 129.Dq Li --more-- 130prompt, the Enter key displays one more entry and prompts again. 131The spacebar displays another page of entries. 132Any other key quits. 133By default the timestamp, filename, and line number are not displayed with 134each log entry. 135If the 136.Cm /v 137modifier is specified, then they are displayed in addition to the normal 138output. 139Note that the events are displayed in reverse chronological order. 140That is, the most recent events are displayed first. 141.Ss Logging ktr to Disk 142The 143.Dv KTR_ALQ 144option can be used to log 145.Nm 146entries to disk for post analysis using the 147.Xr ktrdump 8 148utility. 149This option depends on the 150.Dv ALQ 151option. 152Due to the potentially high volume of trace messages the trace mask should be 153selected carefully. 154This feature is configured through a group of sysctls. 155.Bl -tag -width ".Va debug.ktr.alq_enable" 156.It Va debug.ktr.alq_file 157displays or sets the file that 158.Nm 159will log to. 160By default its value is 161.Pa /tmp/ktr.out . 162If the file name is changed while 163.Nm 164is enabled it will not take effect until 165the next invocation. 166.It Va debug.ktr.alq_enable 167enables logging of 168.Nm 169entries to disk if it is set to one. 170Setting this to 0 will terminate logging. 171.It Va debug.ktr.alq_max 172is the maximum number of entries that will be recorded to disk, or 0 for 173infinite. 174This is helpful for limiting the number of particularly high frequency entries 175that are recorded. 176.It Va debug.ktr.alq_depth 177determines the number of entries in the write buffer. 178This is the buffer that holds entries before they are written to disk and 179defaults to the value of the 180.Dv KTR_ENTRIES 181option. 182.It Va debug.ktr.alq_failed 183records the number of times we failed to write an entry due to overflowing the 184write buffer. 185This may happen if the frequency of the logged 186.Nm 187messages outpaces the depth 188of the queue. 189.It Va debug.ktr.alq_cnt 190records the number of entries that have currently been written to disk. 191.El 192.Sh SEE ALSO 193.Xr ktrdump 8 , 194.Xr alq 9 , 195.Xr ktr 9 196.Sh HISTORY 197The KTR kernel tracing facility first appeared in 198.Bsx 3.0 199and was imported into 200.Fx 5.0 . 201