1 .\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org>
3 .\" Redistribution and use in source and binary forms, with or without
4 .\" modification, are permitted provided that the following conditions
6 .\" 1. Redistributions of source code must retain the above copyright
7 .\" notice, this list of conditions and the following disclaimer.
8 .\" 2. Redistributions in binary form must reproduce the above copyright
9 .\" notice, this list of conditions and the following disclaimer in the
10 .\" documentation and/or other materials provided with the distribution.
12 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
13 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
14 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
15 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
16 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
17 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
18 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
19 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
20 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
21 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 .Nd kernel tracing facility
34 .Cd options KTR_COMPILE=(KTR_LOCK|KTR_INTR|KTR_PROC)
35 .Cd options KTR_CPUMASK=0x3
36 .Cd options KTR_ENTRIES=8192
37 .Cd options KTR_MASK=(KTR_INTR|KTR_PROC)
38 .Cd options KTR_VERBOSE
42 facility allows kernel events to be logged while the kernel executes so that
43 they can be examined later when debugging.
44 The only mandatory option to enable
51 option sets the size of the buffer of events.
52 The size of the buffer in the currently running kernel can be found via the
54 .Va debug.ktr.entries .
55 By default the buffer contains 1024 entries.
57 Event levels can be enabled or disabled to trim excessive and overly verbose
59 First, a mask of events is specified at compile time via the
61 option to limit which events are actually compiled into the kernel.
62 The default value for this option is for all events to be enabled.
64 Secondly, the actual events logged while the kernel runs can be further
65 masked via the run time event mask.
68 option sets the default value of the run time event mask.
69 The runtime event mask can also be set by the
74 It can also be examined and set after booting via the
77 By default the run time mask is set to block any tracing.
78 The definitions of the event mask bits can be found in
81 Furthermore, there is a CPU event mask whose default value can be changed via
85 When two or more parameters to
87 are used, it is important they are not separated by whitespace.
88 A CPU must have the bit corresponding to its logical id set in this bitmask
89 for events that occur on it to be logged.
90 This mask can be set by the
95 It can also be examined and set after booting via the
98 By default, only CPUs specified in
103 for more information.
105 By default, events are only logged to the internal buffer for examination
106 later, but if the verbose flag is set then they are dumped to the kernel
108 This flag can also be set from the loader via the
109 .Va debug.ktr.verbose
110 environment variable, or it can be examined and set after booting via the
111 .Va debug.ktr.verbose
113 If the flag is set to zero, which is the default, then verbose output is
115 If the flag is set to one, then the contents of the log message and the CPU
116 number are printed to the kernel console.
117 If the flag is greater than one, then the filename and line number of the
118 event are output to the console in addition to the log message and the CPU
122 option sets the flag to one.
123 .Ss Examining the Events
124 The KTR buffer can be examined from within
127 .Ic show ktr Op Cm /vV
129 This command displays the contents of the trace buffer one page at a time.
132 prompt, the Enter key displays one more entry and prompts again.
133 The spacebar displays another page of entries.
135 By default the timestamp, filename, and line number are not displayed with
139 modifier is specified, then they are displayed in addition to the normal
143 modifier is specified, then just the timestamp is displayed in
144 addition to the normal output.
145 Note that the events are displayed in reverse chronological order.
146 That is, the most recent events are displayed first.
147 .Ss Logging ktr to Disk
150 option can be used to log
152 entries to disk for post analysis using the
155 This option depends on the
158 Due to the potentially high volume of trace messages the trace mask should be
160 This feature is configured through a group of sysctls.
161 .Bl -tag -width ".Va debug.ktr.alq_enable"
162 .It Va debug.ktr.alq_file
163 displays or sets the file that
166 By default its value is
168 If the file name is changed while
170 is enabled it will not take effect until
172 .It Va debug.ktr.alq_enable
175 entries to disk if it is set to one.
176 Setting this to 0 will terminate logging to disk and revert to
177 logging to the normal ktr ring buffer.
178 Data is not sent to the ring buffer while logging to disk.
179 .It Va debug.ktr.alq_max
180 is the maximum number of entries that will be recorded to disk, or 0 for
182 This is helpful for limiting the number of particularly high frequency entries
184 .It Va debug.ktr.alq_depth
185 determines the number of entries in the write buffer.
186 This is the buffer that holds entries before they are written to disk and
187 defaults to the value of the
190 .It Va debug.ktr.alq_failed
191 records the number of times we failed to write an entry due to overflowing the
193 This may happen if the frequency of the logged
195 messages outpaces the depth
197 .It Va debug.ktr.alq_cnt
198 records the number of entries that have currently been written to disk.
205 The KTR kernel tracing facility first appeared in
207 and was imported into