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32 .Nd kernel tracing facility
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
45 facility allows kernel events to be logged while the kernel executes so that
46 they can be examined later when debugging.
47 The only mandatory option to enable
54 option sets the size of the buffer of events.
55 The size of the buffer in the currently running kernel can be found via the
57 .Va debug.ktr.entries .
58 By default the buffer contains 1024 entries.
60 Event levels can be enabled or disabled to trim excessive and overly verbose
62 First, a mask of events is specified at compile time via the
64 option to limit which events are actually compiled into the kernel.
65 The default value for this option is for all events to be enabled.
67 Secondly, the actual events logged while the kernel runs can be further
68 masked via the run time event mask.
71 option sets the default value of the run time event mask.
72 The runtime event mask can also be set by the
77 It can also be examined and set after booting via the
80 By default the run time mask is set to block any tracing.
81 The definitions of the event mask bits can be found in
84 Furthermore, there is a CPU event mask whose default value can be changed via
88 When two or more parameters to
90 are used, it is important they are not separated by whitespace.
91 A CPU must have the bit corresponding to its logical id set in this bitmask
92 for events that occur on it to be logged.
93 This mask can be set by the
98 It can also be examined and set after booting via the
101 By default, only CPUs specified in
106 for more information.
108 By default, events are only logged to the internal buffer for examination
109 later, but if the verbose flag is set then they are dumped to the kernel
111 This flag can also be set from the loader via the
112 .Va debug.ktr.verbose
113 environment variable, or it can be examined and set after booting via the
114 .Va debug.ktr.verbose
116 If the flag is set to zero, which is the default, then verbose output is
118 If the flag is set to one, then the contents of the log message and the CPU
119 number are printed to the kernel console.
120 If the flag is greater than one, then the filename and line number of the
121 event are output to the console in addition to the log message and the CPU
125 option sets the flag to one.
126 .Ss Examining the Events
127 The KTR buffer can be examined from within
130 .Ic show ktr Op Cm /vV
132 This command displays the contents of the trace buffer one page at a time.
135 prompt, the Enter key displays one more entry and prompts again.
136 The spacebar displays another page of entries.
138 By default the timestamp, filename, and line number are not displayed with
142 modifier is specified, then they are displayed in addition to the normal
146 modifier is specified, then just the timestamp is displayed in
147 addition to the normal output.
148 Note that the events are displayed in reverse chronological order.
149 That is, the most recent events are displayed first.
150 .Ss Logging ktr to Disk
153 option can be used to log
155 entries to disk for post analysis using the
158 This option depends on the
161 Due to the potentially high volume of trace messages the trace mask should be
163 This feature is configured through a group of sysctls.
164 .Bl -tag -width ".Va debug.ktr.alq_enable"
165 .It Va debug.ktr.alq_file
166 displays or sets the file that
169 By default its value is
171 If the file name is changed while
173 is enabled it will not take effect until
175 .It Va debug.ktr.alq_enable
178 entries to disk if it is set to one.
179 Setting this to 0 will terminate logging to disk and revert to
180 logging to the normal ktr ring buffer.
181 Data is not sent to the ring buffer while logging to disk.
182 .It Va debug.ktr.alq_max
183 is the maximum number of entries that will be recorded to disk, or 0 for
185 This is helpful for limiting the number of particularly high frequency entries
187 .It Va debug.ktr.alq_depth
188 determines the number of entries in the write buffer.
189 This is the buffer that holds entries before they are written to disk and
190 defaults to the value of the
193 .It Va debug.ktr.alq_failed
194 records the number of times we failed to write an entry due to overflowing the
196 This may happen if the frequency of the logged
198 messages outpaces the depth
200 .It Va debug.ktr.alq_cnt
201 records the number of entries that have currently been written to disk.
208 The KTR kernel tracing facility first appeared in
210 and was imported into