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31 .Nd kernel tracing facility
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
44 facility allows kernel events to be logged while the kernel executes so that
45 they can be examined later when debugging.
46 The only mandatory option to enable
53 option sets the size of the buffer of events.
54 The size of the buffer in the currently running kernel can be found via the
56 .Va debug.ktr.entries .
57 By default the buffer contains 1024 entries.
59 Event levels can be enabled or disabled to trim excessive and overly verbose
61 First, a mask of events is specified at compile time via the
63 option to limit which events are actually compiled into the kernel.
64 The default value for this option is for all events to be enabled.
66 Secondly, the actual events logged while the kernel runs can be further
67 masked via the run time event mask.
70 option sets the default value of the run time event mask.
71 The runtime event mask can also be set by the
76 It can also be examined and set after booting via the
79 By default the run time mask is set to block any tracing.
80 The definitions of the event mask bits can be found in
83 Furthermore, there is a CPU event mask whose default value can be changed via
87 When two or more parameters to
89 are used, it is important they are not separated by whitespace.
90 A CPU must have the bit corresponding to its logical id set in this bitmask
91 for events that occur on it to be logged.
92 This mask can be set by the
97 It can also be examined and set after booting via the
100 By default, only CPUs specified in
105 for more information.
107 By default, events are only logged to the internal buffer for examination
108 later, but if the verbose flag is set then they are dumped to the kernel
110 This flag can also be set from the loader via the
111 .Va debug.ktr.verbose
112 environment variable, or it can be examined and set after booting via the
113 .Va debug.ktr.verbose
115 If the flag is set to zero, which is the default, then verbose output is
117 If the flag is set to one, then the contents of the log message and the CPU
118 number are printed to the kernel console.
119 If the flag is greater than one, then the filename and line number of the
120 event are output to the console in addition to the log message and the CPU
124 option sets the flag to one.
125 .Ss Examining the Events
126 The KTR buffer can be examined from within
129 .Ic show ktr Op Cm /vV
131 This command displays the contents of the trace buffer one page at a time.
134 prompt, the Enter key displays one more entry and prompts again.
135 The spacebar displays another page of entries.
137 By default the timestamp, filename, and line number are not displayed with
141 modifier is specified, then they are displayed in addition to the normal
145 modifier is specified, then just the timestamp is displayed in
146 addition to the normal output.
147 Note that the events are displayed in reverse chronological order.
148 That is, the most recent events are displayed first.
149 .Ss Logging ktr to Disk
152 option can be used to log
154 entries to disk for post analysis using the
157 This option depends on the
160 Due to the potentially high volume of trace messages the trace mask should be
162 This feature is configured through a group of sysctls.
163 .Bl -tag -width ".Va debug.ktr.alq_enable"
164 .It Va debug.ktr.alq_file
165 displays or sets the file that
168 By default its value is
170 If the file name is changed while
172 is enabled it will not take effect until
174 .It Va debug.ktr.alq_enable
177 entries to disk if it is set to one.
178 Setting this to 0 will terminate logging to disk and revert to
179 logging to the normal ktr ring buffer.
180 Data is not sent to the ring buffer while logging to disk.
181 .It Va debug.ktr.alq_max
182 is the maximum number of entries that will be recorded to disk, or 0 for
184 This is helpful for limiting the number of particularly high frequency entries
186 .It Va debug.ktr.alq_depth
187 determines the number of entries in the write buffer.
188 This is the buffer that holds entries before they are written to disk and
189 defaults to the value of the
192 .It Va debug.ktr.alq_failed
193 records the number of times we failed to write an entry due to overflowing the
195 This may happen if the frequency of the logged
197 messages outpaces the depth
199 .It Va debug.ktr.alq_cnt
200 records the number of entries that have currently been written to disk.
207 The KTR kernel tracing facility first appeared in
209 and was imported into