1 .\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org>
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25 .\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $
26 .\" $DragonFly: src/share/man/man4/ktr.4,v 1.2 2004/12/26 12:37:08 swildner Exp $
33 .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 It should be a power of two.
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 log only
83 The definitions of the event mask bits can be found in
86 Furthermore, there is a CPU event mask whose default value can be changed via
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 events on all CPUs are enabled.
102 By default, events are only logged to the internal buffer for examination
103 later, but if the verbose flag is set then they are dumped to the kernel
105 This flag can also be set from the loader via the
106 .Va debug.ktr.verbose
107 environment variable, or it can be examined and set after booting via the
108 .Va debug.ktr.verbose
110 If the flag is set to zero, which is the default, then verbose output is
112 If the flag is set to one, then the contents of the log message and the CPU
113 number are printed to the kernel console.
114 If the flag is greater than one, then the filename and line number of the
115 event are output to the console in addition to the log message and the CPU
119 option sets the flag to one.
120 .Ss Examining the Events
121 The KTR buffer can be examined from within
124 .Ic show ktr Op Cm /v
126 This command displays the contents of the trace buffer one page at a time.
129 prompt, the Enter key displays one more entry and prompts again.
130 The spacebar displays another page of entries.
132 By default the timestamp, filename, and line number are not displayed with
136 modifier is specified, then they are displayed in addition to the normal
138 Note that the events are displayed in reverse chronological order.
139 That is, the most recent events are displayed first.
143 The KTR kernel tracing facility first appeared in
145 and was imported into