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1.\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org>
2.\" All rights reserved.
3.\"
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25.\" $FreeBSD: src/share/man/man4/ktr.4,v 1.9 2003/09/08 19:57:19 ru Exp $
44cb301e 26.\" $DragonFly: src/share/man/man4/ktr.4,v 1.3 2006/05/26 19:39:39 swildner Exp $
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27.\"
28.Dd February 16, 2001
29.Dt KTR 4
30.Os
31.Sh NAME
32.Nm ktr
33.Nd kernel tracing facility
34.Sh SYNOPSIS
35.Cd options KTR
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
41.Sh DESCRIPTION
42The
43.Nm
44facility allows kernel events to be logged while the kernel executes so that
45they can be examined later when debugging.
46The only mandatory option to enable
47.Nm
48is
49.Dq Li options KTR .
50.Pp
51The
52.Dv KTR_ENTRIES
53option sets the size of the buffer of events.
54It should be a power of two.
55The size of the buffer in the currently running kernel can be found via the
56read-only sysctl
57.Va debug.ktr.entries .
58By default the buffer contains 1024 entries.
59.Ss Event Masking
60Event levels can be enabled or disabled to trim excessive and overly verbose
61logging.
62First, a mask of events is specified at compile time via the
63.Dv KTR_COMPILE
64option to limit which events are actually compiled into the kernel.
65The default value for this option is for all events to be enabled.
66.Pp
67Secondly, the actual events logged while the kernel runs can be further
68masked via the run time event mask.
69The
70.Dv KTR_MASK
71option sets the default value of the run time event mask.
72The runtime event mask can also be set by the
73.Xr loader 8
74via the
75.Va debug.ktr.mask
76environment variable.
77It can also be examined and set after booting via the
78.Va debug.ktr.mask
79sysctl.
80By default the run time mask is set to log only
81.Dv KTR_GEN
82events.
83The definitions of the event mask bits can be found in
44cb301e 84.In sys/ktr.h .
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85.Pp
86Furthermore, there is a CPU event mask whose default value can be changed via
87the
88.Dv KTR_CPUMASK
89option.
90A CPU must have the bit corresponding to its logical id set in this bitmask
91for events that occur on it to be logged.
92This mask can be set by the
93.Xr loader 8
94via the
95.Va debug.ktr.cpumask
96environment variable.
97It can also be examined and set after booting via the
98.Va debug.ktr.cpumask
99sysctl.
100By default events on all CPUs are enabled.
101.Ss Verbose Mode
102By default, events are only logged to the internal buffer for examination
103later, but if the verbose flag is set then they are dumped to the kernel
104console as well.
105This flag can also be set from the loader via the
106.Va debug.ktr.verbose
107environment variable, or it can be examined and set after booting via the
108.Va debug.ktr.verbose
109sysctl.
110If the flag is set to zero, which is the default, then verbose output is
111disabled.
112If the flag is set to one, then the contents of the log message and the CPU
113number are printed to the kernel console.
114If the flag is greater than one, then the filename and line number of the
115event are output to the console in addition to the log message and the CPU
116number.
117The
118.Dv KTR_VERBOSE
119option sets the flag to one.
120.Ss Examining the Events
121The KTR buffer can be examined from within
122.Xr ddb 4
123via the
124.Ic show ktr Op Cm /v
125command.
126This command displays the contents of the trace buffer one page at a time.
127At the
128.Dq Li --more--
129prompt, the Enter key displays one more entry and prompts again.
130The spacebar displays another page of entries.
131Any other key quits.
132By default the timestamp, filename, and line number are not displayed with
133each log entry.
134If the
135.Cm /v
136modifier is specified, then they are displayed in addition to the normal
137output.
138Note that the events are displayed in reverse chronological order.
139That is, the most recent events are displayed first.
140.Sh SEE ALSO
141.Xr ktr 9
142.Sh HISTORY
143The KTR kernel tracing facility first appeared in
144.Bsx 3.0
145and was imported into
146.Fx 5.0
147and
148.Dx 1.1 .