[lttng-ust.git] / doc / man / lttng-ust.3

.TH "LTTNG-UST" "3" "February 16, 2012" "" ""

.SH "NAME"
lttng-ust \(em Linux Trace Toolkit Next Generation User-Space Tracer 2.x

.SH "SYNOPSIS"

.PP
.nf
Link liblttng-ust.so with applications, following this manpage.
.fi
.SH "DESCRIPTION"

.PP
LTTng-UST, the Linux Trace Toolkit Next Generation Userspace Tracer, is
port of the low-overhead tracing capabilities of the LTTng kernel tracer
to user-space. The library "liblttng-ust" enables tracing of
applications and libraries.

.SH "USAGE"
.PP
The simple way to generate the lttng-ust tracepoint probes is to use the
lttng-gen-tp(1) tool. See the lttng-gen-tp(1) manpage for explanation.
.PP

.PP
Here is the way to do it manually, without the lttng-gen-tp(1) helper
script, through an example:
.PP

.SH "CREATION OF TRACEPOINT PROVIDER"

.nf

To create a tracepoint provider, within a build tree similar to
examples/easy-ust installed with lttng-ust documentation, a
sample_component_provider.h for the general layout. This manpage will
focus on the various types that can be recorded into a trace event:

TRACEPOINT_EVENT(
	/*
	 * provider name, not a variable but a string starting with a
	 * letter and containing either letters, numbers or underscores. 
	 * Needs to be the same as TRACEPOINT_PROVIDER. Needs to
	 * follow the namespacing guide-lines in lttng/tracepoint.h:
	 * 
	 * Must be included before include tracepoint provider 
	 * ex.: project_event
	 * ex.: project_component_event
	 *
	 * Optional company name goes here
	 *  ex.: com_efficios_project_component_event
	 *
	 * In this example, "sample" is the project, and "component" is the
	 * component.
	 */
	sample_component,

	/*
	 * tracepoint name, same format as sample provider. Does not
	 * need to be declared before. in this case the name is
	 * "message" 
	 */
	message,

	/*
	 * TP_ARGS macro contains the arguments passed for the tracepoint 
	 * it is in the following format
	 *	      TP_ARGS(type1, name1, type2, name2, ... type10,
				 name10)
	 * where there can be from zero to ten elements. 
	 * typeN is the datatype, such as int, struct or double **. 
	 * name is the variable name (in "int myInt" the name would be
	 * myint) 
	 *	      TP_ARGS() is valid to mean no arguments
	 *	      TP_ARGS(void) is valid too
	 */
	TP_ARGS(int, anint, int, netint, long *, values,
		 char *, text, size_t, textlen,
		 double, doublearg, float, floatarg),

	/*
	 * TP_FIELDS describes how to write the fields of the trace event. 
	 * You can put expressions in the "argument expression" area,
	 * typically using the input arguments from TP_ARGS.
	 */
	TP_FIELDS(
		/*
		 * ctf_integer: standard integer field.
		 * args: (type, field name, argument expression)
		 */
		ctf_integer(int, intfield, anint)
		ctf_integer(long, longfield, anint)

		/*
		 * ctf_integer_hex: integer field printed as hexadecimal.
		 * args: (type, field name, argument expression)
		 */
		ctf_integer_hex(int, intfield2, anint)

		/*
		 * ctf_integer_network: integer field in network byte
		 * order. (_hex: printed as hexadecimal too)
		 * args: (type, field name, argument expression)
		 */
		ctf_integer_network(int, netintfield, netint)
		ctf_integer_network_hex(int, netintfieldhex, netint)

		/*
		 * ctf_array: a statically-sized array.
		 * args: (type, field name, argument expression, value)
		 */ 
		ctf_array(long, arrfield1, values, 3)

		/*
		 * ctf_array_text: a statically-sized array, printed as
		 * a string. No need to be terminated by a null
		 * character.
		 * Behavior is undefined if "text" argument is NULL.
		 */ 
		ctf_array_text(char, arrfield2, text, 10)

		/*
		 * ctf_sequence: a dynamically-sized array.
		 * args: (type, field name, argument expression,
		 *	type of length expression, length expression)
		 * The "type of length expression" needs to be an
		 * unsigned type. As a reminder, "unsigned char" should
		 * be preferred to "char", since the signedness of
		 * "char" is implementation-defined.
		 * Behavior is undefined if "text" argument is NULL.
		 */ 
		ctf_sequence(char, seqfield1, text,
			     size_t, textlen)

		/*
		 * ctf_sequence_text: a dynamically-sized array, printed
		 * as string. No need to be null-terminated.
		 * Behavior is undefined if "text" argument is NULL.
		 */
		ctf_sequence_text(char, seqfield2, text,
			     size_t, textlen)

		/*
		 * ctf_string: null-terminated string.
		 * args: (field name, argument expression)
		 * Behavior is undefined if "text" argument is NULL.
		 */
		ctf_string(stringfield, text)

		/*
		 * ctf_float: floating-point number.
		 * args: (type, field name, argument expression)
		 */
		ctf_float(float, floatfield, floatarg)
		ctf_float(double, doublefield, doublearg)
	)
)
.fi

.SH "ASSIGNING LOGLEVEL TO EVENTS"

.nf

Optionally, a loglevel can be assigned to a TRACEPOINT_EVENT using the
following construct:

	TRACEPOINT_LOGLEVEL(< [com_company_]project[_component] >,
		< event >, < loglevel_name >)

 The first field is the provider name, the second field is the name of
the tracepoint, and the third field is the loglevel name.  A
TRACEPOINT_EVENT should be declared prior to the the TRACEPOINT_LOGLEVEL
for a given tracepoint name. The TRACEPOINT_PROVIDER must be already
declared before declaring a TRACEPOINT_LOGLEVEL.

The loglevels go from 0 to 14. Higher numbers imply the most verbosity
(higher event throughput expected.
  
Loglevels 0 through 6, and loglevel 14, match syslog(3) loglevels
semantic. Loglevels 7 through 13 offer more fine-grained selection of
debug information.
  
   TRACE_EMERG           0
   system is unusable
  
   TRACE_ALERT           1
   action must be taken immediately
  
   TRACE_CRIT            2
   critical conditions
  
   TRACE_ERR             3
   error conditions
  
   TRACE_WARNING         4
   warning conditions
  
   TRACE_NOTICE          5
   normal, but significant, condition
  
   TRACE_INFO            6
   informational message
  
   TRACE_DEBUG_SYSTEM    7
   debug information with system-level scope (set of programs)
  
   TRACE_DEBUG_PROGRAM   8
   debug information with program-level scope (set of processes)
  
   TRACE_DEBUG_PROCESS   9
   debug information with process-level scope (set of modules)
  
   TRACE_DEBUG_MODULE    10
   debug information with module (executable/library) scope (set of
   units)
  
   TRACE_DEBUG_UNIT      11
   debug information with compilation unit scope (set of functions)
  
   TRACE_DEBUG_FUNCTION  12
   debug information with function-level scope
  
   TRACE_DEBUG_LINE      13
   debug information with line-level scope (TRACEPOINT_EVENT default)
  
   TRACE_DEBUG           14
   debug-level message (trace_printf default)

See lttng(1) for information on how to use LTTng-UST loglevels.

.fi

.SH "ADDING TRACEPOINTS TO YOUR CODE"

.nf

Include the provider header in each C files you plan to instrument,
following the building/linking directives in the next section.

For instance, add within a function:

		tracepoint(ust_tests_hello, tptest, i, netint, values,
			text, strlen(text), dbl, flt);

As a call to the tracepoint. It will only be activated when requested by
lttng(1) through lttng-sessiond(8).

Even though LTTng-UST supports tracepoint() call site duplicates having
the same provider and event name, it is recommended to use a
provider event name pair only once within the source code to help
mapping events back to their call sites when analyzing the trace.
.fi

.SH "BUILDING/LINKING THE TRACEPOINT PROVIDER"

.nf
There are 2 ways to compile the Tracepoint Provider with the
application: either statically or dynamically. Please follow
carefully:

  1.1) Compile the Tracepoint provider with the application, either
       directly or through a static library (.a):
    - Into exactly one object of your application: define
      "TRACEPOINT_DEFINE" and include the tracepoint provider.
    - Use "\-I." for the compilation unit containing the tracepoint
      provider include (e.g. tp.c).
    - Link application with "\-ldl".
    - If building the provider directly into the application,
      link the application with "\-llttng-ust".
    - If building a static library for the provider, link the static
      library with "\-llttng-ust".
    - Include the tracepoint provider header into all C files using
      the provider.
    - Example:
      - tests/hello/  hello.c tp.c ust_tests_hello.h Makefile.example

  2) Compile the Tracepoint Provider separately from the application,
     using dynamic linking:
    - Into exactly one object of your application: define
      "TRACEPOINT_DEFINE" _and_ also define
      "TRACEPOINT_PROBE_DYNAMIC_LINKAGE", then include the tracepoint
      provider header.
    - Include the tracepoint provider header into all instrumented C
      files that use the provider.
    - Compile the tracepoint provider with "\-I.".
    - Link the tracepoint provider with "\-llttng-ust".
    - Link application with "\-ldl".
    - Set a LD_PRELOAD environment to preload the tracepoint provider
      shared object before starting the application when tracing is
      needed. Another way is to dlopen the tracepoint probe when needed
      by the application.
    - Example:
      - doc/examples/demo   demo.c  tp*.c ust_tests_demo*.h demo-trace

  - Note about dlclose() usage: it is not safe to use dlclose on a
    provider shared object that is being actively used for tracing due
    to a lack of reference counting from lttng-ust to the used shared
    object.
  - Enable instrumentation and control tracing with the "lttng" command
    from lttng-tools. See lttng-tools doc/quickstart.txt.
  - Note for C++ support: although an application instrumented with
    tracepoints can be compiled with g++, tracepoint probes should be
    compiled with gcc (only tested with gcc so far).

.fi

.SH "USING LTTNG UST WITH DAEMONS"

.nf
Some extra care is needed when using liblttng-ust with daemon
applications that call fork(), clone(), or BSD rfork() without a
following exec() family system call. The library "liblttng-ust-fork.so"
needs to be preloaded for the application (launch with e.g.
LD_PRELOAD=liblttng-ust-fork.so appname).

.fi

.SH "CONTEXT"

.PP
Context information can be prepended by the tracer before each, or some,
events. The following context information is supported by LTTng-UST:
.PP

.PP
.IP "vtid"
Virtual thread ID: thread ID as seen from the point of view of the
process namespace.
.PP

.PP
.IP "vpid"
Virtual process ID: process ID as seen from the point of view of the
process namespace.
.PP

.PP
.IP "procname"
Thread name, as set by exec() or prctl(). It is recommended that
programs set their thread name with prctl() before hitting the first
tracepoint for that thread.
.PP

.PP
.IP "pthread_id"
Pthread identifier. Can be used on architectures where pthread_t maps
nicely to an unsigned long type.
.PP

.SH "ENVIRONMENT VARIABLES"

.PP
.IP "LTTNG_UST_DEBUG"
Activate liblttng-ust debug output.
.PP
.IP "LTTNG_UST_REGISTER_TIMEOUT"
The environment variable "LTTNG_UST_REGISTER_TIMEOUT" can be used to
specify how long the applications should wait for sessiond
"registration done" command before proceeding to execute the main
program. The default is 3000ms (3 seconds). The timeout value is
specified in milliseconds. The value 0 means "don't wait". The value
\-1 means "wait forever". Setting this environment variable to 0 is
recommended for applications with time constraints on the process
startup time.
.PP

.SH "SEE ALSO"

.PP
lttng-gen-tp(1), lttng(1), babeltrace(1), lttng-ust-cyg-profile(3),
lttng-sessiond(8)
.PP
.SH "BUGS"

.PP
No known bugs at this point.

If you encounter any issues or usability problem, please report it on
our mailing list <lttng-dev@lists.lttng.org> to help improve this
project.
.SH "CREDITS"

liblttng-ust is distributed under the GNU Lesser General Public License
version 2.1. The headers are distributed under the MIT license.
.PP
See http://lttng.org for more information on the LTTng project.
.PP
Mailing list for support and development: <lttng-dev@lists.lttng.org>.
.PP
You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
.PP
.SH "THANKS"

Thanks to Ericsson for funding this work, providing real-life use-cases,
and testing.

Special thanks to Michel Dagenais and the DORSAL laboratory at
Polytechnique de Montreal for the LTTng journey.
.PP
.SH "AUTHORS"

.PP
liblttng-ust was originally written by Mathieu Desnoyers, with additional
contributions from various other people. It is currently maintained by
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>.
.PP
Commit	Line	Data
eba411c6 MD	1	.TH "LTTNG-UST" "3" "February 16, 2012" "" ""
	2
	3	.SH "NAME"
77ca1460	4	lttng-ust \(em Linux Trace Toolkit Next Generation User-Space Tracer 2.x
eba411c6 MD	5
	6	.SH "SYNOPSIS"
	7
	8	.PP
	9	.nf
	10	Link liblttng-ust.so with applications, following this manpage.
	11	.fi
	12	.SH "DESCRIPTION"
	13
	14	.PP
	15	LTTng-UST, the Linux Trace Toolkit Next Generation Userspace Tracer, is
	16	port of the low-overhead tracing capabilities of the LTTng kernel tracer
	17	to user-space. The library "liblttng-ust" enables tracing of
	18	applications and libraries.
	19
	20	.SH "USAGE"
	21	.PP
	22	The simple way to generate the lttng-ust tracepoint probes is to use the
	23	lttng-gen-tp(1) tool. See the lttng-gen-tp(1) manpage for explanation.
	24	.PP
	25
	26	.PP
	27	Here is the way to do it manually, without the lttng-gen-tp(1) helper
	28	script, through an example:
	29	.PP
	30
	31	.SH "CREATION OF TRACEPOINT PROVIDER"
	32
	33	.nf
	34
	35	To create a tracepoint provider, within a build tree similar to
	36	examples/easy-ust installed with lttng-ust documentation, a
	37	sample_component_provider.h for the general layout. This manpage will
	38	focus on the various types that can be recorded into a trace event:
	39
	40	TRACEPOINT_EVENT(
	41	/*
	42	* provider name, not a variable but a string starting with a
	43	* letter and containing either letters, numbers or underscores.
	44	* Needs to be the same as TRACEPOINT_PROVIDER. Needs to
	45	* follow the namespacing guide-lines in lttng/tracepoint.h:
	46	*
	47	* Must be included before include tracepoint provider
	48	* ex.: project_event
	49	* ex.: project_component_event
	50	*
	51	* Optional company name goes here
	52	* ex.: com_efficios_project_component_event
	53	*
	54	* In this example, "sample" is the project, and "component" is the
	55	* component.
	56	*/
	57	sample_component,
	58
	59	/*
	60	* tracepoint name, same format as sample provider. Does not
	61	* need to be declared before. in this case the name is
	62	* "message"
	63	*/
	64	message,
	65
	66	/*
	67	* TP_ARGS macro contains the arguments passed for the tracepoint
	68	* it is in the following format
69	* TP_ARGS(type1, name1, type2, name2, ... type10,
70	name10)
71	* where there can be from zero to ten elements.
72	* typeN is the datatype, such as int, struct or double **.
73	* name is the variable name (in "int myInt" the name would be
74	* myint)
75	* TP_ARGS() is valid to mean no arguments
76	* TP_ARGS(void) is valid too
77	*/
78	TP_ARGS(int, anint, int, netint, long *, values,
79	char *, text, size_t, textlen,
80	double, doublearg, float, floatarg),
81
82	/*
83	* TP_FIELDS describes how to write the fields of the trace event.
84	* You can put expressions in the "argument expression" area,
85	* typically using the input arguments from TP_ARGS.
86	*/
87	TP_FIELDS(
88	/*
89	* ctf_integer: standard integer field.
90	* args: (type, field name, argument expression)
91	*/
92	ctf_integer(int, intfield, anint)
93	ctf_integer(long, longfield, anint)
94
95	/*
96	* ctf_integer_hex: integer field printed as hexadecimal.
97	* args: (type, field name, argument expression)
98	*/
99	ctf_integer_hex(int, intfield2, anint)
100
101	/*
102	* ctf_integer_network: integer field in network byte
103	* order. (_hex: printed as hexadecimal too)
104	* args: (type, field name, argument expression)
105	*/
106	ctf_integer_network(int, netintfield, netint)
107	ctf_integer_network_hex(int, netintfieldhex, netint)
108
109	/*
110	* ctf_array: a statically-sized array.
111	* args: (type, field name, argument expression, value)
112	*/
113	ctf_array(long, arrfield1, values, 3)
114
115	/*
116	* ctf_array_text: a statically-sized array, printed as
117	* a string. No need to be terminated by a null
118	* character.
2f65f1f5	119	* Behavior is undefined if "text" argument is NULL.
eba411c6 MD	120	*/
	121	ctf_array_text(char, arrfield2, text, 10)
	122
	123	/*
	124	* ctf_sequence: a dynamically-sized array.
	125	* args: (type, field name, argument expression,
	126	* type of length expression, length expression)
efbad5cc MD	127	* The "type of length expression" needs to be an
	128	* unsigned type. As a reminder, "unsigned char" should
	129	* be preferred to "char", since the signedness of
	130	* "char" is implementation-defined.
2f65f1f5	131	* Behavior is undefined if "text" argument is NULL.
eba411c6 MD	132	*/
	133	ctf_sequence(char, seqfield1, text,
	134	size_t, textlen)
	135
	136	/*
	137	* ctf_sequence_text: a dynamically-sized array, printed
	138	* as string. No need to be null-terminated.
2f65f1f5	139	* Behavior is undefined if "text" argument is NULL.
eba411c6 MD	140	*/
	141	ctf_sequence_text(char, seqfield2, text,
	142	size_t, textlen)
	143
	144	/*
	145	* ctf_string: null-terminated string.
	146	* args: (field name, argument expression)
2f65f1f5	147	* Behavior is undefined if "text" argument is NULL.
eba411c6 MD	148	*/
	149	ctf_string(stringfield, text)
	150
	151	/*
	152	* ctf_float: floating-point number.
	153	* args: (type, field name, argument expression)
	154	*/
	155	ctf_float(float, floatfield, floatarg)
	156	ctf_float(double, doublefield, doublearg)
	157	)
	158	)
	159	.fi
	160
5883c06f MD	161	.SH "ASSIGNING LOGLEVEL TO EVENTS"
	162
	163	.nf
	164
	165	Optionally, a loglevel can be assigned to a TRACEPOINT_EVENT using the
	166	following construct:
	167
	168	TRACEPOINT_LOGLEVEL(< [com_company_]project[_component] >,
	169	< event >, < loglevel_name >)
	170
	171	The first field is the provider name, the second field is the name of
	172	the tracepoint, and the third field is the loglevel name. A
	173	TRACEPOINT_EVENT should be declared prior to the the TRACEPOINT_LOGLEVEL
	174	for a given tracepoint name. The TRACEPOINT_PROVIDER must be already
	175	declared before declaring a TRACEPOINT_LOGLEVEL.
	176
	177	The loglevels go from 0 to 14. Higher numbers imply the most verbosity
	178	(higher event throughput expected.
	179
	180	Loglevels 0 through 6, and loglevel 14, match syslog(3) loglevels
	181	semantic. Loglevels 7 through 13 offer more fine-grained selection of
	182	debug information.
	183
	184	TRACE_EMERG 0
	185	system is unusable
	186
	187	TRACE_ALERT 1
	188	action must be taken immediately
	189
	190	TRACE_CRIT 2
	191	critical conditions
	192
	193	TRACE_ERR 3
	194	error conditions
	195
	196	TRACE_WARNING 4
	197	warning conditions
	198
	199	TRACE_NOTICE 5
	200	normal, but significant, condition
	201
	202	TRACE_INFO 6
	203	informational message
	204
	205	TRACE_DEBUG_SYSTEM 7
	206	debug information with system-level scope (set of programs)
	207
	208	TRACE_DEBUG_PROGRAM 8
	209	debug information with program-level scope (set of processes)
	210
	211	TRACE_DEBUG_PROCESS 9
	212	debug information with process-level scope (set of modules)
	213
	214	TRACE_DEBUG_MODULE 10
	215	debug information with module (executable/library) scope (set of
	216	units)
	217
	218	TRACE_DEBUG_UNIT 11
	219	debug information with compilation unit scope (set of functions)
	220
	221	TRACE_DEBUG_FUNCTION 12
	222	debug information with function-level scope
	223
	224	TRACE_DEBUG_LINE 13
225	debug information with line-level scope (TRACEPOINT_EVENT default)
226
227	TRACE_DEBUG 14
228	debug-level message (trace_printf default)
229
230	See lttng(1) for information on how to use LTTng-UST loglevels.
231
232	.fi
233
eba411c6 MD	234	.SH "ADDING TRACEPOINTS TO YOUR CODE"
	235
	236	.nf
	237
	238	Include the provider header in each C files you plan to instrument,
	239	following the building/linking directives in the next section.
	240
	241	For instance, add within a function:
	242
	243	tracepoint(ust_tests_hello, tptest, i, netint, values,
	244	text, strlen(text), dbl, flt);
	245
	246	As a call to the tracepoint. It will only be activated when requested by
	247	lttng(1) through lttng-sessiond(8).
	248
d646ca64 MD	249	Even though LTTng-UST supports tracepoint() call site duplicates having
	250	the same provider and event name, it is recommended to use a
	251	provider event name pair only once within the source code to help
	252	mapping events back to their call sites when analyzing the trace.
eba411c6 MD	253	.fi
	254
	255	.SH "BUILDING/LINKING THE TRACEPOINT PROVIDER"
	256
	257	.nf
	258	There are 2 ways to compile the Tracepoint Provider with the
	259	application: either statically or dynamically. Please follow
	260	carefully:
	261
	262	1.1) Compile the Tracepoint provider with the application, either
	263	directly or through a static library (.a):
	264	- Into exactly one object of your application: define
	265	"TRACEPOINT_DEFINE" and include the tracepoint provider.
9b6435af	266	- Use "\-I." for the compilation unit containing the tracepoint
eba411c6	267	provider include (e.g. tp.c).
9b6435af	268	- Link application with "\-ldl".
eba411c6	269	- If building the provider directly into the application,
9b6435af	270	link the application with "\-llttng-ust".
eba411c6	271	- If building a static library for the provider, link the static
38f5f440	272	library with "\-llttng-ust".
eba411c6 MD	273	- Include the tracepoint provider header into all C files using
	274	the provider.
	275	- Example:
13fb2d2c	276	- tests/hello/ hello.c tp.c ust_tests_hello.h Makefile.example
eba411c6 MD	277
	278	2) Compile the Tracepoint Provider separately from the application,
	279	using dynamic linking:
	280	- Into exactly one object of your application: define
	281	"TRACEPOINT_DEFINE" _and_ also define
	282	"TRACEPOINT_PROBE_DYNAMIC_LINKAGE", then include the tracepoint
	283	provider header.
	284	- Include the tracepoint provider header into all instrumented C
	285	files that use the provider.
9b6435af AM	286	- Compile the tracepoint provider with "\-I.".
	287	- Link the tracepoint provider with "\-llttng-ust".
	288	- Link application with "\-ldl".
eba411c6 MD	289	- Set a LD_PRELOAD environment to preload the tracepoint provider
eba411c6 MD	290	shared object before starting the application when tracing is
13fb2d2c JG	291	needed. Another way is to dlopen the tracepoint probe when needed
13fb2d2c JG	292	by the application.
eba411c6	293	- Example:
60302adc	294	- doc/examples/demo demo.c tp.c ust_tests_demo.h demo-trace
eba411c6	295
13fb2d2c JG	296	- Note about dlclose() usage: it is not safe to use dlclose on a
	297	provider shared object that is being actively used for tracing due
	298	to a lack of reference counting from lttng-ust to the used shared
	299	object.
eba411c6 MD	300	- Enable instrumentation and control tracing with the "lttng" command
eba411c6 MD	301	from lttng-tools. See lttng-tools doc/quickstart.txt.
2bda849d MD	302	- Note for C++ support: although an application instrumented with
	303	tracepoints can be compiled with g++, tracepoint probes should be
	304	compiled with gcc (only tested with gcc so far).
eba411c6 MD	305
	306	.fi
	307
0a7c55a5 MD	308	.SH "USING LTTNG UST WITH DAEMONS"
	309
	310	.nf
	311	Some extra care is needed when using liblttng-ust with daemon
	312	applications that call fork(), clone(), or BSD rfork() without a
	313	following exec() family system call. The library "liblttng-ust-fork.so"
	314	needs to be preloaded for the application (launch with e.g.
	315	LD_PRELOAD=liblttng-ust-fork.so appname).
	316
	317	.fi
	318
94c9c48d MD	319	.SH "CONTEXT"
	320
	321	.PP
	322	Context information can be prepended by the tracer before each, or some,
	323	events. The following context information is supported by LTTng-UST:
	324	.PP
	325
	326	.PP
	327	.IP "vtid"
	328	Virtual thread ID: thread ID as seen from the point of view of the
	329	process namespace.
	330	.PP
	331
	332	.PP
	333	.IP "vpid"
	334	Virtual process ID: process ID as seen from the point of view of the
	335	process namespace.
	336	.PP
	337
	338	.PP
	339	.IP "procname"
	340	Thread name, as set by exec() or prctl(). It is recommended that
	341	programs set their thread name with prctl() before hitting the first
	342	tracepoint for that thread.
	343	.PP
	344
	345	.PP
	346	.IP "pthread_id"
	347	Pthread identifier. Can be used on architectures where pthread_t maps
	348	nicely to an unsigned long type.
	349	.PP
	350
eba411c6 MD	351	.SH "ENVIRONMENT VARIABLES"
	352
	353	.PP
	354	.IP "LTTNG_UST_DEBUG"
	355	Activate liblttng-ust debug output.
	356	.PP
	357	.IP "LTTNG_UST_REGISTER_TIMEOUT"
	358	The environment variable "LTTNG_UST_REGISTER_TIMEOUT" can be used to
	359	specify how long the applications should wait for sessiond
	360	"registration done" command before proceeding to execute the main
	361	program. The default is 3000ms (3 seconds). The timeout value is
	362	specified in milliseconds. The value 0 means "don't wait". The value
9b6435af	363	\-1 means "wait forever". Setting this environment variable to 0 is
eba411c6 MD	364	recommended for applications with time constraints on the process
	365	startup time.
	366	.PP
	367
	368	.SH "SEE ALSO"
	369
	370	.PP
d1eaa4d7 PW	371	lttng-gen-tp(1), lttng(1), babeltrace(1), lttng-ust-cyg-profile(3),
d1eaa4d7 PW	372	lttng-sessiond(8)
eba411c6 MD	373	.PP
	374	.SH "BUGS"
	375
	376	.PP
60302adc	377	No known bugs at this point.
eba411c6 MD	378
	379	If you encounter any issues or usability problem, please report it on
	380	our mailing list <lttng-dev@lists.lttng.org> to help improve this
	381	project.
	382	.SH "CREDITS"
	383
	384	liblttng-ust is distributed under the GNU Lesser General Public License
	385	version 2.1. The headers are distributed under the MIT license.
	386	.PP
	387	See http://lttng.org for more information on the LTTng project.
	388	.PP
	389	Mailing list for support and development: <lttng-dev@lists.lttng.org>.
	390	.PP
	391	You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
	392	.PP
	393	.SH "THANKS"
	394
	395	Thanks to Ericsson for funding this work, providing real-life use-cases,
	396	and testing.
	397
	398	Special thanks to Michel Dagenais and the DORSAL laboratory at
	399	Polytechnique de Montreal for the LTTng journey.
	400	.PP
	401	.SH "AUTHORS"
	402
	403	.PP
	404	liblttng-ust was originally written by Mathieu Desnoyers, with additional
	405	contributions from various other people. It is currently maintained by
	406	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>.
	407	.PP