[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.
		 */ 
		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.
		 */ 
		ctf_sequence(char, seqfield1, text,
			     size_t, textlen)

		/*
		 * ctf_sequence_text: a dynamically-sized array, printed
		 * as string. No need to be null-terminated.
		 */
		ctf_sequence_text(char, seqfield2, text,
			     size_t, textlen)

		/*
		 * ctf_string: null-terminated string.
		 * args: (field name, argument expression)
		 */
		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.
119	*/
120	ctf_array_text(char, arrfield2, text, 10)
121
122	/*
123	* ctf_sequence: a dynamically-sized array.
124	* args: (type, field name, argument expression,
125	* type of length expression, length expression)
efbad5cc MD	126	* The "type of length expression" needs to be an
	127	* unsigned type. As a reminder, "unsigned char" should
	128	* be preferred to "char", since the signedness of
	129	* "char" is implementation-defined.
eba411c6 MD	130	*/
	131	ctf_sequence(char, seqfield1, text,
	132	size_t, textlen)
	133
	134	/*
	135	* ctf_sequence_text: a dynamically-sized array, printed
	136	* as string. No need to be null-terminated.
	137	*/
	138	ctf_sequence_text(char, seqfield2, text,
	139	size_t, textlen)
	140
	141	/*
	142	* ctf_string: null-terminated string.
	143	* args: (field name, argument expression)
	144	*/
	145	ctf_string(stringfield, text)
	146
	147	/*
	148	* ctf_float: floating-point number.
	149	* args: (type, field name, argument expression)
	150	*/
	151	ctf_float(float, floatfield, floatarg)
	152	ctf_float(double, doublefield, doublearg)
	153	)
	154	)
	155	.fi
	156
5883c06f MD	157	.SH "ASSIGNING LOGLEVEL TO EVENTS"
	158
	159	.nf
	160
	161	Optionally, a loglevel can be assigned to a TRACEPOINT_EVENT using the
	162	following construct:
	163
	164	TRACEPOINT_LOGLEVEL(< [com_company_]project[_component] >,
	165	< event >, < loglevel_name >)
	166
	167	The first field is the provider name, the second field is the name of
	168	the tracepoint, and the third field is the loglevel name. A
	169	TRACEPOINT_EVENT should be declared prior to the the TRACEPOINT_LOGLEVEL
	170	for a given tracepoint name. The TRACEPOINT_PROVIDER must be already
	171	declared before declaring a TRACEPOINT_LOGLEVEL.
	172
	173	The loglevels go from 0 to 14. Higher numbers imply the most verbosity
	174	(higher event throughput expected.
	175
	176	Loglevels 0 through 6, and loglevel 14, match syslog(3) loglevels
	177	semantic. Loglevels 7 through 13 offer more fine-grained selection of
	178	debug information.
	179
	180	TRACE_EMERG 0
	181	system is unusable
	182
	183	TRACE_ALERT 1
	184	action must be taken immediately
	185
	186	TRACE_CRIT 2
	187	critical conditions
	188
	189	TRACE_ERR 3
	190	error conditions
	191
	192	TRACE_WARNING 4
	193	warning conditions
	194
	195	TRACE_NOTICE 5
	196	normal, but significant, condition
	197
	198	TRACE_INFO 6
	199	informational message
	200
	201	TRACE_DEBUG_SYSTEM 7
	202	debug information with system-level scope (set of programs)
	203
	204	TRACE_DEBUG_PROGRAM 8
	205	debug information with program-level scope (set of processes)
	206
	207	TRACE_DEBUG_PROCESS 9
	208	debug information with process-level scope (set of modules)
	209
	210	TRACE_DEBUG_MODULE 10
	211	debug information with module (executable/library) scope (set of
	212	units)
	213
	214	TRACE_DEBUG_UNIT 11
	215	debug information with compilation unit scope (set of functions)
	216
	217	TRACE_DEBUG_FUNCTION 12
	218	debug information with function-level scope
	219
	220	TRACE_DEBUG_LINE 13
221	debug information with line-level scope (TRACEPOINT_EVENT default)
222
223	TRACE_DEBUG 14
224	debug-level message (trace_printf default)
225
226	See lttng(1) for information on how to use LTTng-UST loglevels.
227
228	.fi
229
eba411c6 MD	230	.SH "ADDING TRACEPOINTS TO YOUR CODE"
	231
	232	.nf
	233
	234	Include the provider header in each C files you plan to instrument,
	235	following the building/linking directives in the next section.
	236
	237	For instance, add within a function:
	238
	239	tracepoint(ust_tests_hello, tptest, i, netint, values,
	240	text, strlen(text), dbl, flt);
	241
	242	As a call to the tracepoint. It will only be activated when requested by
	243	lttng(1) through lttng-sessiond(8).
	244
d646ca64 MD	245	Even though LTTng-UST supports tracepoint() call site duplicates having
	246	the same provider and event name, it is recommended to use a
	247	provider event name pair only once within the source code to help
	248	mapping events back to their call sites when analyzing the trace.
eba411c6 MD	249	.fi
	250
	251	.SH "BUILDING/LINKING THE TRACEPOINT PROVIDER"
	252
	253	.nf
	254	There are 2 ways to compile the Tracepoint Provider with the
	255	application: either statically or dynamically. Please follow
	256	carefully:
	257
	258	1.1) Compile the Tracepoint provider with the application, either
	259	directly or through a static library (.a):
	260	- Into exactly one object of your application: define
	261	"TRACEPOINT_DEFINE" and include the tracepoint provider.
9b6435af	262	- Use "\-I." for the compilation unit containing the tracepoint
eba411c6	263	provider include (e.g. tp.c).
9b6435af	264	- Link application with "\-ldl".
eba411c6	265	- If building the provider directly into the application,
9b6435af	266	link the application with "\-llttng-ust".
eba411c6	267	- If building a static library for the provider, link the static
38f5f440	268	library with "\-llttng-ust".
eba411c6 MD	269	- Include the tracepoint provider header into all C files using
	270	the provider.
	271	- Example:
13fb2d2c	272	- tests/hello/ hello.c tp.c ust_tests_hello.h Makefile.example
eba411c6 MD	273
	274	2) Compile the Tracepoint Provider separately from the application,
	275	using dynamic linking:
	276	- Into exactly one object of your application: define
	277	"TRACEPOINT_DEFINE" _and_ also define
	278	"TRACEPOINT_PROBE_DYNAMIC_LINKAGE", then include the tracepoint
	279	provider header.
	280	- Include the tracepoint provider header into all instrumented C
	281	files that use the provider.
9b6435af AM	282	- Compile the tracepoint provider with "\-I.".
	283	- Link the tracepoint provider with "\-llttng-ust".
	284	- Link application with "\-ldl".
eba411c6 MD	285	- Set a LD_PRELOAD environment to preload the tracepoint provider
eba411c6 MD	286	shared object before starting the application when tracing is
13fb2d2c JG	287	needed. Another way is to dlopen the tracepoint probe when needed
13fb2d2c JG	288	by the application.
eba411c6	289	- Example:
60302adc	290	- doc/examples/demo demo.c tp.c ust_tests_demo.h demo-trace
eba411c6	291
13fb2d2c JG	292	- Note about dlclose() usage: it is not safe to use dlclose on a
	293	provider shared object that is being actively used for tracing due
	294	to a lack of reference counting from lttng-ust to the used shared
	295	object.
eba411c6 MD	296	- Enable instrumentation and control tracing with the "lttng" command
eba411c6 MD	297	from lttng-tools. See lttng-tools doc/quickstart.txt.
2bda849d MD	298	- Note for C++ support: although an application instrumented with
	299	tracepoints can be compiled with g++, tracepoint probes should be
	300	compiled with gcc (only tested with gcc so far).
eba411c6 MD	301
	302	.fi
	303
0a7c55a5 MD	304	.SH "USING LTTNG UST WITH DAEMONS"
	305
	306	.nf
	307	Some extra care is needed when using liblttng-ust with daemon
	308	applications that call fork(), clone(), or BSD rfork() without a
	309	following exec() family system call. The library "liblttng-ust-fork.so"
	310	needs to be preloaded for the application (launch with e.g.
	311	LD_PRELOAD=liblttng-ust-fork.so appname).
	312
	313	.fi
	314
94c9c48d MD	315	.SH "CONTEXT"
	316
	317	.PP
	318	Context information can be prepended by the tracer before each, or some,
	319	events. The following context information is supported by LTTng-UST:
	320	.PP
	321
	322	.PP
	323	.IP "vtid"
	324	Virtual thread ID: thread ID as seen from the point of view of the
	325	process namespace.
	326	.PP
	327
	328	.PP
	329	.IP "vpid"
	330	Virtual process ID: process ID as seen from the point of view of the
	331	process namespace.
	332	.PP
	333
	334	.PP
	335	.IP "procname"
	336	Thread name, as set by exec() or prctl(). It is recommended that
	337	programs set their thread name with prctl() before hitting the first
	338	tracepoint for that thread.
	339	.PP
	340
	341	.PP
	342	.IP "pthread_id"
	343	Pthread identifier. Can be used on architectures where pthread_t maps
	344	nicely to an unsigned long type.
	345	.PP
	346
eba411c6 MD	347	.SH "ENVIRONMENT VARIABLES"
	348
	349	.PP
	350	.IP "LTTNG_UST_DEBUG"
	351	Activate liblttng-ust debug output.
	352	.PP
	353	.IP "LTTNG_UST_REGISTER_TIMEOUT"
	354	The environment variable "LTTNG_UST_REGISTER_TIMEOUT" can be used to
	355	specify how long the applications should wait for sessiond
	356	"registration done" command before proceeding to execute the main
	357	program. The default is 3000ms (3 seconds). The timeout value is
	358	specified in milliseconds. The value 0 means "don't wait". The value
9b6435af	359	\-1 means "wait forever". Setting this environment variable to 0 is
eba411c6 MD	360	recommended for applications with time constraints on the process
	361	startup time.
	362	.PP
	363
	364	.SH "SEE ALSO"
	365
	366	.PP
d1eaa4d7 PW	367	lttng-gen-tp(1), lttng(1), babeltrace(1), lttng-ust-cyg-profile(3),
d1eaa4d7 PW	368	lttng-sessiond(8)
eba411c6 MD	369	.PP
	370	.SH "BUGS"
	371
	372	.PP
60302adc	373	No known bugs at this point.
eba411c6 MD	374
	375	If you encounter any issues or usability problem, please report it on
	376	our mailing list <lttng-dev@lists.lttng.org> to help improve this
	377	project.
	378	.SH "CREDITS"
	379
	380	liblttng-ust is distributed under the GNU Lesser General Public License
	381	version 2.1. The headers are distributed under the MIT license.
	382	.PP
	383	See http://lttng.org for more information on the LTTng project.
	384	.PP
	385	Mailing list for support and development: <lttng-dev@lists.lttng.org>.
	386	.PP
	387	You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
	388	.PP
	389	.SH "THANKS"
	390
	391	Thanks to Ericsson for funding this work, providing real-life use-cases,
	392	and testing.
	393
	394	Special thanks to Michel Dagenais and the DORSAL laboratory at
	395	Polytechnique de Montreal for the LTTng journey.
	396	.PP
	397	.SH "AUTHORS"
	398
	399	.PP
	400	liblttng-ust was originally written by Mathieu Desnoyers, with additional
	401	contributions from various other people. It is currently maintained by
	402	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>.
	403	.PP