[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

.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)
		 */ 
		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:
      - tests/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-sessiond(8)
.PP

.SH "COMPATIBILITY"

.PP
Older lttng-ust libraries reject more recent, and incompatible, probe
providers. Newer lttng-ust librairies accept older probe providers, even
though some newer features might not be available with those providers.
.PP

.SH "BUGS"

.PP
LTTng-UST 2.0 and 2.1 lttng-ust libraries do not check for probe
provider version compatibility. This can lead to out-of-bound accesses
when using a more recent probe provider with an older lttng-ust library.
These error only trigger when tracing is active. This issue has been
fixed in LTTng-UST 2.2.

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"
	4	lttng-ust \(em Linux Trace Toolkit Next Generation User-Space Tracer
	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)
126	*/
127	ctf_sequence(char, seqfield1, text,
128	size_t, textlen)
129
130	/*
131	* ctf_sequence_text: a dynamically-sized array, printed
132	* as string. No need to be null-terminated.
133	*/
134	ctf_sequence_text(char, seqfield2, text,
135	size_t, textlen)
136
137	/*
138	* ctf_string: null-terminated string.
139	* args: (field name, argument expression)
140	*/
141	ctf_string(stringfield, text)
142
143	/*
144	* ctf_float: floating-point number.
145	* args: (type, field name, argument expression)
146	*/
147	ctf_float(float, floatfield, floatarg)
148	ctf_float(double, doublefield, doublearg)
149	)
150	)
151	.fi
152
5883c06f MD	153	.SH "ASSIGNING LOGLEVEL TO EVENTS"
	154
	155	.nf
	156
	157	Optionally, a loglevel can be assigned to a TRACEPOINT_EVENT using the
	158	following construct:
	159
	160	TRACEPOINT_LOGLEVEL(< [com_company_]project[_component] >,
	161	< event >, < loglevel_name >)
	162
	163	The first field is the provider name, the second field is the name of
	164	the tracepoint, and the third field is the loglevel name. A
	165	TRACEPOINT_EVENT should be declared prior to the the TRACEPOINT_LOGLEVEL
	166	for a given tracepoint name. The TRACEPOINT_PROVIDER must be already
	167	declared before declaring a TRACEPOINT_LOGLEVEL.
	168
	169	The loglevels go from 0 to 14. Higher numbers imply the most verbosity
	170	(higher event throughput expected.
	171
	172	Loglevels 0 through 6, and loglevel 14, match syslog(3) loglevels
	173	semantic. Loglevels 7 through 13 offer more fine-grained selection of
	174	debug information.
	175
	176	TRACE_EMERG 0
	177	system is unusable
	178
	179	TRACE_ALERT 1
	180	action must be taken immediately
	181
	182	TRACE_CRIT 2
	183	critical conditions
	184
	185	TRACE_ERR 3
	186	error conditions
	187
	188	TRACE_WARNING 4
	189	warning conditions
	190
	191	TRACE_NOTICE 5
	192	normal, but significant, condition
	193
	194	TRACE_INFO 6
	195	informational message
	196
	197	TRACE_DEBUG_SYSTEM 7
	198	debug information with system-level scope (set of programs)
	199
	200	TRACE_DEBUG_PROGRAM 8
	201	debug information with program-level scope (set of processes)
	202
	203	TRACE_DEBUG_PROCESS 9
	204	debug information with process-level scope (set of modules)
	205
	206	TRACE_DEBUG_MODULE 10
	207	debug information with module (executable/library) scope (set of
	208	units)
	209
	210	TRACE_DEBUG_UNIT 11
	211	debug information with compilation unit scope (set of functions)
	212
	213	TRACE_DEBUG_FUNCTION 12
	214	debug information with function-level scope
	215
	216	TRACE_DEBUG_LINE 13
217	debug information with line-level scope (TRACEPOINT_EVENT default)
218
219	TRACE_DEBUG 14
220	debug-level message (trace_printf default)
221
222	See lttng(1) for information on how to use LTTng-UST loglevels.
223
224	.fi
225
eba411c6 MD	226	.SH "ADDING TRACEPOINTS TO YOUR CODE"
	227
	228	.nf
	229
	230	Include the provider header in each C files you plan to instrument,
	231	following the building/linking directives in the next section.
	232
	233	For instance, add within a function:
	234
	235	tracepoint(ust_tests_hello, tptest, i, netint, values,
	236	text, strlen(text), dbl, flt);
	237
	238	As a call to the tracepoint. It will only be activated when requested by
	239	lttng(1) through lttng-sessiond(8).
	240
d646ca64 MD	241	Even though LTTng-UST supports tracepoint() call site duplicates having
	242	the same provider and event name, it is recommended to use a
	243	provider event name pair only once within the source code to help
	244	mapping events back to their call sites when analyzing the trace.
eba411c6 MD	245	.fi
	246
	247	.SH "BUILDING/LINKING THE TRACEPOINT PROVIDER"
	248
	249	.nf
	250	There are 2 ways to compile the Tracepoint Provider with the
	251	application: either statically or dynamically. Please follow
	252	carefully:
	253
	254	1.1) Compile the Tracepoint provider with the application, either
	255	directly or through a static library (.a):
	256	- Into exactly one object of your application: define
	257	"TRACEPOINT_DEFINE" and include the tracepoint provider.
9b6435af	258	- Use "\-I." for the compilation unit containing the tracepoint
eba411c6	259	provider include (e.g. tp.c).
9b6435af	260	- Link application with "\-ldl".
eba411c6	261	- If building the provider directly into the application,
9b6435af	262	link the application with "\-llttng-ust".
eba411c6	263	- If building a static library for the provider, link the static
38f5f440	264	library with "\-llttng-ust".
eba411c6 MD	265	- Include the tracepoint provider header into all C files using
	266	the provider.
	267	- Example:
5ce00218	268	- tests/hello/ hello.c tp.c ust_tests_hello.h Makefile.example
eba411c6 MD	269
	270	2) Compile the Tracepoint Provider separately from the application,
	271	using dynamic linking:
	272	- Into exactly one object of your application: define
	273	"TRACEPOINT_DEFINE" _and_ also define
	274	"TRACEPOINT_PROBE_DYNAMIC_LINKAGE", then include the tracepoint
	275	provider header.
	276	- Include the tracepoint provider header into all instrumented C
	277	files that use the provider.
9b6435af AM	278	- Compile the tracepoint provider with "\-I.".
	279	- Link the tracepoint provider with "\-llttng-ust".
	280	- Link application with "\-ldl".
eba411c6 MD	281	- Set a LD_PRELOAD environment to preload the tracepoint provider
eba411c6 MD	282	shared object before starting the application when tracing is
5ce00218 JG	283	needed. Another way is to dlopen the tracepoint probe when needed
5ce00218 JG	284	by the application.
eba411c6 MD	285	- Example:
	286	- tests/demo/ demo.c tp.c ust_tests_demo.h demo-trace
	287
5ce00218 JG	288	- Note about dlclose() usage: it is not safe to use dlclose on a
	289	provider shared object that is being actively used for tracing due
	290	to a lack of reference counting from lttng-ust to the used shared
	291	object.
eba411c6 MD	292	- Enable instrumentation and control tracing with the "lttng" command
eba411c6 MD	293	from lttng-tools. See lttng-tools doc/quickstart.txt.
2bda849d MD	294	- Note for C++ support: although an application instrumented with
	295	tracepoints can be compiled with g++, tracepoint probes should be
	296	compiled with gcc (only tested with gcc so far).
eba411c6 MD	297
	298	.fi
	299
0a7c55a5 MD	300	.SH "USING LTTNG UST WITH DAEMONS"
	301
	302	.nf
	303	Some extra care is needed when using liblttng-ust with daemon
	304	applications that call fork(), clone(), or BSD rfork() without a
	305	following exec() family system call. The library "liblttng-ust-fork.so"
	306	needs to be preloaded for the application (launch with e.g.
	307	LD_PRELOAD=liblttng-ust-fork.so appname).
	308
	309	.fi
	310
94c9c48d MD	311	.SH "CONTEXT"
	312
	313	.PP
	314	Context information can be prepended by the tracer before each, or some,
	315	events. The following context information is supported by LTTng-UST:
	316	.PP
	317
	318	.PP
	319	.IP "vtid"
	320	Virtual thread ID: thread ID as seen from the point of view of the
	321	process namespace.
	322	.PP
	323
	324	.PP
	325	.IP "vpid"
	326	Virtual process ID: process ID as seen from the point of view of the
	327	process namespace.
	328	.PP
	329
	330	.PP
	331	.IP "procname"
	332	Thread name, as set by exec() or prctl(). It is recommended that
	333	programs set their thread name with prctl() before hitting the first
	334	tracepoint for that thread.
	335	.PP
	336
	337	.PP
	338	.IP "pthread_id"
	339	Pthread identifier. Can be used on architectures where pthread_t maps
	340	nicely to an unsigned long type.
	341	.PP
	342
eba411c6 MD	343	.SH "ENVIRONMENT VARIABLES"
	344
	345	.PP
	346	.IP "LTTNG_UST_DEBUG"
	347	Activate liblttng-ust debug output.
	348	.PP
	349	.IP "LTTNG_UST_REGISTER_TIMEOUT"
	350	The environment variable "LTTNG_UST_REGISTER_TIMEOUT" can be used to
	351	specify how long the applications should wait for sessiond
	352	"registration done" command before proceeding to execute the main
	353	program. The default is 3000ms (3 seconds). The timeout value is
	354	specified in milliseconds. The value 0 means "don't wait". The value
9b6435af	355	\-1 means "wait forever". Setting this environment variable to 0 is
eba411c6 MD	356	recommended for applications with time constraints on the process
	357	startup time.
	358	.PP
	359
	360	.SH "SEE ALSO"
	361
	362	.PP
	363	lttng-gen-tp(1), lttng(1), babeltrace(1), lttng-sessiond(8)
	364	.PP
b3b8f5df MD	365
	366	.SH "COMPATIBILITY"
	367
	368	.PP
	369	Older lttng-ust libraries reject more recent, and incompatible, probe
	370	providers. Newer lttng-ust librairies accept older probe providers, even
	371	though some newer features might not be available with those providers.
	372	.PP
	373
eba411c6 MD	374	.SH "BUGS"
	375
	376	.PP
b3b8f5df MD	377	LTTng-UST 2.0 and 2.1 lttng-ust libraries do not check for probe
	378	provider version compatibility. This can lead to out-of-bound accesses
	379	when using a more recent probe provider with an older lttng-ust library.
	380	These error only trigger when tracing is active. This issue has been
	381	fixed in LTTng-UST 2.2.
eba411c6 MD	382
	383	If you encounter any issues or usability problem, please report it on
	384	our mailing list <lttng-dev@lists.lttng.org> to help improve this
	385	project.
	386	.SH "CREDITS"
	387
	388	liblttng-ust is distributed under the GNU Lesser General Public License
	389	version 2.1. The headers are distributed under the MIT license.
	390	.PP
	391	See http://lttng.org for more information on the LTTng project.
	392	.PP
	393	Mailing list for support and development: <lttng-dev@lists.lttng.org>.
	394	.PP
	395	You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
	396	.PP
	397	.SH "THANKS"
	398
	399	Thanks to Ericsson for funding this work, providing real-life use-cases,
	400	and testing.
	401
	402	Special thanks to Michel Dagenais and the DORSAL laboratory at
	403	Polytechnique de Montreal for the LTTng journey.
	404	.PP
	405	.SH "AUTHORS"
	406
	407	.PP
	408	liblttng-ust was originally written by Mathieu Desnoyers, with additional
	409	contributions from various other people. It is currently maintained by
	410	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>.
	411	.PP