Fix: return NULL on trace chunk registry failure
[lttng-tools.git] / doc / man / lttng-health-check.3
1 .TH LTTNG_HEALTH_CHECK 3 2012-09-19 "LTTng" "LTTng Developer Manual"
2 .SH NAME
3 .B DEPRECATED
4
5 lttng_health_check \- Monitor health of the session daemon
6 .SH SYNOPSIS
7 .nf
8 .B #include <lttng/lttng.h>
9 .sp
10 .BI "int lttng_health_check(enum lttng_health_component c);
11 .fi
12
13 Link with -llttng-ctl.
14 .SH DESCRIPTION
15 The
16 .BR lttng_health_check ()
17 is used to check the session daemon health for either a specific component
18 .BR c
19 or for all of them. Each component represent a subsystem of the session daemon.
20 Those components are set with health counters that are atomically incremented
21 once reached. An even value indicates progress in the execution of the
22 component. An odd value means that the code has entered a blocking state which
23 is not a poll(7) wait period.
24
25 A bad health is defined by a fatal error code path reached or any IPC used in
26 the session daemon that was blocked for more than 20 seconds (default timeout).
27 The condition for this bad health to be detected is that one or many of the
28 counters are odd.
29
30 The health check mechanism of the session daemon can only be reached through
31 the health socket which is a different one from the command and the application
32 socket. An isolated thread serves this socket and only computes the health
33 counters across the code when asked by the lttng control library (using this
34 call). This subsystem is highly unlikely to fail due to its simplicity.
35
36 The
37 .BR c
38 argument can be one of the following values:
39 .TP
40 .BR LTTNG_HEALTH_CMD
41 Command subsystem which handles user commands coming from the liblttng-ctl or
42 the
43 .BR lttng(1)
44 command line interface.
45 .TP
46 .BR LTTNG_HEALTH_APP_MANAGE
47 The session daemon manages application socket in order to route client command
48 and check if they get closed which indicates the application shutdown.
49 .TP
50 .BR LTTNG_HEALTH_APP_REG
51 The application registration mechanism is an important and vital part of for
52 user space tracing. Upon startup, applications instrumented with
53 .BR lttng-ust(3)
54 try to register to the session daemon through this subsystem.
55 .TP
56 .BR LTTNG_HEALTH_KERNEL
57 Monitor the Kernel tracer streams and main channel of communication
58 (/proc/lttng). If this component malfunction, the Kernel tracer is not usable
59 anymore by lttng-tools.
60 .TP
61 .BR LTTNG_HEALTH_CONSUMER
62 The session daemon can spawn up to
63 .BR three
64 consumer daemon for kernel, user space 32 and 64 bit. This subsystem monitors
65 the consumer daemon(s). A bad health state means that the consumer(s) are not
66 usable anymore hence likely making tracing not usable.
67 .TP
68 .BR LTTNG_HEALTH_ALL
69 Check all components. If only one of them is in a bad state, a health check
70 error is returned.
71
72 .SH "RETURN VALUE"
73 Return 0 if the health is OK, or 1 is it's in a bad state. A return code of \-1
74 indicates that the control library was not able to connect to the session
75 daemon health socket.
76
77 .SH "LIMITATIONS"
78
79 For the LTTNG_HEALTH_CONSUMER, you can not know which consumer daemon has
80 failed but only that either the consumer subsystem has failed or that a
81 lttng-consumerd died.
82
83 .SH "AUTHORS"
84 lttng-health-check was originally written by David Goulet and is currently
85 maintained by Jérémie Galarneau <jeremie.galarneau@efficios.com>.
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