doc/man/lttng-health-check.3

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