extras/core-handler/README

   1 LTTng core dump snapshot handler
   2 Christian Babeux, June 2013
   3
   4 This is a custom core dump program that will be called when a core dump
   5 occurs. The program will save the core data in CORE_PATH and also, if a
   6 root session daemon is running, will record a snapshot of tracing data
   7 using the lttng command line utility.
   8
   9 The core dump snapshot handler can be installed by using the provided
  10 install.sh script or by adding the appropriate program pipe line to
  11 /proc/sys/kernel/core_pattern. Refer to core(5) for more information
  12 about the Linux kernel core dump handling and custom handler mechanism.
  13
  14 Installation:
  15
  16 # ./install.sh
  17 Backup current core_pattern in core_pattern.bkp.
  18 Successfully installed core_pattern.
  19
  20 How to use:
  21
  22 You can use the provided test.sh script to test that the core dump snapshot
  23 handler is working properly:
  24
  25 # ./test.sh
  26 Setup...
  27 Spawning a session daemon
  28 Session auto-20130626-224838 created.
  29 Kernel channel chan enabled for session auto-20130626-224838
  30 kernel event sched_switch created in channel chan
  31 Tracing started for session auto-20130626-224838
  32 Sleeping...
  33 Crashing...
  34 ./test.sh: line 35: 16980 Segmentation fault      (core dumped)
  35 $(dirname $0)/crash
  36 Waiting for data availability
  37 Tracing stopped for session auto-20130626-224838
  38 Session auto-20130626-224838 destroyed
  39 Core dump and snapshot will be available in /tmp/lttng/{core,snapshot}.
  40
  41 # tree /tmp/lttng
  42 /tmp/lttng
  43 |-- core
  44 |   `-- core.16980
  45 `-- snapshot
  46     `-- snapshot
  47         |-- chan_0
  48         |-- chan_1
  49         |-- chan_2
  50         |-- chan_3
  51         |-- chan_4
  52         |-- chan_5
  53         |-- chan_6
  54         |-- chan_7
  55         `-- metadata
  56
  57 Chaining with other core dump handler:
  58
  59 Some Linux distributions already use their own core dump handler
  60 (such as systemd 'systemd-coredump' utility). It is possible to chain these
  61 core dump utility with the core dump snapshot handler. In order to achieve
  62 this, the core dump snapshot handler must be first in the chain (e.g.
  63 installed in /proc/sys/kernel/core_pattern) and the other core dump
  64 handler must be called from within the core dump snapshot handler script.
  65
  66 Example (chaining with systemd systemd-coredump):
  67
  68 # cat /proc/sys/kernel/core_pattern
  69 |/path/to/lttng/handler.sh %p %u %g %s %t %h %e %E %c
  70
  71 In LTTng handler.sh script:
  72
  73 [...]
  74 # Save core dump from stdin.
  75 $MKDIR_BIN -p "${CORE_PATH}"
  76
  77 # Optional, chain core dump handler with original systemd script.
  78 $CAT_BIN - | /usr/lib/systemd/systemd-coredump $p $u $g $s $t $e
  79 [...]