README-LIVE

   1 As of LTTng v2.4, we can now process traces while they are being recorded
   2 (called live-tracing). LTTngtop can read live traces either in the ncurses GUI
   3 or in text mode.
   4
   5 In order to use this feature, start by creating a live session with at least
   6 the events and contexts required for LTTngtop (see the manpage for that).  A
   7 simple script to do the basic setup is available in
   8 utils/create-live-session.sh
   9
  10 Once the session is created, you can list the sessions established on the
  11 relay with :
  12 $ lttngtop -r net://relaydhostname
  13
  14 And attach to a session with
  15 $ lttngtop -r net://relaydhostname/host/<hostname/<session-name>
  16
  17 A few seconds later, you should begin to see your live trace being displayed in
  18 lttngtop gui.
  19 To use the textdump feature, use the -t (and see --help for more options). You
  20 can also use the new lttngtrace provided by lttngtop which does all the setup
  21 for a live trace in textdump on localhost.
  22
  23
  24 EXPERIMENTAL :
  25 In order to use the (beta) MMAP live tracing features of LttngTop, you need these
  26 branches :
  27
  28 git clone -b lttngtop-live git://git.dorsal.polymtl.ca/~jdesfossez/lttng-tools
  29 git clone -b lttngtop-live git://git.dorsal.polymtl.ca/~jdesfossez/babeltrace
  30
  31 The only difference between these branches and the master branch is that they
  32 export an additional library that is used by lttngtop to do live tracing.
  33
  34 You have to compile and install lttng-tools before babeltrace since there are
  35 dependencies on the library exposed by this special lttng-tools in babeltrace
  36 for live mmap buffer consuming.
  37
  38 Then you can compile and use the live branch of LttngTop :
  39 git clone -b live git://git.lttng.org/lttngtop.git
  40
  41 Once everything is installed, you can start as root lttng-sessiond and use
  42 lttngtop (as root or from a user part of the "tracing" group).
  43
  44 Note: if lttng-sessiond has been used to record a trace before starting
  45 lttngtop (normal lttng use-case), you need to restart it because it
  46 automatically spawned a consumer that prevents lttngtop from registering its
  47 own consumer. The same applies when you finish using lttngtop, you need to
  48 restart the lttng-sessiond daemon to allow others to record traces again. This
  49 is a know problem of integration that will be fixed.