LTTng » LTTng-tools

Adding context to an empty session has the nasty side-effect of creating the default channel, whether the command succeeded or not:

$ sudo -H lttng create somesession
Session somesession created.
Traces will be written in /root/lttng-traces/somesession-20130531-134523
$ sudo -H lttng list somesession
Tracing session somesession: [inactive]
    Trace path: /root/lttng-traces/somesession-20130531-134523

$ sudo -H lttng add-context -k -t perf:cache-misses
Error: perf:cache-misses: Add kernel context failed
Warning: Some command(s) went wrong
$ sudo -H lttng list somesession
Tracing session somesession: [inactive]
    Trace path: /root/lttng-traces/somesession-20130531-134523

=== Domain: Kernel ===

Channels:
-------------
- channel0: [enabled]

    Attributes:
      write mode: discard
      subbufers size: 262144 bytes
      number of subbufers: 4
      switch timer interval: 0 usec
      read timer interval: 200000 usec
      output: splice()

    Events:
      None

or

$ sudo -H lttng create somesession
Session somesession created.
Traces will be written in /root/lttng-traces/somesession-20130531-144523
$ sudo -H lttng list somesession
Tracing session somesession: [inactive]
    Trace path: /root/lttng-traces/somesession-20130531-144523

$ sudo -H lttng add-context -k -t procname
kernel context procname added to all channels
$ sudo -H lttng list somesession
Tracing session somesession: [inactive]
    Trace path: /root/lttng-traces/somesession-20130531-144523

=== Domain: Kernel ===

Channels:
-------------
- channel0: [enabled]

    Attributes:
      write mode: discard
      subbufers size: 262144 bytes
      number of subbufers: 4
      switch timer interval: 0 usec
      read timer interval: 200000 usec
      output: splice()

    Events:
      None