LTTng » LTTng-tools

Following this discussion on the mailing list¹, it seems that on a system with only a root session-daemon running, applications running as a user that is not part of the tracing group won't be traced.

I have reproduced this issue on Ubuntu 12.04 and Arch Linux.

Revisions used

lttng-tools: a8621b72212889dd024bb39cdb3bab7d54e73e19
lttng-ust: 9d34b2263291fa3007c128d5ec667218884ee50a

Log

jgalar@ubuntu1204-32:~/lttng-traces$ sudo lttng create
Spawning a session daemon
Warning: No tracing group detected
Session auto-20130812-191905 created.
Traces will be written in /home/jgalar/lttng-traces/auto-20130812-191905
jgalar@ubuntu1204-32:~/lttng-traces$ sudo lttng enable-event -u -a
All UST events are enabled in channel channel0
jgalar@ubuntu1204-32:~/lttng-traces$ sudo lttng start
Tracing started for session auto-20130812-191905
jgalar@ubuntu1204-32:~/lttng-traces$ cd ~/EfficiOS/lttng-ust/doc/examples/hello-static-lib/
jgalar@ubuntu1204-32:~/EfficiOS/lttng-ust/doc/examples/hello-static-lib$ ./hello 
Hello, World!
Tracing...  done.
jgalar@ubuntu1204-32:~/EfficiOS/lttng-ust/doc/examples/hello-static-lib$ sudo ./hello 
Hello, World!
Tracing...  done.
jgalar@ubuntu1204-32:~/EfficiOS/lttng-ust/doc/examples/hello-static-lib$ sudo lttng stop
Waiting for data availability
Tracing stopped for session auto-20130812-191905
jgalar@ubuntu1204-32:~/EfficiOS/lttng-ust/doc/examples/hello-static-lib$ sudo lttng destroy
Session auto-20130812-191905 destroyed
jgalar@ubuntu1204-32:~/EfficiOS/lttng-ust/doc/examples/hello-static-lib$ sudo chown -R jgalar ~/lttng-traces/
jgalar@ubuntu1204-32:~/EfficiOS/lttng-ust/doc/examples/hello-static-lib$ cd ~/lttng-traces/auto-20130812-191905/
jgalar@ubuntu1204-32:~/lttng-traces/auto-20130812-191905$ tree
.
??? ust
    ??? uid
        ??? 0
            ??? 32-bit
                ??? channel0_0
                ??? channel0_1
                ??? metadata

4 directories, 3 files

Notice how only UID 0 has a trace.

A root session-daemon should be able to trace all applications running on the system.

[1] http://lists.lttng.org/pipermail/lttng-dev/2013-August/021112.html