[lttng-dev] How to use the lttng-untrack command

[Mathieu Desnoyers]

----- On Sep 1, 2020, at 5:13 AM, 熊毓华 <xiongyuhua at zju.edu.cn> wrote: 

> Hi，dear

> Hello, I have encountered some problems in using LTTNG, which is briefly
> described as follows. I am eager to get your help.

> About the use of the untrack command.It is reproduced as follows:

> I type the following commands in turn to start LTTNG, and set up not to monitor
> a particular process.(For example, I input the "top" command in the terminal,
> the PID of the "top" process is 72598, now I want LTTNG not to monitor the
> "top" process)

>     1. lttng create my-kernel-session --output=/tmp/my-kernel-trace
>     2. lttng add-context -k -t pid
>     3. lttng add-context -k -t tid
>     4. lttng enable-event --kernel --all
>     5. lttng untrack --kernel --pid=72598
>     6. lttng start
>     7. lttng destroy
>     8. babeltrace2 /tmp/my-kernel-trace > babeltrace.txt

> Unfortunately, the output still contains the data for PID72598.
> Even after I changed "lttng untrack --kernel -- PID =72598" to "LTTNG untrack-u
> -- PID =72598", this phenomenon still occurred.

> How do I use the lttng-untrack command to achieve my goal?
Based on the lttng-track(1) man page: 

The lttng track commands adds one or more values to a process attribute 
tracker. 

A process attribute tracker is an inclusion set of process attributes. 
Tracked processes are allowed to emit events, provided those events are 
targeted by enabled event rules (see lttng-enable-event(1)). 

Tracker values can be removed from an inclusion set with lttng- 
untrack(1). 

What you are looking for is a an "exclusion set", which does not exist at this point 
in LTTng. 

Thanks, 

Mathieu 

> Looking forward to your reply.
> thanks,
> yuhua

> ------------------
> Yuhua Xiong
> Lab for Internet and Security Technology
> School of Computer Science and Technology
> Zhejiang University
> Hangzhou, 310007, P.R. China

-- 
Mathieu Desnoyers 
EfficiOS Inc. 
http://www.efficios.com 
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