[lttng-dev] Trace-file size and flight record mode

Anand Neeli anand.neeli at gmail.com
Thu Jan 23 03:36:03 EST 2014

Hi All,
can anyone help me with these queries. These are related to trace modes and
file sizes.
I use the following commands to trace
    ./lttng enable-channel mychannel --userspace --buffers-pid -s mysession
    ./lttng enable-event --channel mychannel --userspace --all -s mysession

here are my queries
1) Trace file should be limited to some defined size and should be
overwritten after it reaches max size.
I want to retain latest N bytes of traces.
can anyone pls provide more details and the command to enable this?

I see -C and -W options. But will the files be overwritten to maintain
latest traces?
and if i use "-W 4" will it create 4xN bytes of latest traces?

2) Flight recorder mode
If i'm not wrong "Flight recorder mode" continuously overwrite the data in
the memory buffers, instead of flushing it to a file on disk.
How to flush this memory buffer to file to see the traces or is there a way
to read this memory?

Anand Neeli
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