[lttng-dev] LTTng snapshot howto

[Brosseau, Yannick]

A question about the snapshot: is there a way to trigger a new state dump?
Le 2013-07-21 14:29, "Mathieu Desnoyers" <mathieu.desnoyers at efficios.com> a
écrit :

> Hi,
>
> I just pushed a LTTng snapshot howto (new feature of lttng 2.3-rc). I'm
> posting it to lttng-dev, since it provides a quick insight on how to use
> the snapshot feature. Comments are welcome!
>
> Thanks,
>
> Mathieu
>
>
> LTTng Flight Recorder Snapshot HOWTO
>
> Mathieu Desnoyers
> July 21st, 2013
>
> This document presents how to use the snapshot feature of LTTng.
>
> Snapshots allow to grab the content of flight recorder tracing buffers
> at the time the snapshot record command is invoked. Flight recorder
> tracing gather trace data in memory, overwriting the oldest information,
> without requiring any disk I/O. The snapshot record command exports the
> snapshot to the destination specified by the user.
>
> Basic usage:
>
> Session daemon started as root for kernel tracing:
>
> # lttng-sessiond -d
>
> From a user part of the tracing group (for kernel tracing):
>
> $ lttng create --snapshot
> $ lttng enable-event -k -a      # enable kernel tracing
> $ lttng enable-event -u -a      # enable user-space tracing
> $ lttng start
>
>     [ do something, generate activity on the system ]
>
> $ lttng snapshot record
>
>     [ do more stuff... ]
>
> $ lttng snapshot record
>
> $ lttng stop
> $ lttng destroy
>
> Each "lttng snapshot" command records a snapshot of the current buffer
> state. "lttng enable --snapshot" automatically setups the buffers in
> overwrite mode for flight recording, and does not attach any output file
> to the trace. The "lttng snapshot record" command can be performed
> either while tracing is started or stopped.
>
> As an example, this generates the following hierarchy under the
> directory reported by the "create" command above:
>
> .
> ├── snapshot-1-20130721-141838-0
> │   ├── kernel
> │   │   ├── channel0_0
> │   │   ├── channel0_1
> │   │   ├── channel0_2
> │   │   ├── channel0_3
> │   │   └── metadata
> │   └── ust
> │       └── uid
> │           └── 1000
> │               └── 64-bit
> │                   ├── channel0_0
> │                   ├── channel0_1
> │                   ├── channel0_2
> │                   ├── channel0_3
> │                   └── metadata
> └── snapshot-1-20130721-141842-1
>     ├── kernel
>     │   ├── channel0_0
>     │   ├── channel0_1
>     │   ├── channel0_2
>     │   ├── channel0_3
>     │   └── metadata
>     └── ust
>         └── uid
>             └── 1000
>                 └── 64-bit
>                     ├── channel0_0
>                     ├── channel0_1
>                     ├── channel0_2
>                     ├── channel0_3
>                     └── metadata
>
>
> Then, running babeltrace on, e.g.
>
> babeltrace snapshot-1-20130721-141838-0
>
> shows the content of the first snapshot.
>
> Please refer to the lttng(1) manpage for details on the snapshot mode.
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
>
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>
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