[lttng-dev] LTTng snapshot howto

[Mathieu Desnoyers]

* Brosseau, Yannick (yannick.brosseau at gmail.com) wrote:
> A question about the snapshot: is there a way to trigger a new state dump?

Not at this point, no.

> 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
> >
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> >

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