Docs: immadiate rotations can be performed with active schedules

[lttng-tools.git] / doc / man / lttng-rotate.1.txt

lttng-rotate(1)
===============


NAME
----
lttng-rotate - Archive a tracing session's current trace chunk


SYNOPSIS
--------
[verse]
*lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *rotate* [option:--no-wait] ['SESSION']


DESCRIPTION
-----------
The `lttng rotate` command archives the current trace chunk of the
current tracing session, or of the tracing session named 'SESSION' if
provided, to the file system. This action is called a tracing session
_rotation_.

Once a trace chunk is archived, LTTng does not manage it anymore: you
can read it, modify it, move it, or remove it.

An archived trace chunk is a collection of metadata and data stream
files which form a self-contained trace.

The _current trace chunk_ of a given tracing session includes:

* The stream files already written to the file system, and which are
  not part of a previously archived trace chunk, since the most recent
  event amongst:
** The first time the tracing session was started with
   man:lttng-start(1).
** The last rotation, either an immediate one with `lttng rotate`, or an
   automatic one from a rotation schedule previously set with
   man:lttng-enable-rotation(1).
* The content of all the non-flushed sub-buffers of the tracing
  session's channels.

You can use `lttng rotate` either at any time when the tracing session
is active (see man:lttng-start(1)), or a single time once the tracing
session becomes inactive (see man:lttng-stop(1)).

By default, the `lttng rotate` command ensures that the rotation is done
before printing the archived trace chunk's path and returning to the
prompt. The printed path is absolute when the tracing session was
created in normal mode and relative to the relay daemon's output
directory (see the nloption:--output option in man:lttng-relayd(8)) when
it was created in network streaming mode (see man:lttng-create(1)).

With the option:--no-wait option, the command finishes immediately,
hence a rotation might not be completed when the command is done. In
this case, there is no easy way to know when the current trace chunk is
archived, and the command does not print the archived trace chunk's
path.

Because a rotation causes the tracing session's current sub-buffers to
be flushed, archived trace chunks are never redundant, that is, they do
not overlap over time like snapshots can (see man:lttng-snapshot(1)).
Also, a rotation does not directly cause discarded event records or
packets.

See <<limitations,LIMITATIONS>> for important limitations regarding
this command.


Trace chunk archive naming
~~~~~~~~~~~~~~~~~~~~~~~~~~
A trace chunk archive is a subdirectory of a tracing session's output
directory (see the nloption:--output option in man:lttng-create(1))
which contains, through tracing domain and possibly UID/PID
subdirectories, metadata and data stream files.

A trace chunk archive is, at the same time:

* A self-contained LTTng trace.
* A member of a set of trace chunk archives which form the complete
  trace of a tracing session.

In other words, an LTTng trace reader can read both the tracing
session output directory (all the trace chunk archives), or a
single trace chunk archive.

When a tracing session rotation occurs, the created trace chunk
archive is named:

[verse]
__BEGIN__-__END__-__ID__

__BEGIN__::
    Date and time of the beginning of the trace chunk archive with
    the ISO 8601-compatible `YYYYmmddTHHMMSS±HHMM` form, where
    `YYYYmmdd` is the date and `HHMMSS±HHMM` is the time with the
    time zone offset from UTC.
+
Example: `20171119T152407-0500`

__END__::
    Date and time of the end of the trace chunk archive with
    the ISO 8601-compatible `YYYYmmddTHHMMSS±HHMM` form, where
    `YYYYmmdd` is the date and `HHMMSS±HHMM` is the time with the
    time zone offset from UTC.
+
Example: `20180118T152407+0930`

__ID__::
    Unique numeric identifier of the trace chunk within its
    tracing session.

Trace chunk archive name example: `20171119T152407-0500-20171119T151422-0500-3`


include::common-cmd-options-head.txt[]


option:-n, option:--no-wait::
    Do not ensure that the rotation is done before returning to
    the prompt.


include::common-cmd-help-options.txt[]


[[limitations]]
LIMITATIONS
-----------
The `lttng rotate` command only works when:

* The tracing session is created in normal mode or in network streaming
  mode (see man:lttng-create(1)).

* No channel was created with a configured trace file count or size
  limit (see the nloption:--tracefile-size and
  nloption:--tracefile-count options in man:lttng-enable-channel(1)).

* No immediate rotation (`lttng rotate`) is currently happening.


include::common-cmd-footer.txt[]


SEE ALSO
--------
man:lttng-enable-rotation(1),
man:lttng-disable-rotation(1),
man:lttng(1)