lttng-rotate.1.txt: update voice and document the `archives` subdir.

[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 LTTng archives a trace chunk, it 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 LTTng 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`:

* At any time when the tracing session is active (see
  man:lttng-start(1)).
* A single time once the tracing session becomes inactive
  (see man:lttng-stop(1)).

By default, the `lttng rotate` command ensures that LTTng finished
performing the tracing session rotation before it prints the archived
trace chunk's path and exits. 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, so
that LTTng might not have completed the rotation when the command exits.
In this case, there is no easy way to know when the current trace chunk
becomes archived, and the command does not print the archived trace
chunk's path.

Because when LTTng performs a tracing session rotation, it flushes the
tracing session's current sub-buffers, 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 the `archives` subdirectory
within a tracing session's output directory (see the nloption:--output
option in man:lttng-create(1) and man:lttng-relayd(8)).

A trace chunk archive 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 LTTng performs a tracing session rotation, it names the resulting
trace chunk archive as such, relative to the tracing session's output
directory:

[verse]
archives/__BEGIN__-__END__-__ID__

__BEGIN__::
    Date and time of the beginning of the trace chunk archive with
    the ISO{nbsp}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{nbsp}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:

----
archives/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)