Fix: relayd: handling of lttng_read errors >= 0

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

lttng-create(1)
===============


NAME
----
lttng-create - Create an LTTng tracing session


SYNOPSIS
--------
Local mode:

[verse]
*lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *create* ['SESSION'] [option:--shm-path='PATH']
      [option:--no-output | option:--output='PATH' | option:--set-url=file://'PATH']

Network streaming mode:

[verse]
*lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *create* ['SESSION'] [option:--shm-path='PATH']
      (option:--set-url='URL' | option:--ctrl-url='URL' option:--data-url='URL')

Snapshot mode:

[verse]
*lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *create* ['SESSION'] option:--snapshot
      [option:--shm-path='PATH'] [option:--set-url='URL' | option:--ctrl-url='URL' option:--data-url='URL']

Live mode:

[verse]
*lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *create* ['SESSION'] option:--live[='DELAYUS']
      [option:--shm-path='PATH'] [option:--set-url='URL' | option:--ctrl-url='URL' option:--data-url='URL']

DESCRIPTION
-----------
The `lttng create` command creates a new tracing session.

A tracing session is a named container of channels, which in turn
contain event rules. It is domain-agnostic, in that channels and event
rules can be enabled for the user space tracer and/or the Linux
kernel tracer.

On execution, an `.lttngrc` file is created, if it does not exist, in the
user's home directory. This file contains the name of the current tracing
session. When creating a new tracing session with `lttng create`, the
current tracing session is set to this new tracing session. The
man:lttng-set-session(1) command can be used to set the current
tracing session without manually editing the `.lttngrc` file.

If 'SESSION' is omitted, a session name is automatically created having
this form: `auto-YYYYmmdd-HHMMSS`. 'SESSION' *must not* contain the
character `/`.

The option:--shm-path option can be used to specify the path to the
shared memory holding the ring buffers. Specifying a location on an
NVRAM file system makes it possible to retrieve the latest recorded
trace data when the system reboots after a crash. To view the events
of ring buffer files after a system crash, use the
man:lttng-crash(1) utility.

Tracing sessions are destroyed using the man:lttng-destroy(1)
command.


Creation modes
~~~~~~~~~~~~~~
There are four tracing session modes:

[[local-mode]]Local mode::
    Traces the local system and writes the trace to the local
    file system. The option:--output option specifies the trace path.
    Using option:--set-url=file://'PATH' is the equivalent of using
    option:--output='PATH'. The file system output can be disabled using
    the option:--no-output option.
+
If none of the options mentioned above are used, then the trace is
written locally in the `$LTTNG_HOME/lttng-traces` directory
(`$LTTNG_HOME` defaults to `$HOME`).

[[network-streaming-mode]]Network streaming mode::
    Traces the local system and sends the trace over the network to
    a listening relay daemon (see man:lttng-relayd(8)).
    The option:--set-url, or option:--ctrl-url and option:--data-url
    options set the trace output destination (see the
    <<url-format,URL format>> section below).

[[snapshot-mode]]Snapshot mode::
    Traces the local system without writing the trace to the local file
    system (implicit option:--no-output option). Channels are automatically
    configured to be snapshot-ready on creation (see
    man:lttng-enable-channel(1)). The man:lttng-snapshot(1)
    command is used to take snapshots of the current ring buffers.
    The option:--set-url, or option:--ctrl-url and option:--data-url
    options set the default snapshot output destination.

[[live-mode]]Live mode::
    Traces the local system, sending trace data to an LTTng relay daemon
    over the network (see man:lttng-relayd(8)). The
    option:--set-url, or option:--ctrl-url and option:--data-url options
    set the trace output destination. The live output URLs cannot use
    the `file://` protocol (see the <<url-format,URL format>>
    section below).


[[url-format]]
URL format
~~~~~~~~~~
The option:--set-url, option:--ctrl-url, and option:--data-url options'
arguments are URLs.

The format of those URLs is one of:

[verse]
file://'TRACEPATH'
'NETPROTO'://('HOST' | 'IPADDR')[:__CTRLPORT__[:__DATAPORT__]][/'TRACEPATH']

The `file://` protocol targets the *local file system* and can only
be used as the option:--set-url option's argument when the session is
created in <<local-mode,local>> or <<snapshot-mode,snapshot>> mode.

'TRACEPATH'::
    Absolute path to trace files on the local file system.

The other version is available when the session is created in
<<network-streaming-mode,network streaming>>,
<<snapshot-mode,snapshot>>, or <<live-mode,live>> mode.

'NETPROTO'::
    Network protocol, amongst:
+
--
`net`::
    TCP over IPv4; the default values of 'CTRLPORT' and 'DATAPORT'
    are respectively {default_network_control_port} and
    {default_network_data_port}.

`net6`::
    TCP over IPv6: same default ports as the `net` protocol.

`tcp`::
    Same as the `net` protocol; can only be used with the
    option:--ctrl-url and option:--data-url options together.

`tcp6`::
    Same as the `net6` protocol; can only be used with the
    option:--ctrl-url and option:--data-url options together.
--

('HOST' | 'IPADDR')::
    Hostname or IP address (IPv6 address *must* be enclosed in brackets
    (`[` and `]`); see https://www.ietf.org/rfc/rfc2732.txt[RFC 2732]).

'CTRLPORT'::
    Control port.

'DATAPORT'::
    Data port.

'TRACEPATH'::
    Path of trace files on the remote file system. This path is relative
    to the base output directory set on the relay daemon side;
    see man:lttng-relayd(8).


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


Mode selection
~~~~~~~~~~~~~~
option:--live[='DELAYUS']::
    Create the session in <<live-mode,live mode>>.
+
The optional 'DELAYUS' parameter, given in microseconds, is the
maximum time the user can wait for the data to be flushed. This mode
can be set with a network URL (options option:--set-url, or
option:--ctrl-url and option:--data-url) and must have a relay
daemon listening (see man:lttng-relayd(8)).
+
By default, 'DELAYUS' is {default_lttng_live_timer} and the network URL
is set to `net://127.0.0.1`.

option:--snapshot::
    Create the session in <<snapshot-mode,snapshot mode>>.
    This is the equivalent of using the option:--no-output option and
    creating all the channels of this new tracing session in overwrite
    mode with an `mmap` output type.


Output
~~~~~~
option:--no-output::
    In <<local-mode,local mode>>, do not output any trace data.

option:-o 'PATH', option:--output='PATH'::
    In <<local-mode,local mode>>, set trace output path to 'PATH'.

option:--shm-path='PATH'::
    Create shared memory holding buffers at 'PATH'.


URL
~~~
See the <<url-format,URL format>> section above for more information
about the syntax of the following options' 'URL' argument.

option:-C 'URL', option:--ctrl-url='URL'::
    Set control path URL to 'URL' (must use option:--data-url option
    also).

option:-D 'URL', option:--data-url='URL'::
    Set data path URL to 'URL' (must use option:--ctrl-url option
    also).

option:-U 'URL', option:--set-url='URL'::
    Set URL destination of the trace data to 'URL'. It is persistent for
    the session lifetime. This option sets both data
    (option:--data-url option) and control (option:--ctrl-url option)
    URLs at the same time.
+
In <<local-mode,local>> mode, 'URL' must start with `file://` followed
by the destination path on the local file system.


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


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


SEE ALSO
--------
man:lttng-destroy(1),
man:lttng-set-session(1),
man:lttng(1)