lttng-create - Man Page

Create an LTTng recording session

Synopsis

Create a local mode recording session:

lttng [GENERAL OPTIONS] create [SESSION] [--shm-path=DIR]
      [--no-output | --output=DIR | --set-url=file://DIR]

Create a network streaming mode recording session:

lttng [GENERAL OPTIONS] create [SESSION] [--shm-path=DIR]
      (--set-url=URL | --ctrl-url=URL --data-url=URL)

Create a snapshot mode recording session:

lttng [GENERAL OPTIONS] create [SESSION] --snapshot [--shm-path=DIR]
      [--no-output | --output=DIR | --set-url=URL |
       --ctrl-url=URL --data-url=URL]

Create a live mode recording session:

lttng [GENERAL OPTIONS] create [SESSION] --live[=DELAYUS]
      [--shm-path=DIR] [--set-url=URL | --ctrl-url=URL --data-url=URL]

Description

The lttng create command creates a new recording session for your Unix user within the connected session daemon (see the “Session daemon connection” section of lttng(1) to learn how a user application connects to a session daemon).

See lttng-concepts(7) to learn more about recording sessions.

Without the SESSION argument, LTTng automatically generates a recording session name having the auto-YYYYmmdd-HHMMSS form, where YYYYmmdd and HHMMSS are the creation date and time. SESSION may NOT contain the character /.

Specify the path of the directory containing the shared memory files holding the channel ring buffers with the --shm-path option. Specifying a location on an NVRAM file system makes it possible to recover the latest recorded trace data when the system reboots after a crash with the lttng-crash(1) utility. Note that, as of LTTng 2.13.14, this feature is only available for user space channels.

By default, the create command automatically spawns:

On success, the create command sets the current recording session (see lttng-concepts(7) to learn more) to the created recording session.

See the “Examples” section below for usage examples.

Show the status of the current recording session with the lttng-status(1) command.

List the recording sessions of your Unix user, or of all users if your Unix user is root, within the connected session daemon with the lttng-list(1) command.

Start and stop a recording session with the lttng-start(1) and lttng-stop(1) commands.

Save and load a recording session with the lttng-save(1) and lttng-load(1) commands.

Allow and disallow specific processes to record events with the lttng-track(1) and lttng-untrack(1) commands.

Archive the current trace chunk of (rotate) a recording session with the lttng-rotate(1) command.

Destroy a recording session with the lttng-destroy(1) command.

Recording session modes

As documented in lttng-concepts(7), LTTng offers four recording session modes:

Local mode

Write the trace data to the local file system.

The trace data output directory is:

With the --no-output option

None: the file system output is disabled.

With the --output=DIR or --set-url=file://DIR option

The directory DIR.

Otherwise

A subdirectory, under the $LTTNG_HOME/lttng-traces ($LTTNG_HOME defaults to $HOME) directory, of which the name contains the recording session name and the date/time.

Network streaming mode

Send the trace data over the network to a listening relay daemon (see lttng-relayd(8)).

Set the trace output destination with the --set-url option, or with the --ctrl-url and --data-url options (see the “URL format” section below).

Snapshot mode (--snapshot option)

Only write the trace data to the local file system or send it to a listening relay daemon (lttng-relayd(8)) when LTTng takes a snapshot (see the lttng-snapshot(1) command).

With this mode, LTTng:

With the --no-output option

Does NOT add any snapshot output to the created recording session.

With the --output option, the --set-url option, or the --ctrl-url and --data-url options

Adds a snapshot output named snapshot-1 using the provided path or URL(s) to the created recording session.

Otherwise

Adds an automatic snapshot output named snapshot-1 to the created recording session.

The automatic snapshot output is a subdirectory, under the $LTTNG_HOME/lttng-traces ($LTTNG_HOME defaults to $HOME) directory, of which the name contains the recording session name and the date/time.

Live mode (--live option)

Send the trace data over the network to a listening relay daemon (see lttng-relayd(8)) for live reading.

Set the trace output destination with the --set-url=URL option, or with the --ctrl-url=URL and --data-url=URL options (see the “URL format” section below). URL may NOT start with file://.

URL format

The argument of the --set-url=URL, --ctrl-url=URL, and --data-url=URL options is an URL.

There are two available URL formats.

Local format

file://TRACEDIR
 

The file:// protocol targets the local file system: you may only use such an URL with the --set-url option when you create the recording session in local or snapshot mode (see the “Recording session modes” section above).

TRACEDIR

Absolute path to the directory containing the trace data on the local file system.

Network format

NETPROTO://(HOST | IPADDR)[:CTRLPORT[:DATAPORT]][/TRACEDIR]
 

This format is only available when you create the recording session in network streaming, snapshot (--snapshot), or live (--live) mode (see the “Recording session modes” section above).

NETPROTO

Network protocol, amongst:

net

TCP over IPv4.

The default values of CTRLPORT and DATAPORT are respectively 5342 and 5343.

net6

TCP over IPv6.

The default values of CTRLPORT and DATAPORT are respectively 5342 and 5343.

tcp

Same as the net protocol.

You may only use this with the --ctrl-url and --data-url options together.

tcp6

Same as the net6 protocol.

You can only be use this with the --ctrl-url and --data-url options together.

(HOST | IPADDR)

Hostname or IP address.

IPv6 address must be enclosed in square brackets ([ and ]); see RFC 2732 <https://www.ietf.org/rfc/rfc2732.txt>.

CTRLPORT

Control TCP port.

DATAPORT

Data TCP port.

TRACEDIR

Path of the directory containing the trace data on the remote file system.

This path is relative to the base output directory of the LTTng relay daemon (see the --output option of lttng-relayd(8)).

Options

See lttng(1) for GENERAL OPTIONS.

Mode selection

See the “Recording session modes” section above.

At most one of:

--live[=DELAYUS]

Create the recording session in live mode.

The optional DELAYUS argument is the maximum time (in µs) you can wait for the data to be flushed (sent to the connected LTTng relay daemon). The default value of DELAYUS is 1000000.

Set the URL of the relay daemon to connect to with the --set-url option, or with the --ctrl-url and --data-url options, instead of using net://127.0.0.1.

The session daemon must be able to connect to a listening relay daemon (see lttng-relayd(8)).

--snapshot

Create the recording session in snapshot mode.

This is equivalent to:

  • One of:
With the --no-output option

Not adding any snapshot output after LTTng creates the recording session.

With the --output option, the --set-url option, or the --ctrl-url and --data-url options

Adding a snapshot output named snapshot-1 using the provided path or URL(s) immediately after LTTng creates the recording session.

Otherwise

Adding an automatic snapshot output named snapshot-1 immediately after LTTng creates the recording session.

The automatic snapshot output is a subdirectory, under the $LTTNG_HOME/lttng-traces ($LTTNG_HOME defaults to $HOME) directory, of which the name contains the recording session name and the date/time.

  • Forcing all the channels to be created for the recording session to be configured with the --override and --output=mmap options (see lttng-enable-channel(1)).

Output

--no-output

Depending on the recording session mode (see the “Recording session modes” section above):

Local mode

Disable the file system output.

Snapshot mode (--snapshot option)

Do NOT add a snapshot output after creating the recording session.

-o DIR, --output=DIR

Equivalent to --set-url=file://DIR.

--shm-path=DIR

Set the path of the directory containing the shared memory files holding the channel ring buffers to DIR on the local file sytem.
Note

As of LTTng 2.13.14, LTTng only considers this option for user space (including Java and Python) channels, but this may change in the future.

URL

See the “URL format” section above to learn more about the syntax of the URL argument of the following options.

-C URL, --ctrl-url=URL

Set the control path URL to URL.

You must also use the --data-url option.

Not available in local mode (see the “Recording session modes” section above).

In snapshot mode, this is equivalent to using the --ctrl-url option of the add-output action of the lttng-snapshot(1) command immediately after creating the recording session.

-D URL, --data-url=URL

Set the trace data path URL to URL.

You must also use the --ctrl-url option.

Not available in local mode (see the “Recording session modes” section above).

In snapshot mode, this is equivalent to using the --data-url option of the add-output action of the lttng-snapshot(1) command immediately after creating the recording session.

-U URL, --set-url=URL

Set the destination URL of the control path and trace data to URL.

This URL remains unchanged as long as the recording session exists.

Depending on the recording session mode (see the “Recording session modes” section above):

Local mode

URL must start with file://, followed with the destination directory path on the local file system.

Network streaming and live modes

Equivalent to using both the --ctrl-url and --data-url options.

Snapshot mode (--snapshot option)

Equivalent to using the URL non-option argument of the add-output action of the lttng-snapshot(1) command immediately after creating the recording session.

Program information

-h,  --help

Show help.

This option attempts to launch /usr/bin/man to view this manual page. Override the manual pager path with the LTTNG_MAN_BIN_PATH environment variable.

--list-options

List available command options and quit.

Exit Status

0

Success

1

Command error

2

Undefined command

3

Fatal error

4

Command warning (something went wrong during the command)

Environment

LTTNG_ABORT_ON_ERROR

Set to 1 to abort the process after the first error is encountered.

LTTNG_HOME

Path to the LTTng home directory.

Defaults to $HOME.

Useful when the Unix user running the commands has a non-writable home directory.

LTTNG_MAN_BIN_PATH

Absolute path to the manual pager to use to read the LTTng command-line help (with lttng-help(1) or with the --help option) instead of /usr/bin/man.

LTTNG_SESSION_CONFIG_XSD_PATH

Path to the directory containing the session.xsd recording session configuration XML schema.

LTTNG_SESSIOND_PATH

Absolute path to the LTTng session daemon binary (see lttng-sessiond(8)) to spawn from the lttng-create(1) command.

The --sessiond-path general option overrides this environment variable.

Files

$LTTNG_HOME/.lttngrc

Unix user’s LTTng runtime configuration.

This is where LTTng stores the name of the Unix user’s current recording session between executions of lttng(1). lttng-create(1) and lttng-set-session(1) set the current recording session.

$LTTNG_HOME/lttng-traces

Default output directory of LTTng traces in local and snapshot modes.

Override this path with the --output option of the lttng-create(1) command.

$LTTNG_HOME/.lttng

Unix user’s LTTng runtime and configuration directory.

$LTTNG_HOME/.lttng/sessions

Default directory containing the Unix user’s saved recording session configurations (see lttng-save(1) and lttng-load(1)).

/usr/local/etc/lttng/sessions

Directory containing the system-wide saved recording session configurations (see lttng-save(1) and lttng-load(1)).

Note

$LTTNG_HOME defaults to the value of the HOME environment variable.

Examples

Example 1. Create a normal mode recording session with a generated name.

$ lttng create

Example 2. Create a normal mode recording session with a custom name.

$ lttng create my-session

Example 3. Create a normal mode recording session with a specific output directory.

See the --output option.

$ lttng create --output=/path/to/traces

Example 4. Create a network streaming mode recording session.

See the “Output directory” section of lttng-relayd(8) to understand where the relay daemon to connect to (10.0.0.242) writes the received traces.

See the --set-url option.

$ lttng create --set-url=net://10.0.0.242/inv4

Example 5. Create a snapshot mode recording session with a default snapshot output.

See the --snapshot option.

$ lttng create --snapshot

Example 6. Create a snapshot mode recording session with a custom snapshot output.

See the --snapshot and --set-url options.

$ lttng create --snapshot \
        --set-url=tcp://192.168.1.102:1234:5678/my-snapshots

Example 7. Create a snapshot mode recording session with no snapshot output.

See the --snapshot and --no-output options.

$ lttng create --snapshot --no-output

Example 8. Create an LTTng live mode recording session with a default relay daemon URL.

See the --live option.

$ lttng create --live

Example 9. Create an LTTng live mode recording session with a custom live timer period and relay daemon URL.

See the --live and --set-url options.

$ lttng create --live=250000 \
               --set-url=tcp://relayd34:4885:4886

Example 10. Create a normal mode recording session with a custom directory containing the ring buffer shared memory files.

See the --shm-path option.

$ lttng create my-session --shm-path=/mnt/nvram2/lttng

Resources

Thanks

Special thanks to Michel Dagenais and the DORSAL laboratory <http://www.dorsal.polymtl.ca/> at École Polytechnique de Montréal for the LTTng journey.

Also thanks to the Ericsson teams working on tracing which helped us greatly with detailed bug reports and unusual test cases.

See Also

lttng(1), lttng-destroy(1), lttng-enable-channel(1), lttng-list(1), lttng-rotate(1), lttng-save(1), lttng-set-session(1), lttng-start(1), lttng-status(1), lttng-track(1), lttng-concepts(7), lttng-relayd(8), lttng-sessiond(8)

Referenced By

babeltrace2-source.ctf.lttng-live(7), lttng(1), lttng-add-context(1), lttng-add-trigger(1), lttng-clear(1), lttng-concepts(7), lttng-crash(1), lttng-destroy(1), lttng-disable-channel(1), lttng-disable-event(1), lttng-disable-rotation(1), lttng-enable-channel(1), lttng-enable-event(1), lttng-enable-rotation(1), lttng-help(1), lttng-list(1), lttng-list-triggers(1), lttng-load(1), lttng-metadata(1), lttng-regenerate(1), lttng-relayd(8), lttng-remove-trigger(1), lttng-rotate(1), lttng-save(1), lttng-sessiond(8), lttng-set-session(1), lttng-snapshot(1), lttng-start(1), lttng-status(1), lttng-stop(1), lttng-track(1), lttng-untrack(1), lttng-version(1), lttng-view(1).

7 December 2021 LTTng 2.13.14 LTTng Manual