lttng-add-context

Synopsis

Add context fields to a channel:

lttng [GENERAL OPTIONS] add-context
      (--kernel | --userspace | --jul | --log4j)
      [--session=SESSION] [--channel=CHANNEL]
      --type=TYPE [--type=TYPE]...

List the available context fields:

lttng [GENERAL OPTIONS] add-context --list

Description

The lttng add-context command adds one or more context fields to a channel.

Channels are created with the lttng-enable-channel(1) command.

When context fields are added to a channel, all the events emitted within this channel contain the dynamic values of those context fields.

If the --session option is omitted, the current tracing session is used. If the --channel option is omitted, the context fields are added to all the selected tracing session’s channels.

Many context fields can be added to a channel at once by repeating the --type option.

perf counters are available as per-CPU (perf:cpu: prefix) as well as per-thread (perf:thread: prefix) counters. Currently, per-CPU counters can only be used in the Linux kernel tracing domain, while per-thread counters can only be used in the user space tracing domain.

It is also possible to enable PMU counters by raw ID using the perf:cpu:raw:rN:NAME (Linux kernel tracing domain) or perf:thread:raw:rN:NAME (user space tracing domain), with:

N

A hexadecimal event descriptor which is the same format as used by perf-record(1): a concatenation of the event number and umask value provided by the processor’s manufacturer. The possible values for this field are processor-specific.

NAME

Custom name to easily recognize the counter.

Application-specific context fields can be added to a channel using the following syntax:

$app.PROVIDER:TYPE

with:

PROVIDER

Provider name.

TYPE

Context type name.

Use the --list option without other arguments to list the available context field names.

See the Limitations section below for a list of limitations to consider.

Options

General options are described in lttng(1).

Limitations

As of this version of LTTng, it is not possible to add context fields to a channel once its tracing session has been started (see lttng-start(1)) at least once.

Environment Variables

LTTNG_ABORT_ON_ERROR

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

LTTNG_HOME

Overrides the $HOME environment variable. Useful when the user running the commands has a non-writable home directory.

LTTNG_MAN_BIN_PATH

Absolute path to the man pager to use for viewing help information about LTTng commands (using lttng-help(1) or lttng COMMAND --help).

LTTNG_SESSION_CONFIG_XSD_PATH

Path in which the session.xsd session configuration XML schema may be found.

LTTNG_SESSIOND_PATH

Full session daemon binary path.

The --sessiond-path option has precedence over this environment variable.

Note that the lttng-create(1) command can spawn an LTTng session daemon automatically if none is running. See lttng-sessiond(8) for the environment variables influencing the execution of the session daemon.

Files

$LTTNG_HOME/.lttngrc

User LTTng runtime configuration.

This is where the per-user current tracing session is stored between executions of lttng(1). The current tracing session can be set with lttng-set-session(1). See lttng-create(1) for more information about tracing sessions.

$LTTNG_HOME/lttng-traces

Default output directory of LTTng traces. This can be overridden with the --output option of the lttng-create(1) command.

$LTTNG_HOME/.lttng

User LTTng runtime and configuration directory.

$LTTNG_HOME/.lttng/sessions

Default location of saved user tracing sessions (see lttng-save(1) and lttng-load(1)).

/usr/local/etc/lttng/sessions

System-wide location of saved tracing sessions (see lttng-save(1) and lttng-load(1)).

Exit Status

0

Success

1

Command error

2

Undefined command

3

Fatal error

4

Command warning (something went wrong during the command)

Bugs

If you encounter any issue or usability problem, please report it on the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-tools>.

Resources

• LTTng project website <https://lttng.org>
• LTTng documentation <https://lttng.org/docs>
• Git repositories <http://git.lttng.org>
• GitHub organization <http://github.com/lttng>
• Continuous integration <http://ci.lttng.org/>
• Mailing list <http://lists.lttng.org> for support and development: lttng-dev@lists.lttng.org
• IRC channel <irc://irc.oftc.net/lttng>: #lttng on irc.oftc.net

Copyrights

This program is part of the LTTng-tools project.

LTTng-tools is distributed under the GNU General Public License version 2 <http://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html>. See the LICENSE <https://github.com/lttng/lttng-tools/blob/master/LICENSE> file for details.

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)

Referenced By

lttng(1), lttng-enable-event(1), lttng-ust(3).