LTTNG-ADD-CONTEXT(1)

NAME
lttng-add-context - Add context fields to an LTTng channel

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.

    Note

    Make sure to single-quote the type when running the command from a shell, as $ is a special character for variable substitution in most shells.

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).

  Domain

One of:

-j, --jul
    Add context to channel in the java.util.logging (JUL) domain.

-k, --kernel
    Add context to channel in the Linux kernel domain.

-l, --log4j
    Add context to channel in the Apache log4j domain.

-u, --userspace
    Add context to channel in the user space domain.

  Target

-c CHANNEL, --channel=CHANNEL
    Add context fields to a channel named CHANNEL instead of adding them to all the channels.

-s SESSION, --session=SESSION
    Add context fields to a channel in the tracing session named SESSION instead of the current tracing session.

  Context

--list
    List the available context fields. Use this option alone.

-t TYPE, --type=TYPE
    Add context field named TYPE. This option can be repeated as many times as needed on the command-line.

  Program information

-h, --help
    Show command help.

    This option, like lttng-help(1), attempts to launch /usr/bin/man to view the command’s man page. The path to the man pager can be overridden by the LTTNG_MAN_BIN_PATH environment variable.

--list-options
    List available command options.

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)).

    Note

    $LTTNG_HOME defaults to $HOME when not explicitly set.

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)