lttng-add-context - Man Page

Add context fields to be recorded by LTTng

Synopsis

Add context fields to be recorded to the event records of one or more event record channels:

lttng [GENERAL OPTIONS] add-context
      (--kernel | --userspace | --jul | --log4j | --log4j2)
      [--session=SESSION] [--channel=CHANNEL]
      --type=TYPE [--type=TYPE]...

List the available context field types:

lttng [GENERAL OPTIONS] add-context --list

Description

The lttng add-context command can:

Without the --list option

Add one or more context fields to be recorded by LTTng to the event records of:

With the --session=SESSION option: The recording session named SESSION.
Without the --session option: The current recording session (see lttng-concepts(7) to learn more about the current recording session).
With the --channel=CHANNEL: The event record channel named CHANNEL.
Without the --channel option: All the event record channels of the selected recording session.

With the --list option

List the available context field types.

See lttng-concepts(7) to learn more about recording sessions and event record channels.

Repeat the --type=TYPE option to add more than one context field to be recorded. TYPE is one of:

A statically-known, or built-in context field name.

A perf counter name:

Per-CPU

Prefix: perf:cpu:

Only available with the --kernel option.

Per-thread

Prefix: perf:thread:

Only available with the --userspace, --jul, --log4j, or --log4j2 option.

Add Performance Monitoring Unit (PMU) counter context fields by raw ID with the perf:cpu:raw:rN:NAME (--kernel option) or perf:thread:raw:rN:NAME (--userspace, --jul, --log4j, or --log4j2 option) types, with:

N

A hexadecimal event descriptor which follows the perf-record(1) format: a concatenation of the event number and umask value which the manufacturer of the processor provides.

The possible values for this part are processor-specific.

NAME

Custom name to identify the counter.

An LTTng application-specific context field name:
```
$app.PROVIDER:TYPE
```
+ PROVIDER:: Provider name.

TYPE: Context type name.

Only available with the --jul, --log4j, and --log4j2 options.

Important: Make sure to single-quote TYPE when you run the add-context command from a shell, as $ is a special character for variable substitution in most shells.
Note: As of LTTng 2.16.0, you may NOT add context fields to be recorded to the event records of a given event record channel once its recording session has been started (see lttng-start(1)) at least once.

See the “Examples” section below for usage examples.

Options

See lttng(1) for GENERAL OPTIONS.

Tracing domain

One of:

-j, --jul: Add context fields to be recorded to the event records of one or more event record channels of the java.util.logging (JUL) tracing domain.
-k, --kernel: Add context fields to be recorded to the event records of one or more event record channels of the Linux kernel tracing domain.
-l, --log4j: Add context fields to be recorded to the event records of one or more event record channels of the Apache log4j 1.x tracing domain.
--log4j2: Add context fields to be recorded to the event records of one or more event record channels of the Apache Log4j 2 tracing domain.
-u, --userspace: Add context fields to be recorded to the event records of one or more event record channels of the user space tracing domain.

Recording target

-c CHANNEL, --channel=CHANNEL: Add context fields to be recorded to the event records of an event record channel named CHANNEL instead of all the event record channels of the selected recording session.
-s SESSION, --session=SESSION: Add context fields to be recorded to the event records of one or more event record channels of the recording session named SESSION instead of the current recording session.

Context field type

--list

List the available context field types.

You may NOT use this option with the --channel, --session, or --type options.

-t TYPE, --type=TYPE

Add a context field having the type TYPE to be recorded.

Repeat this option to add more than one context field.

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_LIST_LEGACY

Set to 1 to use the legacy output format (LTTng 2.14 and earlier) for the lttng-list(1) command instead of the modern output format.

Note that the legacy output doesn’t show anything related to features introduced after LTTng 2.14.

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_NO_UTF_8

Set to 1 to NOT emit multi-byte UTF-8 sequences, even if the locale claims to support it.

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.

LTTNG_TERM_COLOR

Controls when to emit terminal SGR codes in the output.

The NO_COLOR environment variable overrides this.

One of:

auto (default): Only emit SGR codes when the standard output is connected to a color-capable terminal.
always: Always emit SGR codes.
never: Never emit SGR codes.

NO_COLOR

If set and not empty, then it’s equivalent to setting LTTNG_TERM_COLOR to never.

See NO_COLOR <https://no-color.org/> to learn more.

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. List the available context field types.

See the --list option.

$ lttng add-context --list

Example 2. Add a single statically-known context field to be recorded to all the Linux kernel event record channels of the current recording session.

$ lttng add-context --kernel --type=pid

Example 3. Add three statically-known context fields to be recorded to a specific user space event record channel of a specific recording session.

See the --session and --channel options.

$ lttng add-context --userspace --session=my-session \
                    --channel=my-channel \
                    --type=vpid --type=procname --type=ip

Example 4. Add a perf counter context field to be recorded to a specific Linux kernel event record channel of the current recording session.

See the --channel option.

$ lttng add-context --kernel --channel=my-channel \
                    --type=perf:cpu:cache-misses

Example 5. Add an LTTng application-specific context field to be recorded to all the JUL event record channels of the current recording session.

$ lttng add-context --jul --type='$app.my_server:user_cnt'

Resources

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