lttng-add-context — Add context fields to an LTTng channel
lttng add-context command adds one or more context fields to a
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.
Many context fields can be added to a channel at once by repeating the
perf counters are available as per-CPU (
perf:cpu: prefix) as well as
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:
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.
Custom name to easily recognize the counter.
Application-specific context fields can be added to a channel using the following syntax:
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
--list option without other arguments to list the
available context field names.
See the LIMITATIONS section below for a list of limitations to consider.
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.
Set to 1 to abort the process after the first error is encountered.
$HOME environment variable. Useful when the user
running the commands has a non-writable home directory.
Absolute path to the man pager to use for viewing help information
about LTTng commands (using lttng-help(1) or
lttng COMMAND --help).
Path in which the
session.xsd session configuration XML
schema may be found.
Full session daemon binary path.
--sessiond-path option has precedence over this
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.
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.
Default output directory of LTTng traces. This can be overridden
--output option of the lttng-create(1)
User LTTng runtime and configuration directory.
$LTTNG_HOME defaults to
$HOME when not explicitly set.
Command warning (something went wrong during the command)
If you encounter any issue or usability problem, please report it on the LTTng bug tracker.
Special thanks to Michel Dagenais and the DORSAL laboratory 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.