Ubuntu Manpage: lttng-enable-channel - Create or enable LTTng channels

NAME

       lttng-enable-channel - Create or enable LTTng channels

SYNOPSIS

       Create a Linux kernel channel:

       lttng [GENERAL OPTIONS] enable-channel --kernel
             [--discard | --overwrite] [--output=(mmap | splice)]
             [--subbuf-size=SIZE] [--num-subbuf=COUNT]
             [--switch-timer=PERIODUS] [--read-timer=PERIODUS]
             [--monitor-timer=PERIODUS] [--buffers-global]
             [--tracefile-size=SIZE [--tracefile-count=COUNT]]
             [--session=SESSION] CHANNEL

       Create a user space channel:

       lttng [GENERAL OPTIONS] enable-channel --userspace
             [--overwrite | [--discard] --blocking-timeout=TIMEOUTUS]
             [--output=mmap] [--buffers-uid | --buffers-pid]
             [--subbuf-size=SIZE] [--num-subbuf=COUNT]
             [--switch-timer=PERIODUS] [--read-timer=PERIODUS]
             [--monitor-timer=PERIODUS]
             [--tracefile-size=SIZE [--tracefile-count=COUNT]]
             [--session=SESSION] CHANNEL

       Enable channel(s):

       lttng [GENERAL OPTIONS] enable-channel (--userspace | --kernel)
             [--session=SESSION] CHANNEL[,CHANNEL]...

DESCRIPTION

       The lttng enable-channel command does one of:

       •   Create a channel named CHANNEL.

       •   Enable one or more disabled channels named CHANNEL (non-option argument,
           comma-separated).

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

       The channel(s) to create or enable belong to:

       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).

       Note
           The lttng-enable-event(1) command can automatically create a default channel when no
           channel exists for the provided tracing domain.

       See the “EXAMPLES” section below for usage examples.

       List the channels of a given recording session with the lttng-list(1) and lttng-status(1)
       commands.

       Disable an enabled channel with the lttng-disable-channel(1) command.

       Important
           As of LTTng 2.13.7, you may NOT perform the following operations with the enable-
           channel command:

           •   Change an attribute of an existing channel.

           •   Enable a disabled channel once its recording session has been active (started; see
               lttng-start(1)) at least once.

           •   Create a channel once its recording session has been active at least once.

           •   Create a user space channel with a given buffering scheme (--buffers-uid or
               --buffers-pid options) and create a second user space channel with a different
               buffering scheme in the same recording session.

OPTIONS

See lttng(1) for GENERAL OPTIONS.

Tracing domain
One of:

-k, --kernel
Create or enable channels in the Linux kernel domain.

-u, --userspace
Create or enable channels in the user space domain.

Recording target
-s SESSION, --session=SESSION
Create or enable channels in the recording session named SESSION instead of the
current recording session.

Buffering scheme
One of:

--buffers-global
Allocate a single set of ring buffers for the whole system.

Only available with the --kernel option.

As of LTTng 2.13.7, this is the default buffering scheme for the Linux kernel tracing
domain, but this may change in the future.

--buffers-pid
Allocate one set of ring buffers (one per CPU) for each instrumented process of:

If you connect to the root session daemon
All Unix users.

See the “Session daemon connection” section of lttng(1) to learn how a user
application connects to a session daemon.

Otherwise
Your Unix user.

Only available with the --userspace option.

--buffers-uid
Allocate one set of ring buffers (one per CPU) shared by all the instrumented
processes of:

If you connect to the root session daemon
Each Unix user.

See the “Session daemon connection” section of lttng(1) to learn how a user
application connects to a session daemon.

Otherwise
Your Unix user.

Only available with the --userspace option.

As of LTTng 2.13.7, this is the default buffering scheme for the user space tracing
domain, but this may change in the future.

Event record loss mode
--blocking-timeout=TIMEOUTUS
Set the channel’s blocking timeout value to TIMEOUTUS µs for instrumented applications
executed with a set LTTNG_UST_ALLOW_BLOCKING environment variable.

TIMEOUTUS is one of:

0 (default)
Do not block (non-blocking mode).

inf
Block forever until a sub-buffer is available to write the event record.

N, a positive value
Wait for at most N µs when trying to write to a sub-buffer. After N µs, discard
the event record.

This option is only available with both the --userspace and --discard options.

One of:

--discard
Discard event records when there’s no available sub-buffer.

As of LTTng 2.13.7, this is the default event record loss mode, but this may change in
the future.

--overwrite
Overwrite the whole sub-buffer containing the oldest event records when there’s no
available sub-buffer (flight recorder mode).

Sub-buffers
--num-subbuf=COUNT
Use COUNT sub-buffers per ring buffer.

The effective value is COUNT rounded up to the next power of two.

Default values:

--userspace and --buffers-uid options
4

--userspace and --buffers-pid options
4

--kernel and --buffers-global options
4

metadata channel
2

--output=TYPE
Set channel’s output type to TYPE.

TYPE is one of:

mmap
Share ring buffers between the tracer and the consumer daemon with the mmap(2)
system call.

splice
Share ring buffers between the tracer and the consumer daemon with the splice(2)
system call.

Only available with the --kernel option.

Default values:

--userspace and --buffers-uid options
mmap

--userspace and --buffers-pid options
mmap

--kernel and --buffers-global options
splice

metadata channel
mmap

--subbuf-size=SIZE
Set the size of each sub-buffer to SIZE bytes.

The effective value is SIZE rounded up to the next power of two.

The k (KiB), M (MiB), and G (GiB) suffixes are supported.

The minimum sub-buffer size, for each tracer, is the maximum value between the default
below and the system page size (see getconf(1) with the PAGE_SIZE variable).

Default values:

--userspace and --buffers-uid options
524288

--userspace and --buffers-pid options
16384

--kernel and --buffers-global options
1048576

metadata channel
4096

Trace files
--tracefile-count=COUNT
Limit the number of trace files which LTTng writes for this channel to COUNT.

COUNT set to 0 means “unlimited”.

Default: 0.

You must also use the --tracefile-size option with this option.

--tracefile-size=SIZE
Set the maximum size of each trace file which LTTng writes for this channel to
SIZE bytes.

SIZE set to 0 means “unlimited”.

Default: 0.

Note
Data streams which LTTng writes for a channel configured with this option may
inaccurately report discarded event records as of CTF 1.8.

Timers
--monitor-timer=PERIODUS
Set the period of the monitor timer of the channel to PERIODUS µs.

Set PERIODUS to 0 to disable the monitor timer.

Default values:

--userspace and --buffers-uid options
1000000

--userspace and --buffers-pid options
1000000

--kernel and --buffers-global options
1000000

--read-timer=PERIODUS
Set the period of the read timer of the channel to PERIODUS µs.

Set PERIODUS to 0 to disable the read timer.

Default values:

--userspace and --buffers-uid options
0

--userspace and --buffers-pid options
0

--kernel and --buffers-global options
200000

metadata channel
0

--switch-timer=PERIODUS
Set the period of the switch timer of the channel to PERIODUS µs.

Set PERIODUS to 0 to disable the switch timer.

Default values:

--userspace and --buffers-uid options
0

--userspace and --buffers-pid options
0

--kernel and --buffers-global options
0

metadata channel
0

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)).

       /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 Linux kernel channel with default attributes in the current recording
session.

The following command line only creates a new channel if my-channel doesn’t name an
existing Linux kernel channel in the current recording session.

$ lttng enable-channel --kernel my-channel

Example 2. Create a user space channel with a per-process buffering scheme in a specific
recording session.

See the --session and --buffers-pid options.

$ lttng enable-channel --session=my-session --userspace \
--buffers-pid my-channel

Example 3. Create a Linux kernel channel in the current recording session with four 32-MiB
sub-buffers per ring buffer.

See the --num-subbuf and --subbuf-size options.

$ lttng enable-channel --kernel my-channel \
--num-subbuf=4 --subbuf-size=32M

Example 4. Create a user space channel in the current recording session with trace file
rotation.

See the --tracefile-count and --tracefile-size options.

$ lttng enable-channel --userspace my-channel \
--tracefile-count=16 --tracefile-size=8M

Example 5. Enable two user space channels of a specific recording session.

$ lttng enable-channel --session=my-session --userspace \
canal-d,rds

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

COPYRIGHT

       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.

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

EXIT STATUS

ENVIRONMENT

FILES

EXAMPLES

RESOURCES

COPYRIGHT

THANKS

SEE ALSO