lttng-relayd — LTTng 2 relay daemon


lttng-relayd [--background | --daemonize]
             [--control-port=URL] [--data-port=URL] [--live-port=URL]
             [--output=PATH] [-v | -vv | -vvv]


The Linux Trace Toolkit: next generation <> is an open source software package used for correlated tracing of the Linux kernel, user applications, and user libraries.

LTTng consists of Linux kernel modules (for Linux kernel tracing) and dynamically loaded libraries (for user application and library tracing).

The LTTng relay daemon is responsible for receiving trace data from possibly remote LTTng session/consumer daemons and for writing it to the local file system. The relay daemon also accepts LTTng live connections from compatible viewers; this is the official approach to viewing LTTng events as they are emitted.

The relay daemon listens by default on all network interfaces to gather trace data, but only on localhost for LTTng live connections.

The relay daemon does not require any particular permissions, as long as it can write to the output directory and listen on the configured ports. If a user is within a secured network and/or has proper firewall settings, lttng-relayd can listen to LTTng live connections from all network interfaces by specifying --live-port=tcp://localhost:5344.

Once a trace has been streamed completely, the trace can be processed by any tool that can process an LTTng trace located on the local file system.

Output directory

By default, the relay daemon writes the traces to:




Remote hostname.


Full session name.


Tracing domain.

You can override the default output directory prefix ($LTTNG_HOME/lttng-traces) with the --output option. The other parts depend on the remote configuration.

URL format

The --control-port, --data-port, and --live-port options specify URLs.

The format of those URLs is:




Binding hostname or IP address (IPv6 address must be enclosed in brackets ([ and ]); see RFC 2732 <>).


TCP port.



-b, --background

Start as Unix daemon, but keep file descriptors (console) open. Use the --daemonize option instead to close the file descriptors.

-d, --daemonize

Start as Unix daemon, and close file descriptors (console). Use the --background option instead to keep the file descriptors open.

-g GROUP, --group=GROUP

Use GROUP as Unix tracing group (default: tracing).

-o PATH, --output=PATH

Set base directory of written trace data to PATH.

See the Output directory section above for more information.

-v, --verbose

Increase verbosity.

Three levels of verbosity are available, which are triggered by appending additional v letters to the option (that is, -vv and -vvv).


See the URL format section above for more information about the syntax of the following options' URL argument.

-C URL, --control-port=URL

Listen to control data on URL URL (default: tcp://

-D URL, --data-port=URL

Listen to trace data on URL URL (default: tcp://

-L URL, --live-port=URL

Listen to LTTng live connections on URL URL (default: tcp://localhost:5344).

Program information

-h, --help

Show help.

-V, --version

Show version.

Environment Variables


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


Socket connection, receive and send timeout (milliseconds). A value of 0 or -1 uses the timeout of the operating system (default).


Path to relay daemon health’s socket.


Set to 1 to enable TCP keep-alive.

The TCP keep-alive mechanism allows the detection of dead peers (lttng-sessiond(8)) in cases of unclean termination (for example, a hard reset) of a peer.

Supported on Linux and Solaris only. The default behaviour of the TCP keep-alive mechanism is OS-specific.

Search for tcp_keepalive in tcp(7) for more information.


The time threshold in seconds to abort a TCP connection after the keep-alive probing mechanism has failed.

Set to 0 or -1 to use the value chosen by the operating system (default).

Supported on Solaris 11 only.

Search for tcp_keepalive_abort_threshold in tcp(7) for more information.


Number of seconds a connection needs to be idle before TCP begins sending out keep-alive probes.

Set to 0 or -1 to use the value chosen by the operating system (default).

Supported on Linux and Solaris 11 only.

On Solaris 11, the accepted values are -1, 0, and 10 to 864000.

Search for tcp_keepalive_time and tcp_keepalive_interval in tcp(7) on Solaris 11 for more information.


Maximum number of TCP keep-alive probes to send before giving up and killing the connection if no response is obtained from the other end.

Set to 0 or -1 to use the value chosen by the operating system (default).

Supported on Linux only.

Search for tcp_keepalive_probes in tcp(7) for more information.


Number of seconds between TCP keep-alive probes.

Set to 0 or -1 to use the value chosen by the operating system (default).

Supported on Linux only.

Search for tcp_keepalive_intvl in tcp(7) for more information.



User LTTng runtime and configuration directory.


Default output directory of LTTng traces. This can be overridden with the --output option.


$LTTNG_HOME defaults to $HOME when not explicitly set.

Exit Status






Fatal error


As of this version, only the TCP protocol is supported for both control and data ports. In future versions, TCP will remain the sole available protocol for control data since those communications are low-volume and need absolute reliability; trace data could be carried over UDP.

For an unprivileged user running lttng-relayd, the maximum number of file descriptors per process is usually 1024. This limits the number of connections and opened trace files. This limit can be configured with ulimit(3).


If you encounter any issue or usability problem, please report it on the LTTng bug tracker <>.



This program is part of the LTTng-tools project.

LTTng-tools is distributed under the GNU General Public License version 2 <>. See the LICENSE <> file for details.


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.

See Also

lttng(1), lttng-sessiond(8), lttng-crash(1), lttng-ust(3), babeltrace(1)

Referenced By

lttng(1), lttng-crash(1), lttng-create(1), lttng-rotate(1), lttng-sessiond(8).

10/17/2019 LTTng 2.11.0 LTTng Manual