lttng-relayd - Man Page

LTTng relay daemon

Synopsis

lttng-relayd [--background | --daemonize] [--config=PATH]
             [--control-port=URL] [--data-port=URL] [--fd-pool-size=COUNT]
             [--live-port=URL] [--output=DIR] [--group=GROUP]
             [--verbose]... [--working-directory=DIR]
             [--group-output-by-host | --group-output-by-session] [--disallow-clear]

Description

The Linux Trace Toolkit: next generation <https://lttng.org/> 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).

An LTTng relay daemon, lttng-relayd, is a program which receives trace data from (possibly remote) LTTng session/consumer daemons and which writes it to the local file system. The relay daemon also accepts LTTng live connections from compatible readers (for example, babeltrace2(1)); this is the recommended approach to read trace data while the remote recording session is active.

By default, a relay daemon listens on all network interfaces to receive trace data, but only on localhost for LTTng live connections. Override the listening URLs with the --control-port, --data-port, and --live-port options (see the “URL format” section below). For example, use the --live-port=tcp://0.0.0.0:5344 option to make a relay daemon listen to LTTng live connections on all network interfaces.

Once LTTng has completely sent a trace to a relay daemon RD, any LTTng trace reader can read the trace located on the local file system of RD.

By default, lttng-relayd doesn’t start as a daemon. Make it a daemon with the --daemonize or --background option. With those options, lttng-relayd ensures the daemon is listening to incoming connections before it exits.

Daemon configuration

When you run lttng-relayd, it configures itself from, in this order:

  1. The INI configuration file /usr/local/etc/lttng/lttng.conf, if any.
  2. The INI configuration file $LTTNG_HOME/.lttng/lttng.conf, if any.

    $LTTNG_HOME defaults to $HOME.

  3. With the --config=PATH option: the INI configuration file PATH.
  4. The command-line options.

Each step can override a previous configuration property.

In INI configuration files, the session daemon only reads the properties under the relayd INI section. Each INI property is:

Key

The long name of a command-line option to set (see the “Options” section below).

Value

The selected command-line option accepts an argument

Option argument (string).

The selected command-line option is a switch

true, yes, on

Enable the option.

false, no, off

Disable the option.

INI configuration file example:

[relayd]
daemonize=yes
live-port=tcp://0.0.0.0:4567
disallow-clear=yes

Output directory

The relay daemon uses different output path patterns depending on:

  • Its configuration.

    See the “Daemon configuration” section above.

  • The recording session configuration of the connected peer.
  • The LTTng session daemon (see lttng-sessiond(8)) version of the connected peer.

Consider the following variables:

BASE

Base output directory: $LTTNG_HOME/lttng-traces ($LTTNG_HOME defaults to $HOME) or the argument of the --output option.

HOSTNAME

Hostname of the connected peer.

SESSION

Recording session name.

DATETIME

Unique recording session date/time.

TRACEDIR

Custom trace directory path (TRACEDIR part of the argument of the --set-url option of the lttng-create(1) command, if any).

SESSIONDV

The version of the LTTng session daemon of the connected peer.

The relay daemon output path patterns are:

With the --group-output-by-host option (hostname grouping)

Without a custom trace directory

BASE/HOSTNAME/SESSION-DATETIME

With a custom trace directory

BASE/HOSTNAME/TRACEDIR

With the --group-output-by-session option (recording session grouping)

Without a custom trace directory

SESSIONDV is at least 2.4

BASE/SESSION/HOSTNAME-DATETIME
Otherwise

Defaults to the hostname grouping pattern:

BASE/HOSTNAME/SESSION-DATETIME

With a custom trace directory

SESSIONDV is at least 2.4

BASE/SESSION/HOSTNAME-DATETIME/TRACEDIR
Otherwise

Defaults to the hostname grouping pattern:

BASE/HOSTNAME/TRACEDIR

URL format

The argument of the --control-port=URL, --data-port=URL, and --live-port=URL options is an URL.

The format of URL is:

tcp://(HOST | IPADDR):PORT

with:

(HOST | IPADDR)

Binding hostname or IP address.

IPv6 address must be enclosed in square brackets ([ and ]); see RFC 2732 <https://www.ietf.org/rfc/rfc2732.txt>.

PORT

TCP port.

Options

General daemon configuration

-b,  --background

Start as a Unix daemon, but keep file descriptors (console) open.

With this option, lttng-relayd ensures the daemon is listening to incoming connections before it exits.

Use the --daemonize option instead to close the file descriptors.

-f PATH, --config=PATH

Configure the daemon using the INI configuration file PATH in addition to the default configuration files and the command-line options.

See the “Daemon configuration” section above.

-d,  --daemonize

Start as a Unix daemon and close file descriptors (console).

With this option, lttng-relayd ensures the daemon is listening to incoming connections before it exits.

Use the --background option instead to keep the file descriptors open.

-x,  --disallow-clear

Disallow clearing operations (see lttng-clear(1)).

See also the LTTNG_RELAYD_DISALLOW_CLEAR environment variable.

--fd-pool-size=SIZE

Set the size of the file descriptor pool to SIZE file descriptors.

SIZE is the maximum number of file descriptors that the relay daemon may keep open simultaneously.

Default: the soft RLIMIT_NOFILE resource limit of the process (see getrlimit(2)).

-g GROUP, --group=GROUP

Set the Unix tracing group to GROUP instead of tracing.

This option is only meaningful when the root Unix user starts lttng-relayd.

Members of the Unix tracing group may connect to the health check socket of the relay daemon.

See also the LTTNG_RELAYD_HEALTH environment variable.

-w DIR, --working-directory=DIR

Set the working directory of the processes the relay daemon creates to DIR.

See also the LTTNG_RELAYD_WORKING_DIRECTORY environment variable.

-v,  --verbose

Increase verbosity.

Specify this option up to three times to get more levels of verbosity.

Output

See the “Output directory” section above to learn more.

-p,  --group-output-by-host

Group the written trace directories by hostname.

As of LTTng 2.13.7, this is the default output grouping strategy, but this may change in the future.

-s,  --group-output-by-session

Group the written trace directories by recording session name instead of by hostname.

-o DIR, --output=DIR

Set the base output directory of the written trace directories to DIR.

Ports

See the “URL format” section above to learn more about the syntax of the URL argument of the following options.

-C URL, --control-port=URL

Listen to control data on URL URL.

Default: tcp://0.0.0.0:5342.

-D URL, --data-port=URL

Listen to trace data on URL URL.

Default: tcp://0.0.0.0:5343.

-L URL, --live-port=URL

Listen to LTTng live connections on URL URL.

Default: tcp://localhost:5344.

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.

-V,  --version

Show version and quit.

Exit Status

0

Success

1

Error

3

Fatal error

Environment

LTTNG_ABORT_ON_ERROR

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

LTTNG_NETWORK_SOCKET_TIMEOUT

Socket connection, receive, and send timeout (milliseconds).

Set to 0 or -1 to set an infinite timeout (default).

LTTNG_RELAYD_DISALLOW_CLEAR

Set to 1 to disallow clearing operations (see lttng-clear(1)).

The --disallow-clear option overrides this environment variable.

LTTNG_RELAYD_HEALTH

Path to the health check socket of the relay daemon.

LTTNG_RELAYD_TCP_KEEP_ALIVE

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) to learn more.

LTTNG_RELAYD_TCP_KEEP_ALIVE_ABORT_THRESHOLD

The time threshold (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) to learn more.

LTTNG_RELAYD_TCP_KEEP_ALIVE_IDLE_TIME

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 to learn more.

LTTNG_RELAYD_TCP_KEEP_ALIVE_MAX_PROBE_COUNT

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) to learn more.

LTTNG_RELAYD_TCP_KEEP_ALIVE_PROBE_INTERVAL

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) to learn more.

LTTNG_RELAYD_WORKING_DIRECTORY

Working directory of the processes the relay daemon creates.

The --working-directory option overrides this environment variable.

Files

$LTTNG_HOME/.lttng

Unix user’s LTTng runtime and configuration directory.

$LTTNG_HOME/lttng-traces

Default base output directory of LTTng traces.

Override this path with the --output option.

Note

$LTTNG_HOME defaults to $HOME.

Resources

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

babeltrace2(1), lttng(1), lttng-sessiond(8)

Referenced By

babeltrace2-source.ctf.lttng-live(7), lttng(1), lttng-clear(1), lttng-concepts(7), lttng-create(1), lttng-destroy(1), lttng-rotate(1), lttng-snapshot(1).

14 June 2021 LTTng 2.13.7 LTTng Manual