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mosquitto_sub.1.xml
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mosquitto_sub.1.xml
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<?xml version='1.0' encoding='UTF-8'?>
<?xml-stylesheet type="text/xsl" href="manpage.xsl"?>
<refentry xml:id="mosquitto_sub" xmlns:xlink="http:https://www.w3.org/1999/xlink">
<refmeta>
<refentrytitle>mosquitto_sub</refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo class="source">Mosquitto Project</refmiscinfo>
<refmiscinfo class="manual">Commands</refmiscinfo>
</refmeta>
<refnamediv>
<refname>mosquitto_sub</refname>
<refpurpose>an MQTT version 5/3.1.1/3.1 client for subscribing to topics</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>mosquitto_sub</command>
<group choice='req'>
<arg choice='plain'>
<arg><option>-h</option> <replaceable>hostname</replaceable></arg>
<arg><option>--unix</option> <replaceable>socket path</replaceable></arg>
<arg><option>-p</option> <replaceable>port-number</replaceable></arg>
<arg><option>-u</option> <replaceable>username</replaceable></arg>
<arg><option>-P</option> <replaceable>password</replaceable></arg>
<arg choice='plain' rep='repeat'><option>-t</option> <replaceable>message-topic</replaceable></arg>
</arg>
<arg choice='plain'>
<arg choice='plain'><option>-L</option> <replaceable>URL</replaceable></arg>
<arg choice='opt' rep='repeat'><option>-t</option> <replaceable>message-topic</replaceable></arg>
</arg>
</group>
<arg><option>-A</option> <replaceable>bind-address</replaceable></arg>
<arg><option>-c</option></arg>
<arg><option>-C</option> <replaceable>msg-count</replaceable></arg>
<arg><option>-d</option></arg>
<arg><option>-D</option> <replaceable>command</replaceable> <replaceable>identifier</replaceable> <replaceable>value</replaceable></arg>
<arg><option>-E</option></arg>
<arg><option>-i</option> <replaceable>client-id</replaceable></arg>
<arg><option>-I</option> <replaceable>client-id-prefix</replaceable></arg>
<arg><option>-k</option> <replaceable>keepalive-time</replaceable></arg>
<arg><option>-N</option></arg>
<arg><option>--nodelay</option></arg>
<arg><option>--pretty</option></arg>
<arg><option>-q</option> <replaceable>message-QoS</replaceable></arg>
<arg><option>--random-filter</option> <replaceable>chance</replaceable></arg>
<arg><option>--remove-retained</option></arg>
<group choice='opt'>
<arg choice='plain'><option>-R</option></arg>
<arg choice='plain'><option>--retained-only</option></arg>
</group>
<arg><option>--retain-as-published</option></arg>
<arg><option>-S</option></arg>
<arg choice='opt' rep='repeat'><option>-T</option> <replaceable>filter-out</replaceable></arg>
<arg choice='opt' rep='repeat'><option>-U</option> <replaceable>unsub-topic</replaceable></arg>
<arg><option>-v</option></arg>
<arg><option>-V</option> <replaceable>protocol-version</replaceable></arg>
<arg><option>-W</option> <replaceable>message-processing-timeout</replaceable></arg>
<arg><option>-x</option> <replaceable>session-expiry-interval</replaceable></arg>
<arg><option>--proxy</option> <replaceable>socks-url</replaceable></arg>
<arg><option>--quiet</option></arg>
<arg>
<option>--will-topic</option> <replaceable>topic</replaceable>
<arg><option>--will-payload</option> <replaceable>payload</replaceable></arg>
<arg><option>--will-qos</option> <replaceable>qos</replaceable></arg>
<arg><option>--will-retain</option></arg>
</arg>
<group>
<arg>
<group choice='req'>
<arg choice='plain'><option>--cafile</option> <replaceable>file</replaceable></arg>
<arg choice='plain'><option>--capath</option> <replaceable>dir</replaceable></arg>
</group>
<arg><option>--cert</option> <replaceable>file</replaceable></arg>
<arg><option>--key</option> <replaceable>file</replaceable></arg>
<arg><option>--tls-version</option> <replaceable>version</replaceable></arg>
<arg><option>--tls-alpn</option> <replaceable>protocol</replaceable></arg>
<arg><option>--tls-engine</option> <replaceable>engine</replaceable></arg>
<arg><option>--keyform</option>
<group choice='req'>
<arg choice='plain'><replaceable>pem</replaceable></arg>
<arg choice='plain'><replaceable>engine</replaceable></arg>
</group></arg>
<arg><option>--tls-engine-kpass-sha1</option> <replaceable>kpass-sha1</replaceable></arg>
<arg><option>--insecure</option></arg>
</arg>
<arg>
<arg choice='plain'><option>--psk</option> <replaceable>hex-key</replaceable></arg>
<arg choice='plain'><option>--psk-identity</option> <replaceable>identity</replaceable></arg>
<arg><option>--tls-version</option> <replaceable>version</replaceable></arg>
</arg>
</group>
</cmdsynopsis>
<cmdsynopsis>
<command>mosquitto_sub</command>
<group choice='plain'>
<arg><option>--help</option></arg>
</group>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>mosquitto_sub</command> is a simple MQTT version 5/3.1.1
client that will subscribe to topics and print the messages that
it receives.</para>
<para>In addition to subscribing to topics,
<command>mosquitto_sub</command> can filter out received messages
so they are not printed (see the <option>-T</option> option) or
unsubscribe from topics (see the <option>-U</option> option).
Unsubscribing from topics is useful for clients connecting with
clean session set to false. </para>
</refsect1>
<refsect1>
<title>Encrypted Connections</title>
<para><command>mosquitto_sub</command> supports TLS encrypted
connections. It is strongly recommended that you use an encrypted
connection for anything more than the most basic setup.</para>
<para>To enable TLS connections when using x509 certificates, one of
either <option>--cafile</option> or <option>--capath</option> must
be provided as an option.</para>
<para>To enable TLS connections when using TLS-PSK, you must use the
<option>--psk</option> and the <option>--psk-identity</option>
options.</para>
</refsect1>
<refsect1>
<title>Options</title>
<para>The options below may be given on the command line, but may also
be placed in a config file located at
<option>$XDG_CONFIG_HOME/mosquitto_sub</option> or
<option>$HOME/.config/mosquitto_sub</option> with one pair of
<option>-option <replaceable>value</replaceable></option>
per line. The values in the config file will be used as defaults
and can be overridden by using the command line. The exceptions to
this are <option>-t</option> and <option>-T</option>, which if
given in the config file will not be overridden. Note also that
currently some options cannot be negated, e.g.
<option>-S</option>. Config file lines that have a
<option>#</option> as the first character are treated as comments
and not processed any further.</para>
<variablelist>
<varlistentry>
<term><option>-A</option></term>
<listitem>
<para>Bind the outgoing connection to a local ip
address/hostname. Use this argument if you need to
restrict network communication to a particular
interface.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-c</option></term>
<term><option>--disable-clean-session</option></term>
<listitem>
<para>Disable 'clean session' / enable persistent client mode.
When this argument is used, the broker will be instructed
not to clean existing sessions for the same client id when
the client connects, and sessions will never expire when
the client disconnects. MQTT v5 clients can change their
session expiry interval with the <option>-x</option> argument.
</para>
<para>When a session is persisted on the broker, the subscriptions
for the client will be maintained after it disconnects, along
with subsequent QoS 1 and QoS 2 messages that arrive. When the
client reconnects and does not clean the session, it will
receive all of the queued messages.</para>
<para>If using this option, the client id must be set
manually with <option>--id</option></para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--cafile</option></term>
<listitem>
<para>Define the path to a file containing PEM encoded CA
certificates that are trusted. Used to enable SSL
communication.</para>
<para>See also <option>--capath</option></para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--capath</option></term>
<listitem>
<para>Define the path to a directory containing PEM encoded CA
certificates that are trusted. Used to enable SSL
communication.</para>
<para>For <option>--capath</option> to work correctly, the
certificate files must have ".crt" as the file ending
and you must run "openssl rehash <path to capath>" each
time you add/remove a certificate.</para>
<para>See also <option>--cafile</option></para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--cert</option></term>
<listitem>
<para>Define the path to a file containing a PEM encoded
certificate for this client, if required by the
server.</para>
<para>See also <option>--key</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--ciphers</option></term>
<listitem>
<para>An openssl compatible list of TLS ciphers to support
in the client. See
<citerefentry><refentrytitle>ciphers</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for more information.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-C</option></term>
<listitem>
<para>Disconnect and exit the program immediately after
the given count of messages have been received. This
may be useful in shell scripts where on a single status
value is required, for example.</para>
<para>Combine with <option>-R</option> to print only the
first set of fresh messages (i.e. that does not have
the retained flag set), or with <option>-T</option> to
filter which topics are processed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-d</option></term>
<term><option>--debug</option></term>
<listitem>
<para>Enable debug messages.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-D</option></term>
<term><option>--property</option></term>
<listitem>
<para>Use an MQTT v5 property with this publish. If you use
this option, the client will be set to be an MQTT v5
client. This option has two forms:</para>
<para><option>-D command identifier value</option></para>
<para><option>-D command identifier name value</option></para>
<para><option>command</option> is the MQTT command/packet
identifier and can be one of CONNECT, PUBACK, PUBREC,
PUBCOMP, SUBSCRIBE, UNSUBSCRIBE, DISCONNECT, AUTH, or
WILL. The properties available for each command are
listed in the Properties section.</para>
<para><option>identifier</option> is the name of the
property to add. This is as described in the
specification, but with '-' as a word separator. For
example:
<option>payload-format-indicator</option>. More details
are in the <link linkend='properties'>Properties</link>
section.</para>
<para><option>value</option> is the value of the property
to add, with a data type that is property
specific.</para>
<para><option>name</option> is only used for the
<option>user-property</option> property as the first of
the two strings in the string pair. In that case,
<option>value</option> is the second of the strings in
the pair.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-E</option></term>
<listitem>
<para>If this option is given,
<command>mosquitto_sub</command> will exit immediately
that all of its subscriptions have been acknowledged by
the broker. In conjunction with <option>-c</option>
this allows a durable client session to be initialised
on the broker for future use without requiring any
messages to be received.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-F</option></term>
<listitem>
<para>Specify output printing format. This option allows
you to choose what information from each message is
printed to the screen. See the <link
linkend='outputformat'>Output Format</link> section
below for full details.</para>
<para>This option overrides the <option>-v</option> option,
but does not override the <option>-N</option>
option.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--help</option></term>
<listitem>
<para>Display usage information.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-h</option></term>
<term><option>--host</option></term>
<listitem>
<para>Specify the host to connect to. Defaults to localhost.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-i</option></term>
<term><option>--id</option></term>
<listitem>
<para>The id to use for this client. If not given, a client id will
be generated depending on the MQTT version being used. For v3.1.1/v3.1,
the client generates a client id in the format
<option>mosq-XXXXXXXXXXXXXXXXXX</option>, where the
<option>X</option> are replaced with random alphanumeric
characters. For v5.0, the client sends a zero length client id, and the
server will generate a client id for the client.</para>
<para>This option cannot be used at the same time as the
<option>--id-prefix</option> argument.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-I</option></term>
<term><option>--id-prefix</option></term>
<listitem>
<para>Provide a prefix that the client id will be built
from by appending the process id of the client. This is
useful where the broker is using the clientid_prefixes
option. Cannot be used at the same time as the
<option>--id</option> argument.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--insecure</option></term>
<listitem>
<para>When using certificate based encryption, this option
disables verification of the server hostname in the
server certificate. This can be useful when testing
initial server configurations but makes it possible for
a malicious third party to impersonate your server
through DNS spoofing, for example. Use this option in
testing <emphasis>only</emphasis>. If you need to
resort to using this option in a production
environment, your setup is at fault and there is no
point using encryption.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-k</option></term>
<term><option>--keepalive</option></term>
<listitem>
<para>The number of seconds between sending PING commands
to the broker for the purposes of informing it we are still
connected and functioning. Defaults to 60 seconds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--key</option></term>
<listitem>
<para>Define the path to a file containing a PEM encoded
private key for this client, if required by the
server.</para>
<para>See also <option>--cert</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--keyform</option></term>
<listitem>
<para>Specifies the type of private key in use when making
TLS connections.. This can be "pem" or "engine". This
parameter is useful when a TPM module is being used and
the private key has been created with it. Defaults to
"pem", which means normal private key files are
used.</para>
<para>See also <option>--tls-engine</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-L</option></term>
<term><option>--url</option></term>
<listitem>
<para>Specify specify user, password, hostname, port and
topic at once as a URL. The URL must be in the form:
mqtt(s):https://[username[:password]@]host[:port]/topic</para>
<para>If the scheme is mqtt:https:// then the port defaults to
1883. If the scheme is mqtts:https:// then the port defaults
to 8883.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-N</option></term>
<listitem>
<para>Do not append an end of line character to the payload
when printing. This allows streaming of payload data
from multiple messages directly to another application
unmodified. Only really makes sense when not using
<option>-v</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--nodelay</option></term>
<listitem>
<para>Disable Nagle's algorithm for the socket. This means
that latency of sent messages is reduced, which is
particularly noticable for small, reasonably infrequent
messages. Using this option may result in more packets
being sent than would normally be necessary.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-p</option></term>
<term><option>--port</option></term>
<listitem>
<para>Connect to the port specified. If not given, the
default of 1883 for plain MQTT or 8883 for MQTT over
TLS will be used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-P</option></term>
<term><option>--pw</option></term>
<listitem>
<para>Provide a password to be used for authenticating with
the broker. Using this argument without also specifying
a username is invalid when using MQTT v3.1 or v3.1.1.
See also the <option>--username</option> option.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--pretty</option></term>
<listitem>
<para>
When using the JSON output format %j or %J, the default
is to print in an unformatted fashion. Specifying
<option>--pretty</option> prints messages in a prettier,
more human readable format.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--proxy</option></term>
<listitem>
<para>Specify a SOCKS5 proxy to connect through. "None" and
"username" authentication types are supported. The
<option>socks-url</option> must be of the form
<option>socks5h:https://[username[:password]@]host[:port]</option>.
The protocol prefix <option>socks5h</option> means that
hostnames are resolved by the proxy. The symbols %25,
%3A and %40 are URL decoded into %, : and @
respectively, if present in the username or
password.</para>
<para>If username is not given, then no authentication is
attempted. If the port is not given, then the default
of 1080 is used.</para>
<para>More SOCKS versions may be available in the future,
depending on demand, and will use different protocol
prefixes as described in <citerefentry>
<refentrytitle>curl</refentrytitle>
<manvolnum>1</manvolnum> </citerefentry>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--psk</option></term>
<listitem>
<para>Provide the hexadecimal (no leading 0x)
pre-shared-key matching the one used on the broker to
use TLS-PSK encryption support.
<option>--psk-identity</option> must also be provided
to enable TLS-PSK.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--psk-identity</option></term>
<listitem>
<para>The client identity to use with TLS-PSK support. This
may be used instead of a username if the broker is
configured to do so.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-q</option></term>
<term><option>--qos</option></term>
<listitem>
<para>Specify the quality of service desired for the
incoming messages, from 0, 1 and 2. Defaults to 0. See
<citerefentry><refentrytitle>mqtt</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for more information on QoS.</para>
<para>The QoS is identical for all topics subscribed to in
a single instance of mosquitto_sub.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--quiet</option></term>
<listitem>
<para>If this argument is given, no runtime errors will be
printed. This excludes any error messages given in case of
invalid user input (e.g. using <option>--port</option> without a
port).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-R</option></term>
<listitem>
<para>If this argument is given, messages that are received
that have the retain bit set will not be printed.
Messages with retain set are "stale", in that it is not
known when they were originally published. When
subscribing to a wildcard topic there may be a large
number of retained messages. This argument suppresses
their display.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--random-filter</option></term>
<listitem>
<para>This option can be used to reduce the proportion of
messages that mosquitto_sub prints. The default behaviour
is to print all incoming messages. Setting the
<replaceable>chance</replaceable> to a floating point value
between 0.1 and 100.0 will ensure that on average that
percentage of messages will be printed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--remove-retained</option></term>
<listitem>
<para>If this argument is given, the when mosquitto_sub
receives a message with the retained bit set, it will
send a message to the broker to clear that retained
message. This applies to all received messages except
those that are filtered out by the <option>-T</option>
option. This option still takes effect even if
<option>-R</option> is used. See also the
<option>--retain-as-published</option> and
<option>--retained-only</option> options.</para>
<example title="remove-retained-example-1" label="1">
<para>Remove all retained messages on the server,
assuming we have access to do so, and then exit:</para>
<programlisting language="config">
mosquitto_sub -t '#' --remove-retained --retained-only</programlisting>
</example>
<example title="remove-retained-example-2" label="2">
<para>Remove a whole tree, with the exception of a
single topic:</para>
<programlisting language="config">
mosquitto_sub -t 'bbc/#' -T bbc/bbc1 --remove-retained</programlisting>
</example>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--retained-only</option></term>
<listitem>
<para>If this argument is given, only messages that are
received that have the retain bit set will be printed.
Messages with retain set are "stale", in that it is not
known when they were originally published. With this
argument in use, the receipt of the first non-stale
message will cause the client to exit. See also the
<option>--retain-as-published</option> option.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--retain-as-published</option></term>
<listitem>
<para>If this argument is given, the subscriptions will
have the "retain as published" option set. This means
that the retain flag on an incoming message will be
exactly as set by the publishing client, rather than
indicating whether the message is fresh/stale.</para>
<para>This option is not valid for MQTT v3.1/v3.1.1
clients.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-S</option></term>
<listitem>
<para>Use SRV lookups to determine which host to connect
to. Performs lookups to
<option>_mqtt._tcp.<host></option> when used in
conjunction with <option>-h</option>, otherwise uses
<option>_mqtt._tcp.<local dns
domain></option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-t</option></term>
<term><option>--topic</option></term>
<listitem>
<para>The MQTT topic to subscribe to. See
<citerefentry><refentrytitle>mqtt</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for more information on MQTT topics.</para>
<para>This option may be repeated to subscribe to multiple topics.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-T</option></term>
<term><option>--filter-out</option></term>
<listitem>
<para>Suppress printing of topics that match the filter.
This allows subscribing to a wildcard topic and only
printing a partial set of the wildcard
hierarchy.</para>
<para>For example, subscribe to the BBC tree, but suppress output from Radio 3:</para>
<itemizedlist mark="circle">
<listitem><para>mosquitto_sub <literal>-t</literal>
bbc/# <literal>-T</literal>
bbc/radio3</para></listitem>
</itemizedlist>
<para>This option may be repeated to filter out multiple
topics or topic trees.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--tls-alpn</option></term>
<listitem>
<para>Provide a protocol to use when connecting to a broker
that has multiple protocols available on a single port,
e.g. MQTT and WebSockets.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--tls-engine</option></term>
<listitem>
<para>A valid openssl engine id. These can be listed with
openssl engine command.</para>
<para>See also <option>--keyform</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--tls-engine-kpass-sha1</option></term>
<listitem>
<para>SHA1 of the private key password when using an TLS
engine. Some TLS engines such as the TPM engine may
require the use of a password in order to be accessed.
This option allows a hex encoded SHA1 hash of the
password to the engine directly, instead of the user
being prompted for the password.</para>
<para>See also <option>--tls-engine</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--tls-version</option></term>
<listitem>
<para>Choose which TLS protocol version to use when
communicating with the broker. Valid options are
<option>tlsv1.3</option>, <option>tlsv1.2</option> and
<option>tlsv1.1</option>. The default value is
<option>tlsv1.2</option>. Must match the protocol
version used by the broker.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-u</option></term>
<term><option>--username</option></term>
<listitem>
<para>Provide a username to be used for authenticating with
the broker. See also the <option>--pw</option>
argument.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--unix</option></term>
<listitem>
<para>Connect to a broker through a local unix domain socket
instead of a TCP socket. This is a replacement for
<option>-h</option> and <option>-L</option>. For example:
<option>mosquitto_pub --unix /tmp/mosquitto.sock ...</option>
</para>
<para>See the <option>socket_domain</option> option in
<refentrytitle>
<link xlink:href="mosquitto-conf-5.html">mosquitto.conf</link>
</refentrytitle><manvolnum>5</manvolnum>
to configure Mosquitto to listen on a unix socket.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-U</option></term>
<term><option>--unsubscribe</option></term>
<listitem>
<para>A topic that will be unsubscribed from. This may be
used on its own or in conjunction with the
<option>--topic</option> option and only makes sense
when used in conjunction with
<option>--clean-session</option>.</para>
<para>If used with <option>--topic</option> then
subscriptions will be processed before
unsubscriptions.</para>
<para>Note that it is only possible to unsubscribe from
subscriptions that have previously been made. It is not
possible to punch holes in wildcard subscriptions. For
example, subscribing to <option>sensors/#</option> and
then unsubscribing from
<option>sensors/+/temperature</option> as shown below
will still result in messages matching the
<option>sensors/+/temperature</option> being delivered
to the client.</para>
<itemizedlist mark="circle">
<listitem><para>mosquitto_sub <literal>-t</literal> sensors/# <literal>-U</literal> sensors/+/temperature <literal>-v</literal></para></listitem>
</itemizedlist>
<para>Note also that because retained messages are
published by the broker on receipt of a SUBSCRIBE
command, subscribing and unsubscribing to the same
topic may result in messages being received at the
client.</para>
<para>This option may be repeated to unsubscribe from multiple topics.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-v</option></term>
<term><option>--verbose</option></term>
<listitem>
<para>Print received messages verbosely. With this
argument, messages will be printed as "topic payload". When
this argument is not given, the messages are printed as
"payload".</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-V</option></term>
<term><option>--protocol-version</option></term>
<listitem>
<para>Specify which version of the MQTT protocol should be
used when connecting to the remote broker. Can be
<option>5</option>, <option>311</option>,
<option>31</option>, or the more verbose
<option>mqttv5</option>, <option>mqttv311</option>, or
<option>mqttv31</option>.
Defaults to <option>311</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-W</option></term>
<listitem>
<para>Provide a timeout as an integer number of seconds.
mosquitto_sub will stop processing messages and
disconnect after this number of seconds has
passed. The timeout starts just after the client has
connected to the broker.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--will-payload</option></term>
<listitem>
<para>Specify a message that will be stored by the broker
and sent out if this client disconnects unexpectedly. This
must be used in conjunction with <option>--will-topic</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--will-qos</option></term>
<listitem>
<para>The QoS to use for the Will. Defaults to 0. This must
be used in conjunction with <option>--will-topic</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--will-retain</option></term>
<listitem>
<para>If given, if the client disconnects unexpectedly the
message sent out will be treated as a retained message.
This must be used in conjunction with <option>--will-topic</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--will-topic</option></term>
<listitem>
<para>The topic on which to send a Will, in the event that
the client disconnects unexpectedly.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-x</option></term>
<listitem>
<para>Set the session-expiry-interval property on the CONNECT packet.
Applies to MQTT v5 clients only. Set to 0-4294967294 to specify
the session will expire in that many seconds after the client
disconnects, or use -1, 4294967295, or ∞ for a session that does
not expire. Defaults to -1 if -c is also given, or 0 if -c not
given.</para>
<para>If the session is set to never expire, either with -x or -c, then
a client id must be provided.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id='outputformat'>
<title>Output format</title>
<para>There are three ways of formatting the output from mosquitto_sub.
In all cases a new-line character is appended for each message
received unless the <option>-N</option> argument is passed to
mosquitto_sub.</para>
<para>Payload-only is the default output format and will
print the payload exactly as it is received.</para>
<para>Verbose mode is activated with <option>-v</option> and prints the
message topic and the payload, separated by a space.</para>
<para>The final option is formatted output, which allows the user to
define a custom output format. The behaviour is controlled with
the <option>-F format-string</option> option. The format string is
a free text string where interpreted sequences are replaced by
different parameters. The available interpreted sequences are
described below.</para>
<para>Three characters are used to start an interpreted sequence:
<option>%</option>, <option>@</option> and <option>\</option>.
Sequences starting with <option>%</option> are either parameters
related to the MQTT message being printed, or are helper sequences
to avoid the need to type long date format strings for example.
Sequences starting with <option>@</option> are passed to the
<citerefentry><refentrytitle>strftime</refentrytitle><manvolnum>3</manvolnum></citerefentry>
function (with the @ replaced with a % - note that only the
character immediately after the @ is passed to strftime). This
allows the construction of a wide variety of time based outputs.
The output options for strftime vary from platform to platform, so
please check what is available for your platform. mosquitto_sub
does provide one extension to strftime which is
<option>@N</option>, which can be used to obtain the number of
nanoseconds passed in the current second. The resolution of this
option varies depending on the platform. The final sequence
character is <option>\</option>, which is used to input some
characters that would otherwise be difficult to enter.</para>
<refsect2>
<title>MQTT related parameters</title>
<itemizedlist mark="circle">
<listitem><para><option>%%</option> a literal %.</para></listitem>
<listitem><para><option>%A</option> the MQTT v5 topic-alias property, if present.</para></listitem>
<listitem><para><option>%C</option> the MQTT v5 content-type property, if present.</para></listitem>
<listitem><para><option>%D</option> the MQTT v5 correlation-data property, if present. Note that this
property is specified as binary data, so may produce non-printable characters.</para></listitem>
<listitem><para><option>%E</option> the MQTT v5 message-expiry-interval property, if present.</para></listitem>
<listitem><para><option>%F</option> the MQTT v5 payload-format-indicator property, if present.</para></listitem>
<listitem><para><option>%l</option> the length of the payload in bytes.</para></listitem>
<listitem><para><option>%m</option> the message id (only relevant for messages with QoS>0).</para></listitem>
<listitem><para><option>%P</option> the MQTT v5 user-property property, if present. This will be printed in the
form key:value. It is possible for any number of user properties to be attached to a message, and to
have duplicate keys.</para></listitem>
<listitem><para><option>%p</option> the payload raw bytes (may produce non-printable characters depending on the payload).</para></listitem>
<listitem><para><option>%q</option> the message QoS.</para></listitem>
<listitem><para><option>%R</option> the MQTT v5 response-topic property, if present.</para></listitem>
<listitem><para><option>%r</option> the retained flag for the message.</para></listitem>
<listitem><para><option>%S</option> the MQTT v5 subscription-identifier property, if present.</para></listitem>
<listitem><para><option>%t</option> the message topic.</para></listitem>
<listitem><para><option>%x</option> the payload with each byte as a hexadecimal number (lower case).</para></listitem>
<listitem><para><option>%X</option> the payload with each byte as a hexadecimal number (upper case).</para></listitem>
</itemizedlist>
</refsect2>
<refsect2>
<title>Helpers</title>
<itemizedlist mark="circle">
<listitem><para><option>%I</option> ISO-8601 format date and time, e.g. 2016-08-10T09:47:38+0100</para></listitem>
<listitem><para><option>%j</option> JSON output of message
parameters and timestamp, with a quoted and escaped
payload. For example
<code>{"tst":"2020-05-06T22:12:00.000000+0100","topic":"greeting","qos":0,"retain":0,"payload":"hello
world"}</code></para></listitem>
<listitem><para><option>%J</option> JSON output of message
parameters and timestamp, with a non-quoted and
non-escaped payload - this means the payload must
itself be valid JSON. For example:
<code>{"tst":"2020-05-06T22:12:00.000000+0100","topic":"foo","qos":0,"retain":0,"payload":{"temperature":27.0,"humidity":57}}</code>.</para>
<para>If the payload is not valid JSON, then the error message "Error: Message payload is not valid JSON on topic
<topic>" will be printed to stderr.</para></listitem>
<listitem><para><option>%I</option> ISO-8601 format date and time, e.g. 2016-08-10T09:47:38+0100</para></listitem>
<listitem><para><option>%U</option> Unix timestamp with nanoseconds, e.g. 1470818943.786368637</para></listitem>
</itemizedlist>
</refsect2>
<refsect2>
<title>Time related parameters</title>
<itemizedlist mark="circle">
<listitem><para><option>@@</option> a literal @.</para></listitem>
<listitem><para><option>@X</option> pass the character represented
by <option>X</option> to the strftime function as
<option>%X</option>. The options supported are platform
dependent.</para></listitem>
<listitem><para><option>@N</option> the number of nanoseconds that
have passed in the current second, with varying timing
resolution depending on platform.</para></listitem>
</itemizedlist>
</refsect2>
<refsect2>
<title>Escape characters</title>
<itemizedlist mark="circle">
<listitem><para><option>\\</option> a literal \.</para></listitem>
<listitem><para><option>\0</option> a null character. Can be used
to separate different parameters that may contain spaces
(e.g. topic, payload) so that processing with tools such as
<citerefentry><refentrytitle>xargs</refentrytitle><manvolnum>1</manvolnum></citerefentry>
is easier.</para></listitem>
<listitem><para><option>\a</option> alert/bell.</para></listitem>
<listitem><para><option>\e</option> the escape sequence, which can
be used with ANSI colour codes to provide coloured output
for example.</para></listitem>
<listitem><para><option>\n</option> end of line.</para></listitem>
<listitem><para><option>\r</option> carriage return.</para></listitem>
<listitem><para><option>\t</option> horizontal tab.</para></listitem>
<listitem><para><option>\v</option> vertical tab.</para></listitem>
</itemizedlist>
</refsect2>
</refsect1>
<refsect1>
<title>Wills</title>
<para>mosquitto_sub can register a message with the broker that will be
sent out if it disconnects unexpectedly. See
<citerefentry><refentrytitle>mqtt</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for more information.</para>
<para>The minimum requirement for this is to use <option>--will-topic</option> to
specify which topic the will should be sent out on. This will result in
a non-retained, zero length message with QoS 0.</para>
<para>Use the <option>--will-retain</option>, <option>--will-payload</option> and <option>--will-qos</option> arguments to
modify the other will parameters.</para>
</refsect1>
<refsect1 id='properties'>
<title>Properties</title>
<para>The <option>-D</option> / <option>--property</option> option
allows adding properties to different stages of the mosquitto_sub
run. The properties supported for each command are as
follows:</para>
<refsect2>
<title>Connect</title>
<itemizedlist>
<listitem><para><option>authentication-data</option> (binary data - note treated as a string in mosquitto_sub)</para></listitem>
<listitem><para><option>authentication-method</option> (UTF-8 string pair)</para></listitem>
<listitem><para><option>maximum-packet-size</option> (32-bit unsigned integer)</para></listitem>
<listitem><para><option>receive-maximum</option> (16-bit unsigned integer)</para></listitem>
<listitem><para><option>request-problem-information</option> (8-bit unsigned integer)</para></listitem>
<listitem><para><option>request-response-information</option> (8-bit unsigned integer)</para></listitem>
<listitem><para><option>session-expiry-interval</option> (32-bit unsigned integer, note use <option>-x</option> instead)</para></listitem>
<listitem><para><option>topic-alias-maximum</option> (16-bit unsigned integer)</para></listitem>
<listitem><para><option>user-property</option> (UTF-8 string pair)</para></listitem>
</itemizedlist>
</refsect2>
<refsect2>
<title>Subscribe</title>
<itemizedlist>
<listitem><para><option>user-property</option> (UTF-8 string pair)</para></listitem>
</itemizedlist>
</refsect2>
<refsect2>
<title>Unsubscribe</title>
<itemizedlist>
<listitem><para><option>user-property</option> (UTF-8 string pair)</para></listitem>
</itemizedlist>
</refsect2>
<refsect2>
<title>Disconnect</title>
<itemizedlist>
<listitem><para><option>session-expiry-interval</option> (32-bit unsigned integer)</para></listitem>
<listitem><para><option>user-property</option> (UTF-8 string pair)</para></listitem>
</itemizedlist>
</refsect2>
<refsect2>
<title>Will properties</title>
<itemizedlist>
<listitem><para><option>content-type</option> (UTF-8 string)</para></listitem>
<listitem><para><option>correlation-data</option> (binary data - note treated as a string in mosquitto_sub)</para></listitem>
<listitem><para><option>message-expiry-interval</option> (32-bit unsigned integer)</para></listitem>
<listitem><para><option>payload-format-indicator</option> (8-bit unsigned integer)</para></listitem>
<listitem><para><option>response-topic</option> (UTF-8 string)</para></listitem>
<listitem><para><option>user-property</option> (UTF-8 string pair)</para></listitem>
<listitem><para><option>will-delay-interval</option> (32-bit unsigned integer)</para></listitem>
</itemizedlist>
</refsect2>
</refsect1>
<refsect1>
<title>Examples</title>
<para>Note that these really are examples - the subscriptions will work
if you run them as shown, but there must be something publishing
messages on those topics for you to receive anything.</para>
<para>Subscribe to temperature information on localhost with QoS 1:</para>
<itemizedlist mark="circle">
<listitem><para>mosquitto_sub <literal>-t</literal> sensors/temperature <literal>-q</literal> 1</para></listitem>
</itemizedlist>
<para>Subscribe to hard drive temperature updates on multiple
machines/hard drives. This expects each machine to be publishing its
hard drive temperature to
sensors/machines/HOSTNAME/temperature/HD_NAME.</para>
<itemizedlist mark="circle">
<listitem><para>mosquitto_sub <literal>-t</literal> sensors/machines/+/temperature/+</para></listitem>
</itemizedlist>
<para>Subscribe to all broker status messages:</para>
<itemizedlist mark="circle">
<listitem><para>mosquitto_sub <literal>-v</literal> <literal>-t</literal> \$SYS/#</para></listitem>
</itemizedlist>