mosquitto_rr - an MQTT version 5/3.1.1 client for request/response messaging

NAME  SYNOPSIS  DESCRIPTION  ENCRYPTED CONNECTIONS  OPTIONS  OUTPUT FORMAT  MQTT related parameters  Helpers  Time related parameters  Escape characters  WILLS  PROPERTIES  Connect  Publish  Subscribe  Unsubscribe  Disconnect  Will properties  EXIT VALUES  FILES  BUGS  SEE ALSO  AUTHOR 


mosquitto_rr − an MQTT version 5/3.1.1 client for request/response messaging


mosquitto_rr −e response−topic {[−h hostname] [−−unix socket path] [−p port−number] [−u username] [−P password−t message−topic... | −L URL [−t message−topic...] } {−f file | −m message | −n | −s} [−A bind−address] [−c] [−d] [−D command identifier value] [−i client−id] [−I client−id−prefix] [−k keepalive−time] [−N] [−−nodelay] [−−pretty] [−q message−QoS] [−R] [−S] [−v] [−V protocol−version] [−W message−processing−timeout] [−x session−expiry−interval] [−−proxy socks−url] [−−quiet] [−−will−topic topic [−−will−payload payload] [−−will−qos qos] [−−will−retain]] [[{−−cafile file −−capath dir} [−−cert file] [−−key file] [−−ciphers ciphers] [−−tls−version version] [−−tls−alpn protocol] [−−tls−engine engine] [−−keyform {pem engine}] [−−tls−engine−kpass−sha1 kpass−sha1] [−−tls−use−os−certs] [−−insecure]] | [−−psk hex−key −−psk−identity identity [−−ciphers ciphers] [−−tls−version version]]]

mosquitto_rr [−−help]


mosquitto_rr is an MQTT version 5/3.1.1 client that can be used to publish a request message and wait for a response. When using MQTT v5, which is the default, mosquitto_rr will use the Request−Response feature.

The important options are −t, −e, and one of −f, −m, −n, and −s.

Example: mosquitto_rr −t request−topic −e response−topic −m message


mosquitto_rr supports TLS encrypted connections. It is strongly recommended that you use an encrypted connection for anything more than the most basic setup.

To enable TLS connections when using x509 certificates, one of either −−cafile or −−capath can be provided as an option.

Alternatively, if the −p 8883 option is used then the OS provided certificates will be loaded and neither −−cafile or −−capath are needed

To enable TLS connections when using TLS−PSK, you must use the −−psk and the −−psk−identity options.


The options below may be given on the command line, but may also be placed in a config file located at $XDG_CONFIG_HOME/mosquitto_rr or $HOME/.config/mosquitto_rr with one pair of −option value 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 is −t, which if given in the config file will not be overridden. Note also that currently some options cannot be negated, e.g. −S. Config file lines that have a # as the first character are treated as comments and not processed any further.


Bind the outgoing connection to a local ip address/hostname. Use this argument if you need to restrict network communication to a particular interface.

−c, −−disable−clean−session

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 −x argument.

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.

If using this option, the client id must be set manually with −−id


Define the path to a file containing PEM encoded CA certificates that are trusted. Used to enable SSL communication.

See also −−capath


Define the path to a directory containing PEM encoded CA certificates that are trusted. Used to enable SSL communication.

For −−capath 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.

See also −−cafile


Define the path to a file containing a PEM encoded certificate for this client, if required by the server.

See also −−key.


An openssl compatible list of TLS ciphers to support in the client. See ciphers(1) for more information.

−d, −−debug

Enable debug messages.

−D, −−property

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:

−D command identifier value

−D command identifier name value

command 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.

identifier is the name of the property to add. This is as described in the specification, but with '−' as a word separator. For example: payload−format−indicator. More details are in the Properties section.

value is the value of the property to add, with a data type that is property specific.

name is only used for the user−property property as the first of the two strings in the string pair. In that case, value is the second of the strings in the pair.


Response topic. The client will subscribe to this topic to wait for a response.

−f, −−file

Send the contents of a file as the request message.


Specify output printing format. This option allows you to choose what information from each message is printed to the screen. See the Output Format section below for full details.

This option overrides the −v option, but does not override the −N option.


Display usage information.

−h, −−host

Specify the host to connect to. Defaults to localhost.

−i, −−id

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 mosq−XXXXXXXXXXXXXXXXXX, where the X 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.

This option cannot be used at the same time as the −−id−prefix argument.

−I, −−id−prefix

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 −−id argument.


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 only. 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.

−k, −−keepalive

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.


Define the path to a file containing a PEM encoded private key for this client, if required by the server.

See also −−cert.


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.

See also −−tls−engine.

−L, −−url

Specify specify user, password, hostname, port and topic at once as a URL. The URL must be in the form: mqtt(s)://[username[:password]@]host[:port]/topic

If the scheme is mqtt:// then the port defaults to 1883. If the scheme is mqtts:// then the port defaults to 8883.

−m, −−message

Send a single request message from the command line.


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 −v.

−n, −−null−message

Send a null (zero length) request message.


Disable Nagle's algorithm for the socket. This means that latency of sent messages is reduced, which is particularly noticeable for small, reasonably infrequent messages. Using this option may result in more packets being sent than would normally be necessary.

−p, −−port

Connect to the port specified. If not given, the default of 1883 for plain MQTT or 8883 for MQTT over TLS will be used.

−P, −−pw

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 −−username option.


When using the JSON output format %j or %J, the default is to print in an unformatted fashion. Specifying −−pretty prints messages in a prettier, more human readable format.


Specify a SOCKS5 proxy to connect through. "None" and "username" authentication types are supported. The socks−url must be of the form socks5h://[username[:password]@]host[:port]. The protocol prefix socks5h 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.

If username is not given, then no authentication is attempted. If the port is not given, then the default of 1080 is used.

More SOCKS versions may be available in the future, depending on demand, and will use different protocol prefixes as described in curl(1).


Provide the hexadecimal (no leading 0x) pre−shared−key matching the one used on the broker to use TLS−PSK encryption support. −−psk−identity must also be provided to enable TLS−PSK.


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.

−q, −−qos

Specify the quality of service desired for the incoming messages, from 0, 1 and 2. Defaults to 0. See mqtt(7) for more information on QoS.

The QoS is identical for all topics subscribed to in a single instance of mosquitto_rr.


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 −−port without a port).


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.


Use SRV lookups to determine which host to connect to. Performs lookups to _mqtt._tcp.<host> when used in conjunction with −h, otherwise uses _mqtt._tcp.<local dns domain>.

−s, −−stdin−file

Send a request message read from stdin, sending the entire content as a single message.

−t, −−topic

The MQTT topic where the request message will be sent.


Provide a protocol to use when connecting to a broker that has multiple protocols available on a single port, e.g. MQTT and WebSockets.


A valid openssl engine id. These can be listed with openssl engine command.

See also −−keyform.


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.

See also −−tls−engine.


If used, this will load and trust the OS provided CA certificates. This can be used in conjunction with −−cafile and −−capath and can be used on its own to enable TLS mode. This will be set by default if −L mqtts://... is used, or if port is 8883 and no other certificate options are used.


Choose which TLS protocol version to use when communicating with the broker. Valid options are tlsv1.3, tlsv1.2 and tlsv1.1. The default value is tlsv1.2. Must match the protocol version used by the broker.

−u, −−username

Provide a username to be used for authenticating with the broker. See also the −−pw argument.


Connect to a broker through a local unix domain socket instead of a TCP socket. This is a replacement for −h and −L. For example: mosquitto_pub −−unix /tmp/mosquitto.sock ...

See the socket_domain option in mosquitto.conf(5) to configure Mosquitto to listen on a unix socket.

−v, −−verbose

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".

−V, −−protocol−version

Specify which version of the MQTT protocol should be used when connecting to the rmeote broker. Can be 5, 311, 31, or the more verbose mqttv5, mqttv311, or mqttv31. Defaults to 5.


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.


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 −−will−topic.


The QoS to use for the Will. Defaults to 0. This must be used in conjunction with −−will−topic.


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 −−will−topic.


The topic on which to send a Will, in the event that the client disconnects unexpectedly.


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 â for a session that does not expire. Defaults to −1 if −c is also given, or 0 if −c not given.

If the session is set to never expire, either with −x or −c, then a client id must be provided.


There are three ways of formatting the output from mosquitto_rr. In all cases a new−line character is appended for each message received unless the −N argument is passed to mosquitto_rr.

Payload−only is the default output format and will print the payload exactly as it is received.

Verbose mode is activated with −v and prints the message topic and the payload, separated by a space.

The final option is formatted output, which allows the user to define a custom output format. The behaviour is controlled with the −F format−string option. The format string is a free text string where interpreted sequences are replaced by different parameters. The available interpreted sequences are described below.

Three characters are used to start an interpreted sequence: %, @ and \. Sequences starting with % 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 @ are passed to the strftime(3) 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_rr does provide one extension to strftime which is @N, 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 \, which is used to input some characters that would otherwise be difficult to enter.

MQTT related parameters

%% a literal %.

%A the MQTT v5 topic−alias property, if present.

%C the MQTT v5 content−type property, if present.

%D the MQTT v5 correlation−data property, if present. Note that this property is specified as binary data, so may produce non−printable characters.

%E the MQTT v5 message−expiry−interval property, if present.

%F the MQTT v5 payload−format−indicator property, if present.

%l the length of the payload in bytes.

%m the message id (only relevant for messages with QoS>0).

%P 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.

%p the payload raw bytes (may produce non−printable characters depending on the payload).

%q the message QoS.

%R the MQTT v5 response−topic property, if present.

%r the retained flag for the message.

%S the MQTT v5 subscription−identifier property, if present.

%t the message topic.

%x the payload with each byte as a hexadecimal number (lower case).

%X the payload with each byte as a hexadecimal number (upper case).


%I ISO−8601 format date and time, e.g. 2016−08−10T09:47:38+0100

%j JSON output of message parameters and timestamp, with a quoted and escaped payload. For example {"tst":"2020−05−06T22:12:00.000000+0100","topic":"greeting","qos":0,"retain":0,"payload":"hello world"}

%J 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: {"tst":"2020−05−06T22:12:00.000000+0100","topic":"foo","qos":0,"retain":0,"payload":{"temperature":27.0,"humidity":57}}.

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.

%I ISO−8601 format date and time, e.g. 2016−08−10T09:47:38+0100

%U Unix timestamp with nanoseconds, e.g. 1470818943.786368637

Time related parameters

@@ a literal @.

@X pass the character represented by X to the strftime function as %X. The options supported are platform dependent.

@N the number of nanoseconds that have passed in the current second, with varying timing resolution depending on platform.

Escape characters

\\ a literal \.

\0 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 xargs(1) is easier.

\a alert/bell.

\e the escape sequence, which can be used with ANSI colour codes to provide coloured output for example.

\n end of line.

\r carriage return.

\t horizontal tab.

\v vertical tab.


mosquitto_rr can register a message with the broker that will be sent out if it disconnects unexpectedly. See mqtt(7) for more information.

The minimum requirement for this is to use −−will−topic to specify which topic the will should be sent out on. This will result in a non−retained, zero length message with QoS 0.

Use the −−will−retain, −−will−payload and −−will−qos arguments to modify the other will parameters.


The −D / −−property option allows adding properties to different stages of the mosquitto_rr run. The properties supported for each command are as follows:


authentication−data (binary data − note treated as a string in mosquitto_rr)

authentication−method (UTF−8 string pair)

maximum−packet−size (32−bit unsigned integer)

receive−maximum (16−bit unsigned integer)

request−problem−information (8−bit unsigned integer)

request−response−information (8−bit unsigned integer)

session−expiry−interval (32−bit unsigned integer, note use −x instead)

topic−alias−maximum (16−bit unsigned integer)

user−property (UTF−8 string pair)


content−type (UTF−8 string)

correlation−data (binary data − note treated as a string in mosquitto_rr)

message−expiry−interval (32−bit unsigned integer)

payload−format−indicator (8−bit unsigned integer)

response−topic (UTF−8 string)

topic−alias (16−bit unsigned integer)

user−property (UTF−8 string pair)


user−property (UTF−8 string pair)


user−property (UTF−8 string pair)


session−expiry−interval (32−bit unsigned integer)

user−property (UTF−8 string pair)

Will properties

content−type (UTF−8 string)

correlation−data (binary data − note treated as a string in mosquitto_pub)

message−expiry−interval (32−bit unsigned integer)

payload−format−indicator (8−bit unsigned integer)

response−topic (UTF−8 string)

user−property (UTF−8 string pair)

will−delay−interval (32−bit unsigned integer)





Timed out waiting for message

Other non−zero value

Unspecified failure


$XDG_CONFIG_HOME/mosquitto_rr, $HOME/.config/mosquitto_rr

Configuration file for default options.


mosquitto bug information can be found at


mqtt(7), mosquitto_pub(1), mosquitto_sub(1), mosquitto(8), libmosquitto(3), mosquitto-tls(7)


Roger Light <[email protected]>

Updated 2024-01-29 - |