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MOSQUITTO_SUB(1) Commands MOSQUITTO_SUB(1)

NAME

mosquitto_sub - an MQTT version 5/3.1.1/3.1 client for subscribing to topics

SYNOPSIS

mosquitto_sub [options] {-t message-topic... | -U unsubscribe-topic...}

options:
[auth-options] [connection-options] [misc-options] [mqtt-options] [output-options] [tls-certificate-options | tls-psk-options]

auth-options:
[-u username] [-P password]

connection-options:
{[-h hostname] [--unix socket path] [-p port-number] | -L URL }
[-A bind-address] [--nodelay] [-S] [--ws] [--proxy socks-url]

misc-options:
[-E] [-o config-file] [-W message-processing-timeout]

mqtt-options:
[-c] [-D command identifier value] [-i client-id] [-I client-id-prefix] [-k keepalive-time] [-q message-QoS] [--retain-as-published] [--retain-handling always | new | never] [-V protocol-version] [-x session-expiry-interval]
[--will-topic topic [--will-payload payload] [--will-qos qos] [--will-retain]]

output-options:
[-d] [-C msg-count] [--message-rate] [-N] [--pretty] [--random-filter chance] [--remove-retained] [-R | --retained-only] [--quiet] [-T filter-out...] [-v] [-w | --watch]

tls-certificate-options:
[--no-tls]
{--cafile file | --capath dir}
[--tls-use-os-certs]
[--cert file] [--key file]
[--ciphers ciphers] [--insecure] [--tls-alpn protocol] [--tls-keylog file] [--tls-version version]
[--tls-engine engine] [--keyform {pem | engine}] [--tls-engine-kpass-sha1 kpass-sha1]

tls-psk-options:
--psk hex-key --psk-identity identity [--ciphers ciphers] [--tls-version version]

mosquitto_sub [--help]

DESCRIPTION

mosquitto_sub is a simple MQTT version 5/3.1.1 client that will subscribe to topics and print the messages that it receives.

In addition to subscribing to topics, mosquitto_sub can filter out received messages so they are not printed (see the -T option) or unsubscribe from topics (see the -U option). Unsubscribing from topics is useful for clients connecting with clean session set to false.

ENCRYPTED CONNECTIONS

This client 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.

OPTIONS

There are three ways to provide options to mosquitto_sub: the default config file, a specified config file, or options on the command line.

Default Config File

The default config file is located at $XDG_CONFIG_HOME/mosquitto_sub or $HOME/.config/mosquitto_sub on POSIX systems, or %USERPROFILE%\mosquitto_sub on Windows.

The contents of the config file should consist of options, one per line in the format: -option value. If options are also specified on the command line, those options will override the same options set in the config file. The exceptions to this are the message type options, of which only one can be specified. Note also that currently some options cannot be negated, e.g. -S. TLS encryption options can be negated with the --no-tls option.

Config file lines that have a # as the first character are treated as comments and not processed any further.

It is suggested that config files are primarily used for authentication purposes. Use of a config file allows you to authenticate without the need to show the username and password on the command line.

Config File

Available from version 2.1.

A config file can be specified on the command line using -o config-file. If the -o option is used, the default config file will not be loaded.

The format is the same as for the default config file.

The options

-A

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.

--cafile

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

See also --capath

--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

--cert

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

See also --key and the Encrypted Connections section.

--ciphers

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

-C

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.

Combine with -R or --retain-handling never to print only the first set of fresh messages (i.e. that does not have the retained flag set), or with -T to filter which topics are processed.

-d, --debug

Enable debug messages.

-D, --property

Set MQTT v5 properties for with this client. 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, PUBLISH, 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.

-E

If this option is given, mosquitto_sub will exit immediately that all of its subscriptions have been acknowledged by the broker. In conjunction with -c this allows a durable client session to be initialised on the broker for future use without requiring any messages to be received.

-F

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.

--help

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.

-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.

--insecure

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.

--key

Define the path to a file containing a PEM encoded private key for this client, carrying out mutual TLS with the server.

See also --cert and the Encrypted Connections section.

--keyform

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 or ws(s)://[username[:password]@]host[:port]/path

Depending on the scheme, the port will default to different values. mqtt:// - 1883, mqtts:// - 8883, ws:// - 80, wss:// - 443.

--message-rate

Available from version 2.1.

Instead of printing the messages received, print a count of the messages received at one second intervals. Other options related to output formatting are not valid when this option is active.

-N

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.

--nodelay

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.

--no-tls

Available from version 2.1.

Disable all use of TLS encryption. This is useful if you specify TLS options in a configuration file but want to disable those options. It also stops the automatic use of TLS when connecting to port 8883.

-o config-file

Available from version 2.1.

Load options from a config file. See the Default Config File and Config File sections at the start of the Options section.

-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.

--pretty

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.

--proxy

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.

If the host is given as an IPv6 address, it must be enclosed in square brackets, e.g. socks5h://[::1]:1080. Note that square brackets have special meaning in some shells, so the proxy url may need quoting in double or single quotes.

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

--psk

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.

--psk-identity

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 applies to all topics subscribed to in a single instance of this client.

--quiet

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).

-R

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.

See also --retain-handling.

--random-filter

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 chance to a floating point value between 0.1 and 100.0 will ensure that on average that percentage of messages will be printed.

--remove-retained

If this argument is given, then 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 -T option. This option still takes effect even if -R is used. See also the --retain-as-published and --retained-only options.

Example 1.  Remove all retained messages on the server, assuming we have access to do so, and then exit:

	mosquitto_sub -t '#' --remove-retained --retained-only

Example 2.  Remove a whole tree, with the exception of a single topic:

	mosquitto_sub -t 'bbc/#' -T bbc/bbc1 --remove-retained

--retained-only

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 --retain-as-published option.

--retain-as-published

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.

This option is not valid for MQTT v3.1/v3.1.1 clients.

--retain-handling always | new | never

Available from version 2.1.

Use this option to control the retain handling option when making a subscription. This controls under what circumstances an existing retained message is sent to the client when the subscription is made.

•always - always deliver retained messages

•new - deliver retained messages the first time a subscription is made, but not on subsequent subscriptions. This is useful for the case where you have a long running client using a non-clean session. If the connection is dropped briefly, when the client reconnects you will not receive the retained messages again.

•never - never deliver retained messages

-S

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>.

-t, --topic

The MQTT topic to subscribe to. See mqtt(7) for more information on MQTT topics.

This option may be repeated to subscribe to multiple topics.

-T, --filter-out

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.

For example, subscribe to the BBC tree, but suppress output from Radio 3:

•mosquitto_sub -t bbc/# -T bbc/radio3

This option may be repeated to filter out multiple topics or topic trees.

--tls-alpn

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

--tls-engine

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

See also --keyform.

--tls-engine-kpass-sha1

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.

--tls-keylog file

Available from version 2.1.

Log TLS connection information to file. This option allows tools such as tcpdump, wireshark and mqttshark to decrypt TLS traffic and inspect the MQTT traffic. In Wireshark this can be done by setting the (Pre)-Master-Secret log filename option for the Transport Layer Security protocol.

This option should be used for debugging only, it must not be used in production.

--tls-use-os-certs

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.

--tls-version

Choose which TLS protocol version to use when communicating with the broker. Valid options are tlsv1.3 and tlsv1.2. 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.

--unix

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.

-U, --unsubscribe

A topic that will be unsubscribed from. This may be used on its own or in conjunction with the --topic option and only makes sense when used in conjunction with --clean-session.

If used with --topic then subscriptions will be processed before unsubscriptions.

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 sensors/# and then unsubscribing from sensors/+/temperature as shown below will still result in messages matching the sensors/+/temperature being delivered to the client.

•mosquitto_sub -t sensors/# -U sensors/+/temperature -v

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.

This option may be repeated to unsubscribe from multiple topics.

-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".

See also -F.

-V, --protocol-version

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

-W

Provide a timeout as an integer number of seconds. The client 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.

-w, --watch

Available from version 2.1.

Messages will be printed on a fixed line number based on the topic and order in which topics are received. Useful for monitoring multiple topics that have single line payloads. Unexpected behaviour will occur if there are more topics than lines in the terminal, or if the payload occupies more than a single line. This can be used in conjuction with other output options e.g. -F.

Requires ANSI escape code support in the terminal.

--will-payload

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.

--will-qos

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

--will-retain

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.

--will-topic

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

--ws

Connect using WebSockets instead of plain TCP.

-x

Set the session-expiry-interval property on the CONNECT packet. If you use this option, the client will be set to be an MQTT v5 client. 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.

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

OUTPUT FORMAT

There are three ways of formatting the printed output. In all cases a new-line character is appended for each message received unless the -N argument is given.

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. One extension to strftime is provided 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.

Flag characters

The parameters %A, %C, %d, %E, %F, %f, %I, %l, %m, %p, %R, %S, %t, %x, and %X can have optional flags immediately after the % character.

0

The value should be zero padded. This applies to the parameters %A, %E, %d, %F, %f, %l, %m, %S, %X, and %x. It will be ignored for other parameters. If used with the - flag, the 0 flag will be ignored.

-

The value will be left aligned to the field width, padded with blanks. The default is right alignment, with either 0 or blank padding.

Field width

Some of the MQTT related parameters can be formatted with an option to set their field width in a similar way to regular printf style formats, i.e. this sets the minimum width when printing this parameter. If the output length is smaller than this width, the field will be padded to meet this width. This applies to the options %A, %C, %d, %E, %F, %f, %I, %l, %m, %p, %R, %S, %t, %x, %X.

For example %10t would set the minimum topic field width to 10 characters.

Maximum width

Some of the MQTT related parameters can be formatted with an option to set a maximum field width in a similar way to regular printf style formats, for example %.20t for a maximum width of 20. This applies to the options %C, %I, %R, %t.

For example %10.10t would set the minimum topic field width to 10 characters, and the maximum topic width to 10 characters, i.e. the field will always be exactly 10 characters long.

Hexadecimal binary field width

The %x and %X parameters output the payload as a single hexadecimal string by default. It is also possible to split the hexadecimal payload into fields by a chosen length of nibbles. For example, %.2x would split the payload into two nibble or one byte values, separated by spaces and might produce an output of 18 83.

The separator character is a space by default, but can be changed to one of !"#$&'()*+,-./:;<=>?@[\]^_`{|}~ by adding that character after the binary field width. For example %.2:x might produce an output of 18:83.

Floating point number printing consideration

The output format supports only the IEEE 754 floating point standard as described in Annex F of ISO/IEC 9899:1999. Don't try to use %f or %d if the platform of the publisher uses a different floating point representation standard than IEEE 754 or you will get invalid data. If you are unsure what floating representation your platform is using, then it is most likely IEEE 754. If you get malformed or unexpected values, check if the floating point number in the payload from the publisher is encoded in IEEE 754.

If want to print floats, make sure you only subscribe to topics that send only IEEE 754 formatted floats. The processing is very strict about floats and if anything that is not a float is received, an error message will be printed.

•%% 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.

•%d the payload treated as an 8 byte IEEE 754 float (double).

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

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

•%f the payload treated as an 4 byte IEEE 754 float.

•%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).

Helpers

•%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.

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

WILLS

The client 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.

PROPERTIES

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

Connect

•authentication-data (binary data - note treated as a string)

•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)

Subscribe

•user-property (UTF-8 string pair)

Unsubscribe

•user-property (UTF-8 string pair)

Disconnect

•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)

•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)

EXIT STATUS

Zero on success, or non-zero on error. If the connection is refused by the broker at the MQTT level, then the exit code is the CONNACK reason code. If another error occurs, the exit code is a libmosquitto return value.

MQTT v3.1.1 CONNACK codes:

•0 Success

•1 Connection refused: Bad protocol version

•2 Connection refused: Identifier rejected

•3 Connection refused: Server unavailable

•4 Connection refused: Bad username/password

•5 Connection refused: Not authorized

MQTT v5 CONNACK codes:

•0 Success

•128 Unspecified error

•129 Malformed packet

•130 Protocol error

•131 Implementation specific error

•132 Unsupported protocol version

•133 Client ID not valid

•134 Bad username or password

•135 Not authorized

•136 Server unavailable

•137 Server busy

•138 Banned

•139 Server shutting down

•140 Bad authentication method

•141 Keep alive timeout

•142 Session taken over

•143 Topic filter invalid

•144 Topic name invalid

•147 Receive maximum exceeded

•148 Topic alias invalid

•149 Packet too large

•148 Message rate too high

•151 Quota exceeded

•152 Administrative action

•153 Payload format invalid

•154 Retain not supported

•155 QoS not supported

•156 Use another server

•157 Server moved

•158 Shared subscriptions not supported

•159 Connection rate exceeded

•160 Maximum connect time

•161 Subscription IDs not supported

•162 Wildcard subscriptions not supported

Other codes:

•27 Timed out waiting for message

EXAMPLES

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.

Subscribe to temperature information on localhost with QoS 1:

•mosquitto_sub -t sensors/temperature -q 1

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.

•mosquitto_sub -t sensors/machines/+/temperature/+

Subscribe to all broker status messages:

•mosquitto_sub -v -t \$SYS/#

Specify the output format as "ISO-8601 date : topic : payload in hex"

•mosquitto_sub -F '@Y-@m-@dT@H:@M:@S@z : %t : %x' -t '#'

Specify the output format as "seconds since epoch.nanoseconds : retained flag : qos : mid : payload length"

•mosquitto_sub -F '%@s.@N : %r : %q : %m : %l' -q 2 -t '#'

Topic and payload output, but with colour where supported.

•mosquitto_sub -F '\e[92m%t \e[96m%p\e[0m' -q 2 -t '#'

FILES

$XDG_CONFIG_HOME/mosquitto_sub, $HOME/.config/mosquitto_sub, $HOME/snap/mosquitto/current/.config/mosquitto_sub (for snap installs)

Configuration file for default options.

BUGS

mosquitto bug information can be found at https://github.com/eclipse-mosquitto/mosquitto/issues

SEE ALSO

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

AUTHOR

Roger Light <roger@atchoo.org>

05/14/2026 Mosquitto Project