Version: Mosquitto 3.0

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mosquitto_sub

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

Synopsis

mosquitto_sub { [-h hostname] [--unix socket path] [-p port-number] [-u username] [-P password] -t message-topic... | -L URL [-t message-topic...] } [-A bind-address] [-c] [-C msg-count] [-d] [-D command identifier value] [-E] [-i client-id] [-I client-id-prefix] [-k keepalive-time] [-N] [--nodelay] [--pretty] [-q message-QoS] [--random-filter chance] [--remove-retained] [ -R | --retained-only ] [--retain-as-published] [-S] [-T filter-out...] [-U unsub-topic...] [-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] [--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 [--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. mosquitto_sub is a simple MQTT version 5/3.1.1 client that will subscribe to topics and print the messages that it receives.

Encrypted Connections

mosquitto_sub 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 must be provided as an option.

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

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_sub or $HOME/.config/mosquitto_sub 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 are -t and -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.

-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.

Output Format

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 -N argument is passed to mosquitto_sub.

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.

Flag characters

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

The value should be zero padded. This applies to the parameters %A, %E, %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. This applies to the options %A, %C, %E, %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. 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.

%% 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).

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.

%I ISO-8601 format date and time, e.g. 2016-08-10T09:47:38+0100
%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)] (https://linux.die.net/man/1/xargs) 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

mosquitto_sub can register a message with the broker that will be sent out if it disconnects unexpectedly. Read more about Mosquitto [man page] (NEW_manpages-mosquitto.md).

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 in mosquitto_sub)
authentication-method (UTF-8 string)
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)

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 in mosquitto_sub)
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

mosquitto_sub returns 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

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 '#'

Exit Values

Success

27

Timed out waiting for message

Other non-zero value

Unspecified failure

Files

$XDG_CONFIG_HOME/mosquitto_sub,
$HOME/.config/mosquitto_sub

Configuration file for default options.

mosquitto_sub​

Synopsis​

Description​

Encrypted Connections​

Options​

Output Format​

Flag characters​

Field width​

Maximum width​

MQTT related parameters​

Helpers​

Time related parameters​

Escape characters​

Wills​

Properties​

Connect​

Subscribe​

Unsubscribe​

Disconnect​

Will properties​

Exit Status​

Examples​

Exit Values​

Files​