Provided by: mosquitto-clients_1.4.15-2ubuntu0.18.04.3_amd64 bug

NAME

       mosquitto_sub - an MQTT version 3.1 client for subscribing to topics

SYNOPSIS

       mosquitto_sub [-A bind_address] [-c] [-C msg count] [-d] [-h hostname] [-i client_id]
                     [-I client id prefix] [-k keepalive time] [-p port number] [-q message QoS]
                     [-R] [-S] [-N] [--quiet] [-v] [[-u username] [-P password]]
                     [--will-topic topic [--will-payload payload] [--will-qos qos] [--will-retain]]
                     [[{--cafile file | --capath dir} [--cert file] [--key file] [--tls-version version] [--insecure]]
                     | [--psk hex-key --psk-identity identity [--tls-version version]]]
                     [--proxy socks-url] [-V protocol-version] [-T filter-out...]
                     -t message-topic...

       mosquitto_sub [--help]

DESCRIPTION

       mosquitto_sub is a simple MQTT version 3.1 client that will subscribe to a topic and print
       the messages that it receives.

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 the 'clean session' flag. This means that all of 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, it will receive all of the queued
           messages.

           If using this option, it is recommended that the client id is 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.

       --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 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.

       --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, defaults to mosquitto_sub_ appended with
           the process id of the client. 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.

       --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, if
           required by the server.

           See also --cert.

       -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.

       -p, --port
           Connect to the port specified instead of the default 1883.

       -P, --pw
           Provide a password to be used for authenticating with the broker. Using this argument
           without also specifying a username is invalid. This requires a broker that supports
           MQTT v3.1. See also the --username option.

       --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.

           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 is identical for all topics subscribed to in a single instance of
           mosquitto_sub.

       --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.

       -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-version
           Choose which TLS protocol version to use when communicating with the broker. Valid
           options are tlsv1.2, tlsv1.1 and tlsv1. The default value is tlsv1.2. If the installed
           version of openssl is too old, only tlsv1 will be available. Must match the protocol
           version used by the broker.

       -u, --username
           Provide a username to be used for authenticating with the broker. This requires a
           broker that supports MQTT v3.1. See also the --pw argument.

       -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 mqttv31 or mqttv311. Defaults to mqttv31.

       --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.

WILLS

       mosquitto_sub 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.

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/#

FILES

       $XDG_CONFIG_HOME/mosquitto_sub, $HOME/.config/mosquitto_sub
           Configuration file for default options.

BUGS

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

SEE ALSO

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

AUTHOR

       Roger Light <roger@atchoo.org>